Antitumor activity of rapamycin in a Phase I trial for patients with recurrent PTEN-deficient glioblastoma

Complications from pharmacotherapy

The pharmacotherapy management of cancers of the nervous system has significant overlap with systemic solid cancers that may utilize similar drugs or agents. There is however a unique aspect related to central nervous system (CNS) cancers where therapies directed against a malignant process may have enhanced toxicities or toxicities unique to the CNS. In addition, many agents used to treat CNS malignancies have unique CNS toxicities that may require a specific intervention. This chapter attempts to review conventional and biologic therapies utilized for CNS malignancies and characterize expected and, if known, unique toxicities.

ATP-site binding inhibitor effectively targets mTORC1 and mTORC2 complexes in glioblastoma

The PI3K-AKT-mTOR signaling axis is central to the transformed phenotype of glioblastoma (GBM) cells, due to frequent loss of tumor suppressor PTEN (phosphatase and tensin homolog deleted on chromosome 10). The mechanistic target of rapamycin (mTOR) kinase is present in two cellular multi-protein complexes, mTORC1 and mTORC2, which have distinct subunit composition, substrates and mechanisms of action. Targeting the mTOR protein is a promising strategy for GBM therapy. However, neither of these complexes is fully inhibited by the allosteric inhibitor of mTOR, rapamycin or its analogs. Herein, we provide evidence that the combined inhibition of mTORC1/2, using the ATP-competitive binding inhibitor PP242, would effectively suppress GBM growth and dissemination as compared to an allosteric binding inhibitor of mTOR. GBM cells treated with PP242 demonstrated significantly decreased activation of mTORC1 and mTORC2, as shown by reduced phosphorylation of their substrate levels, p70 S6K(Thr389) and AKT(Ser473), respectively, in a dose-dependent manner. Furthermore, insulin induced activation of these kinases was abrogated by pretreatment with PP242 as compared with rapamycin. Unlike rapamycin, PP242 modestly activates extracellular regulated kinase (ERK1/2), as shown by expression of pERK(Thr202/Tyr204). Cell proliferation and S-phase entry of GBM cells was significantly suppressed by PP242, which was more pronounced compared to rapamycin treatment. Lastly, PP242 significantly suppressed the migration of GBM cells, which was associated with a change in cellular behavior rather than cytoskeleton loss. In conclusion, these results underscore the potential therapeutic use of the PP242, a novel ATP-competitive binding inhibitor of mTORC1/2 kinase, in suppression of GBM growth and dissemination.

The challenges and the promise of molecular targeted therapy in malignant gliomas

Malignant gliomas are the most common malignant primary brain tumors and one of the most challenging forms of cancers to treat. Despite advances in conventional treatment, the outcome for patients remains almost universally fatal. This poor prognosis is due to therapeutic resistance and tumor recurrence after surgical removal. However, over the past decade, molecular targeted therapy has held the promise of transforming the care of malignant glioma patients. Significant progress in understanding the molecular pathology of gliomagenesis and maintenance of the malignant phenotypes will open opportunities to rationally develop new molecular targeted therapy options. Recently, therapeutic strategies have focused on targeting pro-growth signaling mediated by receptor tyrosine kinase/RAS/phosphatidylinositol 3-kinase pathway, proangiogenic pathways, and several other vital intracellular signaling networks, such as proteasome and histone deacetylase. However, several factors such as cross-talk between the altered pathways, intratumoral molecular heterogeneity, and therapeutic resistance of glioma stem cells (GSCs) have limited the activity of single agents. Efforts are ongoing to study in depth the complex molecular biology of glioma, develop novel regimens targeting GSCs, and identify biomarkers to stratify patients with the individualized molecular targeted therapy. Here, we review the molecular alterations relevant to the pathology of malignant glioma, review current advances in clinical targeted trials, and discuss the challenges, controversies, and future directions of molecular targeted therapy.

Repurposing existing agents as adjunct therapies for glioblastoma

Numerous non-oncologic medications have been found in the last decade to have anti-cancer properties. While the focus in oncology research should clearly remain on deriving new therapeutic strategies, repurposing these existing medications may offer the potential to rapidly enhance the effectiveness of treatment for resistant cancers. Glioblastoma, the most common and lethal brain cancer, is highly resistant to standard therapies and would benefit from even minor improvements in treatment. Numerous agents already in the clinic for non-cancer applications have been found to also possess potential against cancer or specifically against glioblastoma. These include agents with activities affecting oxidative stress, the immune reponse, epigenetic modifiers, cancer cell metabolism, and angiogenesis and invasiveness. This review serves as a guide for potential ways to repurpose individual drugs alongside standard glioblastoma therapies.

Cellular and molecular effects of the mTOR inhibitor everolimus

mTOR (mechanistic target of rapamycin) functions as the central regulator for cell proliferation, growth and survival. Up-regulation of proteins regulating mTOR, as well as its downstream targets, has been reported in various cancers. This has promoted the development of anti-cancer therapies targeting mTOR, namely fungal macrolide rapamycin, a naturally occurring mTOR inhibitor, and its analogues (rapalogues). One such rapalogue, everolimus, has been approved in the clinical treatment of renal and breast cancers. Although results have demonstrated that these mTOR inhibitors are effective in attenuating cell growth of cancer cells under in vitro and in vivo conditions, subsequent sporadic response to rapalogues therapy in clinical trials has promoted researchers to look further into the complex understanding of the dynamics of mTOR regulation in the tumour environment. Limitations of these rapalogues include the sensitivity of tumour subsets to mTOR inhibition. Additionally, it is well known that rapamycin and its rapalogues mediate their effects by inhibiting mTORC (mTOR complex) 1, with limited or no effect on mTORC2 activity. The present review summarizes the pre-clinical, clinical and recent discoveries, with emphasis on the cellular and molecular effects of everolimus in cancer therapy.

Molecularly targeted therapies for recurrent glioblastoma: current and future targets

OBJECT

Glioblastoma is the most aggressive and diffusely infiltrative primary brain tumor. Recurrence is expected and is extremely difficult to treat. Over the past decade, the accumulation of knowledge regarding the molecular and genetic profile of glioblastoma has led to numerous molecularly targeted therapies. This article aims to review the literature and highlight the mechanisms and efficacies of molecularly targeted therapies for recurrent glioblastoma.

METHODS

A systematic search was performed with the phrase "(name of particular agent) and glioblastoma" as a search term in PubMed to identify all articles published up until 2014 that included this phrase in the title and/or abstract. The references of systematic reviews were also reviewed for additional sources. The review included clinical studies that comprised at least 20 patients and reported results for the treatment of recurrent glioblastoma with molecular targeted therapies.

RESULTS

A total of 42 articles were included in this review. In the treatment of recurrent glioblastoma, various targeted therapies have been tested over the past 10-15 years. The targets of interest include epidermal growth factor receptor, vascular endothelial growth factor receptor, platelet-derived growth factor receptor, Ras pathway, protein kinase C, mammalian target of rapamycin, histone acetylation, and integrins. Unfortunately, the clinical responses to most available targeted therapies are modest at best. Radiographic responses generally range in the realm of 5%-20%. Progression-free survival at 6 months and overall survival were also modest with the majority of studies reporting a 10%-20% 6-month progression-free survival and 5- to 8-month overall survival. There have been several clinical trials evaluating the use of combination therapy for molecularly targeted treatments. In general, the outcomes for combination therapy tend to be superior to single-agent therapy, regardless of the specific agent studied.

CONCLUSIONS

Recurrent glioblastoma remains very difficult to treat, even with molecular targeted therapies and anticancer agents. The currently available targeted therapy regimens have poor to modest activity against recurrent glioblastoma. As newer agents are actively being developed, combination regimens have provided the most promising results for improving outcomes. Targeted therapies matched to molecular profiles of individual tumors are predicted to be a critical component necessary for improving efficacy in future trials.

A phase I dose-escalation study to assess safety, tolerability, pharmacokinetics, and preliminary efficacy of the dual mTORC1/mTORC2 kinase inhibitor CC-223 in patients with advanced solid tumors or multiple myeloma

BACKGROUND

The mammalian target of rapamycin (mTOR) pathway is essential for tumor development, yet mTOR inhibitors have yielded modest results. This phase 1 study investigated the mTORC1/mTORC2 inhibitor CC-223 in patients with advanced cancer.

METHODS

Patients with advanced solid tumors or multiple myeloma received an initial dose of 7.5-60 mg of CC-223, followed by oral daily dosing in 28-day cycles until disease progression. The primary objective was to determine the safety, tolerability, nontolerated dosage, maximum tolerated dosage (MTD), and preliminary pharmacokinetic profile. Secondary objectives were to evaluate pharmacodynamic effects and to describe preliminary efficacy.

RESULTS

Twenty-eight patients were enrolled and received ≥1 dose of CC-223. The most common treatment-related grade 3 adverse events were hyperglycemia, fatigue, and rash. Four patients had dose-limiting toxicities, including hyperglycemia, rash, fatigue, and mucositis. Therefore, 45 mg/d was determined to be the MTD. The pharmacokinetics of CC-223 demonstrated a mean terminal half-life ranging from 4.86 to 5.64 hours and maximum observed plasma concentration ranging from 269 to 480 ng/mL in patients who received CC-223 ≥45 mg/d. Phosphorylation of mTORC1/mTORC2 pathway biomarkers in blood cells was inhibited by CC-223 ≥30 mg/d with an exposure-response relationship. Best responses included 1 partial response (breast cancer; response duration 220 days; 30-mg/d cohort), stable disease (8 patients across ≥15 mg/d cohorts; response duration range, 36-168 days), and progressive disease (12 patients). The disease control rate was 32%.

CONCLUSIONS

CC-223 was tolerable, with manageable toxicities. Preliminary antitumor activity, including tumor regression, and evidence of mTORC1/mTORC2 pathway inhibition were observed.

Phase I dose-escalation study of the PI3K/mTOR inhibitor voxtalisib (SAR245409, XL765) plus temozolomide with or without radiotherapy in patients with high-grade glioma

BACKGROUND

This phase I study aimed to evaluate safety, maximum tolerated dose, pharmacokinetics, pharmacodynamics, and preliminary efficacy of voxtalisib (SAR245409, XL765), a pan-class I phosphoinositide 3-kinase (PI3K) and mammalian target of rapamycin (mTOR) inhibitor, in combination with temozolomide (TMZ), with or without radiation therapy (RT), in patients with high-grade glioma.

METHODS

Patients received voxtalisib 30-90 mg once daily (q.d.) or 20-50 mg twice daily (b.i.d.), in combination with 200 mg/m(2) TMZ (n = 49), or voxtalisib 20 mg q.d. with 75 mg/m(2) TMZ and RT (n = 5). A standard 3 + 3 dose-escalation design was used to determine the maximum tolerated dose. Patients were evaluated for adverse events (AEs), plasma pharmacokinetics, pharmacodynamic effects in skin biopsies, and tumor response.

RESULTS

The maximum tolerated doses were 90 mg q.d. and 40 mg b.i.d. for voxtalisib in combination with TMZ. The most frequently reported treatment-related AEs were nausea (48%), fatigue (43%), thrombocytopenia (26%), and diarrhea (24%). The most frequently reported treatment-related grade ≥3 AEs were lymphopenia (13%), thrombocytopenia, and decreased platelet count (9% each). Pharmacokinetic parameters were similar to previous studies with voxtalisib monotherapy. Moderate inhibition of PI3K signaling was observed in skin biopsies. Best response was partial response in 4% of evaluable patients, with stable disease observed in 68%.

CONCLUSIONS

Voxtalisib in combination with TMZ with or without RT in patients with high-grade gliomas demonstrated a favorable safety profile and a moderate level of PI3K/mTOR pathway inhibition.

Immunohistochemical Assessment of Phosphorylated mTORC1-Pathway Proteins in Human Brain Tumors

Background

Current pathological diagnostics include the analysis of (epi-)genetic alterations as well as oncogenic pathways. Deregulated mammalian target of rapamycin complex 1 (mTORC1) signaling has been implicated in a variety of cancers including malignant gliomas and is considered a promising target in cancer treatment. Monitoring of mTORC1 activity before and during inhibitor therapy is essential. The aim of our study is to provide a recommendation and report on pitfalls in the use of phospho-specific antibodies against mTORC1-targets phospho-RPS6 (Ser235/236; Ser240/244) and phospho-4EBP1 (Thr37/46) in formalin fixed, paraffin embedded material.

Methods and Findings

Primary, established cell lines and brain tumor tissue from routine diagnostics were assessed by immunocyto-, immunohistochemistry, immunofluorescent stainings and immunoblotting. For validation of results, immunoblotting experiments were performed. mTORC-pathway activation was pharmacologically inhibited by torin2 and rapamycin. Torin2 treatment led to a strong reduction of signal intensity and frequency of all tested antibodies. In contrast phospho-4EBP1 did not show considerable reduction in staining intensity after rapamycin treatment, while immunocytochemistry with both phospho-RPS6-specific antibodies showed a reduced signal compared to controls. Staining intensity of both phospho-RPS6-specific antibodies did not show considerable decrease in stability in a timeline from 0–230 minutes without tissue fixation, however we observed a strong decrease of staining intensity in phospho-4EBP1 after 30 minutes. Detection of phospho-signals was strongly dependent on tissue size and fixation gradient. mTORC1-signaling was significantly induced in glioblastomas although not restricted to cancer cells but also detectable in non-neoplastic cells.

Conclusion

Here we provide a recommendation for phospho-specific immunohistochemistry for patient-orientated therapy decisions and monitoring treatment response.

Toward precision medicine in glioblastoma: the promise and the challenges

Integrated sequencing strategies have provided a broader understanding of the genomic landscape and molecular classifications of multiple cancer types and have identified various therapeutic opportunities across cancer subsets. Despite pivotal advances in the characterization of genomic alterations in glioblastoma, targeted agents have shown minimal efficacy in clinical trials to date, and patient survival remains poor. In this review, we highlight potential reasons why targeting single alterations has yielded limited clinical efficacy in glioblastoma, focusing on issues of tumor heterogeneity and pharmacokinetic failure. We outline strategies to address these challenges in applying precision medicine to glioblastoma and the rationale for applying targeted combination therapy approaches that match genomic alterations with compounds accessible to the central nervous system.

Heterogeneity of epidermal growth factor receptor signalling networks in glioblastoma

As tumours evolve, the daughter cells of the initiating cell often become molecularly heterogeneous and develop different functional properties and therapeutic vulnerabilities. In glioblastoma (GBM), a lethal form of brain cancer, the heterogeneous expression of the epidermal growth factor receptor (EGFR) poses a substantial challenge for the effective use of EGFR-targeted therapies. Understanding the mechanisms that cause EGFR heterogeneity in GBM should provide better insights into how they, and possibly other amplified receptor tyrosine kinases, affect cellular signalling, metabolism and drug resistance.

Dual blockade of PI3K/AKT/mTOR (NVP-BEZ235) and Ras/Raf/MEK (AZD6244) pathways synergistically inhibit growth of primary endometrioid endometrial carcinoma cultures, whereas NVP-BEZ235 reduces tumor growth in the corresponding xenograft models

OBJECTIVES

Endometrial carcinoma (EC) is the most common gynecological cancer in the Western World. Treatment options are limited for advanced and recurrent disease. Therefore, new treatment options are necessary. Inhibition of the PI3K/AKT/mTOR and/or the Ras/Raf/MEK pathways is suggested to be clinically relevant. However, the knowledge about the effect of combination targeted therapy in EC is limited. The aim of this study was to investigate the effect of these therapies on primary endometrioid EC cell cultures in vitro and in vivo.

METHODS

Primary endometrioid EC cell cultures were incubated with Temsirolimus (mTORC1 inhibitor), NVP-BKM120 (pan-PI3K inhibitor), NVP-BEZ235 (pan-PI3K/mTOR inhibitor), or AZD6244 (MEK1/2 inhibitor) as single treatment. In vitro, the effect of NVP-BEZ235 with or without AZD6244 was determined for cell viability, cell cycle arrest, apoptosis induction, and cell signaling. In vivo, the effect of NVP-BEZ35 was investigated for 2 subcutaneous xenograft models of the corresponding primary cultures.

RESULTS

NVP-BEZ235 was the most potent PI3K/AKT/mTOR pathway inhibitor. NVP-BEZ235 and AZD6244 reduced cell viability and induced cell cycle arrest and apoptosis, by reduction of p-AKT, p-S6, and p-ERK levels. Combination treatment showed a synergistic effect. In vivo, NVP-BEZ235 reduced tumor growth and inhibited p-S6 expression. The effects of the compounds were independent of the mutation profile of the cell cultures used.

CONCLUSIONS

A synergistic antitumor effect was shown for NVP-BEZ235 and AZD6244 in primary endometrioid EC cells in vitro. In addition, NVP-BEZ235 induced reduction of tumor growth in vivo. Therefore, targeted therapies seem an interesting strategy to further evaluate in clinical trials.

Targeting core (mutated) pathways of high-grade gliomas: challenges of intrinsic resistance and drug efflux

High-grade gliomas are the most common type of primary brain tumor and are among the most lethal types of human cancer. Most patients with a high-grade glioma have glioblastoma multiforme (GBM), the most malignant glioma subtype that is associated with a very aggressive disease course and short overall survival. Standard treatment of newly diagnosed GBM involves surgery followed by chemoradiation with temozolomide. However, despite this extensive treatment the mean overall survival is still only 14.6 months and more effective treatments are urgently needed. Although different types of GBMs are indistinguishable by histopathology, novel molecular pathological techniques allow discrimination between the four main GBM subtypes. Targeting the aberrations in the molecular pathways underlying these subtypes is a promising strategy to improve therapy. In this article, we will discuss the potential avenues and pitfalls of molecularly targeted therapies for the treatment of GBM.

Lipid metabolism emerges as a promising target for malignant glioma therapy

Malignant gliomas are one of the most treatment-refractory cancers. Development of resistance to chemo- and radio-therapies contributes to these tumors' aggressive phenotypes. Elevated lipid levels in gliomas have been reported for the last 50 years. However, the molecular mechanisms of how tumor tissues obtain lipids and utilize them are not well understood. Recently, the oncogenic signaling EGFR/PI3K/Akt pathway has been shown to enhance lipid synthesis and uptake by upregulating SREBP-1, a master transcriptional factor, to control lipid metabolism. This article discusses the analytical chemistry results of lipid components in glioma tissues from different research groups. The molecular mechanisms that link oncogenes with lipid programming, and identification of the key molecular targets and development of effective drugs to inhibit lipid metabolism in malignant gliomas will be discussed.

A signal-on fluorosensor based on quench-release principle for sensitive detection of antibiotic rapamycin

An antibiotic rapamycin is one of the most commonly used immunosuppressive drugs, and also implicated for its anti-cancer activity. Hence, the determination of its blood level after organ transplantation or tumor treatment is of great concern in medicine. Although there are several rapamycin detection methods, many of them have limited sensitivity, and/or need complicated procedures and long assay time. As a novel fluorescent biosensor for rapamycin, here we propose "Q'-body", which works on the fluorescence quench-release principle inspired by the antibody-based quenchbody (Q-body) technology. We constructed rapamycin Q'-bodies by linking the two interacting domains FKBP12 and FRB, whose association is triggered by rapamycin. The fusion proteins were each incorporated position-specifically with one of fluorescence dyes ATTO520, tetramethylrhodamine, or ATTO590 using a cell-free translation system. As a result, rapid rapamycin dose-dependent fluorescence increase derived of Q'-bodies was observed, especially for those with ATTO520 with a lowest detection limit of 0.65 nM, which indicates its utility as a novel fluorescent biosensor for rapamycin.

First-in-Human Pharmacokinetic and Pharmacodynamic Study of the Dual m-TORC 1/2 Inhibitor AZD2014

PURPOSE

AZD2014 is a novel, oral, m-TORC 1/2 inhibitor that has shown in vitro and in vivo efficacy across a range of preclinical human cancer models.

EXPERIMENTAL DESIGN

A rolling six-dose escalation was performed to define an MTD (part A), and at MTD a further cohort of patients was treated to further characterize toxicities and perform pre- and posttreatment biopsies (part B). AZD2014 was administered orally twice a day continuously. Flow cytometry, ELISA, and immunohistochemistry were used to quantify pharmacodynamic biomarkers. Pharmacokinetic analysis was carried out by mass spectrometry.

RESULTS

A total of 56 patients were treated across a dose range of 25 to 100 mg. The MTD was 50 mg twice daily. The dose-limiting toxicities were fatigue and mucositis. At the MTD, the most common adverse events (AE) were fatigue (78%), nausea (51%), and mucositis (49%), but these were equal to or greater than grade 3 in only 5% of patients. Drug levels achieved at the MTD (AUC SS: 6686 ng·h/mL, Cmax ss 1,664 ng/mL) were consistent with activity in preclinical models. A reduction in p-S6 levels and Ki67 staining was observed in 8 of 8 and 5 of 9 evaluable paired biopsy samples. Partial responses were seen in a patient with pancreatic cancer and a patient with breast cancer, who were found to have a PDGFR and ERBB2 mutation, respectively.

CONCLUSIONS

The recommended phase II dose for further evaluation of AZD2014 is 50 mg twice daily, and at this dose it has been possible to demonstrate pharmacologically relevant plasma concentrations, target inhibition in tumor, and clinical responses.

Compensatory glutamine metabolism promotes glioblastoma resistance to mTOR inhibitor treatment

The mechanistic target of rapamycin (mTOR) is hyperactivated in many types of cancer, rendering it a compelling drug target; however, the impact of mTOR inhibition on metabolic reprogramming in cancer is incompletely understood. Here, by integrating metabolic and functional studies in glioblastoma multiforme (GBM) cell lines, preclinical models, and clinical samples, we demonstrate that the compensatory upregulation of glutamine metabolism promotes resistance to mTOR kinase inhibitors. Metabolomic studies in GBM cells revealed that glutaminase (GLS) and glutamate levels are elevated following mTOR kinase inhibitor treatment. Moreover, these mTOR inhibitor-dependent metabolic alterations were confirmed in a GBM xenograft model. Expression of GLS following mTOR inhibitor treatment promoted GBM survival in an α-ketoglutarate-dependent (αKG-dependent) manner. Combined genetic and/or pharmacological inhibition of mTOR kinase and GLS resulted in massive synergistic tumor cell death and growth inhibition in tumor-bearing mice. These results highlight a critical role for compensatory glutamine metabolism in promoting mTOR inhibitor resistance and suggest that rational combination therapy has the potential to suppress resistance.

Prevention of carcinogen and inflammation-induced dermal cancer by oral rapamycin includes reducing genetic damage

Cancer prevention is a cost-effective alternative to treatment. In mice, the mTOR inhibitor rapamycin prevents distinct spontaneous, noninflammatory cancers, making it a candidate broad-spectrum cancer prevention agent. We now show that oral microencapsulated rapamycin (eRapa) prevents skin cancer in dimethylbenz(a)anthracene (DMBA)/12-O-tetradecanoylphorbol-13-acetate (TPA) carcinogen-induced, inflammation-driven carcinogenesis. eRapa given before DMBA/TPA exposure significantly increased tumor latency, reduced papilloma prevalence and numbers, and completely inhibited malignant degeneration into squamous cell carcinoma. Rapamycin is primarily an mTORC1-specific inhibitor, but eRapa did not reduce mTORC1 signaling in skin or papillomas, and did not reduce important proinflammatory factors in this model, including p-Stat3, IL17A, IL23, IL12, IL1β, IL6, or TNFα. In support of lack of mTORC1 inhibition, eRapa did not reduce numbers or proliferation of CD45(-)CD34(+)CD49f(mid) skin cancer initiating stem cells in vivo and marginally reduced epidermal hyperplasia. Interestingly, eRapa reduced DMBA/TPA-induced skin DNA damage and the hras codon 61 mutation that specifically drives carcinogenesis in this model, suggesting reduction of DNA damage as a cancer prevention mechanism. In support, cancer prevention and DNA damage reduction effects were lost when eRapa was given after DMBA-induced DNA damage in vivo. eRapa afforded picomolar concentrations of rapamycin in skin of DMBA/TPA-exposed mice, concentrations that also reduced DMBA-induced DNA damage in mouse and human fibroblasts in vitro. Thus, we have identified DNA damage reduction as a novel mechanism by which rapamycin can prevent cancer, which could lay the foundation for its use as a cancer prevention agent in selected human populations.

Targeting SREBP-1-driven lipid metabolism to treat cancer

Metabolic reprogramming is a hallmark of cancer. Oncogenic growth signaling regulates glucose, glutamine and lipid metabolism to meet the bioenergetics and biosynthetic demands of rapidly proliferating tumor cells. Emerging evidence indicates that sterol regulatory element-binding protein 1 (SREBP-1), a master transcription factor that controls lipid metabolism, is a critical link between oncogenic signaling and tumor metabolism. We recently demonstrated that SREBP-1 is required for the survival of mutant EGFR-containing glioblastoma, and that this pro-survival metabolic pathway is mediated, in part, by SREBP-1-dependent upregulation of the fatty acid synthesis and low density lipoprotein (LDL) receptor (LDLR). These results have identified EGFR/PI3K/Akt/SREBP-1 signaling pathway that promotes growth and survival in glioblastoma, and potentially other cancer types. Here, we summarize recent insights in the understanding of cancer lipid metabolism, and discuss the evidence linking SREBP-1 with PI3K/Akt signaling-controlled glycolysis and with Myc-regulated glutaminolysis to lipid metabolism. We also discuss the development of potential drugs targeting the SREBP-1- driven lipid metabolism as anti-cancer agents.

Discovery of AZD3147: a potent, selective dual inhibitor of mTORC1 and mTORC2

High throughput screening followed by a lead generation campaign uncovered a novel series of urea containing morpholinopyrimidine compounds which act as potent and selective dual inhibitors of mTORC1 and mTORC2. We describe the continued compound optimization campaign for this series, in particular focused on identifying compounds with improved cellular potency, improved aqueous solubility, and good stability in human hepatocyte incubations. Knowledge from empirical SAR investigations was combined with an understanding of the molecular interactions in the crystal lattice to improve both cellular potency and solubility, and the composite parameters of LLE and pIC50-pSolubility were used to assess compound quality and progress. Predictive models were employed to efficiently mine the attractive chemical space identified resulting in the discovery of 42 (AZD3147), an extremely potent and selective dual inhibitor of mTORC1 and mTORC2 with physicochemical and pharmacokinetic properties suitable for development as a potential clinical candidate.

Emerging function of mTORC2 as a core regulator in glioblastoma: metabolic reprogramming and drug resistance

Glioblastoma (GBM) is one of the most lethal human cancers. Genomic analyses define the molecular architecture of GBM and highlight a central function for mechanistic target of rapamycin (mTOR) signaling. mTOR kinase exists in two multi-protein complexes, namely, mTORC1 and mTORC2. These complexes differ in terms of function, regulation and rapamycin sensitivity. mTORC1 is well established as a cancer drug target, whereas the functions of mTORC2 in cancer, including GBM, remains poorly understood. This study reviews the recent findings that demonstrate a central function of mTORC2 in regulating tumor growth, metabolic reprogramming, and targeted therapy resistance in GBM, which makes mTORC2 as a critical GBM drug target.

Immune Suppression during Oncolytic Virotherapy for High-Grade Glioma; Yes or No?

Oncolytic viruses have been seriously considered for glioma therapy over the last 20 years. The oncolytic activity of several oncolytic strains has been demonstrated against human glioma cell lines and in in vivo xenotransplant models. So far, four of these stains have additionally completed the first phase I/II trials in relapsed glioma patients. Though safety and feasibility have been demonstrated, therapeutic efficacy in these initial trials, when described, was only minor. The role of the immune system in oncolytic virotherapy for glioma remained much less studied until recent years. When investigated, the immune system, adept at controlling viral infections, is often hypothesized to be a strong hurdle to successful oncolytic virotherapy. Several preclinical studies have therefore aimed to improve oncolytic virotherapy efficacy by combining it with immune suppression or evasion strategies. More recently however, a new paradigm has developed in the oncolytic virotherapy field stating that oncolytic virus-mediated tumor cell death can be accompanied by elicitation of potent activation of innate and adaptive anti-tumor immunity that greatly improves the efficacy of certain oncolytic strains. Therefore, it seems the three-way interaction between oncolytic virus, tumor and immune system is critical to the outcome of antitumor therapy. In this review we discuss the studies which have investigated how the immune system and oncolytic viruses interact in models of glioma. The novel insights generated here hold important implications for future research and should be incorporated into the design of novel clinical trials.

Novel chemotherapeutic approaches in adult high-grade gliomas

Despite decades of advancing science and clinical trials, average survival remains dismal for individuals with high-grade gliomas. Our understanding of the genetic and molecular aberrations that contribute to the aggressive nature of these tumors is continually growing, as is our ability to target such specific traits. Herein, we review the major classes of such targeted therapies, as well as the relevant clinical trial outcomes regarding their efficacy.

Dramatic antitumor effects of the dual mTORC1 and mTORC2 inhibitor AZD2014 in hepatocellular carcinoma

The mammalian target of rapamycin (mTOR) has emerged as a critical effector in cell growth, proliferation, survival, angiogenesis, and autophagy through direct interaction with mTORC1 (mTOR complex 1) and mTORC2 (mTOR complex 2). The mTOR axis is aberrantly activated in about 50% of human hepatocellular carcinoma (HCC) cases and thus has become an attractive target for drug development in this disease. Allosteric inhibitors of mTORC1, rapamycin and its derivatives have been used to study in patients with HCC but have not shown significant clinical utility, likely because of the lack of inhibition of mTORC2. In the present study, we describe that AZD2014, a small molecular ATP-competitive inhibitor of mTOR, was a highly potent inhibitor of mTORC1 and mTORC2 in human HCC cells, which led to a more thorough inhibition of mTORC1 than rapamycin, and the inhibition of mTORC2 prevented the feedback activation of AKT signaling. Compared with rapamycin, AZD2014 resulted in more profound proliferation suppression, apoptosis, cell cycle arrest, and autophagy in HCC cells. Notably, we found blockage of both mTORC1 and mTORC2 by AZD2014 to be more efficacious than blockage of mTORC1 alone by rapamycin in inhibiting the migration, invasion and EMT progression of HCC cells. In conclusion, our current results highlight mechanistic differentiation between rapamycin and AZD2014 in targeting cancer cell proliferation, cell cycle, apoptosis, autophagy, migration, invasion and EMT progression, and provide support for further investigation of AZD2014 as an antitumor agent for the treatment of HCC in clinic.

Current treatment strategies for inhibiting mTOR in cancer

Mammalian target of rapamycin (mTOR) is a Ser/Thr kinase that regulates a wide range of functions, including cell growth, proliferation, survival, autophagy, metabolism, and cytoskeletal organization. mTOR activity is dysregulated in several human disorders, including cancer. The crucial role of mTOR in cancer cell biology has stimulated interest in mTOR inhibitors, placing mTOR on the radar of the pharmaceutical industry. Several mTOR inhibitors have already undergone clinical trials for treating tumors, without great success, although mTOR inhibitors are approved for the treatment of some types of cancer, including advanced renal cell carcinoma. However, the role of mTOR inhibitors in cancer treatment continues to evolve as new compounds are continuously being disclosed. Here we review the three classes of mTOR inhibitors currently available for treating cancer patients. Moreover, we highlight efforts to identify markers of resistance and sensitivity to mTOR inhibition that could prove useful in the emerging field of personalized medicine.

A Phase I Study of Cixutumumab (IMC-A12) in Combination with Temsirolimus (CCI-779) in Children with Recurrent Solid Tumors: A Children's Oncology Group Phase I Consortium Report

PURPOSE

To determine the MTD, dose-limiting toxicities (DLT), pharmacokinetics, and biologic effects of cixutumumab administered in combination with temsirolimus to children with refractory solid tumors.

EXPERIMENTAL DESIGN

Cixutumumab and temsirolimus were administered intravenously once every 7 days in 28-day cycles. Pharmacokinetic and biology studies, including assessment of mTOR downstream targets in peripheral blood mononuclear cells, were performed during the first cycle.

RESULTS

Thirty-nine patients, median age 11.8 years (range, 1-21.5), with recurrent solid or central nervous system tumors were enrolled, of whom 33 were fully assessable for toxicity. There were four dose levels, which included two dose reductions and a subsequent intermediated dose escalation: (i) IMC-A12 6 mg/kg, temsirolimus 15 mg/m(2); (ii) IMC-A12 6 mg/kg, temsirolimus 10 mg/m(2); (iii) IMC-A12 4 mg/kg, temsirolimus 8 mg/m(2); and (iv) IMC-A12 6 mg/kg, temsirolimus 8 mg/m(2). Mucositis was the predominant DLT. Other DLTs included hypercholesterolemia, fatigue, thrombocytopenia, and increased alanine aminotransferase. Target inhibition (decreased S6K1 and PAkt) in peripheral blood mononuclear cells was noted at all dose levels. Marked interpatient variability in temsirolimus pharmacokinetic parameters was noted. At 8 mg/m(2), the median temsirolimus AUC was 2,946 ng • h/mL (range, 937-5,536) with a median sirolimus AUC of 767 ng • h/mL (range, 245-3,675).

CONCLUSIONS

The recommended pediatric phase II doses for the combination of cixutumumab and temsirolimus are 6 mg/kg and 8 mg/m(2), respectively.

Dual mTORC1/2 blockade inhibits glioblastoma brain tumor initiating cells in vitro and in vivo and synergizes with temozolomide to increase orthotopic xenograft survival

PURPOSE

The EGFR and PI3K/mTORC1/2 pathways are frequently altered in glioblastoma (GBM), but pharmacologic targeting of EGFR and PI3K signaling has failed to demonstrate efficacy in clinical trials. Lack of relevant models has rendered it difficult to assess whether targeting these pathways might be effective in molecularly defined subgroups of GBMs. Here, human brain tumor-initiating cell (BTIC) lines with different combinations of endogenous EGFR wild-type, EGFRvIII, and PTEN mutations were used to investigate response to the EGFR inhibitor gefitinib, mTORC1 inhibitor rapamycin, and dual mTORC1/2 inhibitor AZD8055 alone and in combination with temozolomide (TMZ) EXPERIMENTAL DESIGN: In vitro growth inhibition and cell death induced by gefitinib, rapamycin, AZD8055, and TMZ or combinations in human BTICs were assessed by alamarBlue, neurosphere, and Western blotting assays. The in vivo efficacy of AZD8055 was assessed in subcutaneous and intracranial BTIC xenografts. Kaplan-Meier survival studies were performed with AZD8055 and in combination with TMZ.

RESULTS

We confirm that gefitinib and rapamycin have modest effects in most BTIC lines, but AZD8055 was highly effective at inhibiting Akt/mTORC2 activity and dramatically reduced the viability of BTICs regardless of their EGFR and PTEN mutational status. Systemic administration of AZD8055 effectively inhibited tumor growth in subcutaneous BTIC xenografts and mTORC1/2 signaling in orthotopic BTIC xenografts. AZD8055 was synergistic with the alkylating agent TMZ and significantly prolonged animal survival.

CONCLUSION

These data suggest that dual inhibition of mTORC1/2 may be of benefit in GBM, including the subset of TMZ-resistant GBMs.

A chemical biology approach identified PI3K as a potential therapeutic target for neurofibromatosis type 2

Mutations in the merlin tumor suppressor gene cause Neurofibromatosis type 2 (NF2), which is a disease characterized by development of multiple benign tumors in the nervous system. The current standard of care for NF2 calls for surgical resection of the characteristic tumors, often with devastating neurological consequences. There are currently no approved non-surgical therapies for NF2. In an attempt to identify much needed targets and therapeutically active compounds for NF2 treatment, we employed a chemical biology approach using ultra-high-throughput screening. To support this goal, we created a merlin-null mouse Schwann cell (MSC) line to screen for compounds that selectively decrease their viability and proliferation. We optimized conditions for 384-well plate assays and executed a proof-of-concept screen of the Library of Pharmacologically Active Compounds. Further confirmatory and selectivity assays identified phosphatidylinositol 3-kinase (PI3K) as a potential NF2 drug target. Notably, loss of merlin function is associated with activation of the PI3K/Akt pathway in human schwannomas. We report that AS605240, a PI3K inhibitor, decreased merlin-null MSC viability in a dose-dependent manner without significantly decreasing viability of control Schwann cells. AS605240 exerted its action on merlin-null MSCs by promoting caspase-dependent apoptosis and inducing autophagy. Additional PI3K inhibitors tested also decreased viability of merlin-null MSCs in a dose-dependent manner. In summary, our chemical genomic screen and subsequent hit validation studies have identified PI3K as potential target for NF2 therapy.

Rapamycin and everolimus facilitate hepatitis E virus replication: revealing a basal defense mechanism of PI3K-PKB-mTOR pathway

BACKGROUND & AIMS

Humans are frequently exposed to hepatitis E virus (HEV). Nevertheless, the disease mainly affects pregnant women and immunocompromised individuals. Organ recipients receiving immunosuppressants, such as rapalogs, to prevent rejection have a high risk for developing chronic hepatitis following HEV infection. Rapalogs constitute potent inhibitors of mTOR including rapamycin and everolimus. As a master kinase, the mechanism-of-action of mTOR is not only associated with the immunosuppressive capacity of rapalogs but is also tightly regulated during pregnancy because of increased nutritional demands.

METHODS

We thus investigated the role of mTOR in HEV infection by using two state-of-the-art cell culture models: a subgenomic HEV containing luciferase reporter and a full-length HEV infectious cell culture system.

RESULTS

In both subgenomic and full-length HEV models, HEV infection was aggressively escalated by treatment of rapamycin or everolimus. Inhibition of mTOR was confirmed by Western blot showing the inhibition of its downstream target, S6 phosphorylation. Consistently, stable silencing of mTOR by lentiviral RNAi resulted in a significant increase in intracellular HEV RNA, suggesting an antiviral function of mTOR in HEV infection. By targeting a series of other up- and downstream elements of mTOR signaling, we further revealed an effective basal defense mechanism of the PI3K-PKB-mTOR pathway against HEV, which is through the phosphorylated eIF4E-binding protein 1 (4E-BP1), however independent of autophagy formation.

CONCLUSIONS

The discovery that PI3K-PKB-mTOR pathway limits HEV infection through 4E-BP1 and acts as a gate-keeper in human HEV target cells bears significant implications in managing immunosuppression in HEV-infected organ transplantation recipients.

Targeted therapy in gliomas

The survival outcome of patients with malignant gliomas is still poor, despite advances in surgical techniques, radiation therapy and the development of novel chemotherapeutic agents. The heterogeneity of molecular alterations in signaling pathways involved in the pathogenesis of these tumors contributes significantly to their resistance to treatment. Several molecular targets for therapy have been discovered over the last several years. Therapeutic agents targeting these signaling pathways may provide more effective treatments and may improve survival. This review summarizes the important molecular therapeutic targets and the outcome of published clinical trials involving targeted therapeutic agents in glioma patients.

Distinct signaling mechanisms of mTORC1 and mTORC2 in glioblastoma multiforme: a tale of two complexes

Mechanistic target of rapamycin (mTOR) is a serine-threonine kinase that functions via two multiprotein complexes, namely mTORC1 and mTORC2, each characterized by different binding partners that confer separate functions. mTORC1 function is tightly regulated by PI3-K/Akt and is sensitive to rapamycin. mTORC2 is sensitive to growth factors, not nutrients, and is associated with rapamycin-insensitivity. mTORC1 regulates protein synthesis and cell growth through downstream molecules: 4E-BP1 (also called EIF4E-BP1) and S6K. Also, mTORC2 is thought to modulate growth factor signaling by phosphorylating the C-terminal hydrophobic motif of some AGC kinases such as Akt and SGK. Recent evidence has suggested that mTORC2 may play an important role in maintenance of normal as well as cancer cells by virtue of its association with ribosomes, which may be involved in metabolic regulation of the cell. Rapamycin (sirolimus) and its analogs known as rapalogues, such as RAD001 (everolimus) and CCI-779 (temsirolimus), suppress mTOR activity through an allosteric mechanism that acts at a distance from the ATP-catalytic binding site, and are considered incomplete inhibitors. Moreover, these compounds suppress mTORC1-mediated S6K activation, thereby blocking a negative feedback loop, leading to activation of mitogenic pathways promoting cell survival and growth. Consequently, mTOR is a suitable target of therapy in cancer treatments. However, neither of these complexes is fully inhibited by the allosteric inhibitor rapamycin or its analogs. In recent years, new pharmacologic agents have been developed which can inhibit these complexes via ATP-binding mechanism, or dual inhibition of the canonical PI3-K/Akt/mTOR signaling pathway. These compounds include WYE-354, KU-003679, PI-103, Torin1, and Torin2, which can target both complexes or serve as a dual inhibitor for PI3-K/mTOR. This investigation describes the mechanism of action of pharmacological agents that effectively target mTORC1 and mTORC2 resulting in suppression of growth, proliferation, and migration of tumor and cancer stem cells.

Vertical inhibition of PI3K/Akt/mTOR signaling demonstrates in vitro and in vivo anti-fibrotic activity

BACKGROUND

The mammalian target of rapamycin (mTOR) regulates cellular activity in many diseases, but the complex interplay with PI3K/Akt pathway may hampers its function.

OBJECTIVE

This study was undertaken to determine the activity of PI3K/Akt/mTOR signaling in the fibroblasts from systemic sclerosis (SSc) patients, and compare the effects of vertical inhibiting PI3K/Akt/mTOR by BEZ235 and inhibiting mTOR alone by rapamycin in fibroblast activation and in two complementary established mouse model of SSc.

METHODS

Pharmaceutical specific inhibitors BEZ235 and rapamycin were used to vertical inhibit PI3K/Akt/mTOR signaling and mTOR signaling alone in cultured fibroblasts and in mice. SSc mouse model was established by daily injecting bleomycin subcutaneously or by overexpression of constitutively active type I TGF-β receptor (TβRI(ca)). To delineate the mechanisms underlying the antifibrotic effects of BEZ235 and rapamycin, activity of PI3K/Akt/mTOR signaling was analyzed by determining the expressions of phosphorylated Akt, GSK-3β, mTOR and S6 ribosomal protein (S6).

RESULTS

Primary dermal fibroblasts demonstrated hyperactivity of PI3K/Akt and mTOR signaling. mTOR inhibitor rapamycin failed to inhibit dermal fibrosis in an established SSc mouse model. However, administration of a dual inhibitor for PI3K/Akt and mTOR signaling BEZ235 attenuated dermal fibrosis by reversing increased dermal thickness and collagen deposition in two SSc mouse models. Furthermore, BEZ235 showed superior inhibitory effect on fibroblast activation relative to rapamycin in vitro. Also both BEZ235 and rapamycin could prevent the phosphorylation of mTOR and S6 completely. BEZ235 also blocked the activation of Akt and GSK-3β dramatically, whereas rapamycin has been shown to increase further upregulation of phosphorylated Akt on Ser473 both in vitro and in vivo.

CONCLUSION

These data show that blocking PI3K/Akt/mTOR with BEZ235 leads to superior inhibitory effect for dermal fibrosis, suggesting that vertical inhibition of PI3K/Akt/mTOR signaling may have therapeutic potential for SSc.

Anti-tumour efficacy on glioma models of PHA-848125, a multi-kinase inhibitor able to cross the blood-brain barrier

BACKGROUND AND PURPOSE

Malignant gliomas, the most common primary brain tumours, are highly invasive and neurologically destructive neoplasms with a very bad prognosis due to the difficulty in removing the mass completely by surgery and the limited activity of current therapeutic agents. PHA-848125 is a multi-kinase inhibitor with broad anti-tumour activity in pre-clinical studies and good tolerability in phase 1 studies, which could affect two main pathways involved in glioma pathogenesis, the G1-S phase progression control pathway through the inhibition of cyclin-dependent kinases and the signalling pathways mediated by tyrosine kinase growth factor receptors, such as tropomyosin receptors. For this reason, we tested PHA-848125 in glioma models.

EXPERIMENTAL APPROACH

PHA-848125 was tested on a panel of glioma cell lines in vitro to evaluate inhibition of proliferation and mechanism of action. In vivo efficacy was evaluated on two glioma models both as single agent and in combination with standard therapy.

KEY RESULTS

When tested on a subset of representative glioma cell lines, PHA-848125 blocked cell proliferation, DNA synthesis and inhibited both cell cycle and signal transduction markers. Relevantly, PHA-848125 was also able to induce cell death through autophagy in all cell lines. Good anti-tumour efficacy was observed by oral route in different glioma models both with s.c. and intracranial implantation. Indeed, we demonstrate that the drug is able to cross the blood-brain barrier. Moreover, the combination of PHA-848125 with temozolomide resulted in a synergistic effect, and a clear therapeutic gain was also observed with a triple treatment adding PHA-848125 to radiotherapy and temozolomide.

CONCLUSIONS AND IMPLICATIONS

All the pre-clinical data obtained so far suggest that PHA-848125 may become a useful agent in chemotherapy regimens for glioma patients and support its evaluation in phase 2 trials for this indication.

The search for antiaging interventions: from elixirs to fasting regimens

The phenomenon of aging is an intrinsic feature of life. Accordingly, the possibility to manipulate it has fascinated humans likely since time immemorial. Recent evidence is shaping a picture where low caloric regimes and exercise may improve healthy senescence, and several pharmacological strategies have been suggested to counteract aging. Surprisingly, the most effective interventions proposed to date converge on only a few cellular processes, in particular nutrient signaling, mitochondrial efficiency, proteostasis, and autophagy. Here, we critically examine drugs and behaviors to which life- or healthspan-extending properties have been ascribed and discuss the underlying molecular mechanisms.

Mirk/dyrk1B kinase is upregulated following inhibition of mTOR

The PI3K/PTEN/Akt/mTOR/p70S6K pathway is one of the most frequently deregulated signaling pathways in solid tumors and has a functional role in drug resistance. However, targeting this pathway leads to compensatory activation of several mediators of cell survival. Expression of the reactive oxygen species-controlling kinase Mirk/dyrk1B was increased severalfold by the mammalian target of rapamycin (mTOR) inhibitors RAD001, WYE354 and rapamycin, with less effect by the Akt inhibitors AZD5363 and MK-2206. Upregulation of Mirk messenger RNA (mRNA) expression was mediated by cyclic AMP response element binding protein (CREB) binding to two sites in the Mirk promoter upstream of the transcription start site and one site within exon 4. Depletion of CREB reduced Mirk expression, whereas depletion of mTOR increased it. Moreover, hydroxytamoxifen activation of an Akt-estrogen receptor construct blocked an increase in Mirk mRNA and protein. Addition of a Mirk/dyrk1B kinase inhibitor increased the sensitivity of Panc1 pancreatic cancer cells and three different ovarian cancer cell lines to the mTOR inhibitor RAD001. Targeting Mirk kinase could improve the utility of mTOR inhibitors and so presents an attractive drug target.

The mTOR signaling pathway as a treatment target for intracranial neoplasms

Inhibition of the mammalian target of rapamycin (mTOR) signaling pathway has become an attractive target for human cancer therapy. Hyperactivation of mTOR has been reported in both sporadic and syndromic (hereditary) brain tumors. In contrast to the large number of successful clinical trials employing mTOR inhibitors in different types of epithelial neoplasms, their use to treat intracranial neoplasms is more limited. In this review, we summarize the role of mTOR activation in brain tumor pathogenesis and growth relevant to new human brain tumor trials currently under way using mTOR inhibitors.

Combined targeting of mTOR and c-MET signaling pathways for effective management of epithelioid sarcoma

Background

Epithelioid sarcoma (EpS) is a high-grade malignant soft-tissue sarcoma characterized by local recurrences and distant metastases. Effective treatments for EpS have not been established and thus novel therapeutic approaches against EpS are urgently required. mTOR inhibitors exert antitumor effects on several malignancies but AKT reactivation by mTOR inhibition attenuates the antitumor effects of mTOR inhibitors. This reactivation is receptor tyrosine kinase (RTK)-dependent due to a release of negative feedback inhibition. We found that c-MET was the most highly activated RTK in two human EpS cell lines, Asra-EPS and VAESBJ. Here we investigated the functional and therapeutic relevance of mTOR and/or c-MET signaling pathways in EpS both in vitro and in vivo.

Methods

We first examined the effects of an mTOR inhibitor, RAD001 (everolimus), on cell proliferation, cell cycle, AKT/mTOR signaling, and xenograft tumor growth in EpS cell lines. Next, we determined whether RAD001-induced AKT reactivation was blocked by silencing of c-MET or treatment with a selective c-MET inhibitor, INC280. Finally, we evaluated the antitumor effects of RAD001 combined with INC280 on EpS cell lines compared with either single agent or control in vitro and in vivo.

Results

Constitutive AKT phosphorylation was observed in Asra-EPS and VAESBJ cells. RAD001 suppressed EpS cell growth by inducing cell cycle arrest but enhanced AKT phosphorylation, which resulted in intrinsic resistance to mTOR inhibitors. In both EpS cell lines, RAD001-induced AKT phosphorylation was dependent on c-MET signaling. INC280 inhibited phosphorylation of c-MET and its downstream molecules, and decreased RAD001-induced phosphorylation of both AKT and ERK in EpS. Compared with a single agent or control, the combination of RAD001 and INC280 exerted superior antitumor effects on the growth of EpS cell lines in vitro and in vivo.

Conclusions

Targeting of mTOR and c-MET signaling pathways significantly abrogates the growth of EpS in preclinical models and may be a promising therapeutic approach for patients with EpS.

Electronic supplementary material

The online version of this article (doi:10.1186/1476-4598-13-185) contains supplementary material, which is available to authorized users.

mTOR co-targeting in cetuximab resistance in head and neck cancers harboring PIK3CA and RAS mutations

Background

Cetuximab, a monoclonal blocking antibody against the epidermal growth factor receptor EGFR, has been approved for the treatment of squamous cell carcinomas of the head and neck (HNSCC). However, only few patients display long-term responses, prompting the search for cetuximab resistance mechanisms and new therapeutic options enhancing cetuximab effectiveness.

Methods

Cetuximab-sensitive HNSCC cells were retro-engineered to express PIK3CA and RAS oncogenes. These cells and HNSCC cells harboring endogenous PIK3CA and RAS oncogenes were xenografted into mice (n = 10 per group) and studied for their biochemical, antitumor, antiangiogenic, and antilymphangiogenic responses to cetuximab and mTOR targeting agents. All P values are two-sided.

Results

Cetuximab treatment of PIK3CA- and RAS-expressing HNSCC xenografts promoted an initial antitumor response, but all tumors relapsed within few weeks. In these tumors, cetuximab did not decrease the activity of mTOR, a downstream signaling target of EGFR, PIK3CA, and RAS. The combined administration of cetuximab and mTOR inhibitors exerted a remarkably increased antitumor activity, particularly in HNSCC cells that are resistant to cetuximab as a single agent. Indeed, cotargeting mTOR together with cetuximab caused a rapid tumor collapse of both PIK3CA- and RAS-expressing HNSCC xenografts (P < .001), concomitant with reduced proliferation (P < .001) and lymphangiogenesis (P < .001).

Conclusion

The presence of PIK3CA and RAS mutations and other alterations affecting the mTOR pathway activity in HNSCC could be exploited to predict the potential resistance to cetuximab, and to select the patients that may benefit the most from the concomitant administration of cetuximab and PI3K and/or mTOR inhibitors as a precision molecular therapeutic option for HNSCC patients.

Current and investigational drug strategies for glioblastoma

Medical treatments for glioblastoma face several challenges. Lipophilic alkylators remain the mainstay of treatment, emphasising the primacy of good blood-brain barrier penetration. Temozolomide has emerged as a major contributor to improved patient survival. The roles of procarbazine and vincristine in the procarbazine, lomustine and vincristine (PCV) schedule have attracted scrutiny and several lines of evidence now support the use of lomustine as effective single-agent therapy. Bevacizumab has had a convoluted development history, but clearly now has no major role in first-line treatment, and may even be detrimental to quality of life in this setting. In later disease, clinically meaningful benefits are achievable in some patients, but more impressively the combination of bevacizumab and lomustine shows early promise. Over the last decade, investigational strategies in glioblastoma have largely subscribed to the targeted kinase inhibitor paradigm and have mostly failed. Low prevalence dominant driver lesions such as the FGFR-TACC fusion may represent a niche role for this agent class. Immunological, metabolic and radiosensitising approaches are being pursued and offer more generalised efficacy. Finally, trial design is a crucial consideration. Progress in clinical glioblastoma research would be greatly facilitated by improved methodologies incorporating: (i) routine pharmacokinetic and pharmacodynamic assessments by preoperative dosing; and (ii) multi-stage, multi-arm protocols incorporating new therapy approaches and high-resolution biology in order to guide necessary improvements in science.

Intratumor heterogeneity and its impact on drug distribution and sensitivity

We provide an overview of the available information on the distribution of chemotherapeutics in human tumors, highlighting the progress made to assess the heterogeneity of drug concentrations in relation to the complex neoplastic tissue using novel analytical methods, e.g., mass spectrometry imaging. The increase in interstitial fluid pressure due to abnormal vascularization and stiffness of tumor stroma explains the variable and heterogeneous drug concentrations. Therapeutic strategies to enhance tumor drug distribution, thus possibly increasing efficacy, are discussed.

Glioblastoma multiforme: State of the art and future therapeutics

BACKGROUND

Glioblastoma multiforme (GBM) is the most common and lethal primary malignancy of the central nervous system (CNS). Despite the proven benefit of surgical resection and aggressive treatment with chemo- and radiotherapy, the prognosis remains very poor. Recent advances of our understanding of the biology and pathophysiology of GBM have allowed the development of a wide array of novel therapeutic approaches, which have been developed. These novel approaches include molecularly targeted therapies, immunotherapies, and gene therapy.

METHODS

We offer a brief review of the current standard of care, and a survey of novel therapeutic approaches for treatment of GBM.

RESULTS

Despite promising results in preclinical trials, many of these therapies have demonstrated limited therapeutic efficacy in human clinical trials. Thus, although survival of patients with GBM continues to slowly improve, treatment of GBM remains extremely challenging.

CONCLUSION

Continued research and development of targeted therapies, based on a detailed understanding of molecular pathogenesis can reasonably be expected to yield improved outcomes for patients with GBM.

Prognostic and predictive biomarkers in adult and pediatric gliomas: toward personalized treatment

It is increasingly clear that both adult and pediatric glial tumor entities represent collections of neoplastic lesions, each with individual pathological molecular events and treatment responses. In this review, we discuss the current prognostic biomarkers validated for clinical use or with future clinical validity for gliomas. Accurate prognostication is crucial for managing patients as treatments may be associated with high morbidity and the benefits of high risk interventions must be judged by the treating clinicians. We also review biomarkers with predictive validity, which may become clinically relevant with the development of targeted therapies for adult and pediatric gliomas.

Rationale of personalized immunosuppressive medication for hepatocellular carcinoma patients after liver transplantation

Liver transplantation is the only potentially curative treatment for hepatocellular carcinoma (HCC) that is not eligible for surgical resection. However, disease recurrence is the main challenge to the success of this treatment. Immunosuppressants that are universally used after transplantation to prevent graft rejection could potentially have a significant impact on HCC recurrence. Nevertheless, current research is exclusively focused on mammalian target of rapamycin inhibitors, which are thought to be the only class of immunosuppressive agents that can reduce HCC recurrence. In fact, substantial evidence from the bench to the bedside indicates that other classes of immunosuppressants may also exert diverse effects; for example, inosine monophosphate dehydrogenase inhibitors potentially have antitumor effects. In this article, we aim to provide a comprehensive overview of the potential effects of different types of immunosuppressants on HCC recurrence and their mechanisms of action from both experimental and clinical perspectives. To ultimately improve the outcomes of HCC patients after transplantation, we propose a concept and approaches for developing personalized immunosuppressive medication to be used either as immunosuppression maintenance or during the prevention/treatment of HCC recurrence.

Prognostic role of phospho-PRAS40 (Thr246) expression in gastric cancer

INTRODUCTIONS

Phospho-PRAS40(Thr246) (phosphorylated proline-rich Akt substrate of 40 kilodaltons at Thr246) is a biomarker for phosphatidylinositol 3-kinase (PI3K) pathway activation and AKT inhibitors sensitivity.

MATERIAL AND METHODS

In this study, we immunohistochemically investigated the expression of phospho-PRAS40(Thr246) in 141 gastric cancer tumors, and evaluated its clinicopathological and prognostic significance.

RESULTS

Sixty-four cases (45.4%) were defined as phospho-PRAS40(Thr246) positive. Phospho-PRAS40(Thr246) correlated positively with lymph node metastasis, lymphatic infiltration, vascular infiltration and shorter survival. Furthermore, phospho-PRAS40(Thr246) is an independent prognostic factor for gastric cancer.

CONCLUSIONS

Our data suggest that phospho-PRAS40(Thr246) was frequently expressed in gastric cancers, and correlated with malignant progression and poor prognosis of patients. PI3K pathway-targeted therapies should be considered in the future treatment of gastric cancers.

mTOR inhibitor AZD8055 inhibits proliferation and induces apoptosis in laryngeal carcinoma

The mammalian target of rapamycin (mTOR) kinase forms two multiprotein complexes, mTORC1 and mTORC2, which regulate cell growth, survival, and autophagy. Allosteric inhibitors of mTORC1, such as rapamycin, have been extensively used to study tumor cell growth, proliferation, and autophagy but have shown only limited clinical utility. Here, we describe AZD8055, a novel ATP-competitive inhibitor of mTOR kinase activity, against all class I phosphatidylinositol3-kinase (PI3K) and other members of the PI3K-like kinase family. The study was to determine the effect of AZD8055 on proliferation and apoptosis on Hep-2, a human laryngeal cancer cell line and to investigate the underlying mechanism(s) of action. Hep-2 cells were treated with AZD8055 for 24, 48 or 72 h. MTT was used to determine cell proliferation. Rhodamine 123 and TUNEL staining were used to determine mitochondrial membrane potential and cell apoptosis analyzed by fluorescence-activated cell sorting (FACS). Protein expressions were examined by western blotting. Treatment with AZD8055 inhibited proliferation and induced apoptosis in Hep-2 cells in a dose- and time-dependent manner. During the prolonged treatment with AZD8055, AZD8055 inhibits the mammalian target of rapamycin mTOR. Further experiments showed which signaling cascade p-4EBP1 and substrate EIF4E as well as downstream proteins were down regulated. Furthermore, our study showed that the expression profiles of various BH3-only proteins including Bid, Bad, and Bim, apoptosis regulatory protein cleaved caspase3 was up regulated in a time-dependent manner in Hep-2 cells treated with AZD8055. Thus, in vitro, AZD8055 potently inhibits proliferation and induces apoptosis in head and neck squamous cell carcinoma.

Hsp90 inhibition enhances PI-3 kinase inhibition and radiosensitivity in glioblastoma

PURPOSE

Combined targeting with a PI3-kinase inhibitor, BKM120, and an Hsp90 inhibitor, HSP990, was investigated as a multi-targeted approach to potentiate cell death in glioblastoma (GBM). Additionally, the effect of dual drug treatment combined with cytotoxic stress (radiation therapy) was examined.

METHODS

Four human GBM cell lines containing wild-type or mutated PTEN and/or p53 were studied. The effects of drug treatments on cell viability, apoptosis induction, pAKt activity, cell cycle arrest, clonogenicity, and tumor growth delay were studied.

RESULTS

Combined concurrent treatment with both drugs produced more cell killing in cell viability and apoptosis assays than either drug alone. BKM120 plus HSP990 induced suppression of baseline Akt signaling as well as radiation (RT)-induced pAkt signaling in all cell lines. Cell cycle analysis revealed that HSP990 and BKM120, singly or combined, induced G2/M arrest leading to apoptosis/necrosis and polyploidy. Additionally, the drugs radiosensitized GBM cells in clonogenic assays. In vivo tumor growth delay studies demonstrated the effectiveness of combined drug treatment with HSP990 and BKM120 over single drug treatment, as well as the effectiveness of combined drug treatment in enhancing the effectiveness of radiation therapy.

CONCLUSIONS

In conclusion, HSP990 and BKM120, with and without RT, are active agents against glioma tumors. The sensitivity to these agents does not appear to depend on PTEN/p53status in the cell lines tested. We suggest that the combined action of both drugs is a viable multi-targeted strategy with the potential to improve clinical outcome for patients with high-grade glioma.