One blood sample can be tested for a comprehensive array of cancer cell biomarkers: R&D at WPI
Curator: Marzan Khan, B.Sc
A team of mechanical engineers at Worcester Polytechnic Institute (WPI) have developed a fascinating technology – a liquid biopsy chip that captures and detects metastatic cancer cells, just from a small blood sample of cancer patients(1). This device is a recent development in the scientific field and holds tremendous potential that will allow doctors to spot signs of metastasis for a variety of cancers at an early stage and initiate an appropriate course of treatment(1).
Metastasis occurs when cancer cells break away from their site of origin and spread to other parts of the body via the lymph or the bloodstream, where they give rise to secondary tumors(2). By this time, the cancer is at an advanced stage and it becomes increasingly difficult to fight the disease. The cells that are shed by primary and metastatic cancers are called circulating tumor cells (CTCs) and their numbers lie in the range of 1–77,200/m(3). The basis of the liquid biopsy chip test is to capture these circulating tumor cells in the patient’s blood and identify the cell type through specific interaction with antibodies(4).
The chip is comprised of individual test units or small elements, about 3 millimeters wide(4). Each small element contains a network of carbon nanotube sensors in a well which are functionalized with antibodies(4). These antibodies will bind cell-surface antigens or protein markers unique for each type of cancer cell. Specific interaction between a cell surface protein and its corresponding antibody is a thermodynamic event that causes a change in free energy which is transduced into electricity(3). This electrical signature is picked up by the semi-conducting carbon nanotubes and can be seen as electrical spikes(4). Specific interactions create an increase in electrical signal, whereas non-specific interactions cause a decrease in signal or no change at all(4). Capture efficiency of cancer cells with the chip has been reported to range between 62-100%(4).
The liquid biopsy chip is also more advanced than microfluidics for several reasons. Firstly, the nanotube-chip arrays can capture as well as detect cancer cells, while microfluidics can only capture(4). Samples do not need to be processed for labeling or fixation, so the cell structures are preserved(4). Unlike microfluidics, these nanotubes will also capture tiny structures called exosomes spanning the nanometer range that are produced from cancer cells and carry the same biomarkers(4).
Pancreatic cancer is the fourth leading cause of cancer-associated deaths in the United states, with a survival window of 5 years in only 6% of the cases with treatment(5). In most patients, the disease has already metastasized at the time of diagnosis due to the lack of early-diagnostic markers, affecting some of the major organs such as liver, lungs and the peritoneum(5,6). Despite surgical resection of the primary tumor, the recurrence of local and metastatic tumors is rampant(5). Metastasis is the major cause of mortality in cancers(5). The liquid biopsy chip, that identifies CTCs can thus become an effective diagnostic tool in early detection of cancer as well as provide information into the efficacy of treatment(3). At present, ongoing experiments with this device involve testing for breast cancers but Dr. Balaji Panchapakesan and his team of engineers at WPI are optimistic about incorporating pancreatic and lung cancers into their research.
1.Nanophenotype. Researchers build liquid biopsy chip that detects metastatic cancer cells in blood: One blood sample can be tested for a comprehensive array of cancer cell biomarkers. 27 Dec 2016. Genesis Nanotechnology,Inc
3.F Khosravi, B King, S Rai, G Kloecker, E Wickstrom, B Panchapakesan. Nanotube devices for digital profiling of cancer biomarkers and circulating tumor cells. 23 Dec 2013. IEEE Nanotechnology Magazine 7 (4), 20-26
4.Farhad Khosravi, Patrick J Trainor, Christopher Lambert, Goetz Kloecker, Eric Wickstrom, Shesh N Rai and Balaji Panchapakesan. Static micro-array isolation, dynamic time series classification, capture and enumeration of spiked breast cancer cells in blood: the nanotube–CTC chip. 29 Sept 2016. Nanotechnology. Vol 27, No.44. IOP Publishing Ltd
Li-Fraumeni syndrome (LFS) is a condition that makes individuals prone to developing a wide variety of cancers that occur early on in life, the most common types being- soft tissue sarcoma, osteosarcoma, breast cancer, brain tumors, adrenocortical carcinoma (ACC), and leukemia. (1) Pancreatic cancer is minimally associated with the condition. (2) A survey found the presence of pancreatic cancer in only 1% of 475 tumor samples collected from 91 families who were carriers of p53 mutations, with half of them having LFS. The incidence of breast cancer amongst them was the highest -24%. (2) Pancreatic carcinoma in LFS patients usually occurs in the later stages of life. (3)
The underlying cause of LFS is germline mutations in TP53 gene on chromosome 17p, that encodes the transcription factor p53, crucial in cell cycle regulation and the repair of damaged and/or abnormal cells. (4) In the majority of cases, this mutation is obtained by inheritance. (5) De-novo germline mutations in p53 occur in 7%-20% of the cases. (5)
A person showing symptoms of any type of cancer at an early age or having first or second-degree relatives with cancer are at risk of developing LFS. (5) That is why tracing family history is an important part of diagnosis in LFS patients. Genetic testing can confirm mutations present in the gene, however, there are controversial ethical issues regarding their use, particularly in children and fetuses.
In patients with LFS, it is important to control the manifestations of the disease. They should be monitored closely so that any new cancers that arise are diagnosed and treated during the early stages. (6) Patients are also at risk of developing radiation-induced second and third primary tumors. (6) Therefore, radiation and alkylating agents should be used minimally (6) People at risk can be cautioned to avoid exposure to carcinogens such as sunlight, cigarette smoke, and alcohol consumption. (5) Therapeutic approaches that are aimed at restoring wild-type p53 by gene therapy as well as reactivating non-functional p53 by the use of small-molecule drugs are currently being investigated in many cancers. (7) Unlike radiation therapy, these small-molecule drugs are non-toxic to healthy cells, thus eliminating the risk of forming new tumors.
So far, PRIMA-1 has proven to be quite effective at correcting non-functional p53. (8) PRIMA-1 is changed to its methylated form, PRIMA-1MET that forms covalent adducts to thiol groups in the mutated protein and modifies them. (8) As a result, p53 regains its ability to destroy malignant cells. (8) A research study also found that PRIMA-1 induces apoptosis and increases the sensitivity of pancreatic cancer cells to various chemotherapeutic agents. (9)
Magali Olivier, David E. Goldgar, Nayanta Sodha, Hiroko Ohgaki, Paul Kleihues, Pierre Hainaut and Rosalind A. Eeles. Li-Fraumeni and Related Syndromes. Cancer Res October 15 2003 63 (20) 6643-6650 http://cancerres.aacrjournals.org/content/63/20/6643.abstract
Sorrell, A. D., Espenschied, C. R., Culver, J. O., & Weitzel, J. N. (2013).TP53Testing and Li-Fraumeni Syndrome: Current Status of Clinical Applications and Future Directions. Molecular Diagnosis & Therapy, 17(1), 31–47. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3627545/
Emily J. Lewis. PRIMA-1 as a cancer therapy restoring mutant p53: a reviewBioscience Horizons (2015) 8: hzv006 http://biohorizons.oxfordjournals.org/content/8/hzv006.full
Izetti, Patricia, Agnes Hautefeuille, Ana Lucia Abujamra, Caroline Brunetto de Farias, Juliana Giacomazzi, Bárbara Alemar, Guido Lenz, et al. ‘PRIMA-1, a Mutant p53 Reactivator, Induces Apoptosis and Enhances Chemotherapeutic Cytotoxicity in Pancreatic Cancer Cell Lines’. Investigational New Drugs 32, no. 5 (October 2014): 783–94. https://www.ncbi.nlm.nih.gov/pubmed/24838627
Izetti, Patricia, Agnes Hautefeuille, Ana Lucia Abujamra, Caroline Brunetto de Farias, Juliana Giacomazzi, Bárbara Alemar, Guido Lenz, et al. ‘PRIMA-1, a Mutant p53 Reactivator, Induces Apoptosis and Enhances Chemotherapeutic Cytotoxicity in Pancreatic Cancer Cell Lines’. Investigational New Drugs 32, no. 5 (October 2014): 783–94
Other related articles published in this Online Scientific Journal include the following:
p53 mutation – Li-Fraumeni Syndrome – Likelihood of Genetic or Hereditary conditions playing a role in Intergenerational incidence of Cancer
Deleted in Pancreatic Cancer, locus 4 (DPC4) officially known as SMAD4 is a component of the Transforming Growth Factor Beta (TGFß) pathway with tumour suppressive properties. As its name suggests it is frequently lost in pancreatic cancer, although through a variety of mechanisms in addition to gene deletion. The loss of SMAD4 is important in the progression of pancreatic intraepithelial neoplasia (PanIN) towards pancreatic ductal adenocarcinoma (PDAC). The expression of SMAD4 can suppress metastasis, angiogenesis, and cancer stem-like cell generation. SMAD4 can promote cancer cell apoptosis through a recently described mechanism involving a lethal epithelial to mesenchymal transition (EMT). SMAD4 status has a predictive role in pancreatic cancer personalised medicine. This curation categorises recent publications of note regarding SMAD4.
Role of SMAD4 in neoplastic progression towards PDAC
Garcia-Carracedo, Dario, Chih-Chieh Yu, Nathan Akhavan, Stuart A. Fine, Frank Schönleben, Naoki Maehara, Dillon C. Karg, et al. ‘Smad4 Loss Synergizes with TGFα Overexpression in Promoting Pancreatic Metaplasia, PanIN Development, and Fibrosis’. Edited by Ilse Rooman. PLOS ONE 10, no. 3 (24 March 2015): e0120851. doi:10.1371/journal.pone.0120851.
Norris, A M, A Gore, A Balboni, A Young, D S Longnecker, and M Korc. ‘AGR2 Is a SMAD4-Suppressible Gene That Modulates MUC1 Levels and Promotes the Initiation and Progression of Pancreatic Intraepithelial Neoplasia’. Oncogene 32, no. 33 (15 August 2013): 3867–76. doi:10.1038/onc.2012.394.
Leung, Lisa, Nikolina Radulovich, Chang-Qi Zhu, Dennis Wang, Christine To, Emin Ibrahimov, and Ming-Sound Tsao. ‘Loss of Canonical Smad4 Signaling Promotes KRAS Driven Malignant Transformation of Human Pancreatic Duct Epithelial Cells and Metastasis’. Edited by Hidayatullah G Munshi. PLoS ONE 8, no. 12 (27 December 2013): e84366. doi:10.1371/journal.pone.0084366.
Mechanism of SMAD4 deactivation
Xia, Xiang, Kundong Zhang, Gang Cen, Tao Jiang, Jun Cao, Kejian Huang, Chen Huang, Qian Zhao, and Zhengjun Qiu. ‘MicroRNA-301a-3p Promotes Pancreatic Cancer Progression via Negative Regulation of SMAD4’. Oncotarget 6, no. 25 (28 August 2015): 21046–63. doi:10.18632/oncotarget.4124.
Murphy, Stephen J., Steven N. Hart, Geoffrey C. Halling, Sarah H. Johnson, James B. Smadbeck, Travis Drucker, Joema Felipe Lima, et al. ‘Integrated Genomic Analysis of Pancreatic Ductal Adenocarcinomas Reveals Genomic Rearrangement Events as Significant Drivers of Disease’. Cancer Research 76, no. 3 (1 February 2016): 749–61. doi:10.1158/0008-5472.CAN-15-2198.
Sawai, Yugo, Yuzo Kodama, Takahiro Shimizu, Yuji Ota, Takahisa Maruno, Yuji Eso, Akira Kurita, et al. ‘Activation-Induced Cytidine Deaminase Contributes to Pancreatic Tumorigenesis by Inducing Tumor-Related Gene Mutations’. Cancer Research 75, no. 16 (15 August 2015): 3292–3301. doi:10.1158/0008-5472.CAN-14-3028.
Demagny, Hadrien, and Edward M De Robertis. ‘Point Mutations in the Tumor Suppressor Smad4/DPC4 Enhance Its Phosphorylation by GSK3 and Reversibly Inactivate TGF-β Signaling’. Molecular & Cellular Oncology 3, no. 1 (2 January 2016): e1025181. doi:10.1080/23723556.2015.1025181.
Foster, David. ‘BxPC3 Pancreatic Cancer Cells Express a Truncated Smad4 Protein upon PI3K and mTOR Inhibition’. Oncology Letters, 28 January 2014. doi:10.3892/ol.2014.1833.
Hao, Jun, Shuyu Zhang, Yingqi Zhou, Cong Liu, Xiangui Hu, and Chenghao Shao. ‘MicroRNA 421 Suppresses DPC4/Smad4 in Pancreatic Cancer’. Biochemical and Biophysical Research Communications 406, no. 4 (25 March 2011): 552–57. doi:10.1016/j.bbrc.2011.02.086.
SMAD4 effects on cell motility
Zhang, Xueying, Junxia Cao, Yujun Pei, Jiyan Zhang, and Qingyang Wang. ‘Smad4 Inhibits Cell Migration via Suppression of JNK Activity in Human Pancreatic Carcinoma PANC‑1 Cells’. Oncology Letters, 7 April 2016. doi:10.3892/ol.2016.4427.
Kang, Ya ’an, Jianhua Ling, Rei Suzuki, David Roife, Xavier Chopin-Laly, Mark J. Truty, Deyali Chatterjee, et al. ‘SMAD4 Regulates Cell Motility through Transcription of N-Cadherin in Human Pancreatic Ductal Epithelium’. Edited by Neil A. Hotchin. PLoS ONE 9, no. 9 (29 September 2014): e107948. doi:10.1371/journal.pone.0107948.
Zhou, Zhichao, Juming Lu, Jingtao Dou, Zhaohui Lv, Xi Qin, and Jing Lin. ‘FHL1 and Smad4 Synergistically Inhibit Vascular Endothelial Growth Factor Expression’. Molecular Medicine Reports 7, no. 2 (February 2013): 649–53. doi:10.3892/mmr.2012.1202.
SMAD4 mediated repression of cancer stem-like cells
Hoshino, Yukari, Jun Nishida, Yoko Katsuno, Daizo Koinuma, Taku Aoki, Norihiro Kokudo, Kohei Miyazono, and Shogo Ehata. ‘Smad4 Decreases the Population of Pancreatic Cancer–Initiating Cells through Transcriptional Repression of ALDH1A1’. The American Journal of Pathology 185, no. 5 (2015): 1457–1470. http://www.sciencedirect.com/science/article/pii/S0002944015000802.
David, Charles J., Yun-Han Huang, Mo Chen, Jie Su, Yilong Zou, Nabeel Bardeesy, Christine A. Iacobuzio-Donahue, and Joan Massagué. ‘TGF-β Tumor Suppression through a Lethal EMT’. Cell 164, no. 5 (February 2016): 1015–30. doi:10.1016/j.cell.2016.01.009.
Wang, Qi, Juanjuan Li, Wei Wu, Ruizhe Shen, He Jiang, Yuting Qian, Yanping Tang, et al. ‘Smad4-Dependent Suppressor Pituitary Homeobox 2 Promotes PPP2R2A-Mediated Inhibition of Akt Pathway in Pancreatic Cancer’. Oncotarget 7, no. 10 (8 March 2016): 11208–22. doi:10.18632/oncotarget.7158.
Poorly characterised targets of SMAD4
Fullerton, Paul T., Chad J. Creighton, and Martin M. Matzuk. ‘Insights Into SMAD4 Loss in Pancreatic Cancer From Inducible Restoration of TGF-β Signaling’. Molecular Endocrinology (Baltimore, Md.) 29, no. 10 (October 2015): 1440–53. doi:10.1210/me.2015-1102.
Li, Lei, Zhaoshen Li, Xiangyu Kong, Dacheng Xie, Zhiliang Jia, Weihua Jiang, Jiujie Cui, et al. ‘Down-Regulation of MicroRNA-494 via Loss of SMAD4 Increases FOXM1 and β-Catenin Signaling in Pancreatic Ductal Adenocarcinoma Cells’. Gastroenterology 147, no. 2 (August 2014): 485–497.e18. doi:10.1053/j.gastro.2014.04.048.
Drugs that restore SMAD4
Lin, Sheng-Zhang, Jin-Bo Xu, Xu Ji, Hui Chen, Hong-Tao Xu, Ping Hu, Liang Chen, et al. ‘Emodin Inhibits Angiogenesis in Pancreatic Cancer by Regulating the Transforming Growth Factor-Β/drosophila Mothers against Decapentaplegic Pathway and Angiogenesis-Associated microRNAs’. Molecular Medicine Reports 12, no. 4 (October 2015): 5865–71. doi:10.3892/mmr.2015.4158.
Predictive value of SMAD4 status in personalised medicine
Whittle, Martin C., Kamel Izeradjene, P. Geetha Rani, Libing Feng, Markus A. Carlson, Kathleen E. DelGiorno, Laura D. Wood, et al. ‘RUNX3 Controls a Metastatic Switch in Pancreatic Ductal Adenocarcinoma’. Cell 161, no. 6 (June 2015): 1345–60. doi:10.1016/j.cell.2015.04.048.
Boone, Brian A., Shirin Sabbaghian, Mazen Zenati, J. Wallis Marsh, A. James Moser, Amer H. Zureikat, Aatur D. Singhi, Herbert J. Zeh, and Alyssa M. Krasinskas. ‘Loss of SMAD4 Staining in Pre-Operative Cell Blocks Is Associated with Distant Metastases Following Pancreaticoduodenectomy with Venous Resection for Pancreatic Cancer’. Journal of Surgical Oncology 110, no. 2 (August 2014): 171–75. doi:10.1002/jso.23606.
Herman, Joseph M., Katherine Y. Fan, Aaron T. Wild, Laura D. Wood, Amanda L. Blackford, Ross C. Donehower, Manuel Hidalgo, et al. ‘Correlation of Smad4 Status With Outcomes in Patients Receiving Erlotinib Combined With Adjuvant Chemoradiation and Chemotherapy After Resection for Pancreatic Adenocarcinoma’. International Journal of Radiation Oncology*Biology*Physics 87, no. 3 (November 2013): 458–59. doi:10.1016/j.ijrobp.2013.06.2039.
Other Related Articles Published In This Open Access Online Journal Include The Following:
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
•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 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
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.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
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
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).
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.”
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
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.
Researchers Reveal Role of Transcription Factor Isoforms in Colon Diseases
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
Department of Cell Biology and Neuroscience, University of California, Riverside, Riverside, United States
No competing interests declared
Department of Cell Biology and Neuroscience, University of California, Riverside, Riverside, United States
No competing interests declared
Department of Cell Biology and Neuroscience, University of California, Riverside, Riverside, United States
No competing interests declared
</div>”>Linh M, Vuong
Division of Biomedical Sciences, University of California, Riverside, Riverside, United States
No competing interests declared
Department of Cell Biology, Harvard Medical School, Boston, United States
No competing interests declared
Department of Cell Biology and Neuroscience, University of California, Riverside, Riverside, United States
No competing interests declared
Division of Biomedical Sciences, University of California, Riverside, Riverside, United States
No competing interests declared
Division of Biomedical Sciences, University of California, Riverside, Riverside, United States
No competing interests declared
Department of Cell Biology and Neuroscience, University of California Riverside, Riverside, United Statesfrances.email@example.com
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.
May 16, 2016
By Alex Keown, BioSpace.com Breaking News Staff
BERKELEY, Calif. – Shares of Aduro Biotech (ADRO) have fallen more than 25 percent this morning following news that the company’s Phase II trial for its combination pancreatic cancer drug, CRS-207 did not meet its primary endpoint of survivability.
Aduro said its Eclipse trial of CRS-207 failed to show an improvement in overall survival for patients with pancreatic cancer who had failed at least two prior therapies in the metastatic setting. Median overall survival was 3.8 months for patients treated with the immunotherapy regimen of CRS-207 and the cancer vaccine GVAX pancreas, 5.4 months for patients treated with CRS-207 alone and 4.6 months for patients administered chemotherapy. Aduro said there were no reported safety concerns during the trial and full study findings will be presented at a later date.
Stephen T. Isaacs, chairman, president and chief executive officer of Aduro, called the findings a disappointing and “unexpected outcome.’
“While we are well aware of the very difficult-to-treat nature of late-stage metastatic pancreatic cancer, we are surprised by the divergence of these data from the results of our Phase IIa study. At the same time, we continue to look forward to the interim results later this year from our ongoing Stellar trial, which is evaluating CRS-207 and GVAX Pancreas with and without the anti-PD1 checkpoint inhibitor nivolumab as a second-line therapy for patients with metastatic pancreatic cancer,” Isaacs said in a statement.
Aduro Biotech says its leading clinical trial for its cancer-fighting combination of GVAX and CRS-207 was a flop. The biotech reported this morning that its combo not only failed to hit the primary endpoint, it did worse than the two solo groups in the study.
“Median overall survival (MOS) in this third-line and greater setting was 3.8 months for patients treated with the immunotherapy regimen of CRS-207 and GVAX Pancreas, 5.4 months for patients treated with CRS-207 alone and 4.6 months for patients administered chemotherapy,” the company reported.
Aduro’s stock ($ADRO) plunged 30% on the news in premarket trading.
“While we are well aware of the very difficult-to-treat nature of late-stage metastatic pancreatic cancer, we are surprised by the divergence of these data from the results of our Phase 2a study,” said CEO Stephen Isaacs. But the company hasn’t given up hope on its lead program.
“In the overall survival analysis, we were intrigued by activity seen with CRS-207 as a single-agent. While the median duration of 5.4 months appears greater for CRS-207, the overall survival curve of CRS-207 alone was comparable to overall survival seen with chemotherapy. Of note, due to a disproportionately high dropout rate in the single-agent chemotherapy arm, most of these patients instead received a variety of combination treatments, including chemotherapies, immunotherapies and targeted therapies,” said Dirk Brockstedt, executive vice president, research and development for Aduro.
In a conference call with analysts Aduro execs noted that they are now shelving plans for a pivotal Phase III study in pancreatic cancer, focusing on an ongoing study in the pipeline that includes a checkpoint inhibitor.
The history of cancer vaccines not customized to individual patients has been a litany of failure, with programs for Stimuvax and others experiencing a string of defeats in the clinic. Celldex joined that circle of failure recently with a Phase III miss for Rintega. Aduro, though, doubled down on the cancer vaccine strategy and was able to strike some big-money pacts along the way on the basis of some promising midstage data.
GVAX Pancreas is based on a pancreatic cell line modified to secrete granulocyte-macrophage colony-stimulating factor (GM-CSF), a cytokine known to stimulate the immune system. CRS-207 is made up of attenuated (deactivated) Listeria monocytogenes that express mesothelin, sparking another immune response to a protein concentrated on pancreatic cancer cells. Together, they’re supposed to provide a one-two punch against cancer, with an option to add on additional drugs to continue to build an attack on cancer cells.
That was the only workable strategy with GVAX, which, like other cancer vaccines, wasn’t able to spur a strong enough response to make a significant difference in the fight against cancer as a solo therapy, allowing Aduro to buy it for a song in early 2013. Monday’s conference call included several skeptical remarks from analysts about GVAX’s future, if any.
Aduro was on hand at the 2013 ASCO confab to review the data from a midstage study involving 93 patients with advanced pancreatic cancer. A combination of chemo plus GVAX pancreas and CRS-207 significantly outperformed GVAX and chemo, bumping up overall survival from 3.9 months to 6.1 months. That’s not a big gain, but it was a sign of progress in a very tough field. And it was good enough for the FDA to grant a breakthrough drug designation.
Now the company is forced into a classic defensive crouch, citing its significant cash reserves as it looks to regroup.
The “Guardian Of The Genome” p53 In Pancreatic Cancer
Curator: David Orchard-Webb, PhD
A recent next generation sequencing (NGS) study of PDAC samples found that the “guardian of the genome” p53 (TP53) had a total mutation rate of 50% (the literature suggests up to 75%) . TP53 deletions occurred in 6% of samples. Missense mutation of p53 (44% of samples) can convert it from a tumour suppressor to a neo-oncogene. This curation collates recent articles of note with reference to p53 including function, drug development, and prognostics in pancreatic ductal adenocarcinoma (PDAC).
Katchman, Benjamin A., Rodrigo Barderas, Rizwan Alam, Diego Chowell, Matthew S. Field, Laura J. Esserman, Garrick Wallstrom, et al. ‘Proteomic Mapping of p53 Immunogenicity in Pancreatic, Ovarian, and Breast Cancers’. Proteomics. Clinical Applications, 28 April 2016. doi:10.1002/prca.201500096.
Terashima, Takeshi, Eishiro Mizukoshi, Kuniaki Arai, Tatsuya Yamashita, Mariko Yoshida, Hajime Ota, Ichiro Onishi, et al. ‘P53, hTERT, WT-1, and VEGFR2 Are the Most Suitable Targets for Cancer Vaccine Therapy in HLA-A24 Positive Pancreatic Adenocarcinoma’. Cancer Immunology, Immunotherapy: CII 63, no. 5 (May 2014): 479–89. doi:10.1007/s00262-014-1529-8.
Drug targeting p53
Xu, Jing, Amit Singh, and Mansoor M. Amiji. ‘Redox-Responsive Targeted Gelatin Nanoparticles for Delivery of Combination Wt-p53 Expressing Plasmid DNA and Gemcitabine in the Treatment of Pancreatic Cancer’. BMC Cancer 14, no. 1 (2014): 75. http://www.biomedcentral.com/1471-2407/14/75/.
Camp, E R, C Wang, E C Little, P M Watson, K F Pirollo, A Rait, D J Cole, E H Chang, and D K Watson. ‘Transferrin Receptor Targeting Nanomedicine Delivering Wild-Type p53 Gene Sensitizes Pancreatic Cancer to Gemcitabine Therapy’. Cancer Gene Therapy 20, no. 4 (April 2013): 222–28. doi:10.1038/cgt.2013.9.
Izetti, Patricia, Agnes Hautefeuille, Ana Lucia Abujamra, Caroline Brunetto de Farias, Juliana Giacomazzi, Bárbara Alemar, Guido Lenz, et al. ‘PRIMA-1, a Mutant p53 Reactivator, Induces Apoptosis and Enhances Chemotherapeutic Cytotoxicity in Pancreatic Cancer Cell Lines’. Investigational New Drugs 32, no. 5 (October 2014): 783–94. doi:10.1007/s10637-014-0090-9.
Takei, Y., S. Okamoto, K. Kawamura, Y. Jiang, T. Morinaga, M. Shingyoji, I. Sekine, et al. ‘Expression of p53 Synergistically Augments Caspases-Mediated Apoptosis Induced by Replication-Competent Adenoviruses in Pancreatic Carcinoma Cells’. Cancer Gene Therapy 22, no. 9 (September 2015): 445–53. doi:10.1038/cgt.2015.33.
Li, Jinluan, Jianji Pan, Xianggao Zhu, Ying Su, Lingling Bao, Sufang Qiu, Changyan Zou, Yong Cai, Junxin Wu, and Ivan WK Tham. ‘Recombinant Adenovirus-p53 (Gendicine) Sensitizes a Pancreatic Carcinoma Cell Line to Radiation’. Chinese Journal of Cancer Research 25, no. 6 (2013): 715. http://www.cjcrcn.org/article/html_3076.html.
Hastie, Eric, Marcela Cataldi, Nury Steuerwald, and Valery Z. Grdzelishvili. ‘An Unexpected Inhibition of Antiviral Signaling by Virus-Encoded Tumor Suppressor p53 in Pancreatic Cancer Cells’. Virology 483 (September 2015): 126–40. doi:10.1016/j.virol.2015.04.017.
The Impact of p53 Status on Therapy
Kurahara, Hiroshi, Kosei Maemura, Yuko Mataki, Masahiko Sakoda, Hiroyuki Shinchi, and Shoji Natsugoe. ‘Impact of p53 and PDGFR-β Expression on Metastasis and Prognosis of Patients with Pancreatic Cancer’. World Journal of Surgery, 3 March 2016. doi:10.1007/s00268-016-3477-2.
Xiang, Jin-Feng, Wen-Quan Wang, Liang Liu, Hua-Xiang Xu, Chun-Tao Wu, Jing-Xuan Yang, Zi-Hao Qi, et al. ‘Mutant p53 Determines Pancreatic Cancer Poor Prognosis to Pancreatectomy through Upregulation of Cavin-1 in Patients with Preoperative Serum CA19-9 ≥ 1,000 U/mL’. Scientific Reports 6 (12 January 2016): 19222. doi:10.1038/srep19222.
Rajeshkumar, N. V., Prasanta Dutta, Shinichi Yabuuchi, Roeland F. de Wilde, Gary V. Martinez, Anne Le, Jurre J. Kamphorst, et al. ‘Therapeutic Targeting of the Warburg Effect in Pancreatic Cancer Relies on an Absence of p53 Function’. Cancer Research 75, no. 16 (15 August 2015): 3355–64. doi:10.1158/0008-5472.CAN-15-0108.
Fiorini, Claudia, Marco Cordani, Chiara Padroni, Giovanni Blandino, Silvia Di Agostino, and Massimo Donadelli. ‘Mutant p53 Stimulates Chemoresistance of Pancreatic Adenocarcinoma Cells to Gemcitabine’. Biochimica et Biophysica Acta (BBA) – Molecular Cell Research 1853, no. 1 (January 2015): 89–100. doi:10.1016/j.bbamcr.2014.10.003.
TP53 Function in Pancreatic Cancer
Bailey, J M, A M Hendley, K J Lafaro, M A Pruski, N C Jones, J Alsina, M Younes, et al. ‘p53 Mutations Cooperate with Oncogenic Kras to Promote Adenocarcinoma from Pancreatic Ductal Cells’. Oncogene, 23 November 2015. doi:10.1038/onc.2015.441.
Sheng, Weiwei, Ming Dong, Jianping Zhou, Xin Li, Qingfeng Liu, Qi Dong, and Feng Li. ‘Cooperation among Numb, MDM2 and p53 in the Development and Progression of Pancreatic Cancer’. Cell and Tissue Research 354, no. 2 (November 2013): 521–32. doi:10.1007/s00441-013-1679-6.
Weissmueller, Susann, Eusebio Manchado, Michael Saborowski, John P. Morris, Elvin Wagenblast, Carrie A. Davis, Sung-Hwan Moon, et al. ‘Mutant p53 Drives Pancreatic Cancer Metastasis through Cell-Autonomous PDGF Receptor β Signaling’. Cell 157, no. 2 (April 2014): 382–94. doi:10.1016/j.cell.2014.01.066.
Morton, J. P., P. Timpson, S. A. Karim, R. A. Ridgway, D. Athineos, B. Doyle, N. B. Jamieson, et al. ‘Mutant p53 Drives Metastasis and Overcomes Growth Arrest/senescence in Pancreatic Cancer’. Proceedings of the National Academy of Sciences 107, no. 1 (5 January 2010): 246–51. doi:10.1073/pnas.0908428107.
Hamilton, Garth, Aswin G. Abraham, Jennifer Morton, Oliver Sampson, Dafni E. Pefani, Svetlana Khoronenkova, Anna Grawenda, et al. ‘AKT Regulates NPM Dependent ARF Localization and p53mut Stability in Tumors’. Oncotarget 5, no. 15 (2014): 6142–6167. http://eprints.gla.ac.uk/102649.
Sadagopan, S, M V Veettil, S Chakraborty, N Sharma-Walia, N Paudel, V Bottero, and B Chandran. ‘Angiogenin Functionally Interacts with p53 and Regulates p53-Mediated Apoptosis and Cell Survival’. Oncogene 31, no. 46 (15 November 2012): 4835–47. doi:10.1038/onc.2011.648.
TP53 and Epithelial Mesenchymal Transition (EMT)
Wörmann, Sonja M., Liang Song, Jiaoyu Ai, Kalliope N. Diakopoulos, Kivanc Görgülü, Dietrich Ruess, Andrew Campbell, et al. ‘Loss of P53 Function Activates JAK2-STAT3 Signaling to Promote Pancreatic Tumor Growth, Stroma Modification, and Gemcitabine Resistance in Mice and Is Associated With Patient Survival’. Gastroenterology, 18 March 2016. doi:10.1053/j.gastro.2016.03.010.
Lee, Sun-Hye, Su-Jin Lee, Yeon Sang Jung, Yongbin Xu, Ho Sung Kang, Nam-Chul Ha, and Bum-Joon Park. ‘Blocking of p53-Snail Binding, Promoted by Oncogenic K-Ras, Recovers p53 Expression and Function’. Neoplasia 11, no. 1 (January 2009): 22–IN6. doi:10.1593/neo.81006.
Pancreatic Cancer Risk Factor
Sonoyama, Takayuki. ‘TP53 Codon 72 Polymorphism Is Associated with Pancreatic Cancer Risk in Males, Smokers and Drinkers’. Molecular Medicine Reports, 8 March 2011. doi:10.3892/mmr.2011.449.
3D PDAC in vitro Culture Models
Huang, Ling, Audrey Holtzinger, Ishaan Jagan, Michael BeGora, Ines Lohse, Nicholas Ngai, Cristina Nostro, et al. ‘Ductal Pancreatic Cancer Modeling and Drug Screening Using Human Pluripotent Stem Cell– and Patient-Derived Tumor Organoids’. Nature Medicine 21, no. 11 (26 October 2015): 1364–71. doi:10.1038/nm.3973.
Witkiewicz, Agnieszka K., Elizabeth A. McMillan, Uthra Balaji, GuemHee Baek, Wan-Chi Lin, John Mansour, Mehri Mollaee, et al. ‘Whole-Exome Sequencing of Pancreatic Cancer Defines Genetic Diversity and Therapeutic Targets’. Nature Communications 6 (9 April 2015): 6744. doi:10.1038/ncomms7744.
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In pancreatic cancer KRAS is mutated between 70-90%. Next generation sequencing suggests 90%, however it must be understood that the allelic frequency of KRAS mutation will not be 100% – not all the cells within the tumour will contain a KRAS mutation due to tumour heterogeneity . Regardless of the exact figure KRAS mutation is more frequent in pancreatic ductal adenocarcinoma (PDAC) than in any other cancer and plays a role in cancer initiation and progression. The four most common KRAS mutations in PDAC are G12D > G12V > G12C > G13D . The use of mutant RAS peptides as a cancer vaccine immunotherapy is an established concept and the nordic company Targovax has a RAS vaccine called TG01 in phase I/II clinical trials for pancreatic cancer.
Inhibiting the signalling activity of KRAS in pancreatic cancers is also attractive however failures most notably of the farnesyl transferase inhibitors in clinical trials has led to unwarranted pessimism. Two farnesyl transferase inhibitors have been tested and failed in clinical trials of pancreatic cancer, Tipifarnib (Johnson & Johnson), and L-778.123 (Merck & Co.) . However farnesyltransferase inhibitors may still have a role in the treatment of a rare subset of pancreatic cancer patients. Importantly rare cases of complete response to farnesyltransferase inhibitors are known in pancreatic cancer patients . Recently new drug targets that shut-down mutated RAS signalling have emerged.
Small molecule competitive binders of the prenyl-binding protein PDEδ have been developed by researchers at the Max Planck Institute of Molecular Physiology, Dortmund, Germany. RAS localisation to the membrane is essential for its signalling in cancer. RAS proteins are farnesylated and this modulates their localisation to the plasma membrane. The farnesyl tail of RAS is bound by PDEδ which facilitates its transport to the plasma membrane. A series of compounds with ever greater affinity for the PDEδ pocket that binds RAS have been synthesised. Deltazinone was their first generation compound and Deltarasin their second generation compound [5, 6]. The Dortmund group have shown in pancreatic cancer cell lines with mutated KRAS that these compounds reduce cell proliferation.
A new small molecule called Rigosertib has been developed by the laboratory of E. Premkumar Reddy (New York) and collaborators which binds to the RAS-binding domain (RBD) present in proteins that interact with RAS and thus block this interaction, nullifying activated RAS . Rigosertib dramatically reduced the growth of human HCT116 colon cancer cell line implanted as a mouse xenograft. It also reduced the number of Pancreatic Intraepithelial Neoplasia (PanIN) lesions, precursors of PDAC, present in KRAS mutant mice.
It will be important to further refine these compounds into leads for preclinical development through to investigational new drug (IND) submission as they are very promising developments for RAS active tumours such as PDAC.
Zimmermann, Gunther, Björn Papke, Shehab Ismail, Nachiket Vartak, Anchal Chandra, Maike Hoffmann, Stephan A. Hahn, et al. ‘Small Molecule Inhibition of the KRAS-PDEδ Interaction Impairs Oncogenic KRAS Signalling’. Nature 497, no. 7451 (30 May 2013): 638–42. doi:10.1038/nature12205.
Papke, Björn, Sandip Murarka, Holger A Vogel, Pablo Martín-Gago, Marija Kovacevic, Dina C Truxius, Eyad K Fansa, et al. ‘Identification of Pyrazolopyridazinones as PDEδ Inhibitors’. Nature Communications 7 (20 April 2016): 11360. doi:10.1038/ncomms11360.
Athuluri-Divakar, Sai Krishna, Rodrigo Vasquez-Del Carpio, Kaushik Dutta, Stacey J. Baker, Stephen C. Cosenza, Indranil Basu, Yogesh K. Gupta, et al. ‘A Small Molecule RAS-Mimetic Disrupts RAS Association with Effector Proteins to Block Signaling’. Cell 165, no. 3 (21 April 2016): 643–55. doi:10.1016/j.cell.2016.03.045.
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