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Archive for the ‘Warburg effect’ Category


Agios Pharmaceuticals target the metabolism of cancer cells for making drugs that essentially try to repair cancer cells

Reporter: Aviva Lev-Ari, PhD, RN

A small biotech behind a groundbreaking approach to tackling cancer just got its first drug approved

http://www.businessinsider.com/fda-approves-agios-pharmaceuticals-drug-targeting-cancer-cell-metabolism-2017-8

See

Cancer Metabolism

http://www.agios.com/research/cancer-metabolism/

Metabolic Immuno-Oncology

http://www.agios.com/research/metabolic-immuno-oncology/

 

 

The VOICE of Larry H. Bernstein, MD, FCAP

Cancer cells didn’t need as much oxygen to metabolize sugar as normal cells. 

Not correct. Cancer cells metabolize glucose by aerobic glycolysis (4 ATP) with an impaired mitochondrial oxygen utilization (36 ATP). 

There is a reverse Warburg effect in which the underlying stromal cell carries out crosstalk with the epithelial cell. 

There is also a 3rd dimension. Cells undergo a series of adaptive changes tied to proteostasis. This involves the sulfur amino acid cysteine and disulfide bonds, which is involved with protein oligomerization in the ER, and also signaling in the mitochondria with mDNA and the nucleus. 

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Pancreatic Cancer Targeted Treatment?

Curator: Larry H. Bernstein, MD, FCAP

 

 

MGH study identifies potential treatment target for pancreatic cancer

Molecular signature found in 30 percent of PDAC tumors, associated with more aggressive cancer

http://www.massgeneral.org/about/pressrelease.aspx?id=1933&

 

Massachusetts General Hospital (MGH) investigators have identified the first potential molecular treatment target for the most common form of pancreatic cancer, which kills more than 90 percent of patients. Along with finding that the tumor suppressor protein SIRT6 is inactive in around 30 percent of cases of pancreatic ductal adenocarcinoma (PDAC), the team identified the precise pathway by which SIRT6 suppresses PDAC development, a mechanism different from the way it suppresses colorectal cancer. The paper will appear in the June 2 issue of Cell and have been published online.

“With the advance of cancer genomics, it has become evident that alterations in epigenetic factors – those that control whether and when other genes are expressed – represent some of the most frequent alterations in cancer,” says Raul Mostoslavsky, MD, PhD, of the MGH Cancer Center, senior author of the report.  “Yet, not many of those factors have been described before, and those that have been identified have not been linked to specific downstream targets.  Not only did more than a third of analyzed PDAC patient samples exhibit the molecular signature we identified, those patients also turned out to have very poor prognoses.”

Among its other functions, SIRT6 is known to control how cells process glucose, and a 2012 study by Mostoslavsky’s team found that its ability to suppress colorectal cancer involves control of a process called glycolysis.  But while that study also found reduced SIRT6 expression in PDAC tumor cells, the current investigation indicated that SIRT6 deficiency promotes PDAC through a different mechanism. Experiments in cell lines and animal models revealed that low SIRT6 levels in PDAC were correlated with increased expression of Lin28b, an oncoprotein normally expressed during fetal development.

Lin28b expression proved to be essential to the growth and survival of SIRT6-deficient PDAC cells and acted by preventing a family of tumor-suppressing mRNAs called let-7 from blocking expression of three genes previously associated with increased aggressiveness and metastasis in pancreatic cancers.  All of these hallmarks – reduced SIRT6, increased Lin28b and reduced let-7 expression – were found in tumor samples from patients who died more quickly.

“A general message from these studies is that cancer cells benefit from modulating epigenetic factors like SIRT6 by acquiring the ability to override normal cellular growth control patterns,” says Mostoslavsky, an associate professor of Medicine at Harvard Medical School and an associate member at the Broad Institute.  “Each tumor type may acquire a unique set of capabilities that may provide tumor-specific growth and survival advantages, which may need to be determined for each kind of cancer.  In terms of our findings regarding PDAC, we are intrigued by the downstream pathways controlled by Lin28b and how they increase aggressiveness and metastasis, and we are hopeful that developing in the future Lin28b inhibitors could benefit this subset of PDAC patients, who currently have very few treatment options.”

 

SIRT6 Suppresses Pancreatic Cancer through Control of Lin28b

Sita Kugel, Carlos Sebastián, Julien Fitamant,…., Alon Goren, Vikram Deshpande, Nabeel Bardeesy, Raul Mostoslavsky

Figure thumbnail fx1
Highlights
  • Loss of SIRT6 cooperates with oncogenic Kras to drive pancreatic cancer
  • SIRT6 regulates the oncofetal protein Lin28b through promoter histone deacetylation
  • Lin28b drives the growth and survival of SIRT6-deficient pancreatic cancer
  • SIRT6 and Lin28b expression define prognosis in specific pancreatic cancer subsets

Chromatin remodeling proteins are frequently dysregulated in human cancer, yet little is known about how they control tumorigenesis. Here, we uncover an epigenetic program mediated by the NAD+-dependent histone deacetylase Sirtuin 6 (SIRT6) that is critical for suppression of pancreatic ductal adenocarcinoma (PDAC), one of the most lethal malignancies. SIRT6 inactivation accelerates PDAC progression and metastasis via upregulation of Lin28b, a negative regulator of the let-7 microRNA. SIRT6 loss results in histone hyperacetylation at theLin28b promoter, Myc recruitment, and pronounced induction of Lin28b and downstream let-7 target genes, HMGA2, IGF2BP1, and IGF2BP3. This epigenetic program defines a distinct subset with a poor prognosis, representing 30%–40% of human PDAC, characterized by reduced SIRT6 expression and an exquisite dependence on Lin28b for tumor growth. Thus, we identify SIRT6 as an important PDAC tumor suppressor and uncover the Lin28b pathway as a potential therapeutic target in a molecularly defined PDAC subset.

 

The multifaceted functions of sirtuins in cancer

Angeliki Chalkiadaki & Leonard Guarente  Affiliations  Corresponding author
Nature Reviews Cancer (2015); 15:608–624     http://dx.doi.org:/10.1038/nrc3985

The sirtuins (SIRTs; of which there are seven in mammals) are NAD+-dependent enzymes that regulate a large number of cellular pathways and forestall the progression of ageing and age-associated diseases. In recent years, the role of sirtuins in cancer biology has become increasingly apparent, and growing evidence demonstrates that sirtuins regulate many processes that go awry in cancer cells, such as cellular metabolism, the regulation of chromatin structure and the maintenance of genomic stability. In this article, we review recent advances in our understanding of how sirtuins affect cancer metabolism, DNA repair and the tumour microenvironment and how activating or inhibiting sirtuins may be important in preventing or treating cancer.

 

Figure 1: Overview of the role of sirtuins in the regulation of cancer metabolism

The inhibitory effects of sirtuin 3 (SIRT3), SIRT4 and SIRT6 on metabolic pathways that drive cancer cells are depicted. In normal cells, SIRT6 functions as a co-repressor for the transcription factors hypoxia-inducible factor 1α (HIF1α…

 

Tumor suppressor p53 cooperates with SIRT6 to regulate gluconeogenesis by promoting FoxO1 nuclear exclusion

Ping Zhanga,1, Bo Tua,1, Hua Wangb , Ziyang Caoa , Ming Tanga , … , Bin Gaob , Robert G. Roederd,2, and Wei-Guo Zhua,e,2
PNAS | July 22, 2014;111(29): 10684–10689 |   http://www.pnas.org/content/111/29/10684.full.pdf  http://www.pnas.org/lookup/suppl/doi:10. 1073/pnas.1411026111/-/DCSupplemental.

In mammalian cells, tumor suppressor p53 plays critical roles in the regulation of glucose metabolism, including glycolysis and oxidative phosphorylation, but whether and how p53 also regulates gluconeogenesis is less clear. Here, we report that p53 efficiently down-regulates the expression of phosphoenolpyruvate carboxykinase (PCK1) and glucose-6-phosphatase (G6PC), which encode rate-limiting enzymes in gluconeogenesis. Cell-based assays demonstrate the p53-dependent nuclear exclusion of forkhead box protein O1 (FoxO1), a key transcription factor that mediates activation of PCK1 and G6PC, with consequent alleviation of FoxO1- dependent gluconeogenesis. Further mechanistic studies show that p53 directly activates expression of the NAD+-dependent histone deacetylase sirtuin 6 (SIRT6), whose interaction with FoxO1 leads to FoxO1 deacetylation and export to the cytoplasm. In support of these observations, p53-mediated FoxO1 nuclear exclusion, down-regulation of PCK1 and G6PC expression, and regulation of glucose levels were confirmed in C57BL/J6 mice and in liver-specific Sirt6 conditional knockout mice. Our results provide insights into mechanisms of metabolism-related p53 functions that may be relevant to tumor suppression.

As the “guardian of the genome,” tumor suppressor p53 has been reported to coordinate diverse cellular responses to a broad range of environment stresses (1) and to play antineoplastic roles by activating downstream target genes involved in DNA damage repair, apoptosis, and cell-cycle arrest (2). Recent studies have indicated broader roles for p53 in mediating metabolic changes in cells under various physiological and pathological conditions (3–7). For example, p53 was reported to influence the balance between glycolysis and oxidative phosphorylation by inducing the p53-induced glycolysis and apoptosis regulator (TIGAR) and by regulating the synthesis of cytochrome c oxidase 2 (SCO2) (3), respectively, thus promoting the switch from glycolysis to oxidative phosphorylation. p53 also may impede metabolism by reducing glucose import (4) or by inhibiting the pentose phosphate pathway (PPP) (5). More recently, context-dependent inhibitory (6) or stimulatory (7, 8) effects of p53 on gluconeogenesis have been reported. It thus is clear that p53 plays important roles in glucose regulation in mammalian cells. Glucose homeostasis is maintained by a delicate balance between intestinal absorption of sugar, gluconeogenesis, and the utilization of glucose by the peripheral tissues, irrespective of feeding or fasting (9). The gluconeogenesis pathway is catalyzed by several key enzymes that include the first and last rate-limiting enzymes of the process, phosphoenolpyruvate carboxykinase (PCK1) and glucose-6-phosphatase (G6PC), respectively. The expression of both PCK1 and G6PC is controlled mainly at the transcription level. For example, the transcription factor forkhead box protein O1 (FoxO1) activates gluconeogenesis through direct binding to the promoters of G6PC and PCK1 (10). A dominant negative FoxO1 lacking its transactivation domain significantly decreases gluconeogenesis (11) whereas FoxO1 ablation impairs fasting- and cAMP-induced PCK1 and G6PC expression (12). Therefore, factors influencing expression of FoxO1 or its binding activity to the PCK1 and G6PC promoters are potential targets for gluconeogenesis regulation. The transcription activity of FoxO family members is regulated by a sophisticated signaling network. Various environmental stimuli cause different posttranslational modifications of FoxO proteins, including phosphorylation, acetylation, ubiquitination, and methylation (13–15). The phosphorylation of FoxO proteins is known to be essential for their shuttling between the nucleus and cytoplasm. For example, kinase Akt/PKB phosphorylates FoxO1 at threonine 24 and at serines 256 and 319, which in turn leads to 14-3-3 binding and subsequent cytoplasmic sequestration. The acetylation of FoxO proteins also affects their trafficking and DNA-binding activities (15–17). Sirtuin (SIRT)1, a homolog of the yeast silent information regulator-2 (Sir2), has been identified as a deacetylase for FoxO proteins (15, 17, 18). Of the seven mammalian sirtuins, SIRT1, SIRT6, and SIRT7 are localized to the nucleus (19), and SIRT6 was recently reported to act as a central player in regulating the DNA damage response, glucose metabolism, and aging (20–26). Using a knockout mouse model, it was found that SIRT6 functions as a corepressor of the transcription factor Hif1α to suppress glucose uptake and glycolysis.

Significance: Beyond its canonical functions in processes such as cell-cycle arrest, apoptosis, and senescence, the tumor suppressor p53 has been increasingly implicated in metabolism. Here, in vitro and in vivo studies establish a role for p53 in gluconeogenesis through a previously unidentified mechanism involving (i) direct activation of the gene encoding the NAD-dependent deacetylase sirtuin 6 (SIRT6), (ii) SIRT6-dependent deacetylation and nuclear exclusion of forkhead box protein O1 (FoxO1), and (iii) downregulation of FoxO1-activated genes (G6PC and PCK1) that are rate-limiting for gluconeogenesis. These results have implications for proposed tumor-suppressor functions of p53 through regulation of metabolic pathways.

Among a variety of other functions, SIRT6 was previously connected to glucose metabolism. For example, SIRT6 acts as a corepressor of the transcription factor Hif1-α to suppress glycolysis (23). Conversely, the deletion of Sirt6 in mice results in severe hypoglycemia (33) whereas the liver-specific deletion of Sirt6 leads to increased glycolysis and triglyceride synthesis (23, 34). Our study adds further evidence that SIRT6 plays an important role in glucose metabolism by connecting p53 transcription activity and gluconeogenesis. Our data also reemphasize a previously established role for SIRT6 in regulating the acetylation state and nuclear localization of FoxO proteins, albeit in a divergent manner. Thus, the Caenorhabditis elegans SIRT6/7 homolog SIR-2.4 was implicated in DAF-16 deacetylation and consequent nuclear localization and function in stress responses (35); and the effect was reported to be indirect and to involve a stress-induced inhibition by SIR-2.4 of CBP-mediated acetylation of DAF-16 that is independent of its deacetylase activity. These results, emphasizing context-dependent SIRT6 mechanisms, contrast with the SIRT6 deacetylase activity requirement for FoxO1 nuclear exclusion in the present study and a likely direct effect of SIRT6 on FoxO1 deacetylation based on their direct interaction, the SIRT6 deacetylase activity requirement, and precedent (15, 17, 18) from direct SIRT1-mediated deacetylation of FoxO proteins.

Despite a high genetic diversity, cancer cells exhibit a common set of functional characteristics, one being the “Warburg effect”: i.e., continuous high glucose uptake and a higher rate of glycolysis than that in normal cells (36). To favor the rapid proliferation requirement for high ATP/ADP and ATP/AMP ratios, cancer cells use large amounts of glucose. p53, as one of the most important tumor suppressors, exerts its antineoplastic function through diverse pathways that include the regulation of glucose metabolism. Thus, p53 regulates glucose metabolism by activation of TIGAR (3), which lowers the intracellular concentrations of fructose-2,6-bisphosphate and decreases glycolysis. On the other hand, p53 activation causes down-regulation of several glycolysisrelated factors such as phosphoglycerate mutase (PGM) (37) and the glucose transporters (4). Expression of p53 also can limit the activity of IκBα and IκBβ, thereby restricting the activation of NFκB and dampening the expression of glycolysis-promoting genes such as GLUT3 (38). As a reverse glycolysis pathway, gluconeogenesis generates glucose from noncarbohydrate precursors and is conceivably essential for tumor cell growth. However, the current study further supports the notion (6) that p53 is also involved in a gluconeogenesis inhibition pathway, which in this case is executed by enhanced SIRT6 expression and subsequent FoxO1 nuclear exclusion. These results raise the interesting possibility that an inhibition of gluconeogenesis may contribute to the tumorsuppressive function of p53.

 

http://www.frontiersin.org/Journal/DownloadFile/1/2496/20065/1/21/fphar-03-00022_pdf

http://www.jcpjournal.org/journal/DOIx.php?id=10.15430/JCP.2013.18.3.221
Keywords : Oncogenes, Tumor suppressors, Glutamine metabolism, Cancer cells … p53 is a well-known protein which is involved in many cellular functionsincluding cell … deprivation activates p53 by regulating protein phosphatase 2A ( PP2A). …. and tumor suppressors may affect glutamine metabolism in cancercells

 

Protein controlling glucose metabolism also a tumor suppressor

Finding supports metabolic strategies to control tumor growth

http://www.massgeneral.org/about/pressrelease.aspx?id=1530    December 6, 2012

A protein known to regulate how cells process glucose also appears to be a tumor suppressor, adding to the potential that therapies directed at cellular metabolism may help suppress tumor growth.  In their report in the Dec. 7 issue of Cell, a multi-institutional research team describes finding that cells lacking the enzyme SIRT6, which controls how cells process glucose, quickly become cancerous.  They also found evidence that uncontrolled glycolysis, a stage in normal glucose metabolism, may drive tumor formation in the absence of SIRT6 and that suppressing glycolysis can halt tumor formation.

“Our study provides solid evidence that SIRT6 may function as a tumor suppressor by regulating glycolytic metabolism in cancer cells,” says Raul Mostoslavsky, MD, PhD, of the Massachusetts General Hospital (MGH) Cancer Center, senior author of the report.  “Critically, our findings indicate that, in tumors driven by low SIRT6 levels, drugs that may inhibit glycolysis – currently a hot research topic among biotechnology companies – could have therapeutic benefits.”

The hypothesis that a switch in the way cells process glucose could set off tumor formation was first proposed in the 1920s by German researcher Otto Warburg, who later received the Nobel Prize for discoveries in cellular respiration.  He observed that, while glucose metabolism is normally a two-step process involving glycolysis in the cellular cytoplasm followed by cellular respiration in the mitochondria, in cancer cells rates of glycolysis are up to 200 times higher.  Warburg’s proposition that this switch in glucose processing was a primary cause of cancer did not hold up, as subsequent research supported the role of mutations in oncogenes, which can spur tumor growth if overexpressed, and tumor suppressors, which keep cell proliferation under control.  But recent studies have suggested that alterations in cellular metabolism may be part of the process through which activated oncogenes or inactivated tumor suppressors stimulate cancer formation.

A 2010 study led by Mostoslavsky found that the absence of SIRT6 – one of a family of proteins called sirtuins that regulate many important biological pathways – appears to “flip the switch” from normal glucose processing to the excess rates of glycolysis seen in cancer cells. The current study was specifically designed to investigate whether SIRT6’s control of glucose metabolism also suppresses tumor formation.  The research team first showed that cultured skin cells from embryonic mice lacking SIRT6 proliferated rapidly and quickly formed tumors when injected into adult mice.  They also confirmed elevated glycolysis levels in both cells lacking SIRT6 and tumor cells and found that formation of tumors through SIRT6 deficiency did not appear to involve oncogene activation.

Analysis of tumor samples from patients found reduced SIRT6 expression in many – particularly in colorectal and pancreatic tumors.  Even among patients whose tumors appeared to be more aggressive, higher levels of SIRT6 expression may have delayed or, for some, prevented relapse.   In a mouse model programmed to develop numerous colon polyps, the researchers showed that lack of intestinal SIRT6 expression tripled the formation of polyps, many of which became invasive tumors.  Treating the animals with a glycolytic inhibitor significantly reduced tumor formation, even in the absence of SIRT6.

“Our results indicate that, at least in certain cancers, inhibiting glycolytic metabolism could provide a strong alternative way to halt cancer growth, possibly acting synergistically with current anti-tumor therapies,” says Mostoslavsky, an assistant professor of Medicine at Harvard Medical School.  “Cancer metabolism has only recently emerged as a hallmark of tumorigenesis, and the field is rapidly expanding.  With the current pace of research and the speed at which some basic discoveries are moving into translational studies, it is likely that drugs targeting cancer metabolism may be available to patients in the near future.”

 

THE HISTONE DEACETYLASE SIRT6 IS A NOVEL TUMOR SUPPRESSOR THAT CONTROLS CANCER METABOLISM

Reprogramming of cellular metabolism is a key event during tumorigenesis. Despite being known for decades (Warburg effect), the molecular mechanisms regulating this switch remained unexplored. Here, we identify SIRT6 as a novel tumor suppressor that regulates aerobic glycolysis in cancer cells. Importantly, loss of SIRT6 leads to tumor formation without activation of known oncogenes, while transformed SIRT6-deficient cells display increased glycolysis and tumor growth, suggesting that SIRT6 plays a role in both establishment and maintenance of cancer. Using a conditional SIRT6 allele, we show that SIRT6 deletion in vivoincreases the number, size and aggressiveness of tumors. SIRT6 also functions as a novel regulator of ribosome metabolism by co-repressing MYC transcriptional activity. Lastly, SIRT6 is selectively downregulated in several human cancers, and expression levels of SIRT6 predict prognosis and tumor-free survival rates, highlighting SIRT6 as a critical modulator of cancer metabolism. Our studies reveal SIRT6 to be a potent tumor suppressor acting to suppress cancer metabolism.

Cancer cells are characterized by the acquisition of several characteristics that enable them to become tumorigenic (Hanahan and Weinberg, 2000). Among them, the ability to sustain uncontrolled proliferation represents the most fundamental trait of cancer cells. This hyperproliferative state involves the deregulation of proliferative signaling pathways as well as loss of cell cycle regulation. In addition, tumor cells need to readjust their energy metabolism to fuel cell growth and division. This metabolic adaptation is directly regulated by many oncogenes and tumor suppressors, and is required to support the energetic and anabolic demands associated with cell growth and proliferation (Lunt and Vander Heiden, 2011).

Alteration in glucose metabolism is the best-known example of metabolic reprogramming in cancer cells. Under aerobic conditions, normal cells convert glucose to pyruvate through glycolysis, which enters the mitochondria to be further catabolized in the tricarboxylic acid cycle (TCA) to generate adenosine-5’-triphosphate (ATP). Under anaerobic conditions, mitochondrial respiration is abated; glucose metabolism is shifted towards glycolytic conversion of pyruvate into lactate. This metabolic reprogramming is also observed in cancer cells even in the presence of oxygen and was first described by Otto Warburg several decades ago (Warburg, 1956; Warburg et al., 1927). By switching their glucose metabolism towards “aerobic glycolysis”, cancer cells accumulate glycolytic intermediates that will be used as building blocks for macromolecular synthesis (Vander Heiden et al., 2009). Most cancer cells exhibit increased glucose uptake, which is due, in part, to the upregulation of glucose transporters, mainly GLUT1 (Yamamoto et al., 1990; Younes et al., 1996). Moreover, cancer cells display a high expression and activity of several glycolytic enzymes, including phospho-fructose kinase (PFK)-1, pyruvate kinase M2, lactate dehydrogenase (LDH)-A and pyruvate dehydrogenase kinase (PDK)-1 (Lunt and Vander Heiden, 2011), leading to the high rate of glucose catabolism and lactate production characteristic of these cells. Importantly, downregulation of either LDH-A or PDK1 decreases tumor growth (Bonnet et al., 2007; Fantin et al., 2006; Le et al., 2010) suggesting an important role for these proteins in the metabolic reprogramming of cancer cells.

Traditionally, cancer-associated alterations in metabolism have been considered a secondary response to cell proliferation signals. However, growing evidence has demonstrated that metabolic reprogramming of cancer cells is a primary function of activated oncogenes and inactivated tumor suppressors (Dang et al., 2012;DeBerardinis et al., 2008; Ward and Thompson, 2012). Despite this evidence, whether the metabolic reprogramming observed in cancer cells is a driving force for tumorigenesis remains as yet poorly understood.

Sirtuins are a family of NAD+-dependent protein deacetylases involved in stress resistance and metabolic homeostasis (Finkel et al., 2009). In mammals, there are seven members of this family (SIRT1-7). SIRT6 is a chromatin-bound factor that was first described as a suppressor of genomic instability (Mostoslavsky et al., 2006). SIRT6 also localizes to telomeres in human cells and controls cellular senescence and telomere structure by deacetylating histone H3 lysine 9 (H3K9) (Michishita et al., 2008). However, the main phenotype SIRT6 deficient mice display is an acute and severe metabolic abnormality. At 20 days of age, they develop a degenerative phenotype that includes complete loss of subcutaneous fat, lymphopenia, osteopenia, and acute onset of hypoglycemia, leading to death in less than ten days (Mostoslavsky et al., 2006). Recently, we have demonstrated that the lethal hypoglycemia exhibited by SIRT6 deficient mice is caused by an increased glucose uptake in muscle and brown adipose tissue (Zhong et al., 2010). Specifically, SIRT6 co-represses HIF-1α by deacetylating H3K9 at the promoters of several glycolytic genes and, consequently, SIRT6 deficient cells exhibit increased glucose uptake and upregulated glycolysis even under normoxic conditions (Zhong et al., 2010). Such a phenotype, reminiscent of the “Warburg Effect” in tumor cells, prompted us to investigate whether SIRT6 may protect against tumorigenesis by inhibiting glycolytic metabolism.

Here, we demonstrate that SIRT6 is a novel tumor suppressor that regulates aerobic glycolysis in cancer cells. Strikingly, SIRT6 acts as a first hit tumor suppressor and lack of this chromatin factor leads to tumor formation even in non-transformed cells. Notably, inhibition of glycolysis in SIRT6 deficient cells completely rescues their tumorigenic potential, suggesting that enhanced glycolysis is the driving force for tumorigenesis in these cells. Furthermore, we provide new data demonstrating that SIRT6 regulates cell proliferation by acting as a co-repressor of c-Myc, inhibiting the expression of ribosomal genes. Finally, SIRT6 expression is downregulated in human cancers, strongly reinforcing the idea that SIRT6 is a novel tumor suppressor.

…..

In addition to controlling glucose metabolism in cancer cells, our current work unravels a novel function of SIRT6 as a regulator of ribosomal gene expression. One of the main features of cancer cells is their high proliferative potential. In order to proliferate, cancer cells readjust their metabolism to generate biosynthetic precursors for macromolecular synthesis (Deberardinis et al., 2008). However, protein synthesis also requires the activation of a transcriptional program leading to ribosome biogenesis and mRNA translation (van Riggelen et al., 2010). As a master regulator of cell proliferation, MYC regulates ribosome biogenesis and protein synthesis by controlling the transcription and assembly of ribosome components as well as translation initiation (Dang et al., 2012; van Riggelen et al., 2010). Our results show that SIRT6 specifically regulates the expression of ribosomal genes. In keeping with this, SIRT6-deficient tumor cells exhibit high levels of ribosomal protein gene expression. Beyond ribosome biosynthesis, MYC regulates glucose and glutamine metabolism (Dang et al., 2012). Our results show that glutamine – but not glucose – metabolism is rescued in SIRT6-deficient/MYC knockdown cells, suggesting that SIRT6 and MYC might have redundant roles in regulating glucose metabolism.

Overall, our results indicate that SIRT6 represses tumorigenesis by inhibiting a glycolytic switch required for cancer cell proliferation. Inhibition of glycolysis in SIRT6-deficient cells abrogates tumor formation, providing proof of concept that inhibition of glycolytic metabolism in tumors with low SIRT6 levels could provide putative alternative approaches to modulate cancer growth. Furthermore, we uncover a new role for SIRT6 as a regulator of ribosome biosynthesis by co-repressing MYC transcriptional activity. Our results indicate that SIRT6 sits at a critical metabolic node, modulating both glycolytic metabolism and ribosome biosynthesis (Figure 7L). SIRT6 deficiency deregulates both pathways, leading to robust metabolic reprogramming that is sufficient to promote tumorigenesis bypassing major oncogenic signaling pathway activation.

 

Lack of cellular enzyme triggers switch in glucose processing

Understanding mechanism underlying SIRT6 activity may help treat diabetes, cancer

http://www.massgeneral.org/about/pressrelease.aspx?id=1196   January 21, 2010

A study investigating how a cellular enzyme affects blood glucose levels in mice provides clues to pathways that may be involved in processes including the regulation of longevity and the proliferation of tumor cells. In their report in the January 22 issue of Cell, a Massachusetts General Hospital (MGH)-based team of researchers describes the mechanism by which absence of the enzyme SIRT6 induces a fatal drop in blood sugar in mice by triggering a switch between two critical cellular processes.

“We found that SIRT6 functions as a master regulator of glucose levels by maintaining the normal processes by which cells convert glucose into energy,” says Raul Mostoslavsky, MD, PhD, of the MGH Cancer Center, who led the study. “Learning more about how this protein controls the way cells handle glucose could lead to new approaches to treating type 2 diabetes and even cancer.”

SIRT6 belongs to a family of proteins called sirtuins, which regulate important biological pathways in organisms from bacteria to humans. Originally discovered in yeast, sirtuins in mammals have been shown to have important roles in metabolic regulation, programmed cell death and adaptation to stress. SIRT6 is one of seven mammalian sirtuins, and Mostoslavsky’s team previously showed that mice lacking the protein die in the first month of life from acute hypoglycemia. The current study was designed to investigate exactly how lack of SIRT6 causes this radical drop in blood sugar.

Normally cells convert glucose into energy through a two-step process. The first stage called glycolysis takes place in the cytoplasm, where glucose is broken down into an acid called pyruvate and a few molecules of ATP, the enzyme that provides the energy to power most biological processes. Pyruvate is taken into cellular structures called mitochondria, where it is further processed to release much greater amounts of ATP through a process called cellular respiration.

In a series of experiments in mouse cells, the researchers showed that SIRT6-deficiency hypoglycemia is caused by increased cellular uptake of glucose and not by elevated insulin levels or defects in the absorption of glucose from food. They then found increased levels of glycolysis and reduced mitochondrial respiration in SIRT6-knockout cells, something usually seen when cells are starved for oxygen or glucose, and showed that activation of the switch from cellular respiration to glycolysis is controlled through SIRT6’s regulation of a protein called HIF1alpha. Normally, SIRT6 represses glycolytic genes through its role as a compactor of chromatin – the tightly wound combination of DNA and a protein backbone that makes up chromosomes. In the absence of SIRT6, this structure is opened, causing activation of these glycolytic genes. The investigators’ finding increased expression of glycolytic genes in living SIRT6-knockout mice – which also had elevated levels of lactic acid, characteristic of a switch to glycolytic glucose processing – supported their cellular findings.

Studies in yeast, worms and flies have suggested a role for sirtuins in aging and longevity, and while much of the enzymes’ activity in mammals is unclear, SIRT6’s control of critical glucose-metabolic pathways could signify a contribution to lifespan regulation. Elevated glycolysis also is commonly found in tumor cells, suggesting that a lack of SIRT6 could contribute to tumor growth. Conversely, since knocking out SIRT6 causes blood sugar to drop, limited SIRT6 inhibition could be a novel strategy for treating type 2 diabetes.

“There’s a lot we still don’t know about SIRT6,” adds Mostoslavsky, who is an assistant professor of Medicine at Harvard Medical School. “We need to identify the factors that interact with SIRT6 and determine how it is regulated; investigate whether it acts as a tumor suppressor and how it might help lower glucose levels in diabetes; and determine its target organs in living animals, all of which we are investigating.”

 

A tale of metabolites: the crosstalk between chromatin and energy metabolism

Mitochondrial metabolism influences histone and DNA modifications by retrograde signaling and activation of transcriptional programs. Considering the high number of putative sites for acetylation and methylation in chromatin, we propose in this Perspective that epigenetic modifications might impinge on cellular metabolism by affecting the pool of acetyl-CoA and SAM.

Metabolism can be defined as the sum of chemical reactions that occur within a cell to sustain life. It is also the way that a cell interacts with energy sources: in other words, it is the coordination of energy intake, its utilization and storage that ultimately allows growth and cell division. In animal cells, mitochondria have evolved to become the most efficient system to generate energy. This organelle consumes carbon sources via oxidative phosphorylation to produce ATP, the energy currency of the cell. Additionally, the mitochondria produces intermediate metabolites for the biosynthesis of DNA, proteins and lipids.

Under basic dividing conditions, uptake of nutrients is tightly regulated through growth signaling pathways, thus differentiated cells engage in oxidative metabolism, the most efficient mechanism to produce energy from nutrients. Cells metabolize glucose to pyruvate through glycolysis in the cytoplasm, and this pyruvate is then oxidized into CO2 through the mitochondrial TCA cycle. The electrochemical gradient generated across the inner mitochondrial membrane facilitates ATP production in a highly efficient manner. Studies in recent years indicate that under conditions of nutrient excess, cells increase their nutrient uptake, adopting instead what is known as aerobic glycolysis, an adaptation that convert pyruvate into lactate, enabling cells to produce intermediate metabolites to sustain growth (anabolic metabolism) (1). Interestingly, most cancer cells undergo the same metabolic switch (Warburg Effect), a unique evolutionary trait that allows them to grow unabated. Although aerobic glycolysis generates much less ATP from glucose compared to oxidative phosphorylation, it provides critical intermediate metabolites that are used for anaplerotic reactions, and therefore is an obligatory adaptation among highly proliferative cells. In response to variations in nutrient availability, cells regulate their metabolic output, coordinating biochemical reactions and mitochondrial activity by altering transcription of mitochondrial genes through both activation of transcription factors, such as PGC1α, and chromatin modulators that exert epigenetic changes on metabolic genes.

Mitochondrial dysfunction has been implicated in aging, degenerative diseases and cancer. Proper mitochondrial function can be compromised by the accumulation of mutations in mitochondrial DNA that occur during aging. In addition, reactive oxygen species (ROS) produced during oxidative phosphorylation can promote oxidative damage to DNA, protein and lipids, in turn adversely affecting global cellular functions. In recent years, several studies have illustrated a novel unexpected link between metabolism and gene activity: fluctuations in mitochondrial and cytoplasmic metabolic reactions can reprogram global metabolism by means of impacting epigenetic dynamics. These studies will be briefly summarized in the first part of this article. In the second part, we will propose a provocative novel hypothesis: the crosstalk between metabolism and epigenetics is a two-way street, and defects in chromatin modulators may affect availability of intermediate metabolites, in turn influencing energy metabolism.

Metabolism impacts epigenetics

A regulated crosstalk between metabolic pathways in the mitochondria and epigenetic mechanisms in the nucleus allows cellular adaptations to new environmental conditions. Fine-tuning of gene expression is achieved by changes in chromatin dynamics, including methylation of DNA and posttranslational modifications of histones: acetyl, methyl and phosphate groups can be added by acetyltransferases, methyltransferases and kinases, respectively, to different residues on histones. Given the number of residues that can potentially undergo modifications in histone tails and in the DNA, it is reasonable to consider that metabolic changes affecting the availability of these metabolites will impact epigenetics (as discussed below).

Recently, acetylation of proteins was revealed to be as abundant as phosphorylation (2). This posttranslational modification involves the covalent binding of an acetyl group obtained from acetyl-CoA to a lysine. In histones, acetylation can modify higher order chromatin structure and serve as a docking site for histone code readers. Recent mass spectrometry studies have uncovered the complete acetylome in human cells and revealed that protein acetylation occurs broadly in the nucleus, cytoplasm and mitochondria, affecting more than 1700 proteins (2). Acetylation of proteins depends on the availability of acetyl-CoA in each cellular compartment, but this metabolite is produced in the mitochondria and cannot cross the mitochondrial membrane. In single cell eukaryotes, the pool of acetyl groups required for histone acetylation comes from the production of acetyl-CoA by the enzyme acetyl-CoA synthetase (Acs2p), which is responsible of converting acetate into acetyl-CoA. In mammalian cells, although they have a homolog enzyme to Acs2p, AceCS1, the majority of acetyl-CoA is produced from mitochondrion-derived citrate by the enzyme adenosine triphosphate (ATP)-citrate lyase (ACL) (3). ACL is present in the cytoplasm and in the nucleus, and is responsible for the production of acetyl-CoA from citrate in both compartments. Citrate is generated in the metabolism of glucose and glutamine in the TCA cycle. In contrast to acetyl-CoA, citrate can cross the mitochondrial membrane and diffuse through the nuclear pores into the nucleus, where it can be converted into acetyl-CoA by ACL. Wellen and colleagues found that ACL is required for acetylation of histones under normal growth conditions; knockdown of ACL decreases the pool of acetyl-CoA in the nucleus and reduces the level of histone acetylation (3). Strikingly, reduction in histone acetylation occurs preferentially around glycolytic genes, leading to downregulation of their transcription and therefore inhibition of glycolysis. These observations reveal a process where glucose metabolism dictates histone acetylation that in a feedback mechanism controls the rate of glycolysis.

Notably, deacetylation of histones also exhibits a metabolic influence. Deacetylation of histones is achieved by class I and class II histone deacetylases (HDACs) and by a separate class (class III), also known as sirtuins. Sirtuins use NAD+ as a cofactor for deacetylation, and the ratio of NAD+/NADH regulates their activity. In diets rich in carbohydrates, growth factors stimulate cellular glucose uptake and the production of energy is carried out through glycolysis. In this context, the NAD+/NADH ratio decreases, in turn inhibiting, in theory, sirtuins in the cytoplasm (Sirt2) and nucleus (Sirt1, Sirt6 and Sirt7). In fact, low Sirt1 and Sirt6 activity generates a global increase in protein acetylation. Interestingly, Sirt6, which is exclusively nuclear, deacetylates H3K9 Hif1α target genes, repressing their transcription. Since most of these genes are glycolytic, deacetylation of histones by Sirt6 modulates glycolysis. Indeed, SIRT6-deficient mice experience a dramatic increase in glucose uptake for glycolysis, triggering a fatal hypoglycemia in few weeks (4).

In animal cells, both histone acetylation and deacetylation are under the control of glucose metabolism through the availability of acetyl-CoA and NAD+, respectively. However, is this metabolic control restricted to acetylation, or can other reactions in the nucleus be influenced by the energy status of the cell?

Histone methyltransferases (HMTs) use S-adenosylmethionine (SAM) to transfer a methyl group onto lysine and arginine residues on histone tails. SAM is produced from methionine by the enzyme S-adenosyl methionine transferase (MAT) in a reaction that uses ATP. The recent finding of MAT in the nucleus suggests that the SAM pool could also be controlled locally in this compartment (5). The reverse reaction catalyzed by histone demethylases (HDMs) uses flavin adenine dinucleotide (FAD+) and α-ketoglutarate as coenzymes. FAD is a common redox coenzyme that exists in two different redox states. In its reduced state, FADH2 is a carrier of energy and when oxidized, FAD+ is consumed in the oxidation of succinate to fumarate by the enzyme succinate dehydrogenase (complex II) in one of the last steps of the TCA cycle. On the other hand, α-ketoglutarate is an intermediate in the TCA cycle. It is generated from isocitrate by the enzymes isocitrate dehydrogenase 1 and 2 (IDH1-cytosolic and IDH2-mitochondrial) (Figure 1A–B). Based on these findings, it is easy to infer that the amount of coenzymes used for histone methylation and demethylation could also be controlled by metabolic reactions. Moreover, the different cellular compartments compete for the same metabolites. Indeed, changes in diet that affect the biosynthesis of SAM, FAD and α-ketoglutarate in the mitochondria and cytoplasm have been shown to impact histone methylation (6).

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Figure 1   A) Diagram depicting two-way crosstalk between metabolites in cytoplasm/mitochondria and chromatin.

More recently, some of the metabolic enzymes responsible for producing cofactors for nuclear biochemical reactions have been found mutated in cancer. For instance, IDH1 and IDH2 somatic mutations are recurrent in gliomas and acute myeloid leukemias (AML). These mutations lead not only to a decreased production of α-ketoglutarate but also to a new activity: α-ketoglutarate is in fact converted into 2-hydroxyglutarate (2-HG), a metabolite rarely found in normal cells. The new metabolite is a competitive inhibitor of α-ketoglutarate-dependent dioxygenase enzymes, including the Jumonji C (JmjC) domain containing histone demethylases and the recently discovered TET family of 5-methylcytosine (5mC) hydroxylases involved in DNA demethylation (7). By inhibiting JmjC and TET enzymes, the aberrant production of 2-HG generates a genome-wide histone and DNA hypermethylation phenotype. This is considered to be, at least in part, at the origin of tumorigenesis in IDH1 and IDH2 mutated cells and for this reason, 2-HG may earn its place as an oncometabolite. The discovery that mutations in metabolic enzymes may influence tumorigenesis by means of controlling genome-wide epigenetic changes caused a paradigm shift, indicating that such metabolic abnormalities may affect cancer beyond the Warburg Effect.  ….

Chromatin modifications and cellular metabolism are tightly connected. Thus far the only aspects that have been considered are the retrograde signaling, with mitochondrial metabolites affecting histone modifications, and the anterograde transcriptional regulation of metabolism. A third aspect of the link between nucleus and metabolism has been, in our opinion, omitted so far: a direct influence of chromatin on acetyl-CoA and SAM availability, which may have an essential role also in cancer establishment and development (Figure 1A–B). Notably, a shift towards glycolytic metabolism is now considered a hallmark of cancer cells. It is also true that multiple tumors carry mutations in chromatin modifiers. However, new studies suggest that those two processes may be much more intertwined that previously appreciated, further blurring the limits on their respective roles in tumorigenesis. There is no doubt that changes in metabolite availability can drastically impact chromatin modifications. We believe that the opposite may be true as well. At least in mouse models, deficiency in two chromatin modifiers, SIRT6 and Jhdm2, causes drastic metabolic abnormalities. Even though some of those phenotypes depend on changes in gene-expression, we would like to propose that severe attrition of metabolite pools might as well play a role, a possibility that awaits experimental proof.

……

 

Investigators at UC San Diego say that when they blocked a well known signaling molecule that plays a major role in driving colorectal cancer, an escape pathway emerged that allowed tumors to continue to grow.

The pathway they explored, ERK1/2, is a problem for about a third of all colorectal cancer patients, says Petrus R. de Jong, MD, PhD, a co-first author on the paper.

“Since we were genetically deleting the ERK1/2 pathway, we expected to see less cell proliferation,” said de Jong. “Instead, the opposite occurred. There was more cell growth and loss of organization within the cells.”

The problem was ERK5, the investigators add. And when that was blocked as well in animal models and cell lines for the disease, the combination approach proved more effective in halting cancer growth.

“If you block one pathway, cancer cells usually mutate and find another pathway that ultimately allows for a recurrence of cancer growth,” said co-first author Koji Taniguchi. “Usually, mutations occur over weeks or months. But other times, as in this case, the tumor does not need to develop mutations to find an escape route from targeted therapy. When you find the compensatory pathway and block both, there is no more escape.”

 

GEN News Highlights    May 18, 2016   http://www.genengnews.com/gen-news-highlights/blocking-cancer-signaling-leads-to-discovery-of-new-tumor-promoting-pathway/81252738/
Blocking Cancer Signaling Leads to Discovery of New Tumor-Promoting Pathway

 Immunofluorescent staining of intestinal epithelium tissue shows cell growth (green). In a normal mouse model (left), cell growth is controlled, but in a mouse model with the ERK1/2 pathway blocked (right) increased cell proliferation and loss of organization occurred. [UC San Diego Health]

An international research team lead by scientists at the University of California San Diego School of Medicine uncovered some surprising results while investigating a potential therapeutic target for the ERK1 and two pathways. These signaling pathways are widely expressed and known to drive cancer growth in one-third of patients with colorectal cancer (CRC). The UCSD team found that an alternative pathway immediately emerges when ERK1/2 is halted, thus allowing tumor cell proliferation to continue.

“Since we were genetically deleting the ERK1/2 pathway, we expected to see less cell proliferation,” explained co-lead study author Petrus R. de Jong, M.D., Ph.D., translational scientist at Sanford Burnham Prebys Medical Discovery Institute. “Instead, the opposite occurred. There was more cell growth and loss of organization within the cells.”

The exciting part of this new study is investigators found that treating both ERK1/2 and the compensatory pathway ERK5 concomitantly with a combination of drug inhibitors halted CRC growth more effectively in both mouse models and human CRC cell lines.

“We show that loss of Erk1/2 in intestinal epithelial cells results in defects in nutrient absorption, epithelial cell migration, and secretory cell differentiation,” the authors wrote. “However, intestinal epithelial cell proliferation is not impeded, implying compensatory mechanisms. Genetic deletion ofErk1/2 or pharmacological targeting of MEK1/2 results in supraphysiological activity of the ERK5 pathway. Furthermore, targeting both pathways causes a more effective suppression of cell proliferation in murine intestinal organoids and human CRC lines.”

The findings from this study were published recently in Nature Communications in an article entitled “ERK5 Signalling Rescues Intestinal Epithelial Turnover and Tumour Cell Proliferation upon ERK1/2 Abrogation.”

The ERK pathway plays a critical role in embryonic development and tissue repair because it instructs cells to multiply and start dividing, but when overactivated cancer growth often occurs.

“Therapies aimed at targeting ERK1/2 likely fail because this mechanism is allowing proliferation through a different pathway,” noted senior study author Eyal Raz, M.D., professor of medicine at UC San Diego School of Medicine. “Previously, ERK5 didn’t seem important in colorectal cancer. This is an underappreciated escape pathway for tumor cells. Hence, the combination of ERK1/2 and ERK5 inhibitors may lead to more effective treatments for colorectal cancer patients.”

Currently, there are 1.2 million people living with CRC in the United States, making it the third most common cancer among men and women. In 2016 alone, an estimated 134,490 new cases are expected to be diagnosed, so understanding the molecular mechanisms that drive tumor promotion are paramount to treating this disease effectively.

“If you block one pathway, cancer cells usually mutate and find another pathway that ultimately allows for a recurrence of cancer growth,” remarked co-lead study author Koji Taniguchi, M.D., Ph.D., senior researcher at the Keio University School of Medicine in Tokyo. “Usually, mutations occur over weeks or months. But other times, as in this case, the tumor does not need to develop mutations to find an escape route from targeted therapy. When you find the compensatory pathway and block both, there is no more escape.”

The researchers were excited by their findings but urged caution at over interpretation of their initial findings and suggested that other classes of inhibitors be tested in combination with ERK5 inhibitors in human CRC cells in preclinical mouse models before any patient trial can begin.

 

ERK5 signalling rescues intestinal epithelial turnover and tumour cell proliferation upon ERK1/2 abrogation

Petrus R. de JongKoji TaniguchiAlexandra R. HarrisSamuel BertinNaoki TakahashiJen DuongAlejandro D. CamposGarth PowisMaripat CorrMichael Karin & Eyal Raz
Nature Communications 7, Article number:11551  doi:10.1038/ncomms11551

The ERK1/2 MAPK signalling module integrates extracellular cues that induce proliferation and differentiation of epithelial lineages, and is an established oncogenic driver, particularly in the intestine. However, the interrelation of the ERK1/2 module relative to other signalling pathways in intestinal epithelial cells and colorectal cancer (CRC) is unclear. Here we show that loss of Erk1/2in intestinal epithelial cells results in defects in nutrient absorption, epithelial cell migration and secretory cell differentiation. However, intestinal epithelial cell proliferation is not impeded, implying compensatory mechanisms. Genetic deletion of Erk1/2 or pharmacological targeting of MEK1/2 results in supraphysiological activity of the ERK5 pathway. Furthermore, targeting both pathways causes a more effective suppression of cell proliferation in murine intestinal organoids and human CRC lines. These results suggest that ERK5 provides a common bypass route in intestinal epithelial cells, which rescues cell proliferation upon abrogation of ERK1/2 signalling, with therapeutic implications in CRC.

The extracellular signal-regulated kinases 1 and 2 (ERK1/2) are part of the classical family of mammalian mitogen-activated protein kinases (MAPKs), which also include three c-Jun amino-terminal kinases (JNK1/2/3), four p38 isoforms and its lesser-known counterpart, ERK5. The serine/threonine kinases ERK1 (MAPK3, also known as p44 MAPK) and ERK2 (MAPK1, also known as p42 MAPK) show 83% amino acid identity, are ubiquitously expressed and typically activated by growth factors and phorbol esters, whereas the p38 and JNK pathways are mainly activated by inflammatory cytokines and stress1. MAPKs are involved in regulation of mitosis, gene expression, cell metabolism, cell motility and apoptosis. ERK1/2 are activated by MEK1 and MEK2, which themselves are activated by Raf-1, A-Raf or B-Raf1, 2. Ras proteins (K-Ras, H-Ras or N-Ras) are small GTPases that can be activated by receptor tyrosine kinases (RTKs) or G-protein coupled receptors (GPCRs), which recruit Raf proteins to the plasma membrane where they are activated. Together, these modules constitute the Ras–Raf–MEK–ERK pathway3.

The activation of ERK1/2 results in their nuclear translocation where they can phosphorylate a variety of nuclear targets such as Elk-1, c-Fos and c-Myc1, in addition to p90 ribosomal S6 kinases (p90RSKs) and mitogen- and stress-activated protein kinases, MSK1/2. The full repertoire of substrates for ERK1/2 consists of at least 160 cellular proteins4. These proteins are typically involved in the regulation of cell proliferation—more specifically, G1/S-phase cell cycle progression—and differentiation. However, their cellular effects are context-dependent and determined by the spatial and temporal dynamics of ERK1/2 activity5, which are highly regulated by scaffolding proteins and phosphatases3, 6, 7.

Despite vast literature on the role of ERK1/2 in cell proliferation, the absolute requirement of this signalling module in rapidly dividing tissues relative to other signalling pathways is unknown. The small intestinal epithelium is particularly suitable to address this question given the short (4–8 days) and dynamic life cycle of intestinal epithelial cells (IECs). Lgr5+ intestinal stem cells at the intestinal crypt base produce transit-amplifying cells, which then undergo a number of proliferative cycles before terminal differentiation into absorptive enterocytes at the crypt–villus border. Enterocytes then migrate to the villus tip where they undergo anoikis and are shed into the gut lumen8. All of these cellular events are tightly coordinated by the Wnt, Notch, bone morphogenetic protein (BMP) and Hedgehog pathways9, whereas the roles of ERK1/2 remain to be charted. In the intestines, the ERK1/2 pathway is likely activated by autocrine and paracrine factors downstream of RTKs, such as epidermal growth factor receptor (EGFR)10, and by exogenous microbial-derived substrates that signal through the Toll-like receptor (TLR)/MyD88 pathway11.

To study the effects of ERK1/2 in the adult intestinal epithelium, we generated mice with a conditional (IEC-specific) and tamoxifen-inducible deletion of Erk2 on the Erk1−/− background, which completely abrogates this pathway. We show that the ERK1/2 signalling module, surprisingly, is dispensable for IEC proliferation. Genetic deletion of Erk1/2 in primary IEC or treatment of colorectal cancer (CRC) cell lines with MEK1/2 inhibitors results in compensatory activation of the ERK5 pathway. Moreover, the treatment of human CRC lines with a combination of MEK1/2 and ERK5 inhibitors is more efficacious in the inhibition of cancer cell growth. Thus, compensatory signalling by ERK5 suggests a potential rescue pathway that has clinical implications for targeted therapy in colorectal cancer.

….

Figure 1: Wasting disease associated with malabsorption in Erk1/2ΔIEC mice.

ERK1/2ΔIEC causes wasting and enterocyte dysfunction

Here we show that ERK1/2 signalling in mouse intestinal epithelium is dispensable for cell proliferation, while it resulted in abnormal differentiation of enterocytes, wasting disease and ultimately lethality (Fig. 1). Consistent with these findings, ERK1/2 MAPKs were shown to be associated with the enterocyte brush border and activated upon RTK stimulation or feeding27 or electrical field stimulation in polarized epithelium28. This seems at odds with literature that suggest that maintained ERK1/2 signalling precludes enterocyte differentiation29, 30. A possible explanation for this discrepancy could be that cycling IEC in the transit amplifying zone of the crypt require relatively high levels of active ERK1/2, which is readily blocked by pharmacological intervention, whereas a transition to low level ERK1/2 activity in IEC migrating into the villus compartment promotes the absorptive enterocyte differentiation program that is only perturbed upon complete genetic deletion of Erk1/2. Little is known about the role of ERK1/2 signalling in the life cycle of secretory cells in the gut. A recent report by Heuberger et al.15 described that IEC-specific deletion of non-receptor tyrosine phosphatase, Shp2, resulted in the loss of p-ERK1/2 levels in the small intestine. This coincided with an increased number of Paneth cells at the expense of goblet cells in the small intestine, as well as shortening of villi. They also observed the strongest staining for epithelial p-ERK1/2 in the TA zone. This p-ERK1/2+ staining pattern and the architectural organization of the TA zone were lost in Shp2 knockout mice. Interestingly, the deleterious effects of Shp2 deficiency were rescued by expression of constitutively active MEK1. A model was proposed in which the balance between Wnt/β-catenin and MAPK signalling determines Paneth cell versus goblet cell differentiation, respectively15. This proposed crucial role for ERK1/2 MAPK signalling in intestinal secretory cell differentiation is consistent with our observations inERK1/2ΔIECmice.

Migration and differentiation are functionally intertwined in the intestines, as demonstrated by the immature phenotype of mislocalized Paneth cells observed in ΔIEC mice (Fig. 2). Critical to epithelial cell migration is proper cytoskeleton reorganization mediated by the small GTPases of the Rho family, cell polarization regulated by Cdc42 and dynamic adhesion through cell–matrix and cell–cell interaction via integrin/FAK/Src signalling31. The ERK1/2 module is used as a downstream effector of many of these pathways in the intestine, including Rho GTPases32, FAK33and Src34, and has been suggested to promote cell motility33, 35. RTK signalling also contributes to cell migration, for example, Eph–Ephrin receptor interactions are crucial for correct positioning of Paneth cells36. Ephrin receptor-induced epithelial cell migration has been shown to be mediated by Src and ERK1/2 activation37, 38, which may explain the Paneth cell mislocalization observed in ΔIEC mice. In summary, the ERK1/2 module is indispensable for full maturation of both absorptive enterocytes and the secretory lineage (Fig. 7a), confirming its crucial role in the integration of cellular cues required for determination of epithelial cell fate.

Figure 7: Roles of ERK1/2 and ERK5 in intestinal homeostasis and tumorigenesis.

Roles of ERK1/2 and ERK5 in intestinal homeostasis and tumorigenesis.

(a) When the ERK1/2 pathway is intact, extracellular cues that are transduced via RTKs or GPCRs activate Ras under physiological conditions, or alternatively, Ras is constitutively active in colorectal cancer (RasΔ*), which preferentially activates the Raf–MEK1/2–ERK1/2 module. The nuclear and transcriptional targets of ERK1/2 are crucial for enterocyte and secretory cell differentiation, IEC migration, as well as cell proliferation under homeostatic and oncogenic conditions. Importantly, ERK1/2 activation also results in the activation of negative feedback mechanisms that suppress its upstream kinases (for example, RTKs, son of sevenless, Raf) and activate dual specificity phosphatases (DUSPs), resulting in the silencing of the ERK5 module. (b) Upon abrogation of MEK1/2 or genetic knockout ofErk1/2, the lack of negative feedback mechanisms (that is, feedback activation) results in upregulation of the Ras–Raf–MEK5–ERK5 module, which maintains cell proliferation under physiological conditions, or results in continued tumour cell proliferation in colorectal cancer, respectively. However, the lack of activation of ERK1/2-specific targets results in differentiation and migration defects of intestinal epithelial cells culminating in malabsorption, wasting disease and mortality. Compensatory upregulation of the ERK5 pathway in CRC can be reversed by targeted treatment with its specific inhibitor, XMD8-92.

An unexpected finding was the redundancy of ERK1/2 in the gut with regard to cell proliferation.Erk1/2 deletion was compensated by upregulated ERK5 signalling. Genetic targeting of ERK1/2 in vitro previously showed that Erk2 knockdown is more effective than Erk1 knockdown in suppressing cell proliferation, although this may be related to higher expression levels of the former39. The effect of gene dosage was demonstrated in vivo by the observations that whileErk1−/− mice are viable12 and Erk2−/− mice die in utero13, Erk2+/− mice are only viable when at least one copy of Erk1 is present. However, mice heterozygous (+/−) for both Erk1 and Erk2 alleles were born at lower than Mendelian ratio39. More recently, it was reported that transgenic expression of ERK1 can compensate for Erk2 deletion40, demonstrating functional redundancy between both family members. Deletion of Erk1/2 in adult skin tissue resulted in hypoplasia, which was associated with G2/M cell cycle arrest, without notable differentiation defects of keratinocytes41. These data differ from our observations in the intestines, which might be explained by incomplete and transient siRNA-mediated knockdown of ERK1/2 in primary keratinocyte cultures41, compared with more efficient genomic deletion of Erk1 and Erk2 that is typically achieved by the Villin-Cre-ERT2 system14, possibly resulting in different outcomes.

Both ERK1/2 and ERK5 have been described to promote cell cycle progression, although they have different upstream signalling partners, MEK1/2 and MEK5, respectively1. Furthermore, ERK2 and ERK5 proteins share only about 66% sequence identity, and MEK5 is phosphorylated by MEKK2/3, which can also activate the p38 and JNK pathways42. The ERK5 pathway is classically activated by stress stimuli, in addition to mitogens; thus, it shares features of both the ERK1/2, and p38 and JNK pathways, respectively43. ERK5 induces expression of cyclin D1 (refs 44, 45), and suppresses expression of cyclin dependent kinase inhibitors46, thereby promoting G1/S-phase cell cycle progression. Importantly, the role of ERK5 in IEC differentiation and intestinal homeostasis is currently unknown. Knockout of Erk1/2 in IEC induced activity of ERK5, which was not detectable in naive mice (Fig. 3). These data suggest that the ERK1/2 and ERK5 modules may share proximal signalling components. Although EGFR is a likely candidate in this context19, 20, we found that abrogation of EGFR signalling did not prevent enhanced ERK5 activity upon MEK1/2 inhibition. Although it was originally suggested that ERK5 signalling is independent of Ras20, other groups established that Ras, either through physiological signalling47, or by its oncogenic activity48,49, activates the MEK5–ERK5 signalling axis. Thus, rewiring of signalling networks downstream of Ras could explain the supraphysiological activity of ERK5 upon conditional deletion of Erk1/2 in the intestines. In fact, it has been shown that ERK1/2 signalling mediates negative feedback on ERK5 activity50, possibly through transcriptional activation of dual specificity phosphatases (DUSPs)51. Alternatively, ERK1/2-induced FOS-like antigen 1 (Fra-1) may negatively regulate MEK5 (ref. 52). These data suggest that ERK5 is a default bypass route downstream of RTK-Ras and activated upon loss of ERK1/2-mediated repression, thereby ensuring the transduction of mitogenic signals to the nucleus (Fig. 7b). Consistent with this concept, we found that ERK5 inhibition induces atrophy of ΔIEC intestinal organoids (Fig. 4). In addition, important downstream transcriptional targets of ERK5 and ERK1/2 overlap, such as immediate-early gene Fra1 and oncogene c-Myc, whereas c-Fos and Egr1 were specifically induced by ERK1/2 (Fig. 6 and Supplementary Fig. 7). Specificity of ERK1/2 over ERK5 and other MAPK family members for the activation of c-Fos has been previously described53, demonstrating their differential biological output despite the shared ability to transduce potent mitogenic signals.

Our findings may be relevant for the use of MAPK inhibitors in the treatment of colorectal cancer. Although there was only a mild phenotype in the colons of ΔIEC mice under homeostatic conditions, the Ras–RAF–MEK–ERK pathway is generally upregulated in malignant cells including CRC54. Targeted therapy typically results in feedback activation of upstream players of the targeted kinase, which are then able to reactivate the same pathway or utilize bypass signalling routes55. For example, on activation, ERK1/2 phosphorylates EGFR, son of sevenless56, and Raf57, thereby terminating upstream signalling activity. Knockout of Erk1/2 eliminates this negative feedback. Our data suggest that ERK5 is a putative resistance pathway in the context of targeted treatment with MEK1/2 or ERK1/2 inhibitors (Fig. 7b). Different classes of MEK1/2 inhibitors display various modes of resistance to therapy (innate, adaptive and acquired)58. Since we have only used one MEK1/2 inhibitor (PD0325901) in our studies, it will be necessary to evaluate other classes of inhibitors in combination with ERK5 inhibitors. Importantly, while treatment with either the MEK1/2 or ERK5 inhibitor suppressed tumour growth in murine Apc−/− organoids, only the latter was able to inhibit the proliferation of Apc−/−;KRASG12V organoids (Fig. 6), which are more representative of human CRC. In line with this, suppression of ERK5 expression by forced expression of miR-143/145 inhibited intestinal adenoma formation in the ApcMin/+ model59, and activated MEK5 correlated with more invasive CRC in human60. ERK5 has been previously reported to mediate resistance to cytotoxic chemotherapy-induced apoptosis61. The highly specific and bioavailable ERK5 inhibitor, XMD8-92, has shown antitumour effects in multiple preclinical cancer models by inhibiting tumour angiogenesis, metastasis and chemo-resistance62. Furthermore, ERK5 inhibition does not induce feedback activation of upstream or parallel signalling pathways62. In conclusion, the ERK1/2 and ERK5 MAPK modules display a high degree of signalling plasticity in the intestinal epithelium, which has implications for targeted treatment of colorectal cancer.

 

Researchers Reveal Role of Transcription Factor Isoforms in Colon Diseases

http://www.genengnews.com/gen-news-highlights/researchers-reveal-role-of-transcription-factor-isoforms-in-colon-diseases/81252735/


 

 

 

 

 

 

 

 

Balance between the two isoforms, P1 and P2, of nuclear receptor HNF4a in the colonic crypt influences susceptibility to colitis and colon cancer. P1 is seen here in green. P2 is seen in red. [Poonamjot Deol, Sladek lab, UC Riverside]

Scientists at the University of California, Riverside have determined the distribution of the P1 and P2 isoforms of hepatocyte nuclear factor 4α (HNF4α) in the colons of mice. They report (“Opposing Roles of Nuclear Receptor HNF4α Isoforms in Colitis and Colitis-Associated Colon Cancer”) in eLife that maintaining a balance of P1 and P2 is crucial for reducing risk of contracting colon cancer and colitis.

What is already known in the field of cell biology is that the HNF4α transcription factor plays a key role in both diseases. HNF4α comes in two major isoforms, P1-HNF4α and P2-HNF4α (P1 and P2), but just how each isoform is involved in colitis and colon cancer is not understood.

“P1 and P2 have been conserved between mice and humans for 70 million years,” said Frances M. Sladek, Ph.D., professor of cell biology, who led the research project. “Both isoforms are important and we want to keep an appropriate balance between them in our gut by avoiding foods that would disrupt this balance and consuming foods that help preserve it. What these foods are is our next focus in the lab.”

The intestine is the only adult tissue in the body that expresses both P1 and P2. Dr. Sladek and her team have shown for the first time that these isoforms perform nonredundant functions in the intestine and are relevant to colitis and colitis-associated colon cancer.

“Our study also suggests that finding a drug to stabilize one isoform should be more effective than targeting both isoforms for treating colitis and colon cancer,” said Karthikeyani Chellappa, Ph.D., the first author of the research paper and a former postdoctoral researcher in Sladek’s lab.

Dr. Sladek explained that the colonic epithelial surface has finger-like invaginations (into the colonic wall) called colonic crypts that house stem cells at their base. These stem cells help regenerate new epithelial cells that continuously migrate up toward the surface, thus ensuring complete renewal of the intestinal lining every 3–5 days.

The researchers observed that the P1-positive cells were found in the surface lining and the top portion of the crypt (green in the accompanying image) whereas P2-positive cells were mostly in the proliferative compartment in the lower half of the crypt (the proliferation marker is red in the image.) Furthermore, when transgenic mice genetically engineered to have only either P1 or P2 were subjected to a carcinogen and, subsequently, to an irritant to stress the epithelial lining of the colon, the researchers found that the P1 mice showed fewer tumors than wild-type control mice. When treated with irritant alone, these mice were resistant to colitis. In sharp contrast, mice with only P2 showed more tumors and were much more susceptible to colitis.

The researchers explain these findings by invoking the “barrier function,”  a mucosal barrier generated by the colon’s epithelial cells that prevents bacteria in the gut from entering the body. In the case of P1 mice, this barrier function was enhanced. The P2 mice, on the other hand, showed a compromised barrier function, presumably allowing bacteria to pass through.

Next, the researchers examined genes expressed in the P1 and P2 mice. They found that resistin-like molecule (RELM)-beta, a cytokine (a signaling molecule of the immune system) expressed in the gastrointestinal tract and implicated in colitis, was expressed far more in the P2 mice than the P1 mice.

“This makes sense since a reduced barrier function means bacteria can go across the barrier, which activates RELM-beta,” Dr. Sladek said. “We also found that the P2 protein transcribes RELM-beta more effectively than the P1 protein.”

Next, Poonamjot Deol, Ph.D.,  an assistant project scientist in Dr. Slaked’s lab and the second author of the eLife study, will lead a project aimed at understanding how diet affects the distribution of P1 and P2 in the gut. She and others in the lab also plan to investigate how obesity and colitis may be linked. (Diet studies performed in Dr. Sladek’s lab in the past illustrated soybean oil’s adverse effect on obesity.)

“In the case of colitis, could soybean oil be playing a part in allowing bacteria to get across the barrier function?” Dr. Deol said. “We do not know. We know its detrimental effect on obesity. But more research needs to be done where colitis is concerned.”

Opposing roles of nuclear receptor HNF4α isoforms in colitis and colitis-associated colon cancer

 Karthikeyani Chellappa, 

HNF4α has been implicated in colitis and colon cancer in humans but the role of the different HNF4α isoforms expressed from the two different promoters (P1 and P2) active in the colon is not clear. Here, we show that P1-HNF4α is expressed primarily in the differentiated compartment of the mouse colonic crypt and P2-HNF4α in the proliferative compartment. Exon swap mice that express only P1- or only P2-HNF4α have different colonic gene expression profiles, interacting proteins, cellular migration, ion transport and epithelial barrier function. The mice also exhibit altered susceptibilities to experimental colitis (DSS) and colitis-associated colon cancer (AOM+DSS). When P2-HNF4α-only mice (which have elevated levels of the cytokine resistin-like β, RELMβ, and are extremely sensitive to DSS) are crossed with Retnlb-/- mice, they are rescued from mortality. Furthermore, P2-HNF4α binds and preferentially activates the RELMβ promoter. In summary, HNF4α isoforms perform non-redundant functions in the colon under conditions of stress, underscoring the importance of tracking them both in colitis and colon cancer.

 

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Cholesterol metabolism in pancreatic cancer

Larry H. Bernstein, MD, FCAP, Curator

LPBI

 

 

New Pancreatic Treatment Shows Promise

http://www.genengnews.com/gen-news-highlights/new-pancreatic-treatment-shows-promise/81252686/

Study demonstrates how controlling cholesterol metabolism in pancreatic cancer cells reduces metastasis. [NIH].   http://www.genengnews.com/Media/images/GENHighlight/thumb_May4_2016_NIH_PancreaticCancerCells8616346835.jpg

Scientists say they have shown how controlling cholesterol metabolism in pancreatic cancer cells reduces metastasis, pointing to a potential new treatment using drugs previously developed for atherosclerosis.

“We show for the first time that if you control the cholesterol metabolism you could reduce pancreatic cancer spread to other organs,” said Ji-Xin Cheng, Ph.D., a professor in Purdue University’s Weldon School of Biomedical Engineering and Department of Chemistry. “We chose pancreatic cancer to test this approach because it is the most aggressive disease of all the cancers.”

Dr. Cheng had previously led a team of researchers discovering a link between prostate cancer’s aggressiveness and the accumulation of a compound produced when cholesterol is metabolized in cells, findings that could bring new diagnostic and treatment methods. The new study involved researchers at the Purdue Center for Cancer Research and School of Biomedical Engineering, the Indiana University Simon Cancer Center and School of Medicine, and Purdue’s Department of Biological Sciences, Department of Comparative Pathobiology, and Department of Biochemistry.

The findings, detailed in a paper (“Abrogating Cholesterol Esterification Suppresses Growth and Metastasis of Pancreatic Cancer”) just published in Oncogene, suggest that a class of drugs previously developed to treat atherosclerosis could be repurposed for treatment of pancreatic cancer and other forms of cancer. Atherosclerosis is the buildup of fats, cholesterol, and other substances in arteries, restricting blood flow.

The researchers found accumulations of the compound cholesteryl ester in human pancreatic cancer specimens and cell lines, demonstrating a link between cholesterol esterification and metastasis. Excess quantities of cholesterol result in cholesteryl ester being stored in lipid droplets within cancer cells.

“The results of this study demonstrate a new strategy for treating metastatic pancreatic cancer by inhibiting cholesterol esterification,” said Jingwu Xie, Ph.D., the Jonathan and Jennifer Simmons Professor at the Indiana University School of Medicine and a researcher at the Indiana University Melvin and Bren Simon Cancer Center.

The paper’s lead author is Purdue postdoctoral fellow Junjie Li, Ph.D. Purdue researchers have developed an analytical tool, Raman spectromicroscopy, that allows compositional analysis of single lipid droplets in living cells.

“We identified an aberrant accumulation of cholesteryl ester in human pancreatic cancer specimens and cell lines,” Dr. Li said. “Depletion of cholesterol esterification significantly reduced pancreatic tumor growth and metastasis in mice.”

Findings show that drugs like avasimibe, previously developed for treatment of atherosclerosis, reduced the accumulation of cholesteryl ester. Pancreatic cancer usually kills within a few months of diagnosis. It is hoped the potential new treatment might extend life of these patients for a year, Cheng said.

The accumulation of cholesteryl ester is controlled by an enzyme called acyl-coenzyme A acyltransferase-1 (ACAT-1), and findings have correlated a higher expression of the enzyme with a poor survival rate for patients. The researchers analyzed tissue samples from pancreatic cancer patients and then tested the drug treatment in a type of laboratory mice referred to as an orthotopic mouse model, developed at the IU School of Medicine. Specimens of human pancreatic tissues were obtained from the Simon Cancer Center Solid Tissue Bank.

Imaging showed a decrease of the number of lipid droplets, and Raman spectral analysis verified a significant reduction of cholesteryl ester in the lipid droplets, suggesting that avasimibe acted by blocking cholesterol esterification. The drug did not induce weight loss, and there was no apparent organ toxicity in the liver, kidney, lung and spleen, Dr. Cheng said.

Findings also showed that blocking storage of cholesteryl ester causes cancer cells to die, specifically due to damage to the endoplasmic reticulum, a workhorse of protein and lipid synthesis.

“By using avasimibe, a potent inhibitor of ACAT-1, we found that pancreatic cancer cells were much more sensitive to ACAT-1 inhibition than normal cells,” added Dr. Cheng.

Additional research confirmed that the anticancer effect of avasimibe is specific to ACAT-1 inhibition. The researchers performed various biochemical assays and “genetic ablation” to confirm the drug’s anticancer effect.

“The results showed that avasimibe treatment for four weeks remarkably suppressed tumor size and largely reduced tumor growth rate,” said paper co-author Timothy Ratliff, the Robert Wallace Miller Director of Purdue’s Center for Cancer Research. “Metastatic lesions in lymph nodes and distant organs also were assessed at the end of the study. A much higher number of metastatic lesions in lymph nodes were detected in the control group than the avasimibe-treated group.”

Each mouse in the control group showed at least one metastatic lesion in the liver. In contrast, only three mice in the avasimibe-treated group showed single lesion in liver.

 

Abrogating cholesterol esterification suppresses growth and metastasis of pancreatic cancer

J Li1, D Gu2, S S-Y Lee1, B Song1, S Bandyopadhyay3, S Chen4, S F Konieczny3,5, T L Ratliff5,6, X Liu5,7, J Xie2 and J-X Cheng1,5
O
ncogene 2 May 2016;                                         http://dx.doi.org:/10.1038/onc.2016.168

Cancer cells are known to execute reprogramed metabolism of glucose, amino acids and lipids. Here, we report a significant role of cholesterol metabolism in cancer metastasis. By using label-free Raman spectromicroscopy, we found an aberrant accumulation of cholesteryl ester in human pancreatic cancer specimens and cell lines, mediated by acyl-CoA cholesterol acyltransferase-1 (ACAT-1) enzyme. Expression of ACAT-1 showed a correlation with poor patient survival. Abrogation of cholesterol esterification, either by an ACAT-1 inhibitor or by shRNA knockdown, significantly suppressed tumor growth and metastasis in an orthotopic mouse model of pancreatic cancer. Mechanically, ACAT-1 inhibition increased intracellular free cholesterol level, which was associated with elevated endoplasmic reticulum stress and caused apoptosis. Collectively, our results demonstrate a new strategy for treating metastatic pancreatic cancer by inhibiting cholesterol esterification.

Metastasis is the major cause of cancer-related mortality. Though localized tumors can often be treated by surgery or other therapies, treatment options for metastatic diseases are limited. Cancer metastasis has been revealed to be a multiple step process, including cancer cell migration, local invasion, intravasation, circulation through blood and lymph vessels, extravasation, survival and colonization in distant organs.1, 2, 3Mediators identified in these processes have provided the basis for the development of therapies to target metastasis. Current therapeutic strategies for treating metastatic tumors mainly focus on targeting the adhesive molecules and extracellular proteases.4However, these therapeutics have not been proven to be effective in clinical trials, partially owing to the various escape mechanisms used by the metastatic cancer cells.2, 5, 6 Thus, an unmet need exists to develop new therapeutic strategies for treating metastatic cancers.

Recent advances in cancer metabolism have unveiled many potential therapeutic targets for cancer treatment. Metabolic reprogramming, a strategy used by cancer cells to adapt to the rapid proliferation, is being recognized as a new hallmark of cancer.7 Substantial studies have found increased glycolysis, glutaminolysis, nucleotide and lipid synthesis in cancer cells.7, 8, 9,10 Considering that altered metabolic pathways only happen in cancer cells but not in normal cells, targeting these pathways may provide cancer-specific treatments. A number of inhibitors of metabolic enzymes, such as glycolysis inhibitors, are under clinical trials as targeted cancer therapeutics.11

Of various metabolic pathways, lipid metabolism has been suggested to have an important role in cancer cell migration, invasion and metastasis.12 A recent study reported that surrounding adipocytes provide energy source for ovarian cancer cells to promote its rapid growth and metastasis.13 Blocking lipidde novo synthesis pathway has been shown to suppress tumor regrowth and metastasis after anti-angiogenesis treatment withdrawal.14 In parallel, lipolysis by the enzyme monoacylglycerol lipase was shown to regulate the fatty acid network, which promotes cancer cell migration, invasion and growth.15

Cholesterol, a critical component of the plasma membrane, is also implied to be correlated to cancer metastasis.16 It has been shown that prostate cancer bone metastases contain a high level of cholesterol.17 Modulation of cholesterol level in plasma membrane was shown to regulate the capability of cell migration.18, 19Moreover, cholesterol-enriched lipid rafts were shown to have an essential role in cancer cell adhesion and migration.20 Mammalian cells obtain cholesterol either from de novo synthesis or from the uptake of low-density lipoprotein (LDL).21 Inside cells, excess free cholesterol is esterified and stored as cholesteryl ester (CE) in lipid droplets (LDs), which is mediated by acyl-CoA cholesterol acyltransferase (ACAT).22 Increased CE level has been reported in breast cancer,23 leukemia,24 glioma25 and prostate cancer.26Despite these advances, the role of cholesterol esterification in cancer progression, especially in cancer metastasis, is not well understood.

In this article, we report a link between cholesterol esterification and metastasis in pancreatic cancer. Using stimulated Raman scattering (SRS) microscopy and Raman spectroscopy to map LDs stored inside single cells and analyze the composition of individual LDs, we identified an aberrant accumulation of CE in human pancreatic cancer specimens and cell lines. Abrogation of cholesterol esterification, either by inhibiting ACAT-1 enzyme activity or by shRNA knockdown of ACAT-1 expression, significantly reduced pancreatic tumor growth and metastasis in an orthotopic mouse model. Mechanistically, inhibition of cholesterol esterification disturbed cholesterol homeostasis by increasing intracellular free cholesterol level, which was associated with elevated endoplasmic reticulum (ER) stress and eventually led to apoptosis.

In this study, we revealed a link between CE accumulation and pancreatic cancer metastasis. Accumulation of CE via ACAT-1 provides a mechanism to keep high metabolic activity and avoid toxicity from excess free cholesterol. Previously, CE has been reported in breast cancer,23 leukemia,24 glioma25 and prostate cancer.26 Inhibition of cholesterol esterification was shown to suppress tumor growth or cancer cell proliferation.24, 25, 26 Here, we demonstrate that inhibition of cholesterol esterification can be used to treat metastatic pancreatic cancer.

Cholesterol is an essential lipid having important roles in membrane construction, hormone production and signaling.21Aberrant cholesterol metabolism is known to be associated with cardiovascular diseases and cancers.35, 36 Statins, inhibitors of HMG-CoA reductase, have been explored as potential therapies for pancreatic cancer.37 However, statins were not associated with a reduced risk of pancreatic cancer in clinical trials.38 One possible reason is that HMG-CoA reductase is also required for downstream protein prenylation, a critical process for protein activation.39Thus, the effect of statin is not just inhibiting cholesterol synthesis, but also other pathways which may render toxicity to normal cells. This non-specific toxicity is a possible reason for the limited anti-cancer outcome of statin in clinical trials.

Our study identified cholesterol esterification as a novel target for suppression of pancreatic cancer proliferation and metastasis. Inhibitors of ACAT-1 are expected to have great value as cancer-targeting therapeutics, as CE accumulation only occurs in cancer tissues or cell lines. Our animal studies with avasimibe treatment showed no adverse effect to the animals at a dosage of 15mg/kg. More importantly, modulation of cholesterol esterification suppressed not only tumor growth but also tumor metastasis. These results are expected to stimulate further biological studies to fully appreciate the role of cholesterol metabolism in cancer initiation and progression. As CE accumulation happens in several types of aggressive cancer, blocking cholesterol esterification could be pursued as a therapeutic strategy for other types of cancers. By combining with existing chemotherapies, such as gemcitabine, we believe this metabolic treatment possesses high possibilities to extend patients’ survival time by retarding cancer progression and metastasis.

The molecular mechanism that links CE accumulation to cancer aggressiveness needs further studies. One possible mechanism is that cholesterol esterification keeps signaling pathways active by maintaining a low free cholesterol environment. One of the possible targets is the caveolin-1 signaling pathway. Caveolin-1, a regulator of cellular cholesterol homeostasis, is considered as a marker for pancreatic cancer progression.11 Particularly, a promoting role of caveolin-1 in pancreatic cancer metastasis has been reported.40 Our preliminary studies showed ACAT-1 inhibition reduced the expression level of SREBP1, caveolin-1 and phosphorylated ERK1/2 (unpublished data). The effect on caveolin-1 is probably mediated by SREBP1, which senses the intracellular cholesterol homeostasis.41 Meanwhile, caveolin-1 may have an important role in mediating the action of SREBP1 on MAPK pathways,42, 43 which are known to have essential roles in cancer cell metastasis.44 Therefore, it is possible that increased free cholesterol level induced by ACAT-1 inhibition inactivates SREBP1, leading to downregulation of caveolin-1/MAPK pathway, which contributes to the reduced cancer aggressiveness.

Besides the caveolin-1/MAPK signaling, other possibilities include the potential alteration of the membrane composition, such as lipid rafts, by ACAT-1 inhibition. Lipid rafts are known to provide platforms for multiple cellular signaling pathways.20 Thus, modulation of cholesterol metabolism is likely to have more profound effects via other signaling pathways. Future studies are needed to fully elucidate the molecular mechanism.

 

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Microbe meets cancer

Larry H. Bernstein, MD, FCAP, Curator

LPBI

 

Microbes Meet Cancer

Understanding cancer’s relationship with the human microbiome could transform immune-modulating therapies.

By Kate Yandell | April 1, 2016  http://www.the-scientist.com/?articles.view/articleNo/45616/title/Microbes-Meet-Cancer

 © ISTOCK.COM/KATEJA_FN; © ISTOCK.COM/FRANK RAMSPOTT  http://www.the-scientist.com/images/April2016/feature1.jpg

In 2013, two independent teams of scientists, one in Maryland and one in France, made a surprising observation: both germ-free mice and mice treated with a heavy dose of antibiotics responded poorly to a variety of cancer therapies typically effective in rodents. The Maryland team, led by Romina Goldszmidand Giorgio Trinchieri of the National Cancer Institute, showed that both an investigational immunotherapy and an approved platinum chemotherapy shrank a variety of implanted tumor types and improved survival to a far greater extent in mice with intact microbiomes.1 The French group, led by INSERM’s Laurence Zitvogel, got similar results when testing the long-standing chemotherapeutic agent cyclophosphamide in cancer-implanted mice, as well as in mice genetically engineered to develop tumors of the lung.2

The findings incited a flurry of research and speculation about how gut microbes contribute to cancer cell death, even in tumors far from the gastrointestinal tract. The most logical link between the microbiome and cancer is the immune system. Resident microbes can either dial up inflammation or tamp it down, and can modulate immune cells’ vigilance for invaders. Not only does the immune system appear to be at the root of how the microbiome interacts with cancer therapies, it also appears to mediate how our bacteria, fungi, and viruses influence cancer development in the first place.

“We clearly see shifts in the [microbial] community that precede development of tumors,” says microbiologist and immunologist Patrick Schloss, who studies the influence of the microbiome on colon cancer at the University of Michigan.

But the relationship between the microbiome and cancer is complex: while some microbes promote cell proliferation, others appear to protect us against cancerous growth. And in some cases, the conditions that spur one cancer may have the opposite effect in another. “It’s become pretty obvious that the commensal microbiota affect inflammation and, through that or through other mechanisms, affect carcinogenesis,” says Trinchieri. “What we really need is to have a much better understanding of which species, which type of bug, is doing what and try to change the balance.”

Gut feeling

In the late 1970s, pathologist J. Robin Warren of Royal Perth Hospital in Western Australia began to notice that curved bacteria often appeared in stomach tissue biopsies taken from patients with chronic gastritis, an inflammation of the stomach lining that often precedes the development of stomach cancer. He and Barry J. Marshall, a trainee in internal medicine at the hospital, speculated that the bacterium, now called Helicobacter pylori, was somehow causing the gastritis.3 So committed was Marshall to demonstrating the microbe’s causal relationship to the inflammatory condition that he had his own stomach biopsied to show that it contained no H. pylori, then infected himself with the bacterium and documented his subsequent experience of gastritis.4 Scientists now accept that H. pylori, a common gut microbe that is present in about 50 percent of the world’s population, is responsible for many cases of gastritis and most stomach ulcers, and is a strong risk factor for stomach cancer.5 Marshall and Warren earned the 2005 Nobel Prize in Physiology or Medicine for their work.

H. pylori may be the most clear-cut example of a gut bacterium that influences cancer development, but it is likely not the only one. Researchers who study cancer in mice have long had anecdotal evidence that shifts in the microbiome influence the development of diverse tumor types. “You have a mouse model of carcinogenesis. It works beautifully,” says Trinchieri. “You move to another institution. It works completely differently,” likely because the animals’ microbiomes vary with environment.

IMMUNE INFLUENCE: In recent years, research has demonstrated that microbes living in and on the mammalian body can affect cancer risk, as well as responses to cancer treatment. Although the details of this microbe-cancer link remain unclear, investigators suspect that the microbiome’s ability to modulate inflammation and train immune cells to react to tumors is to blame.
See full infographic: WEB | PDF
© AL GRANBERG

Around the turn of the 21st century, cancer researchers began to systematically experiment with the rodent microbiome, and soon had several lines of evidence linking certain gut microbes with a mouse’s risk of colon cancer. In 2001, for example, Shoichi Kado of the Yakult Central Institute for Microbiological Research in Japan and colleagues found that a strain of immunocompromised mice rapidly developed colon tumors, but that germ-free versions of these mice did not.6 That same year, an MIT-based group led by the late David Schauer demonstrated that infecting mice with the bacterium Citrobacter rodentium spurred colon tumor development.7 And in 2003, MIT’s Susan Erdman and her colleagues found that they could induce colon cancer in immunocompromised mice by infecting them with Helicobacter hepaticus, a relative of? H. pylori that commonly exists within the murine gut microbiome.8

More recent work has documented a similar link between colon cancer and the gut microbiome in humans. In 2014, a team led by Schloss sequenced 16S rRNA genes isolated from the stool of 90 people, some with colon cancer, some with precancerous adenomas, and still others with no disease.9 The researchers found that the feces of people with cancer tended to have an altered composition of bacteria, with an excess of the common mouth microbes Fusobacterium or Porphyromonas. A few months later, Peer Bork of the European Molecular Biology Laboratory performed metagenomic sequencing of stool samples from 156 people with or without colorectal cancer. Bork and his colleagues found they could predict the presence or absence of cancer using the relative abundance of 22 bacterial species, including Porphyromonas andFusobacterium.10 They could also use the method to predict colorectal cancer with about the same accuracy as a blood test, correctly identifying about 50 percent of cancers while yielding false positives less than 10 percent of the time. When the two tests were combined, they caught more than 70 percent of cancers.

Whether changes in the microbiota in colon cancer patients are harbingers of the disease or a consequence of tumor development remained unclear. “What comes first, the change in the microbiome or tumor development?” asks Schloss. To investigate this question, he and his colleagues treated mice with microbiome-altering antibiotics before administering a carcinogen and an inflammatory agent, then compared the outcomes in those animals and in mice that had received only the carcinogenic and inflammatory treatments, no antibiotics. The antibiotic-treated animals had significantly fewer and smaller colon tumors than the animals with an undisturbed microbiome, suggesting that resident bacteria were in some way promoting cancer development. And when the researchers transferred microbiota from healthy mice to antibiotic-treated or germ-free mice, the animals developed more tumors following carcinogen exposure. Sterile mice that received microbiota from mice already bearing malignancies developed the most tumors of all.11

Most recently, Schloss and his colleagues showed that treating mice with seven unique combinations of antibiotics prior to exposing them to carcinogens yielded variable but predictable levels of tumor formation. The researchers determined that the number of tumors corresponded to the unique ways that each antibiotic cocktail modulated the microbiome.12

“We’ve kind of proven to ourselves, at least, that the microbiome is involved in colon cancer,” says Schloss, who hypothesizes that gut bacteria–driven inflammation is to blame for creating an environment that is hospitable to tumor development and growth. Gain or loss of certain components of the resident bacterial community could lead to the release of reactive oxygen species, damaging cells and their genetic material. Inflammation also involves increased release of growth factors and blood vessel proliferation, potentially supporting the growth of tumors. (See illustration above.)

Recent research has also yielded evidence that the gut microbiota impact the development of cancer in sites far removed from the intestinal tract, likely through similar immune-modulating mechanisms.

Systemic effects

In the mid-2000s, MIT’s Erdman began infecting a strain of mice predisposed to intestinal tumors withH. hepaticus and observing the subsequent development of colon cancer in some of the animals. To her surprise, one of the mice developed a mammary tumor. Then, more of the mice went on to develop mammary tumors. “This told us that something really interesting was going on,” Erdman recalls. Sure enough, she and her colleagues found that mice infected with H. hepaticus were more likely to develop mammary tumors than mice not exposed to the bacterium.13The researchers showed that systemic immune activation and inflammation could contribute to mammary tumors in other, less cancer-prone mouse models, as well as to the development of prostate cancer.

MICROBIAL STOWAWAYS: Bacteria of the human gut microbiome are intimately involved in cancer development and progression, thanks to their interactions with the immune system. Some microbes, such as Helicobacter pylori, increase the risk of cancer in their immediate vicinity (stomach), while others, such as some Bacteroides species, help protect against tumors by boosting T-cell infiltration.© EYE OF SCIENCE/SCIENCE SOURCE
http://www.the-scientist.com/images/April2016/immune_2.jpg

 

 

© DR. GARY GAUGLER/SCIENCE SOURCE  http://www.the-scientist.com/images/April2016/immune3.jpg

At the University of Chicago, Thomas Gajewski and his colleagues have taken a slightly different approach to studying the role of the microbiome in cancer development. By comparing Black 6 mice coming from different vendors—Taconic Biosciences (formerly Taconic Farms) and the Jackson Laboratory—Gajewski takes advantage of the fact that the animals’ different origins result in different gut microbiomes. “We deliberately stayed away from antibiotics, because we had a desire to model how intersubject heterogeneity [in cancer development] might be impacted by the commensals they happen to be colonized with,” says Gajewski in an email to The Scientist.

Last year, the researchers published the results of a study comparing the progression of melanoma tumors implanted under the mice’s skin, finding that tumors in the Taconic mice grew more aggressively than those in the Jackson mice. When the researchers housed the different types of mice together before their tumors were implanted, however, these differences disappeared. And transferring fecal material from the Jackson mice into the Taconic mice altered the latter’s tumor progression.14

Instead of promoting cancer, in these experiments the gut microbiome appeared to slow tumor growth. Specifically, the reduced tumor growth in the Jackson mice correlated with the presence of Bifidobacterium, which led to the greater buildup of T?cells in the Jackson mice’s tumors. Bifidobacteriaactivate dendritic cells, which present antigens from bacteria or cancer cells to T?cells, training them to hunt down and kill these invaders. Feeding Taconic mice bifidobacteria improved their response to the implanted melanoma cells.

“One hypothesis going into the experiments was that we might identify immune-suppressive bacteria, or commensals that shift the immune response towards a character that was unfavorable for tumor control,” says Gajewski.  “But in fact, we found that even a single type of bacteria could boost the antitumor immune response.”

http://www.the-scientist.com/images/April2016/immune4.jpg

 

Drug interactions

Ideally, the immune system should recognize cancer as invasive and nip tumor growth in the bud. But cancer cells display “self” molecules that can inhibit immune attack. A new type of immunotherapy, dubbed checkpoint inhibition or blockade, spurs the immune system to attack cancer by blocking either the tumor cells’ surface molecules or the receptors on T?cells that bind to them.

CANCER THERAPY AND THE MICROBIOME

In addition to influencing the development and progression of cancer by regulating inflammation and other immune pathways, resident gut bacteria appear to influence the effectiveness of many cancer therapies that are intended to work in concert with host immunity to eliminate tumors.

  • Some cancer drugs, such as oxaliplatin chemotherapy and CpG-oligonucleotide immunotherapy, work by boosting inflammation. If the microbiome is altered in such a way that inflammation is reduced, these therapeutic agents are less effective.
  • Cancer-cell surface proteins bind to receptors on T cells to prevent them from killing cancer cells. Checkpoint inhibitors that block this binding of activated T cells to cancer cells are influenced by members of the microbiota that mediate these same cell interactions.
  • Cyclophosphamide chemotherapy disrupts the gut epithelial barrier, causing the gut to leak certain bacteria. Bacteria gather in lymphoid tissue just outside the gut and spur generation of T helper 1 and T helper 17 cells that migrate to the tumor and kill it.

As part of their comparison of Jackson and Taconic mice, Gajewski and his colleagues decided to test a type of investigational checkpoint inhibitor that targets PD-L1, a ligand found in high quantities on the surface of multiple types of cancer cells. Monoclonal antibodies that bind to PD-L1 block the PD-1 receptors on T?cells from doing so, allowing an immune response to proceed against the tumor cells. While treating Taconic mice with PD-L1–targeting antibodies did improve their tumor responses, they did even better when that treatment was combined with fecal transfers from Jackson mice, indicating that the microbiome and the immunotherapy can work together to take down cancer. And when the researchers combined the anti-PD-L1 therapy with a bifidobacteria-enriched diet, the mice’s tumors virtually disappeared.14

Gajewski’s group is now surveying the gut microbiota in humans undergoing therapy with checkpoint inhibitors to better understand which bacterial species are linked to positive outcomes. The researchers are also devising a clinical trial in which they will give Bifidobacterium supplements to cancer patients being treated with the approved anti-PD-1 therapy pembrolizumab (Keytruda), which targets the immune receptor PD-1 on T?cells, instead of the cancer-cell ligand PD-L1.

Meanwhile, Zitvogel’s group at INSERM is investigating interactions between the microbiome and another class of checkpoint inhibitors called CTLA-4 inhibitors, which includes the breakthrough melanoma treatment ipilimumab (Yervoy). The researchers found that tumors in antibiotic-treated and germ-free mice had poorer responses to a CTLA-4–targeting antibody compared with mice harboring unaltered microbiomes.15 Particular Bacteroides species were associated with T-cell infiltration of tumors, and feedingBacteroides fragilis to antibiotic-treated or germ-free mice improved the animals’ responses to the immunotherapy. As an added bonus, treatment with these “immunogenic” Bacteroides species decreased signs of colitis, an intestinal inflammatory condition that is a dangerous side effect in patients using checkpoint inhibitors. Moreover, Zitvogel and her colleagues showed that human metastatic melanoma patients treated with ipilimumab tended to have elevated levels of B. fragilis in their microbiomes. Mice transplanted with feces from patients who showed particularly strong B. fragilis gains did better on anti-CTLA-4 treatment than did mice transplanted with feces from patients with normal levels of B. fragilis.

“There are bugs that allow the therapy to work, and at the same time, they protect against colitis,” says Trinchieri. “That is very exciting, because not only [can] we do something to improve the therapy, but we can also, at the same time, try to reduce the side effect.”

And these checkpoint inhibitors aren’t the only cancer therapies whose effects are modulated by the microbiome. Trinchieri has also found that an immunotherapy that combines antibodies against interleukin-10 receptors with CpG oligonucleotides is more effective in mice with unaltered microbiomes.1He and his NCI colleague Goldszmid further found that the platinum chemotherapy oxaliplatin (Eloxatin) was more effective in mice with intact microbiomes, and Zitvogel’s group has shown that the chemotherapeutic agent cyclophosphamide is dependent on the microbiota for its proper function.

Although the mechanisms by which the microbiome influences the effectiveness of such therapies remains incompletely understood, researchers once again speculate that the immune system is the key link. Cyclophosphamide, for example, spurs the body to generate two types of T?helper cells, T?helper 1 cells and a subtype of T?helper 17 cells referred to as “pathogenic,” both of which destroy tumor cells. Zitvogel and her colleagues found that, in mice with unaltered microbiomes, treatment with cyclophosphamide works by disrupting the intestinal mucosa, allowing bacteria to escape into the lymphoid tissues just outside the gut. There, the bacteria spur the body to generate T?helper 1 and T?helper 17 cells, which translocate to the tumor. When the researchers transferred the “pathogenic” T?helper 17 cells into antibiotic-treated mice, the mice’s response to chemotherapy was partly restored.

Microbiome modification

As the link between the microbiome and cancer becomes clearer, researchers are thinking about how they can manipulate a patient’s resident microbial communities to improve their prognosis and treatment outcomes. “Once you figure out exactly what is happening at the molecular level, if there is something promising there, I would be shocked if people don’t then go in and try to modulate the microbiome, either by using pharmaceuticals or using probiotics,” says Michael Burns, a postdoc in the lab of University of Minnesota genomicist Ran Blekhman.

Even if researchers succeed in identifying specific, beneficial alterations to the microbiome, however, molding the microbiome is not simple. “It’s a messy, complicated system that we don’t understand,” says Schloss.

So far, studies of the gut microbiome and colon cancer have turned up few consistent differences between cancer patients and healthy controls. And the few bacterial groups that have repeatedly shown up are not present in every cancer patient. “We should move away from saying, ‘This is a causal species of bacteria,’” says Blekhman. “It’s more the function of a community instead of just a single bacterium.”

But the study of the microbiome in cancer is young. If simply adding one type of microbe into a person’s gut is not enough, researchers may learn how to dose people with patient-specific combinations of microbes or antibiotics. In February 2016, a team based in Finland and China showed that a probiotic mixture dubbed Prohep could reduce liver tumor size by 40 percent in mice, likely by promoting an anti-inflammatory environment in the gut.16

“If it is true that, in humans, we can alter the course of the disease by modulating the composition of the microbiota,” says José Conejo-Garcia of the Wistar Institute in Philadelphia, “that’s going to be very impactful.”

Kate Yandell has been a freelance writer living Philadelphia, Pennsylvania. In February she became an associate editor at Cancer Today.

GENETIC CONNECTION

The microbiome doesn’t act in isolation; a patient’s genetic background can also greatly influence response to therapy. Last year, for example, the Wistar Institute’s José Garcia-Conejo and Melanie Rutkowski, now an assistant professor at the University of Virginia, showed that a dominant polymorphism of the gene for the innate immune protein toll-like receptor 5 (TLR5) influences clinical outcomes in cancer patients by changing how the patients’ immune cells interact with their gut microbes (Cancer Cell, 27:27-40, 2015).

More than 7 percent of people carry a specific mutation in TLR5 that prevents them from mounting a full immune response when exposed to bacterial flagellin. Analyzing both genetic and survival data from the Cancer Genome Atlas, Conejo-Garcia, Rutkowski, and their colleagues found that estrogen receptor–positive breast cancer patients who carry the TLR5 mutation, called the R392X polymorphism, have worse outcomes than patients without the mutation. Among patients with ovarian cancer, on the other hand, those with the TLR5 mutation were more likely to live at least six years after diagnosis than patients who don’t carry the mutation.

Investigating the mutation’s contradictory effects, the researchers found that mice with normal TLR5produce higher levels of the cytokine interleukin 6 (IL-6) than those carrying the mutant version, which have higher levels of a different cytokine called interleukin 17 (IL-17). But when the researchers knocked out the animals’ microbiomes, these differences in cytokine production disappeared, as did the differences in cancer progression between mutant and wild-type animals.

“The effectiveness of depleting specific populations or modulating the composition of the microbiome is going to affect very differently people who are TLR5-positive or TLR5-negative,” says Conejo-Garcia. And Rutkowski speculates that many more polymorphisms linked to cancer prognosis may act via microbiome–immune system interactions. “I think that our paper is just the tip of the iceberg.”

References

  1. N. Iida et al., “Commensal bacteria control cancer response to therapy by modulating the tumor microenvironment,” Science, 342:967-70, 2013.
  2. S. Viaud et al., “The intestinal microbiota modulates the anticancer immune effects of cyclophosphamide,” Science, 342:971-76, 2013.
  3. J.R. Warren, B. Marshall, “Unidentified curved bacilli on gastric epithelium in active chronic gastritis,”Lancet, 321:1273-75, 1983.
  4. B.J. Marshall et al., “Attempt to fulfil Koch’s postulates for pyloric Campylobacter,” Med J Aust, 142:436-39, 1985.
  5. J. Parsonnet et al., “Helicobacter pylori infection and the risk of gastric carcinoma,” N Engl J Med, 325:1127-31, 1991.
  6. S. Kado et al., “Intestinal microflora are necessary for development of spontaneous adenocarcinoma of the large intestine in T-cell receptor β chain and p53 double-knockout mice,” Cancer Res, 61:2395-98, 2001.
  7. J.V. Newman et al., “Bacterial infection promotes colon tumorigenesis in ApcMin/+ mice,” J Infect Dis, 184:227-30, 2001.
  8. S.E. Erdman et al., “CD4+ CD25+ regulatory T lymphocytes inhibit microbially induced colon cancer in Rag2-deficient mice,” Am J Pathol, 162:691-702, 2003.
  9. J.P. Zackular et al., “The human gut microbiome as a screening tool for colorectal cancer,” Cancer Prev Res, 7:1112-21, 2014.
  10. G. Zeller et al., “Potential of fecal microbiota for early-stage detection of colorectal cancer,” Mol Syst Biol, 10:766, 2014.
  11. J.P. Zackular et al., “The gut microbiome modulates colon tumorigenesis,” mBio, 4:e00692-13, 2013.
  12. J.P. Zackular et al., “Manipulation of the gut microbiota reveals role in colon tumorigenesis,”mSphere, doi:10.1128/mSphere.00001-15, 2015.
  13. V.P. Rao et al., “Innate immune inflammatory response against enteric bacteria Helicobacter hepaticus induces mammary adenocarcinoma in mice,” Cancer Res, 66:7395, 2006.
  14. A. Sivan et al., “Commensal Bifidobacterium promotes antitumor immunity and facilitates anti-PD-L1 efficacy,” Science, 350:1084-89, 2015.
  15. M. Vétizou et al., “Anticancer immunotherapy by CTLA-4 blockade relies on the gut microbiota,”Science, 350:1079-84, 2015.

……..

 

Microbially Driven TLR5-Dependent Signaling Governs Distal Malignant Progression through Tumor-Promoting Inflammation

Melanie R. Rutkowski, Tom L. Stephen, Nikolaos Svoronos, …., Julia Tchou,  Gabriel A. Rabinovich, Jose R. Conejo-Garcia
Cancer cell    12 Jan 2015; Volume 27, Issue 1, p27–40  http://dx.doi.org/10.1016/j.ccell.2014.11.009
Figure thumbnail fx1
  • TLR5-dependent IL-6 mobilizes MDSCs that drive galectin-1 production by γδ T cells
  • IL-17 drives malignant progression in IL-6-unresponsive tumors
  • TLR5-dependent differences in tumor growth are abrogated upon microbiota depletion
  • A common dominant TLR5 polymorphism influences the outcome of human cancers

The dominant TLR5R392X polymorphism abrogates flagellin responses in >7% of humans. We report that TLR5-dependent commensal bacteria drive malignant progression at extramucosal locations by increasing systemic IL-6, which drives mobilization of myeloid-derived suppressor cells (MDSCs). Mechanistically, expanded granulocytic MDSCs cause γδ lymphocytes in TLR5-responsive tumors to secrete galectin-1, dampening antitumor immunity and accelerating malignant progression. In contrast, IL-17 is consistently upregulated in TLR5-unresponsive tumor-bearing mice but only accelerates malignant progression in IL-6-unresponsive tumors. Importantly, depletion of commensal bacteria abrogates TLR5-dependent differences in tumor growth. Contrasting differences in inflammatory cytokines and malignant evolution are recapitulated in TLR5-responsive/unresponsive ovarian and breast cancer patients. Therefore, inflammation, antitumor immunity, and the clinical outcome of cancer patients are influenced by a common TLR5 polymorphism.

see also… Immune Influence

In recent years, research has demonstrated that microbes living in and on the mammalian body can affect cancer risk, as well as responses to cancer treatment.

By Kate Yandell | April 1, 2016

http://www.the-scientist.com/?articles.view/articleNo/45644/title/Immune-Influence

Although the details of this microbe-cancer link remain unclear, investigators suspect that the microbiome’s ability to modulate inflammation and train immune cells to react to tumors is to blame. Here are some of the hypotheses that have come out of recent research in rodents for how gut bacteria shape immunity and influence cancer.

HOW THE MICROBIOME PROMOTES CANCER

Gut bacteria can dial up inflammation locally in the colon, as well as in other parts of the body, leading to the release of reactive oxygen species, which damage cells and DNA, and of growth factors that spur tumor growth and blood vessel formation.

http://www.the-scientist.com/images/April2016/ImmuneInfluence1_640px.jpg

http://www.the-scientist.com/images/April2016/ImmuneInfluence2_310px1.jpg

Helicobacter pylori can cause inflammation and high cell turnover in the stomach wall, which may lead to cancerous growth.

HOW THE MICROBIOME STEMS CANCER

Gut bacteria can also produce factors that lower inflammation and slow tumor growth. Some gut bacteria (e.g., Bifidobacterium)
appear to activate dendritic cells,
which present cancer-cell antigens to T cells that in turn kill the cancer cells.

http://www.the-scientist.com/images/April2016/ImmuneInfluence3_310px1.jpg

http://www.the-scientist.com/images/April2016/ImmuneInfluence4_310px1.jpg

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Curbing Cancer Cell Growth & Metastasis-on-a-Chip’ Models Cancer’s Spread

Curator: Larry H. Bernstein, MD, FCAP

 

New Approach to Curbing Cancer Cell Growth

http://www.technologynetworks.com/Metabolomics/news.aspx?ID=189342

Using a new approach, scientists at The Scripps Research Institute (TSRI) and collaborating institutions have discovered a novel drug candidate that could be used to treat certain types of breast cancer, lung cancer and melanoma.

The new study focused on serine, one of the 20 amino acids (protein building blocks) found in nature. Many types of cancer require synthesis of serine to sustain rapid, constant and unregulated growth.

To find a drug candidate that interfered with this pathway, the team screened a large library of compounds from a variety of sources, searching for molecules that inhibited a specific enzyme known as 3-phosphoglycerate dehydrogenase (PHGDH), which is responsible for the first committed step in serine biosynthesis.

“In addition to discovering an inhibitor that targets cancer metabolism, we also now have a tool to help answer interesting questions about serine metabolism,” said Luke L. Lairson, assistant professor of chemistry at TSRI and principal investigator of cell biology at the California Institute for Biomedical Research (CALIBR).

Lairson was senior author of the study, published recently in the Proceedings of the National Academy of Sciences (PNAS), with Lewis Cantley of Weill Cornell Medical College and Costas Lyssiotis of the University of Michigan.

Addicted to Serine

Serine is necessary for nucleotide, protein and lipid biosynthesis in all cells. Cells use two main routes for acquiring serine: through import from the extracellular environment or through conversion of 3-phosphoglycerate (a glycolytic intermediate) by PHGDH.

“Since the late 1950s, it has been known that cancer cells use the process of aerobic glycolysis to generate metabolites needed for proliferative growth,” said Lairson.

This process can lead to an overproduction of serine. The genetic basis for this abundance had remained mysterious until recently, when it was demonstrated that some cancers acquire mutations that increased the expression of PHGDH; reducing PHGDH in these “serine-addicted” cancer cells also inhibited their growth.

The labs of Lewis C. Cantley at Weill Cornell Medical College (in work published in Nature Genetics) and David Sabatini at the Whitehead Institute (in work published in Nature) suggested PHGDH as a potential drug target for cancer types that overexpress the enzyme.

Lairson and colleagues hypothesized that a small molecule drug candidate that inhibited PHGDH could interfere with cancer metabolism and point the way to the development of an effective cancer therapeutic. Importantly, this drug candidate would be inactive against normal cells because they would be able to import enough serine to support ordinary growth.

As Easy as 1-2-800,000

Lairson, in collaboration with colleagues including Cantley, Lyssiotis, Edouard Mullarky of Weill Cornell and Harvard Medical School and Natasha Lucki of CALIBR, screened through a library of 800,000 small molecules using a high-throughput in vitro enzyme assay to detect inhibition of PHGDH. The group identified 408 candidates and further narrowed this list down based on cell-type specific anti-proliferative activity and by eliminating those inhibitors that broadly targeted other dehydrogenases.

With the successful identification of seven candidate inhibitors, the team sought to determine if these molecules could inhibit PHGDH in the complex cellular environment. To do so, the team used a mass spectrometry-based assay (test) to measure newly synthesized serine in a cell in the presence of the drug candidates.

One of the seven small molecules tested, named CBR-5884, was able to specifically inhibit serine synthesis by 30 percent, suggesting that the molecule specifically targeted PHGDH. The group went on to show that CBR-5884 was able to inhibit cell proliferation of breast cancer and melanoma cells lines that overexpress PHGDH.

As expected, CBR-5884 did not inhibit cancer cells that did not overexpress PHGDH, as they can import serine; however, when incubated in media lacking serine, the presence of CBR-5884 decreased growth in these cells.

The group anticipates much optimization work before this drug candidate can become an effective therapeutic. In pursuit of this goal, the researchers plan to take a medicinal chemistry approach to improve potency and metabolic stability.

 

How Cancer Stem Cells Thrive When Oxygen Is Scarce

(Image: Shutterstock)
image: Shutterstock

Working with human breast cancer cells and mice, scientists at The Johns Hopkins University say new experiments explain how certain cancer stem cells thrive in low oxygen conditions. Proliferation of such cells, which tend to resist chemotherapy and help tumors spread, are considered a major roadblock to successful cancer treatment.

The new research, suggesting that low-oxygen conditions spur growth through the same chain of biochemical events in both embryonic stem cells and breast cancer stem cells, could offer a path through that roadblock, the investigators say.

“There are still many questions left to answer but we now know that oxygen poor environments, like those often found in advanced human breast cancers serve as nurseries for the birth of cancer stem cells,” said Gregg Semenza, M.D., Ph.D., the C. Michael Armstrong Professor of Medicine and a member of the Johns Hopkins Kimmel Cancer Center. “That gives us a few more possible targets for drugs that diminish their threat in human cancer.”

A summary of the findings was published online March 21 in the Proceedings of the National Academy of Sciences.

“Aggressive cancers contain regions where the cancer cells are starved for oxygen and die off, yet patients with these tumors generally have the worst outcome. Our new findings tell us that low oxygen conditions actually encourage certain cancer stem cells to multiply through the same mechanism used by embryonic stem cells.”

All stem cells are immature cells known for their ability to multiply indefinitely and give rise to progenitor cells that mature into specific cell types that populate the body’s tissues during embryonic development. They also replenish tissues throughout the life of an organism. But stem cells found in tumors use those same attributes and twist them to maintain and enhance the survival of cancers.

Recent studies showed that low oxygen conditions increase levels of a family of proteins known as HIFs, or hypoxia-inducible factors, that turn on hundreds of genes, including one called NANOG that instructs cells to become stem cells.

Studies of embryonic stem cells revealed that NANOG protein levels can be lowered by a chemical process known as methylation, which involves putting a methyl group chemical tag on a protein’s messenger RNA (mRNA) precursor. Semenza said methylation leads to the destruction of NANOG’s mRNA so that no protein is made, which in turn causes the embryonic stem cells to abandon their stem cell state and mature into different cell types.

Zeroing in on NANOG, the scientists found that low oxygen conditions increased NANOG’s mRNA levels through the action of HIF proteins, which turned on the gene for ALKBH5, which decreased the methylation and subsequent destruction of NANOG’s mRNA. When they prevented the cells from making ALKBH5, NANOG levels and the number of cancer stem cells decreased. When the researchers manipulated the cell’s genetics to increase levels of ALKBH5 without exposing them to low oxygen, they found this also decreased methylation of NANOG mRNA and increased the numbers of breast cancer stem cells.

Finally, using live mice, the scientists injected 1,000 triple-negative breast cancer cells into their mammary fat pads, where the mouse version of breast cancer forms. Unaltered cells created tumors in all seven mice injected with such cells, but when cells missing ALKBH5 were used, they caused tumors in only 43 percent (six out of 14) of mice. “That confirmed for us that ALKBH5 helps preserve cancer stem cells and their tumor-forming abilities,” Semenza said.

How cancer stem cells thrive when oxygen is scarce    https://www.sciencedaily.com/releases/2016/03/160328100159.htm

The new research, suggesting that low-oxygen conditions spur growth through the same chain of biochemical events in both embryonic stem cells and breast cancer stem cells, could offer a path through that roadblock, the investigators say.

“There are still many questions left to answer but we now know that oxygen poor environments, like those often found in advanced human breast cancers serve as nurseries for the birth of cancer stem cells,” says Gregg Semenza, M.D., Ph.D., the C. Michael Armstrong Professor of Medicine and a member of the Johns Hopkins Kimmel Cancer Center.

Chuanzhao Zhang, Debangshu Samanta, Haiquan Lu, John W. Bullen, Huimin Zhang, Ivan Chen, Xiaoshun He, Gregg L. Semenza.
Hypoxia induces the breast cancer stem cell phenotype by HIF-dependent and ALKBH5-mediated m6A-demethylation of NANOG mRNA.
Proceedings of the National Academy of Sciences, 2016; 201602883     DOI: 10.1073/pnas.1602883113

Significance

Pluripotency factors, such as NANOG, play a critical role in the maintenance and specification of cancer stem cells, which are required for primary tumor formation and metastasis. In this study, we report that exposure of breast cancer cells to hypoxia (i.e., reduced O2 availability), which is a critical feature of the tumor microenvironment, induces N6-methyladenosine (m6A) demethylation and stabilization of NANOG mRNA, thereby promoting the breast cancer stem cell (BCSC) phenotype. We show that inhibiting the expression of AlkB homolog 5 (ALKBH5), which demethylates m6A, or the hypoxia-inducible factors (HIFs) HIF-1α and HIF-2α, which activate ALKBH5 gene transcription in hypoxic breast cancer cells, is an effective strategy to decrease NANOG expression and target BCSCs in vivo.

N6-methyladenosine (m6A) modification of mRNA plays a role in regulating embryonic stem cell pluripotency. However, the physiological signals that determine the balance between methylation and demethylation have not been described, nor have studies addressed the role of m6A in cancer stem cells. We report that exposure of breast cancer cells to hypoxia stimulated hypoxia-inducible factor (HIF)-1α- and HIF-2α–dependent expression of AlkB homolog 5 (ALKBH5), an m6A demethylase, which demethylated NANOG mRNA, which encodes a pluripotency factor, at an m6A residue in the 3′-UTR. Increased NANOG mRNA and protein expression, and the breast cancer stem cell (BCSC) phenotype, were induced by hypoxia in an HIF- and ALKBH5-dependent manner. Insertion of the NANOG 3′-UTR into a luciferase reporter gene led to regulation of luciferase activity by O2, HIFs, and ALKBH5, which was lost upon mutation of the methylated residue. ALKBH5 overexpression decreased NANOG mRNA methylation, increased NANOG levels, and increased the percentage of BCSCs, phenocopying the effect of hypoxia. Knockdown of ALKBH5 expression in MDA-MB-231 human breast cancer cells significantly reduced their capacity for tumor initiation as a result of reduced numbers of BCSCs. Thus, HIF-dependent ALKBH5 expression mediates enrichment of BCSCs in the hypoxic tumor microenvironment.

Specific Proteins Found to Jump Start Spread of Cancer Cells

http://www.genengnews.com/gen-news-highlights/specific-proteins-found-to-jump-start-spread-of-cancer-cells/81252417/

Metastatic breast cancer cells. [National Cancer Institute]
http://www.genengnews.com/Media/images/GENHighlight/thumb_Feb29_2016_NCI_MetastaticBreastCancerCells1797514764.jpg

Scientists at the University of California, San Diego School of Medicine and Moores Cancer Center, with colleagues in Spain and Germany, have discovered how elevated levels of particular proteins in cancer cells trigger hyperactivity in other proteins, fueling the growth and spread of a variety of cancers. Their study (“Prognostic Impact of Modulators of G Proteins in Circulating Tumor Cells from Patients with Metastatic Colorectal Cancer”) is published in Scientific Reports.

Specifically, the international team, led by senior author Pradipta Ghosh, M.D., associate professor at the University of California San Diego School of Medicine, found that increased levels of expression of some members of a protein family called guanine nucleotide exchange factors (GEFs) triggered unsuspected hyperactivation of G proteins and subsequent progression or metastasis of cancer.

The discovery suggests GEFs offer a new and more precise indicator of disease state and prognosis. “We found that elevated expression of each GEF is associated with a shorter, progression-free survival in patients with metastatic colorectal cancer,” said Dr. Ghosh. “The GEFs fared better as prognostic markers than two well-known markers of cancer progression, and the clustering of all GEFs together improved the predictive accuracy of each individual family member.”

In recent years, circulating tumor cells (CTCs), which are shed from primary tumors into the bloodstream and act as seeds for new tumors taking root in other parts of the body, have become a prognostic and predictive biomarker. The presence of CTCs is used to monitor the efficacy of therapies and detect early signs of metastasis.

But counting CTCs in the bloodstream has limited utility, said Dr. Ghosh. “Enumeration alone does not capture the particular characteristics of CTCs that are actually tumorigenic and most likely to cause additional malignancies.”

Numerous efforts are underway to improve the value and precision of CTC analysis. According to Dr. Ghosh the new findings are a step in that direction. First, GEFs activate trimeric G proteins, and second, G protein signaling is involved in CTCs. G proteins are ubiquitous and essential molecular switches involved in transmitting external signals from stimuli into cells’ interiors. They have been a subject of heightened scientific interest for many years.

Dr. Ghosh and colleagues found that elevated expression of nonreceptor GEFs activates Gαi proteins, fueling CTCs and ultimately impacting the disease course and survival of cancer patients.

“Our work shows the prognostic impact of elevated expression of individual and clustered GEFs on survival and the benefit of transcriptome analysis of G protein regulatory proteins in cancer biology,” said Dr. Ghosh. “The next step will be to carry this technology into the clinic where it can be applied directly to deciphering a patient’s state of cancer and how best to treat.”

Metastasis-on-a-Chip’ Models Cancer’s Spread

http://www.mdtmag.com/news/2016/03/metastasis-chip-models-cancers-spread?et_cid=5200644&et_rid=461755519

In the journal Biotechnology Bioengineering, the team reports on its “metastasis-on-a-chip” system believed to be one of the first laboratory models of cancer spreading from one 3D tissue to another.

The current version of the system models a colorectal tumor spreading from the colon to the liver, the most common site of metastasis. Skardal said future versions could include additional organs, such as the lung and bone marrow, which are also potential sites of metastasis. The team also plans to model other types of cancer, such as the deadly brain tumor glioblastoma

To create the system, researchers encapsulated human intestine and colorectal cancer cells inside a biocompatible gel-like material to make a mini-organ. A mini-liver composed of human liver cells was made in the same way. These organoids were placed in a “chip” system made up of a set of micro-channels and chambers etched into the chip’s surface to mimic a simplified version of the body’s circulatory system. The tumor cells were tagged with fluorescent molecules so their activity could be viewed under a microscope.

To test whether the system could model metastasis, the researchers first used highly aggressive cancer cells in the colon organoid. Under the microscope, they saw the tumor grow in the colon organoid until the cells broke free, entered the circulatory system and then invaded the liver tissue, where another tumor formed and grew. When a less aggressive form of colon cancer was used in the system, the tumor did not metastasize, but continued to grow in the colon.

To test the system’s potential for screening drugs, the team introduced Marimastat, a drug used to inhibit metastasis in human patients, into the system and found that it significantly prevented the migration of metastatic cells over a 10-day period. Likewise, the team also tested 5-fluorouracil, a common colorectal cancer drug, which reduced the metabolic activity of the tumor cells.

“We are currently exploring whether other established anti-cancer drugs have the same effects in the system as they do in patients,” said Skardal. “If this link can be validated and expanded, we believe the system can be used to screen drug candidates for patients as a tool in personalized medicine. If we can create the same model systems, only with tumor cells from an actual patient, then we believe we can use this platform to determine the best therapy for any individual patient.”

The scientists are currently working to refine their system. They plan to use 3D printing to create organoids more similar in function to natural organs. And they aim to make the process of metastasis more realistic. When cancer spreads in the human body, the tumor cells must break through blood vessels to enter the blood steam and reach other organs. The scientists plan to add a barrier of endothelial cells, the cells that line blood vessels, to the model.

This concept of modeling the body’s processes on a miniature level is made possible because of advances in micro-tissue engineering and micro-fluidics technologies. It is similar to advances in the electronics industry made possible by miniaturizing electronics on a chip.

Scientists Synthesize Anti-Cancer Agent

A schematic shows a trioxacarcin C molecule, whose structure was revealed for the first time through a new process developed by the Rice lab of synthetic organic chemist K.C. Nicolaou. Trioxacarcins are found in bacteria but synthetic versions are needed to study them for their potential as medications. Trioxacarcins have anti-cancer properties. Source: Nicolaou Group/Rice University
A schematic shows a trioxacarcin C molecule, whose structure was revealed for the first time through a new process developed by the Rice lab of synthetic organic chemist K.C. Nicolaou. Trioxacarcins are found in bacteria but synthetic versions are needed to study them for their potential as medications. Trioxacarcins have anti-cancer properties. Source: Nicolaou Group/Rice University  http://www.dddmag.com/sites/dddmag.com/files/ddd1603_rice-anticancer.jpg

A team led by Rice University synthetic organic chemist K.C. Nicolaou has developed a new process for the synthesis of a series of potent anti-cancer agents originally found in bacteria.

The Nicolaou lab finds ways to replicate rare, naturally occurring compounds in larger amounts so they can be studied by biologists and clinicians as potential new medications. It also seeks to fine-tune the molecular structures of these compounds through analog design and synthesis to improve their disease-fighting properties and lessen their side effects.

Such is the case with their synthesis of trioxacarcins, reported this month in the Journal of the American Chemical Society.

“Not only does this synthesis render these valuable molecules readily available for biological investigation, but it also allows the previously unknown full structural elucidation of one of them,” Nicolaou said. “The newly developed synthetic technologies will allow us to construct variations for biological evaluation as part of a program to optimize their pharmacological profiles.”

At present, there are no drugs based on trioxacarcins, which damage DNA through a novel mechanism, Nicolaou said.

Trioxacarcins were discovered in the fermentation broth of the bacterial strain Streptomyces bottropensis. They disrupt the replication of cancer cells by binding and chemically modifying their genetic material.

“These molecules are endowed with powerful anti-tumor properties,” Nicolaou said. “They are not as potent as shishijimicin, which we also synthesized recently, but they are more powerful than taxol, the widely used anti-cancer drug. Our objective is to make it more powerful through fine-tuning its structure.”

He said his lab is working with a biotechnology partner to pair these cytotoxic compounds (called payloads) to cancer cell-targeting antibodies through chemical linkers. The process produces so-called antibody-drug conjugates as drugs to treat cancer patients. “It’s one of the latest frontiers in personalized targeting chemotherapies,” said Nicolaou, who earlier this year won the prestigious Wolf Prize in Chemistry.

Fluorescent Nanoparticle Tracks Cancer Treatment’s Effectiveness in Hours

Bevin Fletcher, Associate Editor    http://www.biosciencetechnology.com/news/2016/03/fluorescent-nanoparticle-tracks-cancer-treatments-effectiveness-hours

Using reporter nanoparticles loaded with either a chemotherapy or immunotherapy, researchers could distinguish between drug-sensitive and drug-resistant tumors in a pre-clinical model of prostate cancer. (Source: Brigham and Women's Hospital)

Using reporter nanoparticles loaded with either a chemotherapy or immunotherapy, researchers could distinguish between drug-sensitive and drug-resistant tumors in a pre-clinical model of prostate cancer. (Source: Brigham and Women’s Hospital)

Bioengineers at Brigham and Women’s Hospital have developed a new technique to help determine if chemotherapy is working in as few as eight hours after treatment. The new approach, which can also be used for monitoring the effectiveness of immunotherapy, has shown success in pre-clinical models.

The technology utilizes a nanoparticle, carrying anti-cancer drugs, that glows green when cancer cells begin dying. Researchers, using  the “reporter nanoparticles” that responds to a particular enzyme known as caspase, which is activated when cells die, were able to distinguish between a tumor that is drug-sensitive or drug-resistant much faster than conventional detection methods such as PET scans, CT and MRI.  The findings were published online March 28 in the Proceedings of the National Academy of Sciences.

“Using this approach, the cells light up the moment a cancer drug starts working,” co-corresponding author Shiladitya Sengupta, Ph.D., principal investigator in BWH’s Division of Bioengineering, said in a prepared statement.  “We can determine if a cancer therapy is effective within hours of treatment.  Our long-term goal is to find a way to monitor outcomes very early so that we don’t give a chemotherapy drug to patients who are not responding to it.”

Cancer killers send signal of success

Nanoparticles deliver drug, then give real-time feedback when tumor cells die   BY   SARAH SCHWARTZ

New lab-made nanoparticles deliver cancer drugs into tumors, then report their effects in real time by lighting up in response to proteins produced by dying cells. More light (right, green) indicates a tumor is responding to chemotherapy.

Tiny biochemical bundles carry chemotherapy drugs into tumors and light up when surrounding cancer cells start dying. Future iterations of these lab-made particles could allow doctors to monitor the effects of cancer treatment in real time, researchers report the week of March 28 in theProceedings of the National Academy of Sciences.

“This is the first system that allows you to read out whether your drug is working or not,” says study coauthor Shiladitya Sengupta, a bioengineer at Brigham and Women’s Hospital in Boston.

Each roughly 100-nanometer-wide particle consists of a drug and a fluorescent dye linked to a coiled molecular chain. Before the particles enter cells, the dye is tethered to a “quencher” molecule that prevents it from lighting up. When injected into the bloodstream of a mouse with cancer, the nanoparticles accumulate in tumor cells and release the drug, which activates a protein that tears a cancer cell apart. This cell-splitting protein not only kills the tumor cell, but also severs the link between the dye and the quencher, allowing the nanoparticles to glow under infrared light.

Reporter nanoparticle that monitors its anticancer efficacy in real time

Ashish Kulkarnia,b,1,Poornima Raoa,b,Siva Natarajana,b,Aaron Goldman, et al.
http://www.pnas.org/content/early/2016/03/28/1603455113.abstract

The ability to identify responders and nonresponders very early during chemotherapy by direct visualization of the activity of the anticancer treatment and to switch, if necessary, to a regimen that is effective can have a significant effect on the outcome as well as quality of life. Current approaches to quantify response rely on imaging techniques that fail to detect very early responses. In the case of immunotherapy, the early anatomical readout is often discordant with the biological response. This study describes a self-reporting nanomedicine that not only delivers chemotherapy or immunotherapy to the tumor but also reports back on its efficacy in real time, thereby identifying responders and nonresponders early on

The ability to monitor the efficacy of an anticancer treatment in real time can have a critical effect on the outcome. Currently, clinical readouts of efficacy rely on indirect or anatomic measurements, which occur over prolonged time scales postchemotherapy or postimmunotherapy and may not be concordant with the actual effect. Here we describe the biology-inspired engineering of a simple 2-in-1 reporter nanoparticle that not only delivers a cytotoxic or an immunotherapy payload to the tumor but also reports back on the efficacy in real time. The reporter nanoparticles are engineered from a novel two-staged stimuli-responsive polymeric material with an optimal ratio of an enzyme-cleavable drug or immunotherapy (effector elements) and a drug function-activatable reporter element. The spatiotemporally constrained delivery of the effector and the reporter elements in a single nanoparticle produces maximum signal enhancement due to the availability of the reporter element in the same cell as the drug, thereby effectively capturing the temporal apoptosis process. Using chemotherapy-sensitive and chemotherapy-resistant tumors in vivo, we show that the reporter nanoparticles can provide a real-time noninvasive readout of tumor response to chemotherapy. The reporter nanoparticle can also monitor the efficacy of immune checkpoint inhibition in melanoma. The self-reporting capability, for the first time to our knowledge, captures an anticancer nanoparticle in action in vivo.

 

Cancer Treatment’s New Direction  
Genetic testing helps oncologists target tumors and tailor treatments
http://www.wsj.com/articles/cancer-treatments-new-direction-1459193085

Evan Johnson had battled a cold for weeks, endured occasional nosebleeds and felt so fatigued he struggled to finish his workouts at the gym. But it was the unexplained bruises and chest pain that ultimately sent the then 23-year-old senior at the University of North Dakota to the Mayo Clinic. There a genetic test revealed a particularly aggressive form of acute myeloid leukemia. That was two years ago.

The harrowing roller-coaster that followed for Mr. Johnson and his family highlights new directions oncologists are taking with genetic testing to find and attack cancer. Tumors can evolve to resist treatments, and doctors are beginning to turn such setbacks into possible advantages by identifying new targets to attack as the tumors change.

His course involved a failed stem cell transplant, a half-dozen different drug regimens, four relapses and life-threatening side effects related to his treatment.

Nine months in, his leukemia had evolved to develop a surprising new mutation. The change meant the cancer escaped one treatment, but the new anomaly provided doctors with a fresh target, one susceptible to drugs approved for other cancers. Doctors adjusted Mr. Johnson’s treatment accordingly, knocked out the disease and paved the way for a second, more successful stem cell transplant. He has now been free of leukemia for a year.

Now patients with advanced cancer who are treated at major centers can expect to have their tumors sequenced, in hopes of finding a match in a growing medicine chest of drugs that precisely target mutations that drive cancer’s growth. When they work, such matches can have a dramatic effect on tumors. But these “precision medicines” aren’t cures. They are often foiled when tumors evolve, pushing doctors to take the next step to identify new mutations in hopes of attacking them with an effective treatment.

Dr. Kasi and his Mayo colleagues—Naseema Gangat, a hematologist, and Shahrukh Hashmi, a transplant specialist—are among the authors of an account of Mr. Johnson’s case published in January in the journal Leukemia Research Reports.

Before qualifying for a transplant, a patient’s blasts need to be under 5%.

To get under 5%, he started on a standard chemotherapy regimen and almost immediately, things went south. His blast cells plummeted, but “the chemo just wiped out my immune system,”

Then as mysteriously as it began, a serious mycotic throat infection stopped. But Mr. Johnson couldn’t tolerate the chemo, and his blast cells were on the rise. A two-drug combination that included the liver cancer drug Nexavar, which targets the FLT3 mutation, knocked back the blast cells. But the stem cell transplant in May, which came from one of his brothers, failed to take, and he relapsed after 67 days, around late July.

He was put into a clinical trial of an experimental AML drug being developed by Astellas Pharma of Japan. He started to regain weight. In November 2014, doctors spotted the initial signs in blood tests that Mr. Johnson’s cancer was evolving to acquire a new mutation. By late January, he relapsed again , but there was a Philadelphia chromosome mutation,  a well-known genetic alteration associated with chronic myeloid leukemia. It also is a target of the blockbuster cancer drug Gleevec and several other medicines.

Clonal evolution of AML on novel FMS-like tyrosine kinase-3 (FLT3) inhibitor therapy with evolving actionable targets

Naseema GangatMark R. LitzowMrinal M. PatnaikShahrukh K. HashmiNaseema Gangat

Highlights
•   The article reports on a case of AML that underwent clonal evolution.
•   We report on novel acquisition of the Philadelphia t(9;22) translocation in AML.
•   Next generation sequencing maybe helpful in these refractory/relapse cases.
•   Novel FLT3-inhibitor targeted therapies are another option in patients with AML.
•   Personalizing cancer treatment based on evolving targets is a viable option.

For acute myeloid leukemia (AML), identification of activating mutations in the FMS-like tyrosine kinase-3 (FLT3) has led to the development of several FLT3-inhibitors. Here we present clinical and next generation sequencing data at the time of progression of a patient on a novel FLT3-inhibitor clinical trial (ASP2215) to show that employing therapeutic interventions with these novel targeted therapies can lead to consequences secondary to selective pressure and clonal evolution of cancer. We describe novel findings alongside data on treatment directed towards actionable aberrations acquired during the process. (Clinical Trial: NCT02014558; registered at: 〈https://clinicaltrials.gov/ct2/show/NCT02014558〉)

The development of kinase inhibitors for the treatment of leukemia has revolutionized the care of these patients. Since the introduction of imatinib for the treatment of chronic myeloid leukemia, multiple other tyrosine kinase inhibitors (TKIs) have become available[1]. Additionally, for acute myeloid leukemia (AML), identification of activating mutations in the FMS-like tyrosine kinase-3 (FLT3) has led to the development of several FLT3-inhibitors [2], [3], [4] and [5]. The article herein reports a unique case of AML that underwent clonal evolution while on a novel FLT3-inhibitor clinical trial.

Our work herein presents clinical and next generation sequencing data at the time of progression to illustrate these important concepts stemming from Darwinian evolution [6]. We describe novel findings alongside data on treatment directed towards actionable aberrations acquired during the process.

Our work focuses on a 23-year-old male who presented with 3 months history of fatigue and easy bruising, a white blood count of 22.0×109/L with 51% circulating blasts, hemoglobin 7.6 g/dL, and a platelet count of 43×109/L. A bone marrow biopsy confirmed a diagnosis of AML. Initial cytogenetic studies identified trisomy 8 in all the twenty metaphases examined. Mutational analysis revealed an internal tandem duplication of the FLT3 gene (FLT3-ITD).

He received standard induction chemotherapy (7+3) with cytarabine (ARA-C; 100 mg/m2for 7 days) and daunorubicin (DNM; 60 mg/m2 for 3 days). His induction chemotherapy was complicated by severe palatine and uvular necrosis of indeterminate etiology (possible mucormycosis).

Bone marrow biopsy at day 28 demonstrated persistent disease with 10% bone marrow blasts (Fig. 1). Due to his complicated clinical course and the presence of a FLT3-ITD, salvage therapy with 5-azacitidine (5-AZA) and sorafenib (SFN) was instituted. Table 1.
The highlighted therapies were employed in this particular case at various time points as shown in Fig. 1.

http://ars.els-cdn.com/content/image/1-s2.0-S221304891530025X-gr1.jpg

References

    • [1]
    • J.E. Cortes, D.W. Kim, J. Pinilla-Ibarz, et al.
    • A phase 2 trial of ponatinib in Philadelphia chromosome-positive leukemias
    • New Engl. J. Med., 369 (19) (2013), pp. 1783–1796
    • [2]
    • F. Ravandi, M.L. Alattar, M.R. Grunwald, et al.
    • Phase 2 study of azacytidine plus sorafenib in patients with acute myeloid leukemia and FLT-3 internal tandem duplication mutation
    • Blood, 121 (23) (2013), pp. 4655–4662
    • [3]
    • N.P. Shah, M. Talpaz, M.W. Deininger, et al.
    • Ponatinib in patients with refractory acute myeloid leukaemia: findings from a phase 1 study
    • Br. J. Haematol., 162 (4) (2013), pp. 548–552
    • [4]
    • Y. Alvarado, H.M. Kantarjian, R. Luthra, et al.
    • Treatment with FLT3 inhibitor in patients with FLT3-mutated acute myeloid leukemia is associated with development of secondary FLT3-tyrosine kinase domain mutations
    • Cancer, 120 (14) (2014), pp. 2142–2149
    • [5]
    • C.C. Smith, C. Zhang, K.C. Lin, et al.
    • Characterizing and overriding the structural mechanism of the Quizartinib-Resistant FLT3 “Gatekeeper” F691L mutation with PLX3397
    • Cancer Discov. (2015)
    • [6]
    • M. Greaves, C.C. Maley
    • Clonal evolution in cancer
    • Nature, 481 (7381) (2012), pp. 306–313

 

 

 

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A Reconstructed View of Personalized Medicine

Author: Larry H. Bernstein, MD, FCAP

 

There has always been Personalized Medicine if you consider the time a physician spends with a patient, which has dwindled. But the current recognition of personalized medicine refers to breakthrough advances in technological innovation in diagnostics and treatment that differentiates subclasses within diagnoses that are amenable to relapse eluding therapies.  There are just a few highlights to consider:

  1. We live in a world with other living beings that are adapting to a changing environmental stresses.
  2. Nutritional resources that have been available and made plentiful over generations are not abundant in some climates.
  3. Despite the huge impact that genomics has had on biological progress over the last century, there is a huge contribution not to be overlooked in epigenetics, metabolomics, and pathways analysis.

A Reconstructed View of Personalized Medicine

There has been much interest in ‘junk DNA’, non-coding areas of our DNA are far from being without function. DNA has two basic categories of nitrogenous bases: the purines (adenine [A] and guanine [G]), and the pyrimidines (cytosine [C], thymine [T], and  no uracil [U]),  while RNA contains only A, G, C, and U (no T).  The Watson-Crick proposal set the path of molecular biology for decades into the 21st century, culminating in the Human Genome Project.

There is no uncertainty about the importance of “Junk DNA”.  It is both an evolutionary remnant, and it has a role in cell regulation.  Further, the role of histones in their relationship the oligonucleotide sequences is not understood.  We now have a large output of research on noncoding RNA, including siRNA, miRNA, and others with roles other than transcription. This requires major revision of our model of cell regulatory processes.  The classic model is solely transcriptional.

  • DNA-> RNA-> Amino Acid in a protein.

Redrawn we have

  • DNA-> RNA-> DNA and
  • DNA->RNA-> protein-> DNA.

Neverthess, there were unrelated discoveries that took on huge importance.  For example, since the 1920s, the work of Warburg and Meyerhoff, followed by that of Krebs, Kaplan, Chance, and others built a solid foundation in the knowledge of enzymes, coenzymes, adenine and pyridine nucleotides, and metabolic pathways, not to mention the importance of Fe3+, Cu2+, Zn2+, and other metal cofactors.  Of huge importance was the work of Jacob, Monod and Changeux, and the effects of cooperativity in allosteric systems and of repulsion in tertiary structure of proteins related to hydrophobic and hydrophilic interactions, which involves the effect of one ligand on the binding or catalysis of another,  demonstrated by the end-product inhibition of the enzyme, L-threonine deaminase (Changeux 1961), L-isoleucine, which differs sterically from the reactant, L-threonine whereby the former could inhibit the enzyme without competing with the latter. The current view based on a variety of measurements (e.g., NMR, FRET, and single molecule studies) is a ‘‘dynamic’’ proposal by Cooper and Dryden (1984) that the distribution around the average structure changes in allostery affects the subsequent (binding) affinity at a distant site.

What else do we have to consider?  The measurement of free radicals has increased awareness of radical-induced impairment of the oxidative/antioxidative balance, essential for an understanding of disease progression.  Metal-mediated formation of free radicals causes various modifications to DNA bases, enhanced lipid peroxidation, and altered calcium and sulfhydryl homeostasis. Lipid peroxides, formed by the attack of radicals on polyunsaturated fatty acid residues of phospholipids, can further react with redox metals finally producing mutagenic and carcinogenic malondialdehyde, 4-hydroxynonenal and other exocyclic DNA adducts (etheno and/or propano adducts). The unifying factor in determining toxicity and carcinogenicity for all these metals is the generation of reactive oxygen and nitrogen species. Various studies have confirmed that metals activate signaling pathways and the carcinogenic effect of metals has been related to activation of mainly redox sensitive transcription factors, involving NF-kappaB, AP-1 and p53.

I have provided mechanisms explanatory for regulation of the cell that go beyond the classic model of metabolic pathways associated with the cytoplasm, mitochondria, endoplasmic reticulum, and lysosome, such as, the cell death pathways, expressed in apoptosis and repair.  Nevertheless, there is still a missing part of this discussion that considers the time and space interactions of the cell, cellular cytoskeleton and extracellular and intracellular substrate interactions in the immediate environment.

There is heterogeneity among cancer cells of expected identical type, which would be consistent with differences in phenotypic expression, aligned with epigenetics.  There is also heterogeneity in the immediate interstices between cancer cells.  Integration with genome-wide profiling data identified losses of specific genes on 4p14 and 5q13 that were enriched in grade 3 tumors with high microenvironmental diversity that also substratified patients into poor prognostic groups. In the case of breast cancer, there is interaction with estrogen , and we refer to an androgen-unresponsive prostate cancer.

Finally,  the interaction between enzyme and substrates may be conditionally unidirectional in defining the activity within the cell.  The activity of the cell is dynamically interacting and at high rates of activity.  In a study of the pyruvate kinase (PK) reaction the catalytic activity of the PK reaction was reversed to the thermodynamically unfavorable direction in a muscle preparation by a specific inhibitor. Experiments found that in there were differences in the active form of pyruvate kinase that were clearly related to the environmental condition of the assay – glycolitic or glyconeogenic. The conformational changes indicated by differential regulatory response were used to present a dynamic conformational model functioning at the active site of the enzyme. In the model, the interaction of the enzyme active site with its substrates is described concluding that induced increase in the vibrational energy levels of the active site decreases the energetic barrier for substrate induced changes at the site. Another example is the inhibition of H4 lactate dehydrogenase, but not the M4, by high concentrations of pyruvate. An investigation of the inhibition revealed that a covalent bond was formed between the nicotinamide ring of the NAD+ and the enol form of pyruvate.  The isoenzymes of isocitrate dehydrogenase, IDH1 and IDH2 mutations occur in gliomas and in acute myeloid leukemias with normal karyotype. IDH1 and IDH2 mutations are remarkably specific to codons that encode conserved functionally important arginines in the active site of each enzyme. In this case, there is steric hindrance by Asp279 where the isocitrate substrate normally forms hydrogen bonds with Ser94.

Personalized medicine has been largely viewed from a lens of genomics.  But genomics is only the reading frame.  The living activities of cell processes are dynamic and occur at rapid rates.  We have to keep in mind that personalized in reference to genotype is not complete without reconciliation of phenotype, which is the reference to expressed differences in outcomes.

 

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Is the Warburg effect an effect of deregulated space occupancy of methylome?

Larry H. Bernstein and Radoslav Bozov, co-curation

LPBI

 

 

It would appear that pyruvate is directly used by cancer cell machinery for sustaining genome independence, and that CRISP-Cas9 system is essentially a modified CAD protein for making small bases.

13C-labeled biochemical probes for the study of cancer metabolism with dynamic nuclear polarization-enhanced magnetic resonance imaging

Lucia Salamanca-Cardona and Kayvan R. Keshari

Cancer & Metabolism 2015; 3:9          http://dx.doi.org:/10.1186/s40170-015-0136-2

In recent years, advances in metabolic imaging have become dependable tools for the diagnosis and treatment assessment in cancer. Dynamic nuclear polarization (DNP) has recently emerged as a promising technology in hyperpolarized (HP) magnetic resonance imaging (MRI) and has reached clinical relevance with the successful visualization of [1-13C] pyruvate as a molecular imaging probe in human prostate cancer. This review focuses on introducing representative compounds relevant to metabolism that are characteristic of cancer tissue: aerobic glycolysis and pyruvate metabolism, glutamine addiction and glutamine/glutamate metabolism, and the redox state and ascorbate/dehydroascorbate metabolism. In addition, a brief introduction of probes that can be used to trace necrosis, pH changes, and other pathways relevant to cancer is presented to demonstrate the potential that HP MRI has to revolutionize the use of molecular imaging for diagnosis and assessment of treatments in cancer.

 

Since the hallmark discovery of the Warburg effect in cancer cells in the 1920s, it has been widely accepted that the metabolic properties of cancer cells are vastly different from those of normal cells [1]. Starting from the observation that many cancerous (neoplastic) cells have higher rates of glucose utilization and lactate production, the development of tools and methods to correlate specific cellular metabolic processes to different types of cancer cells has received increased research focus [2, 3]. Several imaging techniques are currently in use for this purpose, including radiography, scintigraphy, positron emission tomography (PET), single-photon emission computed tomography (SPECT), and magnetic resonance (MR) [4, 5].

For more than 30 years, MR has been a revolutionary diagnostic tool, used in a wide range of settings from the central nervous system to cardiomyopathies and cancers. MR imaging (MRI) can outline molecular and cellular processes with high spatial resolution. Typically, MRI of body tissues is achieved via contrast visualization of the protons (1H) of water, which are present in high abundance in living systems. This can be extended to MR spectroscopy (MRS), which can further differentiate between less abundant, carbon-bearing, biological metabolites in vivo utilizing 1Hs of these compounds [6, 7]. However, despite its usefulness in imaging whole body tissues, 1H MRS has low spectral resolution and poor sensitivity for these less abundant metabolites. In addition,13C MRS is increasingly difficult, in comparison to 1H MRS, in that both the gyromagnetic ratio (approximately 25 % of 1H) and natural abundance (1.1 % of 1H) are significantly lower, making the detection of carbon-bearing compounds difficult [8, 9]. The low spectral resolution of 1H MRS for metabolites can be addressed by using 13C-enriched compounds, and with this direct 13C MRS, metabolic processes can be traced, utilizing enriched tags on specific carbons in a given metabolite [10]. While enrichment of molecules in 13C can also moderately address the sensitivity limitation of MRS, recent work in hyperpolarization (HP) provides a means of dramatically increasing sensitivity and enhancing signals, well beyond that of the equilibrium state obtained via MRS. [11, 12]. The focus of this review will be the introduction of this approach in the setting of cancer metabolism, delineating probes of interest, which have been applied to study metabolic processes in vivo.

Obtaining a hyperpolarized probe

In MR, a desired target is placed in a magnetic field where the nuclear spins of molecules are aligned with or against the direction of the magnetic field. The nuclear spins have thus different energies, and an MR signal is detected upon relaxation of nuclear spins of higher energy. At thermal equilibrium, the number of spins aligned with the magnetic field nearly equals the number of spins opposing the direction of the magnetic field. Thus, at thermal equilibrium, spin polarization is in the order of >0.0005 % resulting in a limited signal. Signal increases on the order of 100,000-fold can be achieved by hyperpolarizing the system via the redistribution of the spin population levels found at equilibrium [10, 13]. There are several techniques that have been used to achieve hyperpolarization of various nuclei: spin-exchange optical pumping of 3He and 129Xe, parahydrogen-induced polarization (PHIP), and dissolution dynamic nuclear polarization (DNP) [11,14, 15]. Both PHIP and DNP techniques can polarize biologically relevant nuclei like 13C and 15N, although there is a wider range of molecules that can be targeted for hyperpolarization using dissolution DNP [14, 1618].

The goal of DNP is the transfer of polarization from highly polarized unpaired electron spins to the nuclear spins of a desired target compound. This is achieved by applying an external magnetic field to a free-radical agent in order to polarize electron spins, followed by saturating the electron spin resonance via microwave irradiation in order to obtain polarization transfer. The free-radical agent is generally a stable organic compound that is compatible with aqueous buffers, which are used as solvent in order to obtain a homogeneous distribution of the radical [13]. Nearly 100 % of the electrons on the free-radical agent are polarized when the free-radical/solvent mixture is subjected to high magnetic fields (≥3.3 T) followed by rapid freezing to 1 K using liquid helium in order to obtain a sample frozen to an amorphous state, which is necessary for retention and transfer of polarization [18]. For biological applications, after transfer of electron spin polarization to the nuclei of interest has occurred, the preparation must exist in solution, which can be achieved utilizing a dissolution process in which the solid sample is rapidly melted via injection of a hot solvent, typically a biologically compatible buffer, into the frozen sample [13]. The dissolution process results in a liquid sample at room temperature, while still preserving the enhanced polarization obtained by the microwave irradiation of the frozen sample [8]. Additionally, the use of chelating agents (e.g., EDTA) with the solvent to eliminate trace metals and more recently the use of gadolinium (Gd) chelates with the DNP sample have been used to further enhance and retain polarization in the liquid sample, albeit with caution over potential toxic effects when applied in vivo and the potential for loss of hyperpolarization due to T 1 shortening [11, 19, 20]. More in-depth exploration of the technical aspects of probe development has been previously reviewed [8, 11].

Considerations in probe selection and current research

The usefulness of a molecule for hyperpolarized MRS is dependent on the polarization lifetime of the nucleus of interest, and this property is determined by the spin-lattice relaxation constant (T1) [21]. Dipolar coupling, the magnetic field range, and molecular size can also affect the T1 of a given nucleus. In general, high magnetic fields and large molecular weights decrease the T1. Dipole-dipole coupling of 13C with 1H is common in biologically relevant molecules, and it shortens relaxation times; therefore, carbon atoms directly bound to 1H are generally not useful as probes for HP. For example, all carbons present in glucose (an important substrate in cancer cells) have relaxation times shorter than 2 s [22]. On the other hand, carbonyl carbons of biologically relevant molecules generally have T1’s above 20 s even at high magnetic fields like [1-13C] pyruvic acid, which has relaxation times of 67, 48, and 44 s at 3, 11.7, and 14.1 T, respectively [2325]. Even carbons that are less oxidized than carbonyls, like the hemi-ketal in [2-13C] fructose have T1’s one order of magnitude higher than glucose carbons. Short spin-lattice relaxation times can sometimes be increased by deuterium enrichment of the sample. With this technique, protons that are directly bound to carbons are exchanged for deuterium atoms which results in the reduction of dipole-dipole relaxation, further preserving the hyperpolarized state [26]. This has resulted in increased T1’s of 13C nuclei in molecules such as glucose (T1 increased from 2 s to 10–14 s), providing the possibility of utilizing them in future metabolic studies [2729]. Despite the effect of deuterium enrichment, research efforts have largely focused on developing carbonyl-bearing molecules as molecular imaging probes. The focus of this review is to introduce representative compounds relevant to metabolism that are characteristic of cancer tissue and have been applied in the work of multiple groups: aerobic glycolysis, glutamine addiction, and the redox state.

Pyruvate and aerobic glycolysis

Of particular interest to cancer metabolism is the increased conversion of glucose to lactate as a result of modulated aerobic glycolysis. This process, also known as the Warburg effect, is characteristic of many tumors with altered metabolism where pyruvate generated from glucose metabolism via glycolysis is preferentially converted to lactate by lactate dehydrogenase (LDH) as opposed to entering the tricarboxylic acid cycle [1]. With this phenotype, cancer cells show a preference for lactate fermentation even in the presence of oxygen, thus bypassing oxidative respiration for ATP generation. Because of this, pyruvate has been the preferred probe for HP MRS research since it is an intermediate metabolite in pathways characteristic of aberrant metabolism in cancer cells, including increased lactate production as a result of aerobic glycolysis where detection of HP pyruvate-derived lactate can be used as a marker for cancer and response to treatment [30, 31] as well as an intermediate in amino acid metabolism (e.g., interconversion to alanine via transamination with glutamate) (Fig. 1). In addition, as mentioned before, carbonyl carbons in pyruvate have long relaxation times where even the methyl carbon can have T1’s above 50 s after deuterium enrichment [32]. The interconversion of pyruvate to lactate has been exploited for MRI by using [1-13C] pyruvate and detecting the accumulation of increased lactate in cancerous tissue as compared to surrounding benign tissue. Increased conversion of pyruvate to lactate and alanine has been demonstrated to precede MYC-driven tumorigenesis by using HP [1-13C] pyruvate in murine models [33]. Furthermore, in the same study, a decrease in the flux of alanine was observed at the tumor stage while a decrease in lactate conversion was indicative of tumor regression [33]. In transgenic adenocarcinoma of mouse prostate (TRAMP) models, in vivo studies using HP [1-13C] pyruvate demonstrated that hyperpolarized pyruvate and its metabolic products can be used non-invasively and with high specificity to obtain a profile of the histologic grade of prostate cancers [34]. In vivo imaging following hyperpolarized pyruvate has also been used to evaluate the role of glutaminase and LDH in human lymphoma models [35] as well as to elucidate metabolism of pyruvate in breast cancer [36] and renal cell carcinoma with treatment [30, 37].
https://i0.wp.com/static-content.springer.com/image/art%3A10.1186%2Fs40170-015-0136-2/MediaObjects/40170_2015_136_Fig1_HTML.gif
Flux of hyperpolarized [1-13C] pyruvate to [1-13C] lactate in prostate regions. a MR image from patient with prostate cancer showing regions of cancerous tissue and surrounding normal tissue. bd Localized dynamic hyperpolarized [1-13C]pyruvate and [1-13C]lactate spectral from voxels overlapping the contralateral region of prostate (turquoise), a region of prostate cancer (yellow), and a vessel outside the prostate (green). Adapted with permission from ref. [43]

Early work that utilized HP pyruvate to assess the response of tumors to treatment was conducted in mice xenografted with EL-4 lymphoma cells and treated with etoposide, a topoisomerase inhibitor that causes rapid cell death [38, 39]. In this study, tumor necrosis was correlated to a decrease in the flux of hyperpolarized lactate which was suggested to be due to a decrease in NAD+ and NADH in the intracellular pool as well as loss of LDH function. More recently, HP [1-13C] pyruvate has been used as a biomarker to evaluate early response to radiation therapy in glioma tumors by observing a decrease in hyperpolarized lactate suggested to be a result of changes in tumor perfusion which can be detected between 24 and 96 h following treatment [40, 41]. HP [1-13C] pyruvate has also been used to detect early response to temozolomide (TMZ) treatment on human glioblastoma rat models [42]. The study successfully showed for the first time detection of response to TMZ therapy 1 day after TMZ administration. The continued reports on using HP pyruvate as an imaging probe for assessing treatment response indicate the potential of the compound to become a standard in the field. Moreover, these studies demonstrate the usefulness of HP [1-13C] pyruvate as a tool for early assessment of therapy response, which can improve treatment selection at the clinical level. Pyruvate has also been validated as a metabolic imaging marker for use in humans [43]. In a two-phase study, patients with biopsy-proven prostate cancer of various histological grades were injected with HP [1-13C] pyruvate. In the first phase, a maximum dose level was determined to establish pharmacological safety of the HP probe while still injecting enough pyruvate to allow visualization. This addressed one of the major challenges faced in translating HP MRI to clinical applications: the potential toxicity of compounds that must be injected into patients. In the second phase, metabolism of pyruvate was visualized in real time and differences in the ratio of [1-13C] lactate to [1-13C] pyruvate between identified cancerous regions and normal tissue regions were successfully observed (Fig. 1ad). [1-13C] lactate in regions that did not contain tumor was not detected, confirming previous biopsy and preclinical studies that demonstrated low flux of [1-13C] pyruvate to lactate and low concentrations of lactate in benign prostate tissues [44, 45]. Preliminary results indicated the possibility of detecting previously unobserved cancerous regions by HP [1-13C] pyruvate, later confirmed to be Gleason 4+3 cancer by biopsy, though further investigation into the relationship between grade and metabolism in prostate cancer patients is needed. While there are challenges associated with translation to clinical use for HP [1-13C] pyruvate, the first in human study demonstrated the feasibility of hyperpolarization technology as a safe diagnostic tool and provides the potential for utilizing this approach in preclinical models with direct translation to the clinic.

Glutamine metabolism

Glutamine is an amino acid that plays an important cellular role as nitrogen donor in the form of an amide group for purine and pyrimidine biosynthesis, leaving a glutamate molecule in the process although glutamine can also be converted to glutamate by glutaminase in a reaction independent of nucleotide biosynthesis. Glutamate is the primary nitrogen donor for the biosynthesis of non-essential amino acids. Transaminases catalyze the transfer of the amine group from glutamate to α-ketoacids to synthesize alanine, aspartate (precursor for asparagine), serine (precursor for glycine and cysteine), ornithine (precursor for arginine), and proline which is derived from the glutamate carbon backbone. Glutamine is considered a non-essential amino acid as it can be recycled from glutamate and ammonia in a reaction catalyzed by glutamine synthetase; however, some cancer cells show increase consumption of glutamine and are unable to grow in the absence of exogenous glutamine [46, 47]. This metabolic characteristic of cells to require exogenous glutamine for growth has been termed “glutamine addiction” and has generated extensive research interest as an indicator of development of cancerous tissues [48]. In particular to the field of HP MRI, the conversion rate of glutamine to glutamate (Fig. 2) was explored in hepatocellular carcinoma (HCC) using a [5-13C] glutamine probe (Fig. 2) [49]. Using the ratio between [5-13C] glutamine and [5-13C] glutamate, it was demonstrated that HCC cells convert glutamine at a higher rate than normal cells supporting the notion of glutamine addiction. One important aspect of this study was the choice of [5-13C] glutamine as a probe as opposed to [1-13C] glutamine, which has a longer T1 (16.1 vs. 24.6 s at 9.4 T) [49, 50]. [5-13C] glutamine was selected because the chemical shift change obtained from [1-13C] in glutamine and glutamate is far too small, which could prevent proper identification and quantification of the peaks. This highlights the importance of understanding not only the target compound to be hyperpolarized but also the metabolic products to be detected and their resulting spectra in MR. This is further emphasized with studies that demonstrate the usefulness of [1-13C] glutamine as a source for [1-13C] glutamate in order to follow the metabolism of α-ketoglutarate to observe the metabolic state of the TCA cycle in transformed cells [51]. Furthermore, [1-13C] α-ketoglutarate has been hyperpolarized and used to visualize other metabolic events involving [1-13C] glutamate such as mutations in IDH1 expression in glioma tumors and pathways dependent on hypoxia-inducible factor (HIF) [5153]. More recently, [5-13C] glutamine has been used to visualize the metabolism of liver cancer in vivo and in vitro, as well as the treatment response of prostate cancer cells in vitro [54]. Based on the promise of glutamine as a biomarker for cancer diagnosis and treatment response, extending the spin-lattice relaxation time of the [5-13C] glutamine has been researched and successfully accomplished. The facile synthesis of [5-13C-4-2H2] glutamine has been reported, and its study showed that by relying on the effect of deuterium enrichment to lessen dipolar coupling effects, the T1 of [5-13C] glutamine could be increased from approximately 15 to 30 s [55]. Visualization of real-time conversion of glutamine to glutamate in SF188 cells was achieved using this probe, demonstrating the promise of [5-13C-4-2H2] glutamine as a probe for molecular imaging of metabolic events in real time. Further investigation of this probe applied to in vivo preclinical models will lay the foundation for its clinical translational potential in the future.
https://i2.wp.com/static-content.springer.com/image/art%3A10.1186%2Fs40170-015-0136-2/MediaObjects/40170_2015_136_Fig2_HTML.gif
Metabolism of [5-13C] glutamine to [5-13C] glutamate. a Time-dependent spectral data following conversion of [5-13C] glutamine to [5-13C] glutamate. The signals are from 13C-enriched [5-13C]glutamate at 181.5 ppm and [5-13C]glutamine at 178.5 ppm and from natural abundance 13C label in [1-13C]glutamate at 175.2 ppm and [1-13C]glutamine at 174.7 ppm. b Plot of the ratio of the signal intensities of [5-13C]glutamate/[5-13C]glutamine showing the ratio in hepatoma cells (shaded circle), cell lysate (square), and control (triangle). These results demonstrated that hepatoma cancer cells convert glutamine to glutamine at a higher rate than normal cells. Adapted with permission from ref. [49]

Dehydroascorbate as a redox sensor

Reactive oxygen species (ROS) like the hydroxyl radical, superoxide, and hydrogen peroxide have been shown to cause DNA damage and can lead to mutations that transform normal cells into cancerous cells [56]. The reduction/oxidation (redox) state, which is dependent on the balance between oxidizing equivalents like ROS and reducing cofactors, can provide insight into the physiological condition of the cell with respect to potential cancer transformations. Furthermore, the presence of ROS in tissue has been implicated to be a factor in developing resistance to radiation therapies [57]. During oxidative stress (i.e., when there is an increase in ROS), redox homeostasis is maintained by the action of antioxidant compounds, such as ascorbate (or vitamin C, VitC), which can scavenge for ROS and reduce the compounds to rid the cells of damaging agents [58]. In this process, ascorbate that is available to cells in high concentrations can be oxidized to dehydroascorbate (DHA) while reducing ROS. DHA can then be transported into the cell where DHA is reduced back to ascorbate resulting in a process of recycling ascorbate and DHA (Fig. 3) [59]. In this sense, the ratio of DHA to ascorbate can be used as a molecular marker to investigate the redox state and thus the physiological state of tissues. Additionally, conversion of DHA to ascorbate can be enzymatically catalyzed in an NADPH-dependent manner or via oxidation of glutathione (GSH) to glutathione sulfide (GSSG); thus, visualization of ascorbate/DHA metabolism offers a method for probing in vivo metabolism of NADPH as well as determination of GSSG to GSH ratio, both of which have been implicated to be indicators of oxidative stress in the cells, particularly for neurodegenerative, cardiovascular, and cancer diseases [6062]. Hyperpolarized [1-13C] DHA was successfully used in murine models to detect increased reducing capacity in prostate cancer with the purpose of developing a non-invasive, early diagnostic tool for improving selection of treatment therapies [62, 63]. DHA demonstrates a relatively long T1 at clinically relevant field strengths (>50 s at 3 T) and adequate chemical shift separation between it and its metabolic product ascorbate (δ = 3.8 ppm). Increased reduction of HP [1-13C] DHA to ascorbate was observed in tumor tissue compared to normal tissue as well as other metabolic organs (Fig. 3). This was additionally demonstrated in lymphoma cells, further supporting the potential for using DHA as a probe in living systems [64]. A following study validated these results, and the correlation between increased DHA reduction and glutathione was established in vivo, thus showing the utility of [1-13C] DHA as a molecular imaging probe to detect events that go beyond the direct metabolism of DHA [63]. Notwithstanding the potential of HP DHA as a diagnostic probe, the toxicity of DHA remains to be validated. Earlier studies on mammalian cells showed DHA toxicity starting at 10 mM, while a study carried on rats demonstrated neurological effects of DHA starting at injections of 50 mg/kg [65, 66]. However, as outlined above, successful use of DHA injections in rats and mice for hyperpolarization has been demonstrated without reported side effects on the animals. More research is needed to determine the parameters regarding the toxicity of DHA in larger animal models using pure formulations to assess its potential for clinical trials. Further work in DHA could demonstrate its applicability for the study of ROS and redox changes in model systems.
https://i2.wp.com/static-content.springer.com/image/art%3A10.1186%2Fs40170-015-0136-2/MediaObjects/40170_2015_136_Fig3_HTML.gif
Determination of redox state by imaging of HP [1-13C] ascorbate (VitC) and [1-13C] dehydroascorbate (DHA). Oxidative stress caused by ROS (1.) can be alleviated by oxidation of ascorbate to DHA (2.), and recycling of DHA to ascorbate can occur indirectly with oxidation of glutathione (3.) or directly with oxidation of NADH (4.). The ratio of [ascorbate] to [DHA] has been successfully used in mice models as a biomarker to determine pH in vivo. Adapted with permission from ref. [62]

Other metabolic imaging probes

While the three probes discussed earlier are the most well studied in metabolic events that are characteristic of cancer cells in general, other molecules have been evaluated in their potential to be used as biomarkers. Hyperpolarized bicarbonate (H13CO3) has been successfully used to determine the pH in extracellular matrix of lymphoma tumors in mice, and a correlation between acidic environments and cancer was established [67]. The relaxation times for bicarbonate compounds at 3 T are between 34 and 50 s, which is enough time to detect the rapid conversion of H13CO3 and 13CO2 catalyzed by carbonic anhydrase [23]. The attractive feature of this probe is based on how ubiquitous acidic extracellular environments are to a wide variety of diseases; thus, HP bicarbonate has the potential for clinical translation beyond cancer research, though extensive work will be necessary to generate a preparation which will result in an adequate dose for the clinic [68, 69]. More recently, the potential of α-ketoisocaproate (KIC) as a molecular probe for in vivo detection of branched chain amino acid transaminase (BCAT) has been explored. BCAT catalyzes the conversion of KIC to leucine, and its expression has been suggested to correlate to genetic characterization of certain tumors. In a pilot study, HP α-keto-[1-13C]-isocaproate was shown to have a T1 of 100 s so its metabolism can be sensitively traced for over a minute after injection [70]. In the same study, metabolism of HP [1-13C] KIC to [1-13C] leucine by BCAT was observed in murine lymphoma tumor tissue but was absent in rat mammary adenocarcinoma with a correlation between BCAT expression and [1-13C] leucine signal detection [70]. Additionally, in the same models, [1-13C] pyruvate conversion to [1-13C] lactate and [1-13C] alanine was detected in both types of tumors. These findings show the promise of using [1-13C] KIC as a discriminative probe in addition to pyruvate in order to diagnose different types of cancer [71, 72]. Furthermore, the correlation between BCAT expression and [1-13C] leucine detection was also shown in rat brain tissue, confirming the usefulness of HP [1-13C] KIC in assessing BCAT activity in vivo [73]. Choline is another compound that has been evaluated as a molecular imaging probe since elevated choline and choline-derived metabolites have been correlated by 1H-MRS imaging to cancer in the brain, breast, colon, cervix, and prostate [7476]. Despite its potential as a global marker for cancer because of the long T1 relaxation times that can be achieved with deuterium and 15N enrichment [77, 78], HP applications of 13C enriched choline are limited due to the small change in chemical shifts of choline and choline-derived metabolites as well as its potential toxicity [16, 79, 80]. It has been shown that choline toxicity occurs at doses of 53 mg/kg in mice, although a recent study successfully detected HP 13C choline in vivo without adverse effects in rats at doses of 50 mg/kg by using atropine to prevent cholinergic intoxication [81, 82] though metabolic products have been difficult to visualize in vivo. As mentioned earlier, the usefulness of glucose as a probe is limited due to the short relaxation times of all the carbons present in the molecule and although the T1’s can be increased through deuterium enrichment, the lifetime of the probe remains a hurdle for clinical applications [27, 28]. Thus, fructose (a pentose analog of glucose) has been successfully used as an alternative to probe glycolytic pathways [83] in TRAMP models where differences in HP [2-13C] fructose uptake and metabolism was visualized in tumor regions compared to surrounding normal tissues. Like choline, the limiting factor in the usefulness of [2-13C] fructose for in vivo studies is in small chemical shifts between the metabolite and its phosphorylated product. Finally, tumor necrosis can be used as a measure of treatment response, particularly early necrosis. HP [1,4-,13C] malate has been visualized in lymphoma mice models after injection of HP [1,4-13C] fumarate [84]. In normal cells, fumarate has a slow rate of transport into the mitochondria; however, in necrotic cells where the mitochondrial membrane is degraded, fumarase has access to the HP fumarate and its ubiquitous cofactor, water, thus facilitating rapid conversion to malate. Preliminary studies have shown the potential for its use in animal models though further work is required to determine the necessary density of necrotic cells for detection and the timings required for adequate visualization in patients.

Conclusions

The application of hyperpolarized 13C imaging has been extensively investigated in preclinical models, and the successful demonstration of HP [1-13C] pyruvate in patients with prostate cancer has validated the potential of HP MRI as a safe diagnostic and treatment assessment tool. Application of other probes beyond pyruvate is still in its infancy, particularly because of the need to further study the currently developed models under conditions that are relevant to a clinical setting (i.e., lower magnetic fields) as well as to study the necessary parameters (probe toxicity dose limits, safety limits for rapid injection) to withstand the necessary hurdles to translation. Nevertheless, these vast research findings are promising and indicate an eventual translation to humans. Furthermore, there is a large variety of biologically relevant molecules that have the potential to be hyperpolarized (Fig. 4), and molecular imaging of metabolic events in real time using not only one single probe but a combination of relevant probes could become an invaluable tool in elucidating so far undiscovered metabolic and proteomic interactions that play a role in cancer development and treatment. This gives HP MRI the great potential to revolutionize current molecular imaging technologies.
https://i0.wp.com/static-content.springer.com/image/art%3A10.1186%2Fs40170-015-0136-2/MediaObjects/40170_2015_136_Fig4_HTML.gif
Metabolic pathways with compounds that can be used as molecular imaging probes for HP MRI. A wide variety of metabolic pathways have already been visualized or have the potential to be visualized using hyperpolarization technology that can be applied to different pathological states of the cell including cardiovascular disease and a large variety of cancers. 1. Metabolism of C1 (red dots) in pyruvate. Theasterisks on selected compounds represent enrichment of 13C in the second pass of pyruvate in TCA cycle. 2. Metabolism of C1 (brown dots) in DHA using a pool of NADPH derived from the pentose phosphate pathway. 3. Metabolism of C1 (blue dots) and C5 (green dots) of glutamine. 4. Metabolism of C1 and C4 (purple dots) of fumarate unrelated to TCA metabolites. 5. Metabolism of extracellular bicarbonate (gray dots). MTC1 monocarboxylate transporter 1, MTC4 monocarboxylate transporter 4,System ASC amino acid transporter, GLUTs glucose transporters, DCT dicarboxylate transporter, DHARdehydroascorbate reductase, GR glutathione reductase, GSH glutathione, GSSG glutathione disulfide,LDH lactate dehydrogenase, ALT alanine transaminase, CA carbonic anhydrase, PC pyruvate carboxylase,PDH pyruvate dehydrogenase, CS citrate synthase, GLS glutaminase, GLDH glutamate dehydrogenase,IDH isocitrate dehydrogenase, OGDC oxoglutarate dehydrogenase complex, SCS succinyl CoA synthetase, SQR succinate dehydrogenase, FH fumarate hydratase, MDH malate dehydrogenase, FUMfumarase. Cofactors have been omitted for brevity

Abbreviations

ALT:   alanine transaminase;   BCAT:  branched chain amino acid transaminase;   DHA:  dehydroascorbate;   DNP:  dynamic nuclear polarization;   EDTA:  ethylenediaminetetraacetic acid;   GSH:  glutathione;   GSSG:   glutathione sulfide;   HCC:  hepatocellular carcinoma;   HIF:  hypoxia-inducible factor;   HP:  hyperpolarized/hyperpolarization;   IDH:  isocitrate dehydrogenase;   KIC:  ketoisocaproate;   LDH:  lactate dehydrogenase;   MR: magnetic resonance;   MRI:  Magnetic resonance imaging;   MRS:  magnetic resonance spectroscopy;   NAD(H):  nicotinamide adenine dinucleotide;   NADP(H):  nicotinamide adenine dinucleotide phosphate;   PET:  positron emission tomography;   ROS:  reactive oxygen species;   SPECT:  single-photon emission computed tomography;   TRAMP:  transgenic adenocarcinoma of mouse prostate

References

  1. Warburg O. On the origin of cancer cells. Science. 1956;123:309–14.View ArticlePubMed
  2. Gatenby RA, Gillies RJ. Why do cancers have high aerobic glycolysis? Nat Rev Cancer. 2004;4(11):891–9.View ArticlePubMed
  3. Vander Heiden MG, Cantley LC, Thompson CB. Understanding the Warburg effect: the metabolic requirements of cell proliferation. Science. 2009;324:1029–33.View ArticlePubMed CentralPubMed
  4. Shie P, Cardarelli R, Brandon D, Erdman W, AbdulRahim N. Meta-analysis: comparison of F-18 fluorodeoxyglucose-positron emission tomography and bone scintigraphy in the detection of bone metastases in patients with breast cancer. Clin Nucl Med. 2008;33:97–101.View ArticlePubMed
  5. Frangioni JV. New technologies for human cancer imaging. J Clin Oncol. 2008;26:4012–21.View ArticlePubMed CentralPubMed
  6. Castillo M, Kwock L, Mukherji SK. Clinical applications of proton MR spectroscopy. Am J Neuroradiol. 1996;17:1–16.PubMed
  7. Barker PB, Bizzi A, De Stefano N, Gullapalli R, Lin DD. Clinical MR spectroscopy: techniques and applications. Cambridge University Press; 2009.
  8. Comment A, Merritt ME. Hyperpolarized magnetic resonance as a sensitive detector of metabolic function. Biochemistry. 2014;53:7333–57.View ArticlePubMed
  9. Rider OJ, Tyler DJ. Clinical implications of cardiac hyperpolarized magnetic resonance imaging. J Cardiov Magn Reson. 2013;15:93.View Article
  10. Golman K, Olsson LE, Axelsson O, Månsson S, Karlsson M, Petersson JS. Molecular imaging using hyperpolarized 13C. Br J Radiol. 2003;76 Suppl 2:S118–S27.View ArticlePubMed

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sjwilliamspa commented on Is the Warburg effect an effect of deregulated space occupancy of methylome?

Is the Warburg effect an effect of deregulated space occupancy of methylome? Larry H. Bernstein and Radoslav Bozov, …

It would be an interesting figure, although I am not sure anyone has been able to measure it, is the spatial distribution of lactate and pyruvate over the tumor as a function of diffusion distance such as a heat map to see if pyruvate and lactate levels have a gradiant over a solid tumor. I am not sure it would but interesting to see where tumor cells, which undergo Warburg type metabolic phenotype actually exist, if it is a function of angiogenesis or a function of the proliferative capacity of cells in situ.

Response by LHB…

Radoslav Bozov has repeatedly referred to the real problem of space/time in the required experimental view that is intractable, as seen by Erwin Schroedinger.  It is confounded by
the restrictions imposed by research, and to an extent also the dilemma of location and velocity.

I think it is to an extent also inherent in the modern revelations of autophagy and apoptosis that were not part of the view in the mid 20th century.  However, the work of B. Chance led to a substantially better understanding of the hydride transfer in the NAD/NADH.  What is overlooked is the important role cited by NO Kaplan of NADPH/NADP vs NADH/NAD associated with synthetic and, alternatively, catabolic processes in the cell. What role the pyridine nucleotide transhydrogenase would play is anyones guess.   In any case the proliferation of malignant cells is dependent on NADPH.  This would limit the NAD/NADH related reactions. The effect in the cytoplasm is PYR –> LAC, with generation of NAD from NADH.  In addition, the type of isoenzyme favored should be consequential.  For instance, the M-type LDH does not form an abortive ternary complex LDH*NAD+*PYR. In addition, Bernstein, Everse and Grisham showed that in cancer there is an aberrant cytoplasmic MDH.

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