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Posts Tagged ‘mTOR’


Larry H. Benstein, MD, FCAP, Gurator and writer

https://pharmaceuticalintelligence.com/7/8/2014/Update on mitochondrial function, respiration, and associated disorders

This is a condensed account of very recent published work on respiration and disturbed mitochondrail function.  We know that their is an equilibrium between respiration and autophagy in eukaryotic cells.  The Krebs Cycle produces 32 ATPs in oxidative phosphorylation, which is far more efficient than glycolysis.  There is also a different contribution of mitochondrial metabolism, in the balance, between tissues that are synthetic and those that are catabolic.  This is a subject long understood, essential for cellular energetics, and not adequately explored.

 

Gain-of-Function Mutant p53 Promotes Cell Growth and Cancer Cell Metabolism via Inhibition of AMPK Activation.

Zhou G1Wang J2Zhao M2Xie TX2Tanaka N2, et al.
Mol Cell. 
2014 Jun 19;54(6):960-974.   doi: 10.1016/j.molcel.2014.04.024. 

Many mutant p53 proteins (mutp53s) exert oncogenic gain-of-function (GOF) properties, but the mechanisms mediating these functions remain poorly defined.

We show here that GOF mutp53s inhibit AMP-activated protein kinase (AMPK) signaling in head and neck cancer cells.

Conversely, downregulation of GOF mutp53s enhances AMPK activation under energy stress, decreasing the activity of the anabolic factors acetyl-CoA carboxylase and ribosomal protein S6 and inhibiting aerobic glycolytic potential and invasive cell growth.

Under conditions of energy stress, GOF mutp53s, but not wild-type p53, preferentially bind to the AMPKα subunit and inhibit AMPK activation.

Given the importance of AMPK as an energy sensor and tumor suppressor that inhibits anabolic metabolism, our findings reveal that direct inhibition of AMPK activation is an important mechanism through which mutp53s can gain oncogenic function. PMID:24857548

Investigating and Targeting Chronic Lymphocytic Leukemia Metabolism with the HIV Protease Inhibitor Ritonavir and Metformin.

Adekola KUAydemir SDMa SZhou ZRosen STShanmugam M.
Leuk Lymphoma. 2014 May 14:1-23.

Chronic Lymphocytic Leukemia (CLL) remains fatal due to the development of resistance to existing therapies. Targeting abnormal glucose metabolism sensitizes various cancer cells to chemotherapy and/or elicits toxicity.

Examination of glucose dependency in CLL demonstrated variable sensitivity to glucose deprivation. Further evaluation of metabolic dependencies of CLL cells resistant to glucose deprivation revealed increased engagement of fatty acid oxidation upon glucose withdrawal.

Investigation of glucose transporter expression in CLL reveals up-regulation of glucose transporter GLUT4. Treatment of CLL cells with HIV protease inhibitor ritonavir, that inhibits GLUT4, elicits toxicity similar to that elicited upon glucose-deprivation.

CLL cells resistant to ritonavir are sensitized by co-treatment with metformin, potentially targeting compensatory mitochondrial complex 1 activity. Ritonavir and metformin have been administered in humans for treatment of diabetes in HIV patients, demonstrating the tolerance of this combination in humans. Our studies strongly substantiate further investigation of FDA approved ritonavir and metformin for CLL.

KEYWORDS:  Basic Biology; Chemotherapeutic approaches; Lymphoid Leukemia; Signal transduction             PMID: 24828872

Utilizing hydrogen sulfide as a novel anti-cancer agent by targeting cancer glycolysis and pH imbalance.

Lee ZW1Teo XYTay EYTan CHHagen TMoore PKDeng LW.
Br J Pharmacol. 2014 May 15.    doi: 10.1111/bph.12773

Many disparate studies have reported the ambiguous role of hydrogen sulfide (H2 S) in cell survival. The present study investigated the effect of H2 S on viability of cancer and non-cancer cells.

Cancer and non-cancer cells were exposed to H2 S (using sodium hydrosulfide, NaHS and GYY4137) and cell viability was examined by crystal violet assay. We then examined cancer cellular glycolysis process by in vitro enzymatic assays and pH regulator activity. Lastly, intracellular pH (pHi) was determined by ratiometric pHi measurement using BCECF staining.

Continuous, but not single, exposure to H2 S decreased cell survival more effectively in cancer cells, as compared to non-cancer cells. Slow H2 S-releasing donor, GYY4137, significantly increased glycolysis leading to overproduction of lactate. H2 S also decreased anion exchanger and sodium/proton exchanger activity. The combination of increased metabolic acid production and defective pH regulation resulted in an uncontrolled intracellular acidification leading to cancer cell death. In contrast, no significant intracellular acidification or cell death was observed in non-cancer cells.

Low and continuous exposure to H2 S targets metabolic processes and pH homeostasis in cancer cells, potentially serving as a novel and selective anti-cancer strategy.

KEYWORDS:  cancer cell death; cancer glucose metabolism; hydrogen sulfide; pH homeostasis          PMID: 24827113


Agonism of the 5-Hydroxytryptamine 1F Receptor Promotes Mitochondrial Biogenesis and Recovery from Acute Kidney Injury

Garrett SMWhitaker RMBeeson CC, and Schnellmann RG

Center for Cell Death, Injury, and Regeneration, Department of Drug Discovery and Biomedical Sciences, Medical University of South Carolina, Charleston, South Carolina (S.M.G., R.M.W., C.C.B., R.G.S.); and Ralph H. Johnson Veterans Affairs Medical Center, Charleston, South Carolina (R.G.S.)
Address correspondence to: Dr. Rick G. Schnellmann, Department of Drug Discovery and Biomedical Sciences, MUSC, Charleston, SC 29425.
E-mail: schnell@musc.edu

Many acute and chronic conditions, such as acute kidney injury, chronic kidney disease, heart failure, and liver disease, involve mitochondrial dysfunction. Although we have provided evidence that drug-induced stimulation of mitochondrial biogenesis (MB) accelerates mitochondrial and cellular repair, leading to recovery of organ function, only a limited number of chemicals have been identified that induce MB.

The goal of this study was to assess the role of the 5-hydroxytryptamine 1F (5-HT1F) receptor in MB. Immunoblot and quantitative polymerase chain reaction analyses revealed 5-HT1F receptor expression in renal proximal tubule cells (RPTC). A MB screening assay demonstrated that two selective 5-HT1F receptor agonists,

  1. LY334370 (4-fluoro-N-[3-(1-methyl-4-piperidinyl)-1H-indol-5-yl]benzamide) and
  2. LY344864 (N-[(3R)-3-(dimethylamino)-2,3,4,9-tetrahydro-1H-carbazol-6-yl]-4-fluorobenzamide; 1–100 nM)

increased carbonylcyanide-p-trifluoromethoxyphenylhydrazone–uncoupled oxygen consumption in RPTC, and

  • validation studies confirmed both agonists increased mitochondrial proteins  in vitro.
    [e.g., ATP synthase β, cytochrome c oxidase 1 (Cox1), and NADH dehydrogenase (ubiquinone) 1β subcomplex subunit 8 (NDUFB8)]

Small interfering RNA knockdown of the 5-HT1F receptor

  • blocked agonist-induced MB.

Furthermore, LY344864 increased

  • peroxisome proliferator–activated receptor (PPAR) coactivator 1-α, Cox1, and
  • NDUFB8 transcript levels and
  • mitochondrial DNA (mtDNA) copy number

in murine renal cortex, heart, and liver.

Finally, LY344864 accelerated recovery of renal function, as indicated by

  • decreased blood urea nitrogen and kidney injury molecule 1 and
  • increased mtDNA copy number

following ischemia/reperfusion-induced acute kidney injury (AKI).

In summary, these studies reveal that

  • the 5-HT1F receptor is linked to MB, 5-HT1F receptor agonism promotes MB in vitro and in vivo, and

5-HT1F receptor agonism promotes recovery from AKI injury.

Induction of MB through 5-HT1F receptor agonism represents a new target and approach to treat mitochondrial organ dysfunction.

Footnotes

  • Portions of this work have been presented previously: Garrett SM, Wills LP, and Schnellmann RG (2012) Serotonin (5-HT) 1F receptor agonism as a potential treatment for acceleration of recovery from acute kidney injury.American Society of Nephrology Annual Meeting; 2012 Nov 1–4; San Diego, CA.
  • dx.doi.org/10.1124/jpet.114.214700.

Ca2+ regulation of mitochondrial function in neurons.

Rueda CB1Llorente-Folch I1Amigo I1Contreras L1González-Sánchez P1Martínez-Valero P1Juaristi I1Pardo B1Del Arco A2Satrústegui J3

Biochim Biophys Acta. 2014 May 10. pii: S0005-2728(14)00126-1.
doi: 10.1016/j.bbabio.2014.04.010.

Calcium is thought to regulate respiration but it is unclear whether this is dependent on the increase in ATP demand caused by any Ca2+ signal or to Ca2+ itself.

[Na+]i, [Ca2+]i and [ATP]i dynamics in intact neurons exposed to different workloads in the absence and presence of Ca2+ clearly showed that

  • Ca2+-stimulation of coupled respiration is required to maintain [ATP]i levels.

Ca2+ may regulate respiration by

  1. activating metabolite transport in mitochondria from outer face of the inner mitochondrial membrane, or
  2. after Ca2+ entry in mitochondria through the calcium uniporter (MCU).

Two Ca2+-regulated mitochondrial metabolite transporters are expressed in neurons,

  1. the aspartate-glutamate exchanger ARALAR/AGC1/Slc25a12, a component of the malate-aspartate shuttle, with a Kd for Ca2+ activation of 300nM, and
  2. the ATP-Mg/Pi exchanger SCaMC-3/Slc25a23, with S0.5 for Ca2+ of 300nM and 3.4μM, respectively.

The lack of SCaMC-3 results in a smaller Ca2+-dependent stimulation of respiration only at high workloads, as caused by veratridine, whereas

  • the lack of ARALAR reduced by 46% basal OCR in intact neurons using glucose as energy source and the Ca2+-dependent responses to all workloads (veratridine, K+-depolarization, carbachol).

The lack of ARALAR caused a reduction of about 65-70% in the response to the high workload imposed by veratridine, and

  • completely suppressed the OCR responses to moderate (K+-depolarization) and small (carbachol) workloads,
  • effects reverted by pyruvate supply.

For K+-depolarization, this occurs in spite of the presence of large [Ca2+]mit signals and increased reduction of mitochondrial NAD(P)H.

These results show that ARALAR-MAS is a major contributor of Ca2+-stimulated respiration in neurons

  • by providing increased pyruvate supply to mitochondria.

In its absence and under moderate workloads, matrix Ca2+ is unable to stimulate pyruvate metabolism and entry in mitochondria suggesting a limited role of MCU in these conditions.

This article was invited for a Special Issue entitled: 18th European Bioenergetic Conference.    Copyright © 2014. Published by Elsevier B.V.

KEYWORDS:  ATP-Mg/Pi transporter; Aspartate–glutamate transporter; Calcium; Calcium-regulated transport; Mitochondrion; Neuronal respiration PMID: 24820519

 

Sestrin2 inhibits uncoupling protein 1 expression through suppressing reactive oxygen species.

Ro SH1Nam M2Jang I1Park HW1Park H1Semple IA1Kim M1et al.
Proc Natl Acad Sci U S A. 2014 May 27;111(21):7849-54.
doi: 10.1073/pnas.1401787111.

Uncoupling protein 1 (Ucp1), which is localized in the mitochondrial inner membrane of mammalian brown adipose tissue (BAT), generates heat by uncoupling oxidative phosphorylation. Upon cold exposure or nutritional abundance, sympathetic neurons stimulate BAT to express Ucp1 to induce energy dissipation and thermogenesis. Accordingly, increased Ucp1 expression reduces obesity in mice and is correlated with leanness in humans.

Despite this significance, there is currently a limited understanding of how Ucp1 expression is physiologically regulated at the molecular level. Here, we describe the involvement of Sestrin2 and reactive oxygen species (ROS) in regulation of Ucp1 expression. Transgenic overexpression of Sestrin2 in adipose tissues inhibited both basal and cold-induced Ucp1 expression in interscapular BAT, culminating in decreased thermogenesis and increased fat accumulation.

Endogenous Sestrin2 is also important for suppressing Ucp1 expression because BAT from Sestrin2(-/-) mice exhibited a highly elevated level of Ucp1 expression. The redox-inactive mutant of Sestrin2 was incapable of regulating Ucp1 expression, suggesting that Sestrin2 inhibits Ucp1 expression primarily through reducing ROS accumulation.

Consistently, ROS-suppressing antioxidant chemicals, such as butylated hydroxyanisole and N-acetylcysteine, inhibited cold- or cAMP-induced Ucp1 expression as well. p38 MAPK, a signaling mediator required for cAMP-induced Ucp1 expression, was inhibited by either Sestrin2 overexpression or antioxidant treatments.

Taken together, these results suggest that Sestrin2 and antioxidants inhibit Ucp1 expression through suppressing ROS-mediated p38 MAPK activation, implying a critical role of ROS in proper BAT metabolism.

KEYWORDS: aging; homeostasis; mouse; β-adrenergic signaling      PMID: 24825887     PMCID:  PMC4040599

Mitochondrial EF4 links respiratory dysfunction and cytoplasmic translation in Caenorhabditis elegans.

Yang F1Gao Y1Li Z2Chen L3Xia Z4Xu T5Qin Y6
Biochim Biophys Acta. 2014 May 15. pii: S0005-2728(14)00499-X.
doi: 10.1016/j.bbabio.2014.05.353.

How animals coordinate cellular bioenergetics in response to stress conditions is an essential question related to aging, obesity and cancer. Elongation factor 4 (EF4/LEPA) is a highly conserved protein that promotes protein synthesis under stress conditions, whereas its function in metazoans remains unknown.

Here, we show that, in Caenorhabditis elegans, the mitochondria-localized CeEF4 (referred to as mtEF4) affects mitochondrial functions, especially at low temperature (15°C).

At worms’ optimum growing temperature (20°C), mtef4 deletion leads to self-brood size reduction, growth delay and mitochondrial dysfunction.

Transcriptomic analyses show that mtef4 deletion induces retrograde pathways, including mitochondrial biogenesis and cytoplasmic translation reorganization.

At low temperature (15°C), mtef4 deletion reduces mitochondrial translation and disrupts the assembly of respiratory chain supercomplexes containing complex IV.

These observations are indicative of the important roles of mtEF4 in mitochondrial functions and adaptation to stressful conditions.

Copyright © 2014. Published by Elsevier B.V.

KEYWORDSC. elegans; EF4(LepA/GUF1); Mitochondrial dysfunction; Retrograde pathways; Translation    PMID:  24837196

The metabolite α-ketoglutarate extends lifespan by inhibiting ATP synthase and TOR.

Chin RM1Fu X2Pai MY3Vergnes L4Hwang H5Deng G6Diep S2, et al.
Nature  2014 Jun 19;509(7505):397-401. doi: 10.1038/nature13264. 

Metabolism and ageing are intimately linked. Compared with ad libitum feeding, dietary restriction consistently extends lifespan and delays age-related diseases in evolutionarily diverse organisms. Similar conditions of nutrient limitation and genetic or pharmacological perturbations of nutrient or energy metabolism also have longevity benefits.

Recently, several metabolites have been identified that modulate ageing; however, the molecular mechanisms underlying this are largely undefined. Here we show that α-ketoglutarate (α-KG), a tricarboxylic acid cycle intermediate, extends the lifespan of adult Caenorhabditis elegans.

ATP synthase subunit β is identified as a novel binding protein of α-KG using a small-molecule target identification strategy termed drug affinity responsive target stability (DARTS). The ATP synthase, also known as complex V of the mitochondrial electron transport chain, is the main cellular energy-generating machinery and is highly conserved throughout evolution.

Although complete loss of mitochondrial function is detrimental, partial suppression of the electron transport chain has been shown to extend C. elegans lifespan.

We show that α-KG inhibits ATP synthase and, similar to ATP synthase knockdown, inhibition by α-KG leads to reduced ATP content, decreased oxygen consumption, and increased autophagy in both C. elegans and mammalian cells.

We provide evidence that the lifespan increase by α-KG requires ATP synthase subunit β and is dependent on target of rapamycin (TOR) downstream.

Endogenous α-KG levels are increased on starvation and α-KG does not extend the lifespan of dietary-restricted animals, indicating that α-KG is a key metabolite that mediates longevity by dietary restriction.

Our analyses uncover new molecular links between a common metabolite, a universal cellular energy generator and dietary restriction in the regulation of organismal lifespan, thus suggesting new strategies for the prevention and treatment of ageing and age-related diseases.

PMID: 24828042

 

 

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Author: Ziv Raviv PhD

 

Part A: Introduction to the PI3K/Akt pathway

Background

Akt/Protein kinase B (PKB) is a cytosolic serine/threonine kinase that promotes cell survival by inactivation of targets of the apoptotic pathways [1], and is implicated in the execution of many other cellular processes including:  cell proliferation, angiogenesis, glucose metabolism [2], protein translation, and gene transcription, all are mediated by extracellular and intracellular signals. In many cancers Akt is overexpressed and has central role in cancer progression and cancer cell survival [3,4], what makes it an attractive target for cancer therapy.

The Akt signaling pathway

Upstream signaling:

The Akt signaling pathway is initiated by growth factors leading to the recruiting and activation of phosphoinositol-3-kinase (PI3K) on receptor tyrosine kinases (RTKs). PI3K is then translocated to the cell membrane where it phosphorylates inositol ring at the D3 position of phosphatidylinositol  to form phosphatidylinositol (3,4,5)-triphosphate (PIP3). PIP3 serves to anchor Akt to the plasma membrane where it is phosphorylated at Thr308 by PDK1 and is further completely activated by mTOR by phosphorylation of Ser473. In certain circumstances activated Ras can also activate PI3K.

Downstream signaling:

Upon activation Akt is transducing its signals to downstream substrates to induce various intracellular processes, among them are: Activation of mTOR and its downstream effector S6K – to facilitate activation of translation; Phosphorylation of Bad – that inhibits apoptosis ; Phosphorylation of the tumor suppressor gene FOXO1 – inducing its ubiquitination and subsequent degradation by the proteasome;  Inhibition by phosphorylation of glycogen synthase kinase 3 (GSK-3) – which results in increase of glycogen synthesis.   Regulation of cell growth and survival is executed also by blocking apoptosis by Akt-associated survivin (BRC5) upregulation and via the NF-κB pathway by activation of IκB kinase (IKK).

  • Watch a Video on Akt Signaling Pathway

Figure 1: The Akt signaling pathway

AKT_cClick on image to enlarge

Taken from: Targeting the PI3K-AKT-mTOR pathway: progress, pitfalls, and promises. Workman P et al. Curr Opin Pharmacol. 2008 Aug;8(4):393-412

Negative regulation:

PI3K-dependent Akt activation is negatively regulated by the tumor suppressor protein PTEN, which works essentially opposite to PI3K, namely,  PTEN acts as a phosphatase and dephosphorylates PIP3 back to PIP2. This step removes Akt from its membrane anchoring through PIP3 resulting in substantial decreased rate of Akt activation and consequently inactivation of Akt-depended downstream pathways. In addition, PIP3 can also be dephosphorylated by the SHIP family of inositol phosphatases form PIP2.

Involvement of Akt  in cancer

The PI3K/Akt pathway is frequently altered and deregulated in many human malignancies. Hyper-activation of AKT kinases is one of the most common molecular findings in human malignancies and account for malignant transformation. Mechanisms for Akt pathway activation include loss of tumor suppressor PTEN function, amplification or mutation of PI3K, amplification or mutation of Akt, activation of growth factor receptors, inactivation of the translation repressor protein 4E-BP1 [5], and exposure to carcinogens [3 ,4]. For instance, heterozygous deletion of PTEN in mice elicits spontaneous tumors attributed mainly to activation of Akt. In addition, the production PIP3 by PI3K is over-activated in a wide range of tumor types. On the other hand, Akt knockout mice demonstrate that Akt is required for both cancer cell survival and oncogenic transformation. That activation of Akt is oncogenic, could be explained by preventing normal apoptosis of cells, thereby enabling accumulation of more oncogenic mutations in these cells. In addition, activation of Akt can also abrogate cell cycle checkpoints and can overcome G2/M cell-cycle arrest mediated by DNA mismatch repair. Thus, cells in which Akt is activated can accumulate mutations because the G2 cell-cycle point is abrogated and survive and continue to divide because of the anti-apoptotic activity of Akt. It is, therefore, proposed that this dual activity of Akt activation may explain the frequent activation of Akt in human malignancies [6].

Taken together, Akt activation has an effective role in cancer and through its downstream substrates Akt controls many cancer related cellular processes such as cell metabolism, growth and survival, proliferation, and motility, all of which contribute to tumor initiation and progression. Therefore, this pathway is an attractive therapeutic target for cancer treatment because it serves as a convergence point for many growth stimuli. Moreover, activation of the PI3/Akt pathway confers resistance to many chemotherapeutic drags [6], and is a poor prognostic factor for many types of cancers. Therefore, small molecule agents that block PI3K/Akt signaling might block many aspects of the tumor-cell phenotype [7,8]. Indeed, the Akt pathway is a major target for anticancer drug development by pharmaceutical companies.

  • The below Part B review the efforts to develop targeted Akt therapies for cancer.

 

Part B: Clinically available/in clinical development PI3K/Akt/mTOR inhibitors 

As described in Part Athe PI3/Akt cascade is a major intracellular signaling route conferring pro-survival signals to the cell. In cancer, there are many conditions where the PI3K/Akt pathway is deregulated, an attribute that is contributing to cancer formation and propagation. Given that Akt servers as convergence point to many pro-survival signals together with it being deregulated frequently in cancers, make Akt as a valuable target for developing anti-cancer therapy.

In addition, Akt shortens patient survival by allowing cancer cells to escape the cytotoxic effects of standard chemotherapy drugs. The importance of the Akt pathway in cancer thus is also evident from its significant role in the resistance of tumors to chemotherapies. A considerable route in developing anti- Akt based therapies is thus combining Akt inhibitors with standard chemotherapy rather than the using of Akt inhibitors as single agents.

Even in targeted therapies for cancer, such those that target receptor tyrosine kinases (RTKs) and other signaling pathways, it has been demonstrated that when applying a targeted agent such as trastuzumab  (Herceptin) a compensation reaction of increasing of downstream and parallel signaling pathways components, among them Akt, occurs in response, which enables cancer cells to be spared the effects of these targeted drugs. Therefore a multi-targeting approach with selective inhibitors would be useful, and inhibiting Akt directly will restore sensitivity to agents such as trastuzumab.

(i) Inhibitors that are in clinical use

Temsirolimus (CCI-779; marked as Torisel by Pfizer), an analog of sirolimus (rapamycin), is an immunophilin-binding antibiotic that blocks the initiation of the translation of mRNA by inhibiting mammalian target of rapamycin (mTOR) in a highly specific manner. Rapamycin itself is toxic and found in the clinic however as an immunosuppressant to prevent rejection in organ transplantation. Temsirolimus acts by interacting with mTOR, preventing the phosphorylation of eIF4E-BP1 and p70S6K, and thereby inhibiting the initiation of the translation of mRNA. The main mechanism of temsirolimus is inhibition of proliferation by G1 phase arrest induction, yet without inducing apoptosis. Temsirolimus was introduced only recently to treat renal cell carcinoma (RCC). In this cancer type HIF-1a levels are accumulated since its degradation is reduced significantly due to mutations of von Hippel Lindau tumor-suppressor gene and the activation of mTOR only worsen that accumulation of HIF1-a, which is its downstream effector. Therefore by blocking mTOR function temsirolimus is reducing the accumulation of HIF-1a. Temsirolimus has been generally well tolerated by advanced RCC patients that could be attributed to its high specificity toward mTOR. However, temsirolimus is associated with a small, but significant increased risk of developing a fatal adverse event. Nevertheless, temsirolimus benefit the overall patient population with the approved indications, including RCC. In the pivotal phase III study, temsirolimus demonstrated median overall survival (OS) in previously untreated patients of 10.9 months in patients with advanced RCC with poor prognostic risk, compared with 7.3 months for interferon-alpha. Temsirolimus remains the only treatment that shows a significant improvement in OSin treatment-naive, poor-risk patients with advanced RCC. Temsirolimus approved cancer indications are RCC and mantle cell lymphoma (MCL), and many other cancer conditions are found in advanced clinical development processes, including various solid tumors, diffused tumors (leukemias and lymphomas), and even in soft tissue sarcomas (STS).

Everolimus (RAD001; marketed by Novartis  as Afinitor) is an ester derivative of rapamycin and is also an inhibitor mTOR.  The drug inhibits oncogenic signaling in tumor cells and angiogenic signaling in vascular endothelial cells. Key features of everolimus include good tolerability, unique mechanism of action, G1 arrest, and induction of apoptosis. In vitro studies have demonstrated a cooperative effect between everolimus and gefitinib in various cancer cell lines. Treatment of human cancer cell lines with everolimus results in a decrease in p-4E-BP1, p-p70S6K, and p-S6 levels while increasing p-AKT levels. The rise of p-AKT is accompanied with a parallel increase in downstream p-GSK-3a/ß, suggesting feedback activation of the AKT pathway. Thus AKT activation could revert the antitumor activity of everolimus. Gefitinib completely prevents everolimus-induced p-AKT increase and markedly enhances the everolimus mediated decrease in p-4E-BP1 and p-p70S6K.

Everolimus is approved for the treatment of RCC, progressive pancreatic neuroendocrine tumors, breast cancer in post-menopausal women with advanced hormone receptor (HR)-positive/HER2-negative. In addition the drug is used as a preventive drug of organ rejection after renal transplantation. As with the case of temsirolimus, everolimus has also a slight increase of mortality risk over other drugs.

Cancer indications that are now in clinical development for treatment by everolimus, some of which are in advanced clinical studies, include various forms of leukemias and lymphomas such as AML, ALL CML, T-cell leukemia, diffuse large B-cell lymphoma (DLBCL), non-Hodgkin’s lymphoma (NHL), and MCL. Everolimus is particularly applicable to the treatment of leukemia because mTOR-related messengers, particularly PI3K, AKT, p70S6K kinase and 4E-BP1, are known to be both constitutively activated in hematologic malignancies and interfere with the activity of current anti-leukemia therapy. Solid tumors such as lung, breast, prostate, and colorectal at various stages, as well as brain cancers and STS are also in developmental stages for everolimus treatment.

(ii) Inhibitors that are in advanced clinical development (phase II/III)

Perifosine (KRX-0401) by AEterna Zentaris – among Akt inhibitors under development for cancer therapy, perifosine is found in advanced stages of clinical development and is moving toward phase III clinical trials. It belongs to alkylphosphocholines (ALP) – phospholipid-like molecules – which disrupt lipid-mediated signal transduction pathways that are necessary for tumor cell growth and survival. ALP induce apoptotic cell death in a variety of tumor cell lines. Perifosine primarily acts on the cell membrane where it inhibits signaling that could explain its capability to inhibit Akt, as Akt interaction with PIP3 in the cytosolic face of the plasma cell membrane is essential to its activation. In addition to Akt, perifosine inhibits also JNK and NF-kB, both are also associated with apoptosis, cell growth, differentiation, and survival. In addition to its potential efficacy as a single agent, perifosine may provide synergistic effects when combined with established cancer treatments such as radiotherapy, chemotherapy, tyrosine kinase inhibitors such as commercially available EGFR inhibitors, and endocrine therapies.

Many clinical trials were/are conducted with perifosine in various cancer conditions and settings. Especially successive phase II studies engaged perifosine were with colorectal cancer (CRC), where patients with metastatic disease treated with the combination of capecitabine and perifosine had more than doubled the median time to progression (TTP) of the disease, which led to an ongoing phase III study. Other solid cancer indications phase II studies employing perifosine that had encouraging results include metastatic RCC (mRCC) and non-small lung cancer (NSLC). Perifosine is also exmined in clinical trials with hematological cancers. Advanced stages clinical studies were conducted in multiple myeloma (MM), where patients treated with the combination of perifosine + bortezomib (proteasome inhibitor) and dexamethasone, in which after, a phase III study was conducted on that basis. However, that phase III study was terminated in March 2013 upon recommendation by data safety monitoring board to discontinue the experiment since it was highly unlikely that the trial would achieve a significant difference in progression-free survival (PFS).  Another potential benefit for perifosine has been documented in Waldenström’s macroglobulinemia (WM).  In addition, perifosine is examined in other hematologic cancers such as in AML, CLL and lymphomas.

MK-2206 – MK-2206 by Merck is an allosteric inhibitor of Akt that is currently widely examined in tens of clinical experimentation where some of them are in phase II status.  In preclinical experiments, MK-2206, demonstrated synergistic activity when combined with other targeted therapies, such as erlotinib in NSCLC cell lines, and lapatinib in breast cancer cell lines and in xenograft mice bearing ovarian cancer, MK-2206 treatment led to substantial growth inhibition and sustained inhibition of Akt.

Several phase II research studies employing MK-2206 are in progress, among them found a multicenter study with advanced ovarian cancer resistant to platinum therapy, and another multicenter study with breast cancer patients. Phase I/II study is conducted also for CLL patients. Many others phase I studies are in progress, among them trails testing the combinations of MK-2206 with other targeted drugs as well as chemotherapy. For instance an ongoing phase I study is evaluating the addition of MK-2206 to trastuzumab in patients with solid tumors HER2 positive, or another study is conducted to evaluate MK-2206 in combination with trastuzumab and lapatinib for the treatment of HER2 positive, advanced solid tumors. MK-2206 is testing also in advanced NSCLC with the combination of gefitinib in one study and with erlotinib in another. In another relatively large phase I study, patients with advanced solid tumors were randomized to MK-2206 either given with carboplatin and paclitaxel, docetaxel, or erlotinib. Another study with patients bearing locally advanced or metastatic solid tumors or metastatic breast cancer examined MK-2206 given with and paclitaxel (Taxol). Finally MK-2206 and selumetinib administration was tested in phase I studies in patients with advanced CRC. Other cancer indications that are investigated MK-2206 as single agent or in combination with chemotherapy in phase I studies include prostate cancer,  head and neck cancer, large B cell lymphoma, leukemias such as AML, and melanoma.

Ridaforolimus (AP23573/MK-8669,; Taltorvic by Merck) – Ridaforolimus is an oral mTOR inhibitor found in several clinical trials. A compressive phase III experiment was conducted with ridaforolimus in metastatic STS and metastatic bone sarcomas (SUCCEED – Sarcoma Multi-Center Clinical Evaluation of the Efficacy of Ridaforolimus) by Merck and Ariad Pharmaceuticals that had presented positive data at the beginning showing that patients that have received ridaforolimus had a median progression-free survival (PFC) – the primary endpoint of the study – of 17.7 weeks compared with 14.6 weeks for those received placebo. However, FDA’s oncologic drugs advisory committee (ODAC) panel (March 2012) did not approved the use of ridaforolimus as maintenance therapy for patients with metastatic soft-tissue sarcoma or bone sarcoma. The committee did not think that a significant difference was observed between the groups in terms of OS and although patients did experience a longer disease-free period before their cancer returned when receiving ridaforolimus, the delay was not significant. There was also a concern regarding side effects. In a complete response letter, (June 2012) the FDA did not approve the SUCCEED application in its present form, therefore, Merck formally withdrawn the marketing authorization application for ridaforolimus for sarcoma. However, Merck still continue experimenting ridaforolimus in other cancer indications. A phase II study is conducted in breast cancer patients examining ridaforolimus alone, ridaforolimus + dalotuzumab, or ridaforolimus + Exemestane. Another phase II study is conducted in female adult patients harboring recurrent or persistent endometrial cancer. A third Phase II study is examining ridaforolimus in patients with taxane-resistant androgen-independent prostate cancer. Many phase I experiments are conducted with ridaforolimus among them: experiment in pediatric patients with solid tumors treated with dalotuzumab given alone or in combination with ridaforolimus; Bicalutamide and ridaforolimus in men with prostate cancer; Combinations of carboplatin/paclitaxel/ridaforolimus in endometrial and ovarian tumors; Safety study examining ridaforolimus  in patients with progressive or recurrent glioma, and others. Given the consequences as with the SUCCEED experiment; it remains to see whether ridaforolimus alone or in combinations would be approved and be valid in the clinical arena.

RX-0201 (Archexin) by Rexahn Pharmaceuticals is an antisense oligonucleotide directed toward Akt1 mRNA. RX-0201 was demonstrated to significantly downregulated the expression of AKT1 at both the mRNA and protein levels. In addition combined treatment of RX-0201with several cytotoxic drugs resulted in an additive growth inhibition of Caki-1 clear cell carcinoma cells. In addition, preclinical experiments demonstrated that RX-0201 given at nano-molars as a single agent induced substantial growth inhibition in various types of human cancer cells. Furthermore, in vivo studies using nude mice xenografts have resulted in significant inhibition of tumor growth and tumor formation treated with RX-0201. Therefore RX-0201 was further tested in phase I studies in patients with solid tumors. The only dose limiting toxicity (DLT) observed was Grade 3 fatigue. Phase II studies of RX-0201 were approved thus in advanced RCC. Furthermore, another phase II study was completed last year with encouraging results.  This phase II trial was conducted in metastatic pancreatic cancer, assessing the combination of RX-0201 and gemcitabine. The study enrolled 31 patients and the primary endpoint was overall survival following 4 cycles of therapy with a 6-month follow-up. The study demonstrated that treatment with RX-0201 in combination with gemcitabine resulted in a median survival of 9.1 months compared to the published survival data of 5.65 months for gemcitabine given alone. The most frequently side effects were constipation, nausea, abdominal pain, and pyrexia, regardless of relatedness.

BKM120 – by Novartis is an oral selective class-I PI3K inhibitor, induces its inhibition in an ATP-competitive manner, thereby inhibiting the production of the secondary messenger PIP3 and activation of downstream signaling pathway. BKM120 was shown to induce pro-apoptotic effects in vitro and anti-tumor activity in vivo. BKM120 is enrolled in many clinical trials at all levels for several cancer indications. Phase I experiments are performed with the following cancers: CRC in combination with panitumumab; RCC; breast cancer (HR+/HER2+); breast cancer (triple negative, recurrent); ovarian cancer; and leukemias.  Phase II trials include: endometrial cancer; metastatic NSCLC; malignant melanoma (Braf V600 mutated); prostate; and glioblastoma multiforme (GBM).

A phase III study is currently enrolled with postmenopausal breast cancer patients with HR+/HER2- (local, advanced or metastatic), examining BKM120 in combination with fulvestrant. In preliminary clinical experiments activity was observed with BKM120 in patients with breast cancer, as a single agent or in combination with letrozole, or trastuzumab. In this phase III study, postmenopausal women with HR+/HER2- breast cancer whom were treated with aromatase inhibitor (AI), and are refractory to endocrine and mTOR inhibition (mTORi) combination therapy, are randomized to receive continuous BKM120 or placebo daily, with fulvestrant. The rational for this experiment is that the use of PI3K inhibition may overcome resistance to mTORi in breast cancer by targeting the PI3K pathway upstream.  The primary endpoint of the trail is PFS and the secondary endpoint is OS. Other secondary endpoints are overall response rate and clinical benefit rate, safety, pharmacokinetics of BKM120, and patient-reported quality of life.

CAL-101 (Idelalisib) – by Gilead Sciences is an orally bio-available, small molecule inhibitor of PI3K delta proposed for the treatment hematologic malignancies. In preclinical efficacy studies, CAL-101 inhibited the PI3K pathway and decreased cellular proliferation in primary CLL and AML cells, and in a range of NHL cell lines. The delta form of PI3K is expressed primarily in blood-cell lineages, including cells that cause or mediate hematologic malignancies, inflammation, autoimmune diseases and allergies. Therefore, CAL-101 as specific inhibitor of the PI3K-delta is expected to have therapeutic effects in these diseases without inhibiting PI3K signaling that is critical to the normal function of healthy cells. A variety of studies have shown that inhibition of other PI3K forms can cause significant toxicities, particularly with respect to glucose metabolism, which is essential for normal cell activity. CAL-101 was shown to block constitutive PI3K signaling, resulting in decreased phosphorylation of Akt and other downstream effectors, an increase in PARP and caspase cleavage, and an induction of apoptosis across a broad range of immature and mature B-cell malignancies. Importantly, CAL-101 does not promote apoptosis in normal T cells or NK cells, nor does it diminish antibody-dependent cellular cytotoxicity (ADCC) but decreased activated T-cell production of various inflammatory and anti-apoptotic cytokines. These findings provide rationale for the clinical development of CAL-101 as a first-in-class targeted therapy for CLL and related B-cell proliferative disorders. Indeed several clinical trials are currently enrolled for Hodgkin’s lymphoma, NHL, and CLL. Phase III clinical trials for CLL are now recruiting patients aimed to examine CAL-101 in combination with Bendamustine and Rituximab in one study;  CAL-101 + Rituximab;  and the combinations of CAL-101 with Ofatumumab in third phase III study. Both Rituximab and Ofatumumab are monoclonal Abs for CD20, which is primarily found on the surface of B cells. In addition, another phase III study of CAL-101 in combination with Bendamustine and Rituximab for indolent NHLs is also now recruiting patients.

(iii) Other Akt pathway inhibitors in clinical development.

There are dozens of agents targeting Akt pathway that are found at preclinical and clinical development. The various inhibitors are targeting various elements of the Akt pathway including: Akt itself, PI3K, mTOR, and PDK1. Most of these agents are small molecules inhibitors, some are extracts while others are synthetic, but also include an antisense oligonucleotide (RX-0201 to Akt).

The list below describes shortly agents which currently reached phase II stage and their relevant indications:

XL-147 – sponsored by Sanofi, small molecule-pan PI3K inhibitor for breast cancer and endometrial cancer.

XL-765 – also of Sanofi, inhibitor of the activity of PI3K and mTOR, for HR+/HER2- breast cancer patients.

BN108 – by Bionovo, an aqueous extract of Anemarrhena asphodeloides, is an orally available dual inhibitor, that induces apoptotic cancer cell death by rapid inactivation of both Akt and mTOR pathways, for breast cancer.

GDC-0068 – by Genentech, is an orally available small molecule pan-Akt inhibitor, for prostate cancer.

BEZ235 – by Novartis is a dual ATP-competitive PI3K and mTOR inhibitor, prevents PI3K signaling and inhibits growth of cancer cells with activating PI3K mutations. Phase II study is recruiting patients with metastatic or unresectable malignant PEComa (perivascular epithelioid cell tumors), other phase II include endometrial cancer indications and metastatic HR+/HER2-breast cancer patients.

BAY 80-6946 – is a pan class I PI3K inhibitor by BayerPhase II for NHL, currently recruiting.

Nelfinavir  – by ViiV Healthcare is an HIV protease inhibitor found to downregulate Akt phosphorylation by inhibiting proteasomal activity and inducing the unfolded protein response (UPR). HIV-1 protease inhibitor was found induces growth arrest and apoptosis of human prostate cancer cells in vitro and in vivo in conjunction with blockade of androgen receptor, STAT3 and AKT signaling. A phase I/II trial is enrolled for patients with locally advanced CRC to test Nelfinavir in combination with chemo/radiotherapy.

Triciribine  Triciribine phosphate monohydrate (TCN-PM) is a specific AKT inhibitor used also in the basic research arena but undergo also several clinical studies. Currently a phase II sponsored by Cahaba Pharmaceuticals is recruiting, to examine triciribine with paclitaxel in patients with locally advanced breast cancer. And a phase I/II experiment of combination with carboplatin in ovarian patients is planned.

GSK2110183 – by GlaxoSmithKline  is an oral panAkt inhibitor. Phase II is recruiting subjects with solid tumors and hematologic malignancies.

(iv) Conclusive remarks

Given the broaden arsenal of agents targeting Akt that are in pre-clinical and clinical development, it is extremely important to figure out how to use them optimally and to elucidate carefully which of them have the greatest potential to proceed into advanced stages of clinical trials and to clinical approval.  One of the various considerations in developing valid Akt inhibitors for the clinic use should be choosing a relevant cancer in which Akt has a central role in its development/propagation (e.g. mRCC). Since there is cross-talk between the Akt pathway to other pathways especially by involvement of RTKs (e.g. VEGFR), there is a rational to apply Akt inhibitions in cancer indications that had good results with inhibition of RTKs where combinations of Akt with agents such as sunitinib, could results in a synergistic anti-cancer effect. The combinations of Akt inhibitors with RTKs inhibitors could also overcome the compensate reaction to agents such as Herceptin that confer resistance. It is important to introduce efficient Akt inhibitor on the background of existing anti-cancer chemotherapies where Akt inhibitors can complement these therapies by circumvent frequent resistance to these drugs. Finally, the developing of biomarkers for a validation of the efficacy of candidate Akt inhibitor to be developed in further advance clinical studies for specific cancer indications is essentially needed, to ensure that accurate efforts would be invested at the most validate Akt inhibitors. Such biomarkers could be levels of phosphorylated Akt in blood or mRNA levels to be monitored upon treatment with Akt inhibitors and the correlation to the efficacy of these inhibitors, and that is besides of their prognostic value. The status of mutations of PI3K and PTEN could also serve as a marker for the efficiency of Akt inhibitors and how to use them optimally.

 

References

1. Song G, Ouyang G, Bao S (2005) The activation of Akt/PKB signaling pathway and cell survival. J Cell Mol Med 9 (1):59-71

2. Gonzalez E, McGraw TE (2009) The Akt kinases: isoform specificity in metabolism and cancer. Cell Cycle 8 (16):2502-2508

3. Vivanco I, Sawyers CL (2002) The phosphatidylinositol 3-Kinase AKT pathway in human cancer. Nat Rev Cancer 2 (7):489-501

4. Altomare DA, Testa JR (2005) Perturbations of the AKT signaling pathway in human cancer. Oncogene 24 (50):7455-7464

5. She QB, Halilovic E, Ye Q, Zhen W, Shirasawa S, Sasazuki T, Solit DB, Rosen N (2010) 4E-BP1 is a key effector of the oncogenic activation of the AKT and ERK signaling pathways that integrates their function in tumors. Cancer Cell 18 (1):39-51

6. Kim D, Dan HC, Park S, Yang L, Liu Q, Kaneko S, Ning J, He L, Yang H, Sun M, Nicosia SV, Cheng JQ (2005) AKT/PKB signaling mechanisms in cancer and chemoresistance. Front Biosci 10:975-987

7. Pal SK, Reckamp K, Yu H, Figlin RA (2010) Akt inhibitors in clinical development for the treatment of cancer. Expert Opin Investig Drugs 19 (11):1355-1366

8. Hsieh AC, Truitt ML, Ruggero D (2011) Oncogenic AKTivation of translation as a therapeutic target. Br J Cancer 105 (3):329-336

9. Alexander W (2011) Inhibiting the Akt pathway in cancer treatment. P T.  April; 36(4): 225–227

10. LoPiccolo J, Blumenthal GM, Bernstein WB, Dennis PA.(2008) Targeting the PI3K/Akt/mTOR pathway: effective combinations and clinical considerations. Drug Resist Updat.  Feb-Apr;11(1-2):32-50

11. Weigelt B and Downward J (2012) Genomic Determinants of PI3K Pathway Inhibitor Response in Cancer. Front Oncol. 2012;2:109

12. Janna Elizabeth Hutz. Genetic analysis of the PI3k/AKT/mTOR signaling pathway. udini.proquest.com

Resources

New medicine Oncology KnowledgeBASE (nmOK)

ClinicalTrials.gov

Related articles on this Open Access Online Scientific Journal

AKT signaling variable effects. Reporter: Larry H Bernstein, MD

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Intratumor Heterogeneity and Branched Evolution Revealed by Multiregion Sequencing[1]

Curator and Reporter: Stephen J. Williams, Ph.D.

Genomic instability is considered a hallmark and necessary for generating the mutations which drive tumorigenesis. Multiple studies had suggested that there may be multiple driver mutations and a plethora of passenger mutations driving a single tumor.  This diversity of mutational spectrum is even noticed in cultured tumor cells (refer to earlier post Genome-Wide Detection of Single-Nucleotide and Copy-Number Variation of a Single Human Cell).  Certainly, intratumor heterogeneity has been a concern to clinicians in determining the proper personalized therapy for a given cancer patient, and has been debated if multiple biopsies of a tumor is required to acquire a more complete picture of a tumor’s mutations.  In the New England Journal of Medicine, lead author Dr. Marco Gerlinger in the laboratory of Dr. Charles Swanton of the Cancer Research UK London Research Institute, and colleagues reported the results of a study to determine if intratumoral differences exist in the mutational spectrum of primary and metastatic renal carcinomas, pre- and post-treatment with the mTOR (mammalian target of rapamycin) inhibitor, everolimus (Afinitor®)[1].

The authors compared exome sequencing of multiregion biopsies from four patients with metastatic renal-cell carcinoma who had been enrolled in the Personalized RNA Interference to Enhance the Delivery of Individualized Cytotoxic and Targeted Therapeutics clinical trial of everolimus (E-PREDICT) before and after cytoreductive surgery.

Biopsies taken:

  • Multiregion spatial biopsy of primary tumor (representing 9 regions of the tumor)
  • Chest-wall metastases
  • Perinephric metastases
  • Germline DNA as control

Multiple platforms were used to determine aberrations as follows:

  1. Illumina Genome Analyzer IIx and Hiseq: for sequencing and mutational analysis
  2. Illumina Omni 2.5: for SNP (single nucleotide polymorphism)-array-based allelic imbalance detection for chromosomal imbalance and ploidy analysis
  3. Affymetrix Gene 1.0 Array: for mRNA analysis

A phylogenetic reconstruction of all somatic mutations occurring in primary disease and associated metastases was  performed to determine the clonal evolution of the metastatic disease given the underlying heterogeneity of the tumor.  Basically the authors wanted to know if the mutational spectra of one metastasis could be found in biopsies taken from the underlying primary tumor or if the mutational landscape of metastases had drastically changed.

Results

Multiregion exon-capture sequencing of DNA from pretreatment biopsy samples of the primary tumor, chest wall metastases, and perinephrous metastasis revealed 128 mutations classified as follows:

  • 40 ubiquitous mutations
  • 59 mutations shared by several but not all regions
  • 29 mutations unique to specific regions
  • 31 mutations shared by most primary tumor regions
  • 28 mutations shared by most metastatic regions

The authors mapped these mutations out with respect to their location, in order to determine how the metastatic lesions evolved from the primary tumor, given the massive heterogeneity in the primary tumor.  Construction of this “phylogenetic tree” (see Merlo et. al[2]) showed that the disease evolves in a branched not linear pattern, with one branch of clones evolving into a metastatic disease while another branch of clones and mutations evolve into the primary disease.

One of the major themes of the study is shown by results that an average of 70 somatic mutations were found in a single biopsy (a little more than just half of all tumor mutations) yet only 34% of the mutations in multiregion biopsies were detected in all tumor regions.

This indicated to the authors that “a single biopsy was not representative of the mutational landscape of the entire bulk tumor”. In addition, microarray studies concluded that gene-expression signatures from a single biopsy would not be able to predict outcome.

Everolimus therapy did not change the mutational landscape.  Interestingly, allelic composition and ploidy analyses revealed an extensive intratumor heterogeneity, with ploidy heterogeneity in two of four tumors and 26 of 30 tumor samples containing divergent allelic-imbalances.  This strengthens the notion that multiple clones with diverse genomic instability exist in various regions of the tumor.

 The intratumor heterogeneity reveals a convergent tumor evolution with associated heterogeneity in target function

Genes commonly mutated in clear cell carcinoma[3, 4] (and therefore considered the prevalent driver mutations for renal cancer) include:

Only VHL mutations were found in all regions of a given tumor, however there were three distinct SETD2 mutations (frameshift, splice site, missense) which were located in different regions of the tumor.

SETD2 trimethylates histones at various lysine residues, such as lysine residue 36 (H3K36).  The trimethylation of H3K36 is found on many actively transcribed genes.  Immunohistochemistry showed trimethylated H3K36 was reduced in cancer cells but positive in most stromal cells and in SETD2 wild-type clear-cell carcinomas.

Interestingly most regions of the primary tumor, except one, contained a kinase-domain activating mutation in mTOR.  Immunohistochemistry analysis of downstream target genes of mTOR revealed that mTOR activity was enhanced in regions containing this mutation.  Therefore the intratumoral heterogeneity corresponded to therapeutic activity, leading to the impression that a single biopsy may result in inappropriate targeted therapy.   Additional downstream biomarkers of activity confirmed both the intratumoral heterogeneity of mutational spectrum as well as an intratumoral heterogeneity of therapeutic-target function.

The authors conclude that “intratumor heterogeneity can lead to underestimation of the tumor genomics landscape from single tumor biopsies and may present major challenges to personalized-medicine and biomarker development”.

In an informal interview with Dr. Swanton, he had stressed the importance of performing these multi-region biopsies and the complications that intratumoral heterogeneity would present for personalized medicine, biomarker development, and chemotherapy resistance.

Q: Your data clearly demonstrates that multiple biopsies must be done to get a more complete picture of the tumor’s mutational landscape.  In your study, what percentage of the tumor would be represented by the biopsies you had performed?

Dr. Swanton: Realistically this is a very difficult question to answer, the more biopsies we sequence, the more we find, in the near term it may be very difficult to ever formally address this in large metastatic tumours

Q:  You have very nice data which suggest that genetic intratumor heterogeneity complicates the tumor biomarker field? do you feel then that quests for prognostic biomarkers may be impossible to attain?

Dr. Swanton: Not necessarily although heterogeneity is likely to complicate matters

Identifying clonally dominant lesions may provide better drug targets

Predicting resistance events may be difficult given the potential impact of tumour sampling bias and the concern that in some tumours a single biopsy may miss a relevant subclonal mutation that may result in resistance

Q:  Were you able to establish the degree of genomic instability among the various biopsies?

Dr. Swanton:  Yes, we did this by allelic imbalance analysis and found that the metastases were more genomically unstable than the primary region from which the metastasis derived

Q: I was actually amazed that there was a heterogeneity of mTOR mutations and SETD2 after everolimus therapy?   Is it possible these clones obtained a growth advantage?

Dr. Swanton: We think so yes, otherwise we wouldn’t identify recurrent mutations in these “driver genes”

Dr. Swanton will present his results at the 2013 AACR meeting in Washington D.C. (http://www.aacr.org/home/scientists/meetings–workshops/aacr-annual-meeting-2013.aspx)

The overall points of the article are as follows:

  • Multiple biopsies of primary tumor and metastases are required to determine the full mutational landscape of a patients tumor
  • The intratumor heterogeneity will have an impact on the personalized therapy strategy for the clinician

 

  • Metastases arising from primary tumor clones will have a greater genomic instability and mutational spectrum than the tumor from which it originates

 

  • Tumors and their metastases do NOT evolve in a linear path but have a branched evolution and would complicate biomarker development and the prognostic and resistance outlook for the patient

A great video of Dr. Swanton discussing his research can be viewed here

VIEW VIDEO

Everolimus: an inhibitor of mTOR

The following information was taken from the New Medicine Oncology Database (http://www.nmok.net)

Developer

Designation

Description

Approved/Filed Indications

Novartis PharmaCurrent as of: August 30, 2012 Generic Name: Everolimus
Brand Name: Afinitor
Other Designation: RAD001, RAD001C
RAD001, an ester of the macrocytic immunosuppressive agent sirolimus (rapamycin), is an inhibitor of mammalian target of rapamycin (mTOR) kinase.Administration Route: intravenous (IV) • PO • solid organ transplant
• renal cell carcinoma (RCC), metastatic after failure of treatment with sunitinib, sorafenib, or sunitinib plus sorafenib
• renal cell carcinoma, advanced, refractory to treatment with vascular endothelial growth factor (VEGF)-targeted therapy
• treatment of progressive neuroendocrine tumors (NET) of pancreatic origin (PNET) in patients with inoperable, locally advanced or metastatic disease

Marker Designation
Alias
Gene Location

Marker Description

Indications

5’-AMP-activated Protein Kinase (AMPK)AMPK beta 1 (beta1 non-catalytic subunit) • HAMPKb (beta1 non-catalytic subunit) • MGC17785 (beta1 non-catalytic subunit) • AMPK2 (alpha1 catalytic subunit) • PRKAA (alpha1 catalytic subunit) • AMPK alpha 1 (alpha1 catalytic subunit) • AMPKa1 ( AMPK is a member of a metabolite-sensing protein kinase family found in all eukaryotes. It functions as a cellular fuel sensor and its activation strongly suppresses cell proliferation in non-malignant cells and cancer cells. AMPK regulates the cell cycle by upregulating the p53-p21 axis and modulating the TSC2-mTOR (mammalian target of rapamycin) pathway. The AMPK signaling network contains a number of tumor suppressor genes including LKB1, p53, TSC1 and TSC2, and modulates growth factor signaling involving proto-oncogenes including PI3K, Akt and ERK. AMPK activation is therefore therapeutic target for cancer (Motoshima H, etal, J Physiol, 1 Jul 2006; 574(Pt 1): 63–71).AMPK is a protein serine/threonine kinase consisting of a heterotrimeric complex of a catalytic alpha subunit and regulatory ß and gamma subunits. AMPK is activated by increased AMP/ATP ratio, under conditions such as glucose deprivation, hypoxia, ischemia and heat shock. It is also activated by several hormones and cytokines. AMPK inhibits ATP-consuming cellular events, protein synthesis, de novo fatty acid synthesis, and generation of mevalonate and the downstream products in the cholesterol synthesis pathway (Motoshima H, etal, J Physiol, 1 Jul 2006; 574(Pt 1): 63–71). – ovarian cancer
– brain cancer
– liver cancer
– leukemia
– colon cancer
CREB regulated transcription coactivator 2 (CRTC2)TOR complex 2 (TORC2, mTORC2) • RP11-422P24.6 • transducer of regulated cAMP response element-binding protein (CREB)2 • transducer of CREB protein 2 • TOR1Location: 1q21.3 The mammalian target of rapamycin (mTOR) exists in two complexes, TORC1 and TORC2, which are differentially sensitive to rapamycin. cAMP response element-binding protein (CREB) regulated transcription coactivator 2 (CRTC2) or TORC2 is a multimeric kinase composed of mTOR, mLST8, mSin1, and rictor. The complex is insensitive to acute rapamycin exposure and functions in controlling cell growth and actin cytoskeletal assembly.TORC2 controls gene silencing, telomere length maintenance, and survival under DNA-damaging conditions. It is primaily located in the cytoplasm but also shuttles into the nucleus (Schonbrun M, etal, Mol Cell Biol, Aug 2009;29(16):4584-94). – brain cancer
Hypoxia inducible factor 1 alpha (HIF1A)HIF1-alpha (HIF-1 alpha) • HIF-1A • PASD8 • MOP1 • bHLHe78Location: 14q21-q24 The alpha subunit of the hypoxia inducible factor 1 (HIF-1alpha) is a 826 amino acid antigen consisting of a basic helix-loop-helix (bHLH)-PAS domain at its N-terminus. HIF-1alpha is rapidly degraded by the proteasome under normal conditions, but is stabilized by hypoxia resulting in the transactivation of several proangiogenic genes. HIF-1alpha is responsible for inducing production of new blood vessels as needed when tumors outgrow existing blood supplies. HIF-1alpha serves as a transcriptional factor that regulates gene expression involved in response to hypoxia and promotes angiogenesis.HIF-1alpha is a proangiogenic transcription factor induced primarily by tumor hypoxia that is critically involved in tumor progression, metastasis and overall tumor survival. HIF-1alpha functions as a survival factor that is required for tumorigenesis in many types of malignancies, and is expressed in a majority of metastases and late-stage tumors. HIF-1alpha is overexpressed in brain, breast, colon, endometrial, head and neck, lung, ovarian, and pancreatic cancer, and is associated with increased microvessel density and/or VEGF expression – prostate cancer
– bladder cancer
– nasopharyngeal cancer
– head and neck cancer
– kidney cancer
– pancreatic cancer
– endometrial cancer
– breast cancer
Mammalian target of rapamycin (mTOR)FK506 binding protein 12-rapamycin associated protein 1 • RAFT1 • FK506 binding protein 12-rapamycin associated protein 2 • FRAP • FRAP1 • FRAP2 • RAPT1 • FKBP-rapamycin associated protein • FKBP12-rapamycin complex-associated protein 1 • rapamycin target protein • TOR • FLJ44809 • MTORC1 • MTORC2 • RPTOR • RAPTOR • KIAA1303 • mammalian target of rapamycin complex 1Location: 1p36.22 The mammalian target of rapamycin (mTOR) is a large serine/threonine protein (Mr 300,000) having heat repeats, and protein-protein interaction domains at its amino terminus, and a protein kinase domain at its carboxy terminus. mTOR is a member of the phosphoinositide 3-kinase (PI3K)-related kinase (PIKK) family and a central modulator of cell growth. It regulates cell growth, proliferation and survival by impacting on protein synthesis and transcription. mTOR is present in two multi-protein complexes, a rapamycin-sensitive complex, TOR complex 1 (TORC1), defined by the presence of Raptor and a rapamycin insensitive complex, TOR complex 2 (TORC2), with Rictor, Protor and Sin1. Rapamycin selectively inhibits mTORC1 by binding indirectly to the mTOR/Raptor complex via FKBP12, resulting in inhibition of p70S6kinase but not the mTORC2 substrate AKTSer473. Selective inhibition of p70S6K attenuates negative feedback loops to IRS1 and TORC2 resulting in an increase in pAKT which may limit the activity of rapamycin.In a hypoxic environment the increase in mass of solid tumors is dependent on the recruitment of mitogens and nutrients. As a function of nutrient levels, particularly essential amino acids, mTOR acts as a checkpoint for ribosome biogenesis and cell growth. Ribosome biogenesis has long been recognized in the clinics as a predictor of cancer progression; increase in size and number of nucleoli is known to be associated with the most aggressive tumors and a poor prognosis. In bacteria, ribosome biogenesis is independently regulated by amino acids and energy charge. The mTOR pathway is controlled by intracellular ATP levels, independent of amino acids, and mTOR itself is an ATP sensor (Kozma SC, etal, AACR02, Abs. 5628). – breast cancer
– pancreatic cancer
– multiple myeloma
– liver cancer
– brain cancer
– prostate cancer
– kidney cancer
– lymphoma
Signal transducer and activator of transcription 3 (STAT3)Stat-3 • acute-phase response factor (APRF) • FLJ20882 • HIESLocation: 17q21 Signal transducer and activator of transcription 3 (STAT3) is a member of the STAT protein family. STAT3, plays a critical role in hematopoiesis. STAT3 is located in the cytoplasm and translocated to the nucleus after tyrosine phosphorylation. In response to cytokines and growth and other activation factors, STAT family members are phosphorylated by the receptor associated kinases and then form homo- or heterodimers, which translocate to the cell nucleus where they act as transcription activators. – multiple myeloma
– hematologic malignancy
– lymphoma
Sonic hedgehog homolog (SHH)Shh • HHG1 • HHG-1 • holoprosencephaly 3 (HPE3) • HLP3 • SMMCILocation: 7q36 Sonic hedgehog, a secreted hedgehog ligand, is a human homolog of the Drosophila segment polarity gene hedgehog, cloned by investigators at Harvard University (Marigo V, etal, Genomics, 1 Jul 1995;28 (1):44-51).The mammalian sonic hedgehog (Shh) pathway controls proliferation of granule cell precursors in the cerebellum and is essential for normal embryonic development. Shh signaling is disrupted in a variety of malignancies. – pancreatic cancer
– CNS cancer

References:

1.         Gerlinger M, Rowan AJ, Horswell S, Larkin J, Endesfelder D, Gronroos E, Martinez P, Matthews N, Stewart A, Tarpey P et al: Intratumor heterogeneity and branched evolution revealed by multiregion sequencing. The New England journal of medicine 2012, 366(10):883-892.

2.         Merlo LM, Pepper JW, Reid BJ, Maley CC: Cancer as an evolutionary and ecological process. Nature reviews Cancer 2006, 6(12):924-935.

3.         Varela I, Tarpey P, Raine K, Huang D, Ong CK, Stephens P, Davies H, Jones D, Lin ML, Teague J et al: Exome sequencing identifies frequent mutation of the SWI/SNF complex gene PBRM1 in renal carcinoma. Nature 2011, 469(7331):539-542.

4.         Dalgliesh GL, Furge K, Greenman C, Chen L, Bignell G, Butler A, Davies H, Edkins S, Hardy C, Latimer C et al: Systematic sequencing of renal carcinoma reveals inactivation of histone modifying genes. Nature 2010, 463(7279):360-363.

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LEADERS in Genome Sequencing of Genetic Mutations for Therapeutic Drug Selection in Cancer Personalized Treatment: Part 2

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In Focus: Targeting of Cancer Stem Cells

Modulating Stem Cells with Unread Genome: microRNAs

What can we expect of tumor therapeutic response?

 

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