Enhanced sensitivity of PTEN-deficient tumors to inhibition of FRAP/mTOR

The fate of chemoresistance in triple negative breast cancer (TNBC)

BACKGROUND

Treatment options for women presenting with triple negative breast cancer (TNBC) are limited due to the lack of a therapeutic target and as a result, are managed with standard chemotherapy such as paclitaxel (Taxol®). Following chemotherapy, the ideal tumour response is apoptotic cell death. Post-chemotherapy, cells can maintain viability by undergoing viable cellular responses such as cellular senescence, generating secretomes which can directly enhance the malignant phenotype.

SCOPE OF REVIEW

How tumour cells retain viability in response to chemotherapeutic engagement is discussed. In addition we discuss the implications of this retained tumour cell viability in the context of the development of recurrent and metastatic TNBC disease. Current adjuvant and neo-adjuvant treatments available and the novel potential therapies that are being researched are also reviewed.

MAJOR CONCLUSIONS

Cellular senescence and cytoprotective autophagy are potential mechanisms of chemoresistance in TNBC. These two non-apoptotic outcomes in response to chemotherapy are inextricably linked and are neglected outcomes of investigation in the chemotherapeutic arena. Cellular fate assessments may therefore have the potential to predict TNBC patient outcome.

GENERAL SIGNIFICANCE

Focusing on the fact that cancer cells can bypass the desired cellular apoptotic response to chemotherapy through cellular senescence and cytoprotective autophagy will highlight the importance of targeting non-apoptotic survival pathways to enhance chemotherapeutic efficacy.

Targeting Glutamatergic Signaling and the PI3 Kinase Pathway to Halt Melanoma Progression

Our group has previously reported that the majority of human melanomas (> 60%) express the metabotropic glutamate receptor 1 (GRM1) and that the glutamate release inhibitor riluzole, a drug currently used to treat amyotrophic lateral sclerosis, can induce apoptosis in GRM1-expressing melanoma cells. Our group previously reported that in vitro riluzole treatment reduces cell growth in three-dimensional (3D) soft agar colony assays by 80% in cells with wildtype phosphoinositide 3-kinase (PI3K) pathway activation. However, melanoma cell lines harboring constitutive activating mutations of the PI3K pathway (PTEN and NRAS mutations) showed only a 35% to 40% decrease in colony formation in soft agar in the presence of riluzole. In this study, we have continued our preclinical studies of riluzole and its effect on melanoma cells alone and in combination with inhibitors of the PI3 kinase pathway: the AKT inhibitor, API-2, and the mammalian target of rapamycin (mTOR) inhibitor, rapamycin. We modeled these combinatorial therapies on various melanoma cell lines in 3D and 2D systems and in vivo. Riluzole combined with mTOR inhibition is more effective at halting melanoma anchorage-independent growth and xenograft tumor progression than either agent alone. PI3K signaling changes associated with this combinatorial treatment shows that 3D (nanoculture) modeling of cell signaling more closely resembles in vivo signaling than monolayer models. Riluzole combined with mTOR inhibition is effective at halting tumor cell progression independent of BRAF mutational status. This makes this combinatorial therapy a potentially viable alternative for metastatic melanoma patients who are BRAF WT and are therefore ineligible for vemurafenib therapy.

A Phase I/II Study of the mTOR Inhibitor Everolimus in Combination with HyperCVAD Chemotherapy in Patients with Relapsed/Refractory Acute Lymphoblastic Leukemia

PURPOSE

Previous studies suggest a potential therapeutic role for mTOR inhibition in lymphoid malignancies. This single-center phase I/II study was designed to test the safety and efficacy of the mTOR inhibitor everolimus in combination with HyperCVAD chemotherapy in relapsed/refractory acute lymphoblastic leukemia (ALL).

EXPERIMENTAL DESIGN

Twenty-four patients were treated; 15 received everolimus 5 mg/day and 9 received 10 mg/day with HyperCVAD.

RESULTS

The median age of patients was 25 years (range, 11-64) and median number of prior treatments was 2 (range, 1-7). Grade 3 mucositis was the dose-limiting toxicity and the maximum tolerated everolimus dose was 5 mg/day. Responses included complete remission (CR) in 6 patients (25%), CR without platelet recovery (CRp) in 1 (4%), and CR without recovery of counts (CRi) in 1 (4%), for an overall response rate of 33%. In addition, partial response (PR) was noted in 2 patients (8%). Seven of 11 patients treated in first salvage achieved CR/CRp (64%). The median OS was 29 weeks for patients in first salvage versus 15 weeks for patients in second salvage and beyond (P ≤ 0.001). A response was noted in 5 of 10 (50%) heavily pretreated T-ALL patients (median of 4 prior salvage regimens). Everolimus significantly inhibited phosphorylation of S6RP, but this did not correlate with response. No significant decreases in p4EBP1 and pAkt levels were noted. Responders had higher everolimus dose-adjusted area under the curve (P = 0.025) and lower clearance (P = 0.025) than nonresponders.

CONCLUSIONS

The combination of HyperCVAD and everolimus is well tolerated and moderately effective in relapsed ALL, specifically T-ALL.

Loss of Tuberous Sclerosis Complex 2 (TSC2) Is Frequent in Hepatocellular Carcinoma and Predicts Response to mTORC1 Inhibitor Everolimus

Hepatocellular carcinoma (HCC) is the third leading cause of cancer deaths worldwide and hyperactivation of mTOR signaling plays a pivotal role in HCC tumorigenesis. Tuberous sclerosis complex (TSC), a heterodimer of TSC1 and TSC2, functions as a negative regulator of mTOR signaling. In the current study, we discovered that TSC2 loss-of-function is common in HCC. TSC2 loss was found in 4 of 8 HCC cell lines and 8 of 28 (28.6%) patient-derived HCC xenografts. TSC2 mutations and deletions are likely to be the underlying cause of TSC2 loss in HCC cell lines, xenografts, and primary tumors for most cases. We further demonstrated that TSC2-null HCC cell lines and xenografts had elevated mTOR signaling and, more importantly, were significantly more sensitive to RAD001/everolimus, an mTORC1 inhibitor. These preclinical findings led to the analysis of TSC2 status in HCC samples collected in the EVOLVE-1 clinical trial of everolimus using an optimized immunohistochemistry assay and identified 15 of 139 (10.8%) samples with low to undetectable levels of TSC2. Although the sample size is too small for formal statistical analysis, TSC2-null/low tumor patients who received everolimus tended to have longer overall survival than those who received placebo. Finally, we performed an epidemiology survey of more than 239 Asian HCC tumors and found the frequency of TSC2 loss to be approximately 20% in Asian HBV(+) HCC. Taken together, our data strongly argue that TSC2 loss is a predictive biomarker for the response to everolimus in HCC patients.

Pleiotropic roles in cancer biology for multifaceted proteins FKBPs

BACKGROUND

FK506 binding proteins (FKBP) are multifunctional proteins highly conserved across the species and abundantly expressed in the cell. In addition to a well-established role in immunosuppression, FKBPs modulate several signal transduction pathways in the cell, due to their isomerase activity and the capability to interact with other proteins, inducing changes in conformation and function of protein partners. Increasing literature data support the concept that FKBPs control cancer related pathways.

SCOPE OF THE REVIEW

The aim of the present article is to review current knowledge on FKBPs roles in regulation of key signaling pathways associated with cancer.

MAJOR CONCLUSIONS

Some family members appear to promote disease while others are protective against tumorigenesis.

GENERAL SIGNIFICANCE

FKBPs family proteins are expected to provide new biomarkers and small molecular targets, in the near future, increasing diagnostic and therapeutic opportunities in the cancer field. This article is part of a Special Issue entitled Proline-Directed Foldases: Cell Signaling Catalysts and Drug Targets.

The PI3K/Akt/mTOR pathway in ovarian cancer: therapeutic opportunities and challenges

The phosphatidylinositol 3 kinase (PI3K) pathway is frequently altered in cancer, including ovarian cancer (OC). Unfortunately, despite a sound biological rationale and encouraging activity in preclinical models, trials of first-generation inhibitors of mammalian target of rapamycin (mTOR) in OC have demonstrated negative results. The lack of patient selection as well as resistance to selective mTOR complex-1 (mTORC1) inhibitors could explain the disappointing results thus far. Nonetheless, a number of novel agents are being investigated, including dual mTORC1/mTORC2, Akt, and PI3K inhibitors. Although it is likely that inhibition of the PI3K/Akt/mTOR pathway may have little effect in unselected OC patients, certain histological types, such as clear cell or endometrioid OC with frequent phosphatidylinositol-4,5-biphosphate 3-kinase, catalytic subunit alpha (PIK3CA) and/or phosphatase and tensin homolog (PTEN) alterations, may be particularly suited to this approach. Given the complexity and redundancy of the PI3K signaling network, PI3K pathway inhibition may be most useful in combination with either chemotherapy or other targeted therapies, such as MEK inhibitors, anti-angiogenic therapy, and hormonal therapy, in appropriately selected OC patients. Here, we discuss the relevance of the PI3K pathway in OC and provide an up-to-date review of clinical trials of novel PI3K inhibitors alone or in combination with cytotoxics and novel therapies in OC. In addition, the challenges of drug resistance and predictive biomarkers are addressed.

The PI3K/Akt/mTOR pathway in ovarian cancer: therapeutic opportunities and challenges

The phosphatidylinositol 3 kinase (PI3K) pathway is frequently altered in cancer, including ovarian cancer (OC). Unfortunately, despite a sound biological rationale and encouraging activity in preclinical models, trials of first-generation inhibitors of mammalian target of rapamycin (mTOR) in OC have demonstrated negative results. The lack of patient selection as well as resistance to selective mTOR complex-1 (mTORC1) inhibitors could explain the disappointing results thus far. Nonetheless, a number of novel agents are being investigated, including dual mTORC1/mTORC2, Akt, and PI3K inhibitors. Although it is likely that inhibition of the PI3K/Akt/mTOR pathway may have little effect in unselected OC patients, certain histological types, such as clear cell or endometrioid OC with frequent phosphatidylinositol-4,5-biphosphate 3-kinase, catalytic subunit alpha (PIK3CA) and/or phosphatase and tensin homolog (PTEN) alterations, may be particularly suited to this approach. Given the complexity and redundancy of the PI3K signaling network, PI3K pathway inhibition may be most useful in combination with either chemotherapy or other targeted therapies, such as MEK inhibitors, anti-angiogenic therapy, and hormonal therapy, in appropriately selected OC patients. Here, we discuss the relevance of the PI3K pathway in OC and provide an up-to-date review of clinical trials of novel PI3K inhibitors alone or in combination with cytotoxics and novel therapies in OC. In addition, the challenges of drug resistance and predictive biomarkers are addressed.

RNA-seq reveals aurora kinase-driven mTOR pathway activation in patients with sarcomatoid metastatic renal cell carcinoma

Sarcomatoid metastatic renal cell carcinoma (mRCC) is associated with a poor prognosis, and the biology of the disease has been inadequately characterized. RNA sequencing (RNA-seq) was performed on adjacent benign, clear cell, and sarcomatoid components from clinical specimens with sarcomatoid mRCC. M phase and cell-cycle pathways were enriched in sarcomatoid versus adjacent clear cell components, suggesting greater cell proliferation. The expression of aurora kinase A (AURKA) was increased as part of these pathways, and its increased expression was validated by quantitative PCR (qPCR). Immunohistochemical (IHC) analysis revealed that AURKA levels were increased in sarcomatoid tissue compared with their benign or clear cell parts. The increase in AURKA correlated with increased mTOR pathway activity, as evidenced by increased expression of phosphorylated mTOR (S2448) and ribosomal protein S6K (T389). When AURKA was stably expressed in a RCC cell line (Renca), it resulted in increased expression and activity of mTOR, suggesting that overexpression of AURKA can activate the mTOR pathway. These results warrant the analysis of a larger clinical cohort and suggest that targeting AURKA and/or mTOR in patients with sarcomatoid mRCC should be explored.

IMPLICATIONS

Comparative RNA-seq of adjacent sarcomatoid and clear cell histology of RCC indicates a proliferative phenotype and increased AURKA-dependent activation of mTOR signaling in sarcomatoid RCC, which could be targeted by available agents.

TEMHEAD: a single-arm multicentre phase II study of temsirolimus in platin- and cetuximab refractory recurrent and/or metastatic squamous cell carcinoma of the head and neck (SCCHN) of the German SCCHN Group (AIO)

BACKGROUND

Squamous cell carcinoma of the head and neck (SCCHN) is a common disease, which has a poor prognosis after failure of therapy. Activation of the PI3K-AKT-mTOR axis is commonly detected in recurrent or metastatic SCCHN, and provided the rationale for the clinical phase II trial in pretreated SCCHN.

PATIENTS AND METHODS

The primary end point was the progression-free survival rate (PFR) at 12 weeks. Forty eligible patients have been recruited after failure of platinum chemotherapy and cetuximab. A preplanned futility analysis was successfully passed after ≥1 success was detected in 20 patients. Secondary objectives consisted of progression-free survival (PFS), disease control rate (DCR), overall survival (OS), safety and tolerability, and predictive biomarkers for KRAS, BRAF, PIK3CA mutations, and HPV status. Archived tumor tissue was analyzed for DNA sequence.

RESULTS

A total of 40 patients were eligible. The PFR at 12 weeks was 40% (95% CI 25.0-54.6). The median PFS and OS were 56 days (95% CI 36-113 days) and 152 days (76-256 days), respectively. In 33 assessable patients, disease stabilization occurred in 57.6%, with tumor shrinkage in 13 patients (39.4%). Overall, the treatment was well tolerated. Fatigue (47.5%), anemia (25.0%), nausea (20.0%), and pneumonia (20.0%) were the most common adverse events. Neither PIK3CA mutations, nor HPV status were predictive for success with temsirolimus treatment. No mutations were found for KRAS or BRAF.

CONCLUSION

Tumor shrinkage and efficacy parameter indicate that inhibition of the PI3K-AKT-mTOR axis was a putative novel treatment paradigm for SCCHN. We could not identify parameters predictive for treatment success of temsirolimus, which underscores the need for refinement of the molecular analysis in future studies.

CLINICAL TRIALS NUMBER

NCT01172769.

Why should cancer biologists care about tRNAs? tRNA synthesis, mRNA translation and the control of growth

Transfer RNAs (tRNAs) are essential for mRNA translation. They are transcribed in the nucleus by RNA polymerase III and undergo many modifications before contributing to cytoplasmic protein synthesis. In this review I highlight our understanding of how tRNA biology may be linked to the regulation of mRNA translation, growth and tumorigenesis. First, I review how oncogenes and tumour suppressor signalling pathways, such as the PI3 kinase/TORC1, Ras/ERK, Myc, p53 and Rb pathways, regulate Pol III and tRNA synthesis. In several cases, this regulation contributes to cell, tissue and body growth, and has implications for our understanding of tumorigenesis. Second, I highlight some recent work, particularly in model organisms such as yeast and Drosophila, that shows how alterations in tRNA synthesis may be not only necessary, but also sufficient to drive changes in mRNA translation and growth. These effects may arise due to both absolute increases in total tRNA levels, but also changes in the relative levels of tRNAs in the overall pool. Finally, I review some recent studies that have revealed how tRNA modifications (amino acid acylation, base modifications, subcellular shuttling, and cleavage) can be regulated by growth and stress cues to selectively influence mRNA translation. Together these studies emphasize the importance of the regulation of tRNA synthesis and modification as critical control points in protein synthesis and growth. This article is part of a Special Issue entitled: Translation and Cancer.

Building high-resolution synthetic lethal networks: a 'Google map' of the cancer cell

The most commonly used therapies for cancer involve delivering high doses of radiation or toxic chemicals to the patient that also cause substantial damage to normal tissue. To overcome this, researchers have recently resorted to a basic biological concept called 'synthetic lethality' (SL) that takes advantage of interactions between gene pairs. The identification of SL interactions is of considerable therapeutic interest because if a particular gene is SL with a tumor-causing mutation, then the targeting that gene carries therapeutic advantages. Mapping these interactions in the context of human cancer cells could hold the key to effective, targeted cancer treatments. In this review, we cover the recent advances that aim to identify these SL interactions using unbiased genetic screens.

Switch in signaling control of mTORC1 activity after oncoprotein expression in thyroid cancer cell lines

CONTEXT

Thyroid growth is regulated by TSH and requires mammalian target of rapamycin (mTOR). Thyroid cancers frequently exhibit mutations in MAPK and/or phosphoinositol-3-kinase-related kinase effectors.

OBJECTIVE

The objective of the study was to explore the contribution of RET/PTC, RAS, and BRAF to mTOR regulation and response to mTOR inhibitors.

METHODS

PCCL3 cells conditionally expressing RET/PTC3, HRAS(G12V), or BRAF(V600E) and human thyroid cancer cells harboring mutations of these genes were used to test pathways controlling mTOR and its requirement for growth.

RESULTS

TSH/cAMP-induced growth of PCCL3 cells requires mTOR, which is stimulated via protein kinase A in a MAPK kinase (MEK)- and AKT-independent manner. Expression of RET/PTC3, HRAS(G12V), or BRAF(V600E) in PCCL3 cells induces mTOR but does not entirely abrogate the cAMP-mediated control of its activity. Acute oncoprotein-induced mTOR activity is regulated by MEK and AKT, albeit to differing degrees. By contrast, mTOR was not activated by TSH/cAMP in human thyroid cancer cells. Tumor genotype did not predict the effects of rapamycin or the mTOR kinase inhibitor AZD8055 on growth, with the exception of a PTEN-null cell line. Selective blockade of MEK did not influence mTOR activity of BRAF or RAS mutant cells. Combined MEK and mTOR kinase inhibition was synergistic on growth of BRAF- and RAS-mutant thyroid cancer cells in vitro and in vivo.

CONCLUSION

Thyroid cancer cells lose TSH/cAMP dependency of mTOR signaling and cell growth. mTOR activity is not decreased by the MEK or AKT inhibitors in the RAS or BRAF human thyroid cancer cell lines. This may account for the augmented effects of combining the mTOR inhibitors with selective antagonists of these oncogenic drivers.

Phase II study of temozolomide (TMZ) and everolimus (RAD001) therapy for metastatic melanoma: a North Central Cancer Treatment Group study, N0675

OBJECTIVE

Mammalian target of rapamycin (mTOR) pathway is activated in malignant melanoma and in situ lesions as opposed to benign nevi. Inhibition of PI3K-Akt-mTOR signaling is implicated in sensitization of melanoma cells to alkylating agents (temozolomide [TMZ]) and inhibition of tumor angiogenesis.

METHODS

We conducted a single-arm phase II multi-institution cooperative group study to assess the antitumor activity and safety profile of the combination of TMZ and the rapamycin derivative everolimus in patients with metastatic unresectable malignant melanoma. Patients received 10 mg/d of RAD001 for 5 of 7 days (ie, 50 mg/wk) and 200 mg/m/d of TMZ for 5 days each cycle.

RESULTS

Of the first 39 eligible patients, 17 were PFS-9 successes, for a predetermined threshold of 18/39 patients for a positive trial. Overall, 21 of 48 patients were progression free at 9 weeks, for an event-free survival rate of 44% (95% confidence interval, 29%-59%). The median progression-free survival was 2.4 months and the median overall survival was 8.6 months. Four patients achieved a partial response; the median duration of response was 15.1 months. No complete remissions were observed. Treatment was in general well tolerated with only 1 patient discontinuing therapy due to toxicity (hyperlipidemia).

CONCLUSIONS

The combination of TMZ and RAD001 was well tolerated but failed to meet/exceed our study threshold for promising clinical activity in patients with metastatic melanoma.

NOTCH1 activation in breast cancer confers sensitivity to inhibition of SUMOylation

Breast cancer is genetically heterogeneous, and recent studies have underlined a prominent contribution of epigenetics to the development of this disease. To uncover new synthetic lethalities with known breast cancer oncogenes, we screened an epigenome-focused short hairpin RNA library on a panel of engineered breast epithelial cell lines. Here we report a selective interaction between the NOTCH1 signaling pathway and the SUMOylation cascade. Knockdown of the E2-conjugating enzyme UBC9 (UBE2I) as well as inhibition of the E1-activating complex SAE1/UBA2 using ginkgolic acid impairs the growth of NOTCH1-activated breast epithelial cells. We show that upon inhibition of SUMOylation NOTCH1-activated cells proceed slower through the cell cycle and ultimately enter apoptosis. Mechanistically, activation of NOTCH1 signaling depletes the pool of unconjugated small ubiquitin-like modifier 1 (SUMO1) and SUMO2/3 leading to increased sensitivity to perturbation of the SUMOylation cascade. Depletion of unconjugated SUMO correlates with sensitivity to inhibition of SUMOylation also in patient-derived breast cancer cell lines with constitutive NOTCH pathway activation. Our investigation suggests that SUMOylation cascade inhibitors should be further explored as targeted treatment for NOTCH-driven breast cancer.

Susceptibility of PTEN-positive metastatic tumors to small interfering RNA targeting the mammalian target of rapamycin

PTEN-positive tumors are not susceptible to the treatment with rapamycin, an inhibitor of the mammalian target of rapamycin (mTOR). Here, we determined the susceptibility of PTEN-positive cells to small interfering RNA for mTOR (si-mTOR) by using a novel liposomal delivery system. We prepared dicetyl phosphate-tetraethylenepentamine-based polycation liposomes (TEPA-PCL) decorated with polyethylene glycol (PEG) grafting Ala-Pro-Arg-Pro-Gly (APRPG), a VRGFR-1-targeting peptide. APRPG-PEG-decorated TEPA-PCL carrying si-mTOR (APRPG-TEPA-PCL/si-mTOR) had an antiproliferative effect against B16F10 murine melanoma cells (PTEN-positive) and significantly inhibited both the proliferation and tube formation of mouse 2H-11 endothelial-like cells (PTEN-positive). APRPG-TEPA-PCL/si-mTOR treatment did not induce Akt phosphorylation (Ser473) in either B16F10 or 2H-11 cells although there was strong phosphorylation of Akt in response to rapamycin treatment. Intravenous injection of APRPG-TEPA-PCL/si-mTOR significantly suppressed the tumor growth compared with rapamycin treatment in mice bearing B16F10 melanoma. These findings suggest that APRPG-TEPA-PCL/si-mTOR is useful for the treatment of PTEN-positive tumors.

p70 Ribosomal protein S6 kinase (Rps6kb1): an update

The Rps6kb1 gene encodes the 70 kDa ribosomal protein S6 kinase (p70S6K), which is a serine/threonine kinase regulated by phosphoinositide 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) pathway. p70S6K plays a crucial role in controlling cell cycle, growth and survival. The PI3K/mTOR signalling pathway is one of the major mechanisms for controlling cell survival, proliferation and metabolism and is the central regulator of translation of some components of protein synthesis system. Upon activation, this kinase phosphorylates S6 protein of ribosomal subunit 40S resulting in selective translation of unique family of mRNAs that contain oligopyrimidine tract on 5' transcriptional site (5'TOP). 5'TOP mRNAs are coding the components of translational apparatus including ribosomal proteins and elongation factors. Due to the role of p70S6K in protein synthesis and also its involvement in a variety of human diseases ranging from diabetes and obesity to cancer, p70S6K is now being considered as a new therapeutic target for drug development. Furthermore, p70S6K acts as a biomarker for response to immunosuppressant as well as anticancer effects of inhibitors of the mTOR. Because of the narrow therapeutic index of mTOR inhibitors, drug monitoring is essential, and this is usually done by measuring blood drug levels, therapeutic response and drug-induced adverse effects. Recent studies have suggested that plasma p70S6K is a reliable index for the monitoring of patient response to mTOR inhibitors. Therefore, a better understanding of p70S6K and its role in various pathological conditions could enable the development of strategies to aid diagnosis, prognosis and treatment schedules.

PI3K/Akt-mediated regulation of p53 in cancer

Mutations activating the PI3K (phosphoinositide 3-kinase)/Akt signalling pathway and inactivating the TP53 tumour-suppressor gene are common mechanisms that cancer cells require to proliferate and escape pre-programmed cell death. In a well-described mechanism, Akt mediates negative control of p53 levels through enhancing MDM2 (murine double minute 2)-mediated targeting of p53 for degradation. Accumulating evidence is beginning to suggest that, in certain circumstances, PTEN (phosphatase and tensin homologue deleted on chromosome 10)/PI3K/Akt also promotes p53 translation and protein stability, suggesting that additional mechanisms may be involved in the Akt-mediated regulation of p53 in tumours. In the present article, we discuss these aspects in the light of clinical PI3K/Akt inhibitors, where information regarding the effect on p53 activity will be a crucial factor that will undoubtedly influence therapeutic efficacy.

Interaction of TIF-90 and filamin A in the regulation of rRNA synthesis in leukemic cells

Akt/FLNA/TIF-90 signaling regulates rRNA synthesis in acute myelogenous leukemia cells. Direct targeting of Akt has potential therapeutic applications in acute myelogenous leukemia treatment.

The discovery of potent ribosomal S6 kinase inhibitors by high-throughput screening and structure-guided drug design

The ribosomal P70 S6 kinases play a crucial role in PI3K/mTOR regulated signalling pathways and are therefore potential targets for the treatment of a variety of diseases including diabetes and cancer. In this study we describe the identification of three series of chemically distinct S6K1 inhibitors. In addition, we report a novel PKA-S6K1 chimeric protein with five mutations in or near its ATP-binding site, which was used to determine the binding mode of two of the three inhibitor series, and provided a robust system to aid the optimisation of the oxadiazole-substituted benzimidazole inhibitor series. We show that the resulting oxadiazole-substituted aza-benzimidazole is a potent and ligand efficient S6 kinase inhibitor, which blocks the phosphorylation of RPS6 at Ser235/236 in TSC negative HCV29 human bladder cancer cells by inhibiting S6 kinase activity and thus provides a useful tool compound to investigate the function of S6 kinases.

Targeting the genetic alterations of the PI3K-AKT-mTOR pathway: its potential use in the treatment of bladder cancers

Urothelial carcinoma of the bladder is the most frequent tumor of the urinary tract and represents the fifth cause of death by cancer worldwide. The current first line chemotherapy is a combination of cisplatin and gemcitabine with median survival not exceeding 15months. Vinflunine is the only drug approved by EMEA as second-line treatment and few progresses have been made for the past 20years to increase the survival of metastatic patients, especially those who are not eligible for cisplatin-based regimen. The recent studies characterizing the genetic background of urothelial cancers of the bladder, revealed chromosomal alterations that are not seen at the same level in other types of cancers. This is especially the case for mutations of genes involved in the PI3K/AKT/mTOR signaling pathway that occupies a major place in the etiology of these tumors. Here, we describe the mutations leading to constitutive activation of the PI3K/AKT/mTOR pathway and discuss the potential use of the different classes of PI3K/AKT/mTOR inhibitors in the treatment of urothelial bladder cancers. Despite the recent pivotal study evidencing specific mutations of TSC1 in bladder cancer patients responding to everolimus and the encouraging results obtained with other derivatives than rapalogs, few clinical trials are ongoing in bladder cancers. Because of the genetic complexity of these tumors, the cross-talks of the PI3K/AKT/mTOR pathway with other pathways, and the small number of eligible patients, it will be of utmost importance to carefully choose the drugs or drug combinations to be further tested in the clinic.

Pathologic scoring of PTEN immunohistochemistry in endometrial carcinoma is highly reproducible

Endometrial carcinomas show frequent PTEN-PI3K pathway abnormalities, and there are currently multiple trials focused on PI3K pathway inhibitors in patients with endometrial carcinoma. PTEN immunohistochemistry may help to select patients with potential for response to targeted therapy, making it important to develop and validate this stain in formalin-fixed, paraffin-embedded tissue. Immunohistochemistry for PTEN was performed and scored independently on 118 cases of endometrial carcinomas from 2 cancer centers using monoclonal DAKO 6H2.1 antibody. Cases were scored as positive, negative, or heterogeneous; reproducibility of PTEN staining and interpretation was assessed. Overall interobserver agreement was good (weighted κ=0.80), with 82% concordance, similar for nonendometrioid (81%) and endometrioid carcinomas (85%). Twenty-one of 118 cases showed discrepant results (17%) that resulted from differences in interpretation and not staining. Our study shows that evaluation of PTEN loss by immunohistochemistry is highly reproducible with the application of standard immunohistochemical techniques and simple scoring criteria.

Tailoring mTOR-based therapy: molecular evidence and clinical challenges

The mTOR signaling pathway integrates inputs from a variety of upstream stimuli to regulate diverse cellular processes including proliferation, growth, survival, motility, autophagy, protein synthesis and metabolism. The mTOR pathway is dysregulated in a number of human pathologies including cancer, diabetes, obesity, autoimmune disorders, neurological disease and aging. Ongoing clinical trials testing mTOR-targeted treatments number in the hundreds and underscore its therapeutic potential. To date mTOR inhibitors are clinically approved to prevent organ rejection, to inhibit restenosis after angioplasty, and to treat several advanced cancers. In this review we discuss the continuously evolving field of mTOR pharmacogenomics, as well as highlight the emerging efforts in identifying diagnostic and prognostic markers, including miRNAs, in order to assess successful therapeutic responses.

Emerging strategies to overcome the resistance to current mTOR inhibitors in renal cell carcinoma

The mammalian target of rapamycin (mTOR) has emerged as an attractive cancer therapeutic target. Treatment of metastatic renal cell carcinoma (mRCC) has improved significantly with the advent of agents targeting the mTOR pathway, such as temsirolimus and everolimus. Unfortunately, a number of potential mechanisms that may lead to resistance to mTOR inhibitors have been proposed. In this paper, we discuss the mechanisms underlying resistance to mTOR inhibitors, which include the downstream effectors of the phosphoinositide 3-kinase (PI3K)/AKT/mTOR pathway, the activation of hypoxia-inducible factor (HIF), the PIM kinase family, PTEN expression, elevated superoxide levels, stimulation of autophagy, immune cell response and ERK/MAPK, Notch and Aurora signaling pathways. Moreover, we present an updated analysis of clinical trials available on PubMed Central and www.clinicaltrials.gov, which were pertinent to the resistance to rapalogs. The new frontier of inhibiting the mTOR pathway is to identify agents targeting the feedback loops and cross talks with other pathways involved in the acquired resistance to mTOR inhibitors. The true goal will be to identify biomarkers predictive of sensitivity or resistance to efficiently develop novel agents with the aim to avoid toxicities and to better choose the active drug for the right patient.

Targeted therapy for sarcomas

Sarcomas are tumors of mesenchymal origin that make up approximately 1% of human cancers. They may arise as primary tumors in either bone or soft tissue, with approximately 11,280 soft tissue tumors and 2,650 bone tumors diagnosed each year in the United States. There are at least 50 different subtypes of soft tissue sarcoma, with new ones described with ever-increasing frequency. One way to look at sarcomas is to divide them into categories on the basis of their genetic make-up. One group of sarcomas has an identifiable, relatively simple genetic signature, such as the X:18 translocation seen in synovial sarcoma or the 11:22 translocation seen in Ewing's sarcoma. These specific abnormalities often lead to the presence of fusion proteins, such as EWS-FLI1 in Ewing's sarcoma, which are helpful as diagnostic tools and may become therapeutic targets in the future. Another group of sarcomas is characterized by complex genetic abnormalities as seen in leiomyosarcoma, osteosarcoma, and undifferentiated sarcoma. It is important to keep these distinctions in mind when contemplating the development of targeted agents for sarcomas. Different abnormalities in sarcoma could be divided by tumor subtype or by the molecular or pathway abnormality. However, some existing drugs or drugs in development may interfere with or alter more than one of the presented pathways.

Torin1-mediated TOR kinase inhibition reduces Wee1 levels and advances mitotic commitment in fission yeast and HeLa cells

The target of rapamycin (TOR) kinase regulates cell growth and division. Rapamycin only inhibits a subset of TOR activities. Here we show that in contrast to the mild impact of rapamycin on cell division, blocking the catalytic site of TOR with the Torin1 inhibitor completely arrests growth without cell death in Schizosaccharomyces pombe. A mutation of the Tor2 glycine residue (G2040D) that lies adjacent to the key Torin-interacting tryptophan provides Torin1 resistance, confirming the specificity of Torin1 for TOR. Using this mutation, we show that Torin1 advanced mitotic onset before inducing growth arrest. In contrast to TOR inhibition with rapamycin, regulation by either Wee1 or Cdc25 was sufficient for this Torin1-induced advanced mitosis. Torin1 promoted a Polo and Cdr2 kinase-controlled drop in Wee1 levels. Experiments in human cell lines recapitulated these yeast observations: mammalian TOR (mTOR) was inhibited by Torin1, Wee1 levels declined and mitotic commitment was advanced in HeLa cells. Thus, the regulation of the mitotic inhibitor Wee1 by TOR signalling is a conserved mechanism that helps to couple cell cycle and growth controls.

The relationship between mTOR signalling pathway and recombinant antibody productivity in CHO cell lines

Background

High recombinant protein productivity in mammalian cell lines is often associated with phenotypic changes in protein content, energy metabolism, and cell growth, but the key determinants that regulate productivity are still not clearly understood. The mammalian target of rapamycin (mTOR) signalling pathway has emerged as a central regulator for many cellular processes including cell growth, apoptosis, metabolism, and protein synthesis. This role of this pathway changes in response to diverse environmental cues and allows the upstream proteins that respond directly to extracellular signals (such as nutrient availability, energy status, and physical stresses) to communicate with downstream effectors which, in turn, regulate various essential cellular processes.

Results

In this study, we have performed a transcriptomic analysis using a pathway-focused polymerase chain reaction (PCR) array to compare the expression of 84 target genes related to the mTOR signalling in two recombinant CHO cell lines with a 17.4-fold difference in specific monoclonal antibody productivity (q_p). Eight differentially expressed genes that exhibited more than a 1.5-fold change were identified. Pik3cd (encoding the Class 1A catalytic subunit of phosphatidylinositol 3-kinase [PI3K]) was the most differentially expressed gene having a 71.3-fold higher level of expression in the high producer cell line than in the low producer. The difference in the gene’s transcription levels was confirmed at the protein level by examining expression of p110δ.

Conclusion

Expression of p110δ correlated with specific productivity (q_p) across six different CHO cell lines, with a range of expression levels from 3 to 51 pg/cell/day, suggesting that p110δ may be a key factor in regulating productivity in recombinant cell lines.

Repositioning metformin in cancer: genetics, drug targets, and new ways of delivery

After sitting many years on the shelves of drug stores as a harmless antidiabetic drug, metformin comes back in the spotlight of the scientific community as a surprisingly effective antineoplastic drug. Metformin targets multiple pathways that play pivotal roles in cancer progression, impacting various cellular processes, such as proliferation, cell death, metabolism, and even the cancer stemness features. The biomolecular characteristics of tumors, such as appropriate expression of organic cation transporters or genetic alterations including p53, K-ras, LKB1, and PI3K may impact metformin's anticancer efficiency. This could indicate a need for tumor genetic profiling in order to identify patients most likely to benefit from metformin treatment. Considering that the majority of experimental models suggest that higher, supra-clinical doses of metformin should be used in order to obtain an antineoplastic effect, new ways of drug delivery could be developed, such as metformin-loaded nanoparticles or incorporation of metformin into microparticles used in transarterial chemoembolization, with the aim of obtaining higher intratumoral drug concentrations and a targeted therapy which will ultimately maximize metformin's efficacy.

New treatment strategies for malignant gliomas

Malignant gliomas are the most prevalent type of primary brain tumor in adults. Despite progress in brain tumor therapy, the prognosis of malignant glioma patients remains dismal. The median survival of patients with glioblastoma multiforme, the most common grade of malignant glioma, is 10-12 months. Conventional therapy of surgery, radiation and chemotherapy is largely palliative. Essentially, tumor recurrence is inevitable. Salvage treatments upon recurrence are palliative at best and rarely provide significant survival benefit. Therapies targeting the underlying molecular pathogenesis of brain tumors are urgently required. Common genetic abnormalities in malignant glioma specimens are associated with aberrant activation or suppression of cellular signal transduction pathways and resistance to radiation and chemotherapy. Several low molecular weight signal transduction inhibitors have been examined in preclinical and clinical malignant glioma trials. The efficacy of these agents as monotherapies has been modest, at best; however, small subsets of patients who harbor specific genetic changes in their tumors may display favorable clinical responses to defined small molecule inhibitors. Multitargeted kinase inhibitors or combinations of agents targeting different mitogenic pathways may overcome the resistance of tumors to single-agent targeted therapies. Well designed studies of small molecule kinase inhibitors will include assessment of safety, drug delivery, target inhibition and correlative biomarkers to define mechanisms of response or resistance to these agents. Predictive biomarkers will enrich for patients most likely to respond in future clinical trials. Additional clinical studies will combine novel targeted therapies with radiation, chemotherapies and immunotherapies.

Novel therapies for patients with chronic myeloid leukemia

The most immediate issues that will have a major impact on the long-term survival of patients with chronic myeloid leukemia is the optimal use of imatinib mesylate (Gleevec, Novartis) and the development of effective therapies for those patients who are intolerant of, or become resistant to, optimal doses of this agent. Of the multiple new agents that are currently being developed for patients with chronic myeloid leukemia, most are being investigated in patients who have developed resistance to imatinib, which is a confounding factor in itself. The mechanisms of action of novel agents are diverse and they may have a variably synergistic therapeutic relationship with imatinib. The complete blockade of the intracellular pathways that are triggered by Bcr-Abl, combined with successful reversal of apoptotic and/or angiogenic abnormalities in chronic myeloid leukemia, may well lead to a cure for the majority of patients.

Temsirolimus

Temsirolimus, an ester of sirolimus (rapamycin), selectively inhibits the kinase mammalian target of rapamycin (mTOR) and consequently blocks the translation of cell cycle regulatory proteins and prevents overexpression of angiogenic growth factors. It has been found to have antitumour activity in patients with relapsed or refractory mantle cell lymphoma (MCL). In addition, patients with advanced renal cell carcinoma (RCC) and a poor prognosis who received a once-weekly intravenous (IV) infusion of temsirolimus 25 mg experienced significant survival benefits compared with patients receiving standard interferon-α (IFN-α) therapy in a large phase III clinical study. In this study, median overall survival was 10.9 versus 7.3 months and objective response rates were 8.6% in temsirolimus recipients versus 4.8% IFN-α recipient group. Temsirolimus monotherapy recipients experienced significantly fewer grade 3 or 4 adverse events and had fewer withdrawals for adverse events than patients receiving IFN-α. The role of temsirolimus in sequential and combination therapy is yet to be found.

A genetic mouse model of invasive endometrial cancer driven by concurrent loss of Pten and Lkb1 Is highly responsive to mTOR inhibition

Signals from the tumor suppressors PTEN and LKB1 converge on mTOR to negatively regulate its function in cancer cells. Notably, both of these suppressors are attenuated in a significant fraction of human endometrial tumors. In this study, we generated a genetic mouse model of endometrial cancer driven by concomitant loss of these suppressors to gain pathophysiological insight into this disease. Dual loss of Pten and Lkb1 in the endometrial epithelium led to rapid development of advanced endometrioid endometrial tumors with 100% penetrance and short host survival. The tumors displayed dysregulated phosphatidylinositol 3-kinase (PI3K)/Akt and Lkb1/Ampk signaling with hyperactivation of mTOR signaling. Treatment with a dual PI3K/mTOR inhibitor, BEZ235, extended the time before tumor onset and prolonged overall survival. The PI3K inhibitor GDC-0941 used as a single agent reduced the growth rate of primary tumor implants in Pten/Lkb1-deficient mice, and the mTOR inhibitor RAD001 was unexpectedly as effective as BEZ235 in triggering tumor regression. In parallel, we also found that ectopic expression of LKB1 in PTEN/LKB1-deficient human endometrial cancer cells increased their sensitivity to PI3K inhibition. Together, our results demonstrated that Pten/Lkb1-deficient endometrial tumors rely strongly on deregulated mTOR signaling, and they provided evidence that LKB1 status may modulate the response of PTEN-deficient tumors to PI3K or mTOR inhibitors.

When overgrowth bumps into cancer: the PTEN-opathies

PTEN is a dual-specificity phosphatase and well-known tumor suppressor gene. When functioning properly, it works in its canonical pathway to inhibit AKT/mTOR and MAPK signaling, leading to cell death and growth regulation. PTEN mutations cause dysregulation of these pathways, resulting in cellular proliferation and overgrowth. When germline mutations are present as in patients with PTEN Hamartoma Tumor Syndrome (PHTS), benign and malignant neoplasias occur as well as cerebral overgrowth and neurodevelopmental abnormalities. This review article will summarize recent laboratory and clinical investigations relating to PTEN, highlighting the overgrowth aspects of this syndrome and the molecular drivers behind these key phenotypes. Finally, therapies developed targeted the PI3K/AKT/mTOR pathway for other tumor predisposition syndromes will be discussed.

Genomic Rearrangements of PTEN in Prostate Cancer

The phosphatase and tensin homolog gene (PTEN) on chromosome 10q23.3 is a negative regulator of the PIK3/Akt survival pathway and is the most frequently deleted tumor suppressor gene in prostate cancer. Monoallelic loss of PTEN is present in up to 60% of localized prostate cancers and complete loss of PTEN in prostate cancer is linked to metastasis and androgen-independent progression. Studies on the genomic status of PTEN in prostate cancer initially used a two-color fluorescence in situ hybridization (FISH) assay for PTEN copy number detection in formalin fixed paraffin embedded tissue preparations. More recently, a four-color FISH assay containing two additional control probes flanking the PTEN locus with a lower false-positive rate was reported. Combined with the detection of other critical genomic biomarkers for prostate cancer such as ERG, androgen receptor, and MYC, the evaluation of PTEN genomic status has proven to be invaluable for patient stratification and management. Although less frequent than allelic deletions, point mutations in the gene and epigenetic silencing are also known to contribute to loss of PTEN function, and ultimately to prostate cancer initiation. Overall, it is clear that PTEN is a powerful biomarker for prostate cancer. Used as a companion diagnostic for emerging therapeutic drugs, FISH analysis of PTEN is promisingly moving human prostate cancer closer to more effective cancer management and therapies.

PTEN deletions are related to disease progression and unfavourable prognosis in early bladder cancer

AIMS

This study aimed to determine the prevalence and clinical significance of deletions of the tumour suppressor gene PTEN in bladder cancer.

METHODS AND RESULTS

A tissue microarray with 686 bladder cancers was analysed for PTEN deletions by fluorescence in-situ hybridization. PTEN mutations were analysed in nine tumours with heterozygous PTEN deletion. Heterozygous PTEN deletions were present in 16.5% of tumours and were associated with grade (P = 0.0024) and p53 status (P = 0.0141), but not linked to stage (P = 0.0965). PTEN deletions were seen in 5.8% of pTaG1, 10.9% of pTaG2, 29.0% of pTaG3, 16.7% of pT1G2, 22.2% of pT1G3, 17.7% of pT2-4G2 and 20.9% of pT2-4G3 tumours (P = 0.0235). PTEN deletions were associated significantly with recurrences in pTa tumours (P = 0.0173), progression in pT1 tumours (P = 0.0016), but not with overall or cancer-specific survival in pT2 tumours. Multivariate analyses including grade and PTEN deletions revealed that PTEN deletions but not grade were associated independently with recurrence in pTa tumours (P = 0.0377) and progression in pT1 tumours (P = 0.0030). No inactivating PTEN mutations were found.

CONCLUSIONS

PTEN is linked to aggressive tumour phenotype and to unfavourable outcome in early bladder cancer. Heterozygous PTEN loss, i.e. reduced PTEN gene dosage, might be sufficient to cause aggressive tumour behaviour in bladder cancer cells.

PTEN deficiency is associated with reduced sensitivity to mTOR inhibitor in human bladder cancer through the unhampered feedback loop driving PI3K/Akt activation

Background:

Preclinical studies have shown that PTEN loss enhances sensitivity to mammalian target of Rapamycin (mTOR) inhibitors because of facilitated PI3K (phosphatidylinositol-3 kinase)/Akt activation and consecutive stimulation of the mTOR pathway. In patients with advanced transitional cell carcinoma (TCC) treated with the mTOR inhibitor everolimus, PTEN loss was, however, associated with resistance to treatment.

Methods:

Transitional cell carcinoma specimens, human bladder cancer cells and derived mouse xenografts were used to evaluate how the PTEN status influences the activity of mTOR inhibitors.

Results:

Transitional cell carcinoma patients with a shorter progression-free survival under everolimus exhibited PTEN deficiency and increased Akt activation. Moreover, PTEN-deficient bladder cancer cells were less sensitive to rapamycin than cells expressing wild-type PTEN, and rapamycin strikingly induced Akt activation in the absence of functional PTEN. Inhibition of Akt activation by the PI3K inhibitor wortmannin interrupted this rapamycin-induced feedback loop, thereby enhancing the antiproliferative effects of the mTOR inhibitor both in vitro and in vivo.

Conclusion:

Facilitation of Akt activation upon PTEN loss can have a more prominent role in driving the feedback loop in response to mTOR inhibition than in promoting the mTOR pathway. These data support the use of both PI3K and mTOR inhibitors to treat urothelial carcinoma, in particular in the absence of functional PTEN.

An isogenic cell panel identifies compounds that inhibit proliferation of mTOR-pathway addicted cells by different mechanisms

The mTOR pathway is a critical integrator of nutrient and growth factor signaling. Once activated, mTOR promotes cell growth and proliferation. Several components of the mTOR pathway are frequently deregulated in tumors, leading to constitutive activation of the pathway and thus contribute to uncontrolled cell growth. We performed a high-throughput screen with an isogenic cell line system to identify compounds specifically inhibiting proliferation of PTEN/mTOR-pathway addicted cells. We show here the characterization and mode of action of two such compound classes. One compound class inhibits components of the PTEN/mTOR signaling pathway, such as S6 ribosomal protein phosphorylation, and leads to cyclin D3 downregulation. These compounds are not adenosine triphosphate competitive inhibitors for kinases in the pathway, nor do they require FKBP12 for activity like rapamycin. The other compound class turned out to be a farnesylation inhibitor, blocking the activity of GTPases, as well as an inducer of oxidative stress. Our results demonstrate that an isogenic cell system with few specific mutations in oncogenes and tumor suppressor genes can identify different classes of compounds selectively inhibiting proliferation of PTEN/mTOR pathway-addicted isogenic clones. The identified mechanisms are in line with the known cellular signaling networks activated by the altered oncogenes and suppressor genes in the isogenic system.

Targets, structures, and recent approaches in malignant melanoma chemotherapy

Malignant metastatic melanoma is one of the oncologic diseases with the worst clinical prognosis, due primarily to resistance phenomena against chemotherapeutic agents in current use. However, over the last few years, characterization of the molecular mechanisms involved in the development and progression of the disease has contributed to elucidation of the main pathways by which tissue invasion and metastasis can occur. More importantly, the identification of abnormalities in signaling cascades in melanoma cells has facilitated new therapeutic approaches against malignant melanoma through the design of highly potent and selective drugs with low associated toxicity. Ultimately, recognition of the restricted applicability of new chemotherapies in certain genetic contexts has led to significant improvements in the results of clinical trials, anticipating the existing need for investment in personalized therapies, and taking into account the molecular alterations observed in tumors. Although significant advances have been made in terms of extending the median overall survival rate and improving the quality of life for patients, the mechanisms that compromise in vivo drug efficacy remain poorly understood, particularly those concerning therapeutic resistance phenomena. This review summarizes recently validated targets from the perspective of the medicinal chemistry carried out in the design of the most promising structures.

TORC1 signaling is governed by two negative regulators in fission yeast

The target of rapamycin (TOR) is a highly conserved protein kinase that regulates cell growth and metabolism. Here we performed a genome-wide screen to identify negative regulators of TOR complex 1 (TORC1) in Schizosaccharomyces pombe by isolating mutants that phenocopy Δtsc2, in which TORC1 signaling is known to be up-regulated. We discovered that Δnpr2 displayed similar phenotypes to Δtsc2 in terms of amino acid uptake defects and mislocalization of the Cat1 permease. However, Δnpr2 and Δtsc2 clearly showed different phenotypes in terms of rapamycin supersensitivity and Isp5 transcription upon various treatments. Furthermore, we showed that Tor2 controls amino acid homeostasis at the transcriptional and post-transcriptional levels. Our data reveal that both Npr2 and Tsc2 negatively regulate TORC1 signaling, and Npr2, but not Tsc2, may be involved in the feedback loop of a nutrient-sensing pathway.

Marchantin M: a novel inhibitor of proteasome induces autophagic cell death in prostate cancer cells

We previously reported that marchantin M (Mar) is an active agent to induce apoptosis in human prostate cancer (PCa), but the molecular mechanisms of action remain largely unknown. Here, we demonstrate that Mar potently inhibited chymotrypsin-like and peptidyl-glutamyl peptide-hydrolyzing activities of 20S proteasome both in in vitro and intracellular systems and significantly induced the accumulation of polyubiquitinated proteins in PCa cells. The computational modeling analysis suggested that Mar non-covalently bound to active sites of proteasome β5 and β1 subunits, resulting in a non-competitive inhibition. Proteasome inhibition by Mar subsequently resulted in endoplasmic reticulum (ER) stress, as evidenced by elevated glucose-regulated protein 78 and CHOP, increased phospho-eukaryotic translation initiation factor 2α (eIF_2α), splicing of X-box-binding protein-1 and dilation of the ER. However, Mar-mediated cell death was not completely impaired by a pan inhibitor of caspases. Further studies revealed that the Mar-induced cell death was greatly associated with the activation of autophagy, as indicated by the significant induction of microtubule-associated protein-1 light chain-3 beta (LC3B) expression and conversion. Electron microscopic and green fluorescent protein-tagged LC3B analyses further demonstrated the ability of autophagy induction by Mar. Time kinetic studies revealed that Mar induced a rapid and highly sustained processing of LC3B in treated cells and simultaneously decreased the expression of p62/SQSTM1. Pharmacological blockade or knockdown of LC3B and Atg5 attenuated Mar-mediated cell death. The autophagic response triggered by Mar required the activation of RNA-dependent protein kinase-like ER kinase/eIF_2α and suppression of the phosphatidylinositol-3 kinase/Akt/mammalian target of rapamycin axis via preventing activation and expression of Akt. Our results identified a novel mechanism for the cytotoxic effect of Mar, which strengthens it as a potential agent in cancer chemotherapy.

Targeting genomic alterations in squamous cell lung cancer

Squamous cell lung cancer causes approximately 400,000 deaths worldwide per year. Identification of specific molecular alterations, such as activating mutations in the epidermal growth factor receptor kinase and echinoderm microtubule-associated protein-like 4/anaplastic lymphoma kinase fusions have led to significant therapeutic gains in patients with adenocarcinoma. However, meaningful therapeutic gains based on the molecular pathobiology of squamous cell lung cancer have not yet been realized. A comprehensive genomic characterization of 178 cases of squamous cell lung cancer has recently been reported. Squamous cell lung cancer appears to be characterized by a broader and more complex group of genomic alterations than adenocarcinoma. In this review, potentially targetable genes or pathways in squamous cell lung cancer are emphasized in relation to available therapeutic agents in development or active clinical trials. This organization of data will provide a framework for development for clinical investigation. Squamous cell lung cancer appears to be characterized by not only driver mutations in candidate genes but also gene copy number alterations resulting in tumor proliferation and survival. Better understanding of these genetic alterations and their use as therapeutic targets will require broad collaboration between industry, government, the cooperative groups, and academic institutions with the ultimate goal of rapid translation of scientific advancement to patient benefit.

Role of PI3K, mTOR and Akt2 signalling in hepatic tumorigenesis via the control of PKM2 expression

To sustain increased growth, rapidly proliferating cells, such as tumour cells, undergo metabolic adaptations. In recent years, the mechanisms of glycolysis activation as a key metabolic adaptation in proliferating cells became the topic of intense research. Although this phenomenon was described more than 50 years ago by Otto Warburg, the molecular mechanisms remained elusive. Only recently, it was demonstrated that the expression of specific glycolytic enzymes, namely PKM2 (pyruvate kinase M2) and HK2 (hexokinase 2), occurs simultaneously with the glycolytic addiction of cancer cells. The PI3K (phosphoinositide 3-kinase)/mTOR [mammalian (or mechanistic) target of rapamycin] signalling pathway is a central signalling hub co-ordinating the growth in response to growth factor signalling and nutrient availability. Not surprisingly, it is found to be activated in the majority of the tumour cells. In the present article, we discuss the requirement of different PI3K/mTOR downstream effectors for the metabolic adaptation in liver cancer cells driven by this signalling pathway. We provide evidence for a selective involvement of the mTOR target Akt2 in tumoral growth. In addition, PTEN (phosphatase and tensin homologue deleted on chromosome 10)-negative human hepatocellular carcinoma cell lines display an up-regulation of PKM2 expression in an Akt2-dependent manner, providing an advantage for cell proliferation and anchorage-independent growth. Our data have implications on the link between the metabolic action of insulin signal transduction and tumorigenesis, identifying Akt2 as a potential therapeutical target in liver malignancies depending on cancer genotype.

Metastatic renal cell carcinoma: update on epidemiology, genetics, and therapeutic modalities

The treatment of advanced renal cell carcinoma (RCC) remains a major therapeutic challenge for clinicians. Despite advances in the understanding of the immunobiology of RCC and the availability of several novel targeted agents, there has been little improvement in the survival of patients with metastatic RCC. This review will focus on the recent understanding of risk factors and treatment options and outcomes of metastatic RCC, in particular, targeted therapeutic agents that inhibit vascular endothelial growth factor and mammalian target of rapamycin pathways. Prospective studies are required to determine whether sequential targeted therapy will further improve progression-free survival in RCC. Ongoing research to develop novel agents with better tolerability and enhanced efficacy in the treatment of metastatic RCC is required.