MET and PI3K/mTOR as a potential combinatorial therapeutic target in malignant pleural mesothelioma

Combined treatment with crizotinib and temsirolimus is an effective strategy in mantle cell lymphoma and can overcome acquired resistance to temsirolimus

Constitutive activation of the PI3K/AKT/mTOR-pathway plays an important role in the pathogenesis of mantle cell lymphoma (MCL), leading to approval of the mTOR inhibitor temsirolimus for relapsed or refractory MCL. Yet, despite favorable initial response rates, early relapses under treatment have been observed. Therefore, understanding the underlying mechanisms of temsirolimus resistance and developing strategies to overcome it is highly warranted. Here, we established a new temsirolimus-resistant MCL cell line to evaluate the molecular background of resistance to this drug. Transcriptome profiling and gene set enrichment analysis comparing temsirolimus-sensitive and -resistant cell lines showed significant upregulation of PI3K/AKT/mTor-, RAS signaling- and the RTK-dependent PDGFR-, FGFR-, Met- and ALK-signaling-pathways in the resistant cells. Furthermore, MET, known as important proto-oncogene and mediator of drug resistance, was among the most upregulated genes in the resistant cells. Importantly, Met protein was overexpressed in both, MCL cells with acquired as well as intrinsic temsirolimus resistance, but could not be detected in any of the temsirolimus sensitive ones. Combined pharmacological inhibition of mTOR and Met signaling with temsirolimus and the RTK inhibitor crizotinib significantly restored sensitivity to temsirolimus. Furthermore, this combined treatment proved to be synergistic in all MCL cell lines investigated and was also active in primary MCL cells. In summary, we showed for the first time that overexpression of MET plays an important role for mediating temsirolimus resistance in MCL and combined treatment with temsirolimus and crizotinib is a very promising therapeutic approach for MCL and an effective strategy to overcome temsirolimus resistance.

Indolyl-chalcone derivatives trigger apoptosis in cisplatin-resistant mesothelioma cells through aberrant tubulin polymerization and deregulation of microtubule-associated proteins

Introduction

Malignant pleural mesothelioma (MPM) is a neoplasm with dismal prognosis and notorious resistance to the standard therapeutics cisplatin and pemetrexed. Chalcone derivatives are efficacious anti-cancer agents with minimal toxicity and have, therefore, gained pharmaceutical interest. Here, we investigated the efficacy of CIT-026 and CIT-223, two indolyl-chalcones (CITs), to inhibit growth and viability of MPM cells and defined the mechanism by which the compounds induce cell death.

Methods

The effects of CIT-026 and CIT-223 were analyzed in five MPM cell lines, using viability, immunofluorescence, real-time cell death monitoring, and tubulin polymerization assays, along with siRNA knockdown. Phospho-kinase arrays and immunoblotting were used to identify signaling molecules that contribute to cell death.

Results

CIT-026 and CIT-223 were toxic in all cell lines at sub-micromolar concentrations, in particular in MPM cells resistant to cisplatin and pemetrexed, while normal fibroblasts were only modestly affected. Both CITs targeted tubulin polymerization via (1) direct interaction with tubulin and (2) phosphorylation of microtubule regulators STMN1, CRMP2 and WNK1. Formation of aberrant tubulin fibers caused abnormal spindle morphology, mitotic arrest and apoptosis. CIT activity was not reduced in CRMP2-negative and STMN1-silenced MPM cells, indicating that direct tubulin targeting is sufficient for toxic effects of CITs.

Discussion

CIT-026 and CIT-223 are highly effective inducers of tumor cell apoptosis by disrupting microtubule assembly, with only modest effects on non-malignant cells. CITs are potent anti-tumor agents against MPM cells, in particular cells resistant to standard therapeutics, and thus warrant further evaluation as potential small-molecule therapeutics in MPM.

LncRNAs and related molecular basis in malignant pleural mesothelioma: challenges and potential

Malignant pleural mesothelioma (MPM) is a rare but invasive cancer, which mainly arises from mesothelial tissues of pleura, peritoneum and pericardium. Despite significant advances in treatments, the prognosis of MPM patients remains poor, and the 5-year survival rate is less than 10%. Therefore, it is urgent to explore novel therapeutic targets for the treatment of MPM. Growing evidence has indicated that long non-coding RNAs (lncRNAs) potentially could be promising therapeutic targets for numerous cancers. In this regard, lncRNAs might also potentially therapeutic targets for MPM. Recent advances have been made to investigate the molecular basis of MPM. This review first provides a comprehensive overview of roles of lncRNAs in MPM and then discusses the relationship between molecular basis of MPM and MPM-related lncRNAs to implement them as promising therapeutic targets for MPM.

The Genes-Stemness-Secretome Interplay in Malignant Pleural Mesothelioma: Molecular Dynamics and Clinical Hints

MPM has a uniquely poor somatic mutational landscape, mainly driven by environmental selective pressure. This feature has dramatically limited the development of effective treatment. However, genomic events are known to be associated with MPM progression, and specific genetic signatures emerge from the exceptional crosstalk between neoplastic cells and matrix components, among which one main area of focus is hypoxia. Here we discuss the novel therapeutic strategies focused on the exploitation of MPM genetic asset and its interconnection with the surrounding hypoxic microenvironment as well as transcript products and microvesicles representing both an insight into the pathogenesis and promising actionable targets.

Mesothelioma-associated fibroblasts enhance proliferation and migration of pleural mesothelioma cells via c-Met/PI3K and WNT signaling but do not protect against cisplatin

BACKGROUND

Pleural mesothelioma (PM) is an aggressive malignancy with poor prognosis. Unlike many other cancers, PM is mostly characterized by inactivation of tumor suppressor genes. Its highly malignant nature in absence of tumor driving oncogene mutations indicates an extrinsic supply of stimulating signals by cells of the tumor microenvironment (TME). Cancer-associated fibroblasts (CAFs) are an abundant cell type of the TME and have been shown to drive the progression of several malignancies. The aim of the current study was to isolate and characterize patient-derived mesothelioma-associated fibroblasts (Meso-CAFs), and evaluate their impact on PM cells.

METHODS

Meso-CAFs were isolated from surgical specimens of PM patients and analyzed by array comparative genomic hybridization, next generation sequencing, transcriptomics and proteomics. Human PM cell lines were retrovirally transduced with GFP. The impact of Meso-CAFs on tumor cell growth, migration, as well as the response to small molecule inhibitors, cisplatin and pemetrexed treatment was investigated in 2D and 3D co-culture models by videomicroscopy and automated image analysis.

RESULTS

Meso-CAFs show a normal diploid genotype without gene copy number aberrations typical for PM cells. They express CAF markers and lack PM marker expression. Their proteome and secretome profiles clearly differ from normal lung fibroblasts with particularly strong differences in actively secreted proteins. The presence of Meso-CAFs in co-culture resulted in significantly increased proliferation and migration of PM cells. A similar effect on PM cell growth and migration was induced by Meso-CAF-conditioned medium. Inhibition of c-Met with crizotinib, PI3K with LY-2940002 or WNT signaling with WNT-C59 significantly impaired the Meso-CAF-mediated growth stimulation of PM cells in co-culture at concentrations not affecting the PM cells alone. Meso-CAFs did not provide protection of PM cells against cisplatin but showed significant protection against the EGFR inhibitor erlotinib.

CONCLUSIONS

Our study provides the first characterization of human patient-derived Meso-CAFs and demonstrates a strong impact of Meso-CAFs on PM cell growth and migration, two key characteristics of PM aggressiveness, indicating a major role of Meso-CAFs in driving PM progression. Moreover, we identify signaling pathways required for Meso-CAF-mediated growth stimulation. These data could be relevant for novel therapeutic strategies against PM.

The Evolving Therapeutic Landscape for Malignant Pleural Mesothelioma

PURPOSE OF REVIEW

For patients with malignant pleural mesothelioma, prognosis is poor with extremely low 5-year survival rates and limited therapeutic options. Here, we review the current treatment landscape for mesothelioma and highlight promising future therapeutic directions.

RECENT FINDINGS

Evolving frontline therapeutic options for mesothelioma include VEGF inhibition in combination with chemotherapy and dual immune checkpoint inhibition, with synergisms between the therapies and response prediction via biomarkers also being explored. Evolving experimental treatments for mesothelioma include PARP and ALK inhibitors, dendritic and CAR T-cell therapies, anti-mesothelin vaccines, and oncolytic viral therapies, representing timely advances in the field. The therapeutic landscape for malignant pleural mesothelioma is evolving and preferred treatment in the frontline and later settings will likely evolve with it. However, this does not preclude the evidence for including multi-modal therapies spanning angiogenesis and immune checkpoint inhibitors, and biomarker utilization, in current clinical trials and management.

Malignant Pleural Mesothelioma: Current Understanding of the Immune Microenvironment and Treatments of a Rare Disease

Simple Summary

Malignant pleural mesothelioma is a rare disease with an annual incidence of around 3000 cases a year in the United States. Most cases are caused by asbestos exposure, with a latency period of up to 40 years but overall survival of approximately only 6–12 months after the time of diagnosis. Often, the treatment is multimodal and consists of surgery, chemotherapy, and radiation. While the survival benefit of treatment is impactful, overall prolongation remains marginal. Nevertheless, the advent of new treatment approaches involving the interactions of targeted immune therapies and the tumor microenvironment appear to offer some promise. Furthering our understanding of these complex interactions in conjunction with the host immune system will likely prove to be pivotal in advancing current treatment options for malignant pleural mesothelioma.

Abstract

Malignant pleural mesothelioma is a rare disease with an annual incidence of around 3000 cases a year in the United States. Most cases are caused by asbestos exposure, with a latency period of up to 40 years. Pleural mesothelioma is an aggressive disease process with overall survival of roughly 6–12 months after the time of diagnosis. It is divided into three subtypes: epithelioid, mixed type, and sarcomatoid type, with the epithelioid subtype having the best overall survival. Often, the treatment is multimodality with surgery, chemotherapy, and radiation. The survival benefit is improved but remains marginal. New treatment options involving targeted immune therapies appear to offer some promise. The tumor microenvironment is the ecosystem within the tumor that interacts and influences the host immune system. Understanding this complex interaction and how the host immune system is involved in the progression of the disease process is important to define and guide potential treatment options for this devastating and rare disease.

DNA repair and damage pathways in mesothelioma development and therapy

Malignant mesothelioma (MMe) is an aggressive neoplasm that occurs through the transformation of mesothelial cells. Asbestos exposure is the main risk factor for MMe carcinogenesis. Other important etiologies for MMe development include DNA damage, over-activation of survival signaling pathways, and failure of DNA damage response (DDR). In this review article, first, we will describe the most important signaling pathways that contribute to MMe development and their interaction with DDR. Then, the contribution of DDR failure in MMe progression will be discussed. Finally, we will review the latest MMe therapeutic strategies that target the DDR pathway.

Expression of phosphorylated ribosomal protein S6 in mesothelioma patients - correlation with clinico-pathological characteristics and outcome: results from the European Thoracic Oncology Platform (ETOP) Mesoscape project

Pleural mesothelioma (PM) is an aggressive malignancy with poor prognosis. Although histology and pathologic stage are important prognostic factors, better prognostic biomarkers are needed. The ribosomal protein S6 is a downstream target of the phosphatidylinositol 3-kinase (PI3K) pathway involved in protein synthesis and cell proliferation. In previous studies, low phosphorylated S6 (pS6) immunoreactivity was significantly correlated with longer progression-free survival (PFS) and overall survival (OS) in PM patients. We aimed to correlate pS6 expression to clinical data in a large multi-centre PM cohort as part of the European Thoracic Oncology Platform (ETOP) Mesoscape project. Tissue Micro Arrays (TMAs) of PM were constructed and expression of pS6 was evaluated by a semi-quantitatively aggregate H-score. Expression results were correlated to patient characteristics as well as OS/PFS. pS6 IHC results of 364 patients from 9 centres, diagnosed between 1999 and 2017 were available. The primary histology of included tumours was epithelioid (70.3%), followed by biphasic (24.2%) and sarcomatoid (5.5%). TMAs included both treatment-naïve and tumour tissue taken after induction chemotherapy. High pS6 expression (181 patients with H-score>1.41) was significantly associated with less complete resection. In the overall cohort, OS/PFS were not significantly different between pS6-low and pS6-high patients. In a subgroup analysis non-epithelioid (biphasic and sarcomatoid) patients with high pS6 expression showed a significantly shorter OS (p < 0.001, 10.7 versus 16.9 months) and PFS (p < 0.001, 6.2 versus 10.8 months). In subgroup analysis, in non-epithelioid PM patients high pS6 expression was associated with significantly shorter OS and PFS. These exploratory findings suggest a clinically relevant PI3K pathway activation in non-epithelioid PM which might lay the foundation for future targeted treatment strategies.

Biological basis for novel mesothelioma therapies

Mesothelioma is an aggressive cancer that is associated with exposure to asbestos. Although asbestos is banned in several countries, including the UK, an epidemic of mesothelioma is predicted to affect middle-income countries during this century owing to their heavy consumption of asbestos. The prognosis for patients with mesothelioma is poor, reflecting a failure of conventional chemotherapy that has ultimately resulted from an inadequate understanding of its biology. However, recent work has revolutionised the study of mesothelioma, identifying genetic and pathophysiological vulnerabilities, including the loss of tumour suppressors, epigenetic dysregulation and susceptibility to nutrient stress. We discuss how this knowledge, combined with advances in immunotherapy, is enabling the development of novel targeted therapies.

Protein Phosphatase 2A as a Therapeutic Target in Small Cell Lung Cancer

Protein phosphatase 2A (PP2A), a serine/threonine phosphatase involved in the regulation of apoptosis, proliferation, and DNA-damage response, is overexpressed in many cancers, including small cell lung cancer (SCLC). Here we report that LB100, a small molecule inhibitor of PP2A, when combined with platinum-based chemotherapy, synergistically elicited an antitumor response both in vitro and in vivo with no apparent toxicity. Using inductively coupled plasma mass spectrometry, we determined quantitatively that sensitization via LB100 was mediated by increased uptake of carboplatin in SCLC cells. Treatment with LB100 alone or in combination resulted in inhibition of cell viability in two-dimensional culture and three-dimensional spheroid models of SCLC, reduced glucose uptake, and attenuated mitochondrial and glycolytic ATP production. Combining LB100 with atezolizumab increased the capacity of T cells to infiltrate and kill tumor spheroids, and combining LB100 with carboplatin caused hyperphosphorylation of the DNA repair marker γH2AX and enhanced apoptosis while attenuating MET signaling and invasion through an endothelial cell monolayer. Taken together, these data highlight the translational potential of inhibiting PP2A with LB100 in combination with platinum-based chemotherapy and immunotherapy in SCLC.

Increased production of matrix metalloproteinase-7 (MMP-7) by asbestos exposure enhances tissue migration of human regulatory T-like cells

The effects of asbestos on immunocompetent cells have been investigated. In particular, attention was paid to regulatory T cell function, which was observed using the HTLV-1 immortalized human polyclonal T cell line MT-2. Exposure to asbestos (approximately more than 25 μg/mL for 1-3 day) induced apoptosis, and we observed an increase in regulatory T cell function and acceleration of the cell cycle with continuous exposure to low concentrations of asbestos (5-10 μg/mL for more than eight months). Furthermore, cDNA microarray analysis in this study revealed that expression of matrix metalloproteinase-7 (MMP-7) was markedly higher in exposed sublines compared to original MT-2 cells. It was determined that MMP-7 had no effect on Treg function, as determined by examination of sublines and by addition of recombinant MMP-7 and neutralizing antibodies or inhibitors of MMP-7. However, when examining melting of the extracellular matrix (an MMP-7-mediated event) or the extent to which the MT-2 parent strain or long-term exposed subline cells pass through a fibronectin-coated filter, more filter passes were observed for the subline. These results suggest that the effect of asbestos fibers on Treg cells results in excessive migration of the tumor microenvironment through hypersecretion of MMP-7 together with an increase in suppressive function and enhancement of cell cycle progression. Therefore, one possible way to prevent the development of asbestos-induced cancer is to reduce the function (including MMP-7 production) or amount of Treg cells by physiologically active substances or food ingredients. Alternatively, it may be possible to invoke immune checkpoint treatments when carcinogenesis occurs.

Preclinical Models of Malignant Mesothelioma

Rodent models of malignant mesothelioma help facilitate the understanding of the biology of this highly lethal cancer and to develop and test new interventions. Introducing the same genetic lesions as found in human mesothelioma in mice results in tumors that show close resemblance with the human disease counterpart. This includes the extensive inflammatory responses that characterize human malignant mesothelioma. The relatively fast development of mesothelioma in mice when the appropriate combination of lesions is introduced, with or without exposure to asbestos, make the autochthonous models particularly useful for testing new treatment strategies in an immunocompetent setting, whereas Patient-Derived Xenograft models are particularly useful to assess effects of inter- and intra-tumor heterogeneity and human-specific features of mesothelioma. It is to be expected that new insights obtained by studying these experimental systems will lead to new more effective treatments for this devastating disease.

Combined MEK and PI3K/p110β Inhibition as a Novel Targeted Therapy for Malignant Mesothelioma Displaying Sarcomatoid Features

Among malignant mesotheliomas (MM), the sarcomatoid subtype is associated with higher chemoresistance and worst survival. Due to its low incidence, there has been little progress in the knowledge of the molecular mechanisms associated with sarcomatoid MM, which might help to define novel therapeutic targets. In this work, we show that loss of PTEN expression is frequent in human sarcomatoid MM and PTEN expression levels are lower in sarcomatoid MM than in the biphasic and epithelioid subtypes. Combined Pten and Trp53 deletion in mouse mesothelium led to nonepithelioid MM development. In Pten;Trp53-null mice developing MM, the Gαi2-coupled receptor subunit activated MEK/ERK and PI3K, resulting in aggressive, immune-suppressed tumors. Combined inhibition of MEK and p110β/PI3K reduced mouse tumor cell growth in vitro. Therapeutic inhibition of MEK and p110β/PI3K using selumetinib (AZD6244, ARRY-142886) and AZD8186, two drugs that are currently in clinical trials, increased the survival of Pten;Trp53-null mice without major toxicity. This drug combination effectively reduced the proliferation of primary cultures of human pleural (Pl) MM, implicating nonepithelioid histology and high vimentin, AKT1/2, and Gαi2 expression levels as predictive markers of response to combined MEK and p110β/PI3K inhibition. Our findings provide a rationale for the use of selumetinib and AZD8186 in patients with MM with sarcomatoid features. This constitutes a novel targeted therapy for a poor prognosis and frequently chemoresistant group of patients with MM, for whom therapeutic options are currently lacking. SIGNIFICANCE: Mesothelioma is highly aggressive; its sarcomatoid variants have worse prognosis. Building on a genetic mouse model, a novel combination therapy is uncovered that is relevant to human tumors.

Small Cell Lung Cancer Therapeutic Responses Through Fractal Measurements: From Radiology to Mitochondrial Biology

Small cell lung cancer (SCLC) is an aggressive neuroendocrine disease with an overall 5 year survival rate of ~7%. Although patients tend to respond initially to therapy, therapy-resistant disease inevitably emerges. Unfortunately, there are no validated biomarkers for early-stage SCLC to aid in early detection. Here, we used readouts of lesion image characteristics and cancer morphology that were based on fractal geometry, namely fractal dimension (FD) and lacunarity (LC), as novel biomarkers for SCLC. Scanned tumors of patients before treatment had a high FD and a low LC compared to post treatment, and this effect was reversed after treatment, suggesting that these measurements reflect the initial conditions of the tumor, its growth rate, and the condition of the lung. Fractal analysis of mitochondrial morphology showed that cisplatin-treated cells showed a discernibly decreased LC and an increased FD, as compared with control. However, treatment with mdivi-1, the small molecule that attenuates mitochondrial division, was associated with an increase in FD as compared with control. These data correlated well with the altered metabolic functions of the mitochondria in the diseased state, suggesting that morphological changes in the mitochondria predicate the tumor’s future ability for mitogenesis and motogenesis, which was also observed on the CT scan images. Taken together, FD and LC present ideal tools to differentiate normal tissue from malignant SCLC tissue as a potential diagnostic biomarker for SCLC.

Cytoreductive surgery with hyperthermic intraperitoneal chemotherapy for peritoneal mesothelioma: patient selection and special considerations

Malignant peritoneal mesothelioma (MPM) is a rare, aggressive malignancy that typically presents with vague symptoms, ascites, and/or diffuse peritoneal studding. Despite findings of advanced disease within the peritoneal cavity, spread beyond the abdomen is uncommon. Although advances in systemic chemotherapy have been made, cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC) remain the mainstay of treatment. Median overall survival of approximately 50 months with CRS/HIPEC has been demonstrated, with age, gender, histologic subtype, peritoneal carcinomatosis index, comorbidities, nodal and extra-abdominal metastases, and completeness of cytoreduction all playing a role in prognosis. In patients with refractory malignant ascites and unresectable disease, complete resolution of ascites and improvement in quality of life have been demonstrated with palliative HIPEC. In appropriately selected patients, CRS/HIPEC plays a critical role in the treatment and palliation of MPM.

The Role of PI3K in Met Driven Cancer: A Recap

The Receptor Tyrosine Kinase (RTK) Met, overexpressed or mutated in cancer, plays a major role in cancer progression and represents an attractive target for cancer therapy. However RTK inhibitors can lead to drug resistance, explaining the necessity to develop therapies that target downstream signaling. Phosphatidylinositide 3-kinase (PI3K) is one of the most deregulated pathways in cancer and implicated in various types of cancer. PI3K signaling is also a major signaling pathway downstream of RTK, including Met. PI3K major effectors include Akt and "mechanistic Target of Rapamycin" (mTOR), which each play key roles in numerous and various cell functions. Advancements made due to the development of molecular and pharmaceutical tools now allow us to delve into the roles of each independently. In this review, we summarize the current understanding we possess of the activation and role of PI3K/Akt/mTOR, downstream of Met, in cancer.

Discovery and Therapeutic Exploitation of Mechanisms of Resistance to MET Inhibitors in Glioblastoma

PURPOSE

Glioblastoma (GBM) is the most common and most lethal primary malignant brain tumor. The receptor tyrosine kinase MET is frequently upregulated or overactivated in GBM. Although clinically applicable MET inhibitors have been developed, resistance to single modality anti-MET drugs frequently occurs, rendering these agents ineffective. We aimed to determine the mechanisms of MET inhibitor resistance in GBM and use the acquired information to develop novel therapeutic approaches to overcome resistance.Experimental Design: We investigated two clinically applicable MET inhibitors: crizotinib, an ATP-competitive small molecule inhibitor of MET, and onartuzumab, a monovalent monoclonal antibody that binds to the extracellular domain of the MET receptor. We developed new MET inhibitor-resistant cells lines and animal models and used reverse phase protein arrays (RPPA) and functional assays to uncover the compensatory pathways in MET inhibitor-resistant GBM.

RESULTS

We identified critical proteins that were altered in MET inhibitor-resistant GBM including mTOR, FGFR1, EGFR, STAT3, and COX-2. Simultaneous inhibition of MET and one of these upregulated proteins led to increased cell death and inhibition of cell proliferation in resistant cells compared with either agent alone. In addition, in vivo treatment of mice bearing MET-resistant orthotopic xenografts with COX-2 or FGFR pharmacological inhibitors in combination with MET inhibitor restored sensitivity to MET inhibition and significantly inhibited tumor growth.

CONCLUSIONS

These data uncover the molecular basis of adaptive resistance to MET inhibitors and identify new FDA-approved multidrug therapeutic combinations that can overcome resistance.

Peritoneal Metastases from Malignant Mesothelioma

Diffuse malignant peritoneal mesothelioma (MPM) is a rare cancer that is ultimately fatal in almost all afflicted individuals. Morbidity and mortality from MPM is due to its propensity to progress locoregionally within the abdominal cavity. Patients with MPM most commonly present with nonspecific abdominal symptoms that usually lead to diagnosis when the condition is relatively advanced. MPM is considered a chemotherapy-resistant malignancy.

Inactivation of Tp53 and Pten drives rapid development of pleural and peritoneal malignant mesotheliomas

Malignant mesothelioma (MM) is a therapy-resistant cancer arising primarily from the lining of the pleural and peritoneal cavities. The most frequently altered genes in human MM are cyclin-dependent kinase inhibitor 2A (CDKN2A), which encodes components of the p53 (p14ARF) and RB (p16INK4A) pathways, BRCA1-associated protein 1 (BAP1), and neurofibromatosis 2 (NF2). Furthermore, the p53 gene (TP53) itself is mutated in ~15% of MMs. In many MMs, the PI3K-PTEN-AKT-mTOR signaling node is hyperactivated, which contributes to tumor cell survival and therapeutic resistance. Here, we demonstrate that the inactivation of both Tp53 and Pten in the mouse mesothelium is sufficient to rapidly drive aggressive MMs. Pten^L/L ;Tp53^L/L mice injected intraperitoneally or intrapleurally with adenovirus-expressing Cre recombinase developed high rates of peritoneal and pleural MMs (92% of mice with a median latency of 9.4 weeks and 56% of mice with a median latency of 19.3 weeks, respectively). MM cells from these mice showed consistent activation of Akt-mTor signaling, chromosome breakage or aneuploidy, and upregulation of Myc; occasional downregulation of Bap1 was also observed. Collectively, these findings suggest that when Pten and Tp53 are lost in combination in mesothelial cells, DNA damage is not adequately repaired and genomic instability is widespread, whereas the activation of Akt due to Pten loss protects genomically damaged cells from apoptosis, thereby increasing the likelihood of tumor formation. Additionally, the mining of an online dataset (The Cancer Genome Atlas) revealed codeletions of PTEN and TP53 and/or CDKN2A/p14ARF in ~25% of human MMs, indicating that cooperative losses of these genes contribute to the development of a significant proportion of these aggressive neoplasms and suggesting key target pathways for therapeutic intervention.

A subgroup of pleural mesothelioma expresses ALK protein and may be targetable by combined rapamycin and crizotinib therapy

Malignant pleural mesothelioma (MPM) is a neoplasm with inferior prognosis and notorious chemotherapeutic resistance. Targeting aberrantly overexpressed kinases to cure MPM is a promising therapeutic strategy. Here, we examined ALK, MET and mTOR as potential therapeutic targets and determined the combinatorial efficacy of ALK and mTOR targeting on tumor cell growth in vivo.

First, ALK overexpression, rearrangement and mutation were studied in primary MPM by qRT-PCR, FISH, immunohistochemistry and sequence analysis; mTOR and MET expression by qRT-PCR and immunohistochemistry. Overexpression of full-length ALK transcripts was observed in 25 (19.5%) of 128 primary MPM, of which ten expressed ALK protein. ALK overexpression was not associated with gene rearrangement, amplification or kinase-domain mutation. mTOR protein was detected in 28.7% MPM, co-expressed with ALK or MET in 5% and 15% MPM, respectively. The ALK/MET inhibitor crizotinib enhanced the anti-tumor effect of the mTOR-inhibitor rapamycin in a patient-derived MPM xenograft with co-activated ALK/mTOR: combined therapy achieved tumor shrinkage in 4/5 tumors and growth stagnation in one tumor. Treatment effects on proliferation, apoptosis, autophagy and pathway signaling were assessed using Ki-67 immunohistochemistry, TUNEL assay, LC3B immunofluorescence, and immunoblotting. Co-treatment significantly suppressed cell proliferation and induced autophagy and caspase-independent, necrotic cell death. Rapamycin/crizotinib simultaneously inhibited mTORC1 (evidenced by S6 kinase and RPS6 dephosphorylation) and ALK signaling (ALK, AKT, STAT3 dephosphorylation), and crizotinib suppressed the adverse AKT activation induced by rapamycin.

In conclusion, co-treatment with rapamycin and crizotinib is effective in suppressing MPM tumor growth and should be further explored as a therapeutic alternative in mesothelioma.

Curcumin blocks autophagy and activates apoptosis of malignant mesothelioma cell lines and increases the survival of mice intraperitoneally transplanted with a malignant mesothelioma cell line

Malignant mesothelioma (MM) is a primary tumor arising from the serous membranes. The resistance of MM patients to conventional therapies, and the poor patients’ survival, encouraged the identification of molecular targets for MM treatment. Curcumin (CUR) is a “multifunctional drug”. We explored the in vitro effects of CUR on cell proliferation, cell cycle regulation, pro-survival signaling pathways, apoptosis, autophagy of human (MM-B1, H-Meso-1, MM-F1), and mouse (#40a) MM cells. In addition, we evaluated the in vivo anti-tumor activities of CUR in C57BL/6 mice intraperitoneally transplanted with #40a cells forming ascites.

CUR in vitro inhibited MM cells survival in a dose- and time-dependent manner and increased reactive oxygen species’intracellular production and induced DNA damage. CUR triggered autophagic flux, but the process was then blocked and was coincident with caspase 8 activation which activates apoptosis. CUR-mediated apoptosis was supported by the increase of Bax/Bcl-2 ratio, increase of p53 expression, activation of caspase 9, cleavage of PARP-1, increase of the percentage of cells in the sub G1 phase which was reduced (MM-F1 and #40a) or abolished (MM-B1 and H-Meso-1) after MM cells incubation with the apoptosis inhibitor Z-VAD-FMK. CUR treatment stimulated the phosphorylation of ERK1/2 and p38 MAPK, inhibited that of p54 JNK and AKT, increased c-Jun expression and phosphorylation and prevented NF-κB nuclear translocation. Intraperitoneal administration of CUR increased the median survival of C57BL/6 mice intraperitoneally transplanted with #40a cells and reduced the risk of developing tumors. Our findings may have important implications for the design of MM treatment using CUR.

Tumor and circulating biomarkers in patients with second-line hepatocellular carcinoma from the randomized phase II study with tivantinib

ARQ 197-215 was a randomized placebo-controlled phase II study testing the MET inhibitor tivantinib in second-line hepatocellular carcinoma (HCC) patients. It identified tumor MET as a key biomarker in HCC.Aim of this research was to study the prognostic and predictive value of tumor (MET, the receptor tyrosine kinase encoded by the homonymous MNNG-HOS transforming gene) and circulating (MET, hepatocyte growth factor [HGF], alpha-fetoprotein [AFP], vascular endothelial growth factor [VEGF]) biomarkers in second-line HCC. Tumor MET-High status was centrally assessed by immunohistochemistry. Circulating biomarkers were centrally analyzed on serum samples collected at baseline and every 4-8 weeks, using medians as cut-off to determine High/Low status. Tumor MET, tested in 77 patients, was more frequently High after (82%) versus before (40%) sorafenib. A significant interaction (p = 0.04) between tivantinib and baseline tumor MET in terms of survival was observed. Baseline circulating MET and HGF (102 patients) High status correlated with shorter survival (HR 0.61, p = 0.03, and HR 0.60, p = 0.02, respectively), while the association between AFP (104 patients) or VEGF (103 patients) status and survival was non-significant.

CONCLUSIONS

Tumor MET levels were higher in patients treated with sorafenib. Circulating biomarkers such as MET and HGF may be prognostic in second-line HCC. These results need to be confirmed in larger randomized clinical trials.

Focal adhesion kinase a potential therapeutic target for pancreatic cancer and malignant pleural mesothelioma

The non-receptor cytoplasmic tyrosine kinase, Focal Adhesion Kinase (FAK) is known to play a key role in a variety of normal and cancer cellular functions such as survival, proliferation, migration and invasion. It is highly active and overexpressed in various cancers including Pancreatic Ductal Adenocarcinoma (PDAC) and Malignant Pleural Mesothelioma (MPM). Here, initially, we demonstrate that FAK is overexpressed in both PDAC and MPM cell lines. Then we analyze effects of two small molecule inhibitors PF-573228, and PF-431396, which are dual specificity inhibitors of FAK and proline rich tyrosine kinase 2 (PYK2), as well as VS-6063, another small molecule inhibitor that specifically inhibits FAK but not PYK2 for cell growth, motility and invasion of PDAC and MPM cell lines. Treatment with PF-573228, PF-431396 and VS-6063 cells resulted in a dose-dependent inhibition of growth and anchorage-independent colony formation in both cancer cell lines. Furthermore, these compounds suppressed the phosphorylation of FAK at its active site, Y397, and functionally induced significant apoptosis and cell cycle arrest in both cell lines. Using the ECIS (Electric cell-substrate impedance sensing) system, we found that treatment of both PF compounds suppressed adherence and migration of PDAC cells on fibronectin. Interestingly, 3D-tumor organoids derived from autochthonous KC (Kras;PdxCre) mice treated with PF-573228 revealed a significant decrease in tumor organoid size and increase in organoid cell death. Taken together, our results show that FAK is an important target for mesothelioma and pancreatic cancer therapy that merit further translational studies.

Current Management and Future Opportunities for Peritoneal Metastases: Peritoneal Mesothelioma

PURPOSE

Diffuse malignant peritoneal mesothelioma (MPM) is a rare and ultimately fatal cancer that was first described just over a century ago. It is a diffuse malignancy arising from the mesothelial lining of the peritoneum; morbidity and mortality from MPM is due to its propensity to progress locoregionally within the abdominal cavity.

METHODS

The purpose of this article is to review the current state-of-the-science related to the diagnosis, staging, and treatment of MPM.

RESULTS

The condition afflicts men and women equally and the peak incidence is between 55 and 60 years of age although it can arise in the young and elderly. Patients afflicted with MPM most commonly present with nonspecific abdominal symptoms that usually lead to diagnosis when the condition is relatively advanced. Historically, median overall survival for MPM patients without treatment is < 1 year. The couplet of systemic pemetrexed and cisplatin has an overall response rate of approximately 25% and a median overall survival of approximately 1 year.

CONCLUSION

The available data, almost all retrospective in nature, have shown that in selected patients, operative cytoreduction (CRS) and regional chemotherapy administered as hyperthermic intraoperative peritoneal chemotherapy (HIPEC) or early postoperative intraperitoneal chemotherapy (EPIC) is associated with long-term survival. Studies on the molecular biology of MPM have yielded new insights relating to the potentially important role of the phosphoinsitide-3-kinase/mammalian target of rapamycin (PI3 K/mTOR) pathways and immune checkpoint inhibitors that may translate into new therapeutic options for patients with diffuse MPM.

Target therapy: new drugs or new combinations of drugs in malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is a disease with a poor prognosis due to its aggressive nature. The management of patients with MPM is controversial. Considering that the contribution of surgery and radiation therapy in the management of this disease is not yet established, systemic treatments are predominantly considered during the course of MPM. Unfortunately, the currently therapeutic armamentarium is scarce and its outcomes still appear modest. New treatment strategies are needed. In preclinical setting, cell cycle regulation, apoptosis, growth factor pathways, and angiogenesis pathways involved in the development of MPM have been identified. However, in clinical setting, several drugs targeting these pathways resulted without a significant activity. A deeper knowledge of the biology and pathogenesis of this disease is required to develop more effective tools for diagnosis, therapy and prevention. This paper reviews therapeutic advances in MPM, with a particular focus on new drugs and new association of drugs of target therapy.

A link between the fibroblast growth factor axis and the miR-16 family reveals potential new treatment combinations in mesothelioma

Malignant pleural mesothelioma (MPM) is an aggressive malignancy with very limited therapeutic options. Fibroblast growth factor (FGF) signals play important roles in mesothelioma cell growth. Several FGFs and FGF receptors (FGFRs) are predicted targets of the miR‐15/16 family, which is downregulated in MPM. The aim of this study was to explore the link between the miR‐15/16 family and the FGF axis in MPM. Expression analyses via RT‐qPCR showed downregulation of the FGF axis after transfection with miR‐15/16 mimics. Direct interaction was confirmed by luciferase reporter assays. Restoration of miR‐15/16 led to dose‐dependent growth inhibition in MPM cell lines, which significantly correlated with their sensitivity to FGFR inhibition. Treatment with recombinant FGF2 prevented growth inhibition and further reduced the levels of FGF/R‐targeting microRNAs, indicating a vicious cycle between miR‐15/16 down‐ and FGF/FGFR signaling upregulation. Combined inhibition of two independent miR‐15/16 targets, the FGF axis and Bcl‐2, resulted in additive or synergistic activity. Our data indicate that post‐transcriptional repression of FGF‐mediated signals contributes to the tumor suppressor function of the microRNA‐15/16 family. Inhibiting hyperactivated FGF signals and Bcl‐2 might serve as a novel therapeutic combination strategy in MPM.

CAR T-cell immunotherapy of MET-expressing malignant mesothelioma

Mesothelioma is an incurable cancer for which effective therapies are required. Aberrant MET expression is prevalent in mesothelioma, although targeting using small molecule-based therapeutics has proven disappointing. Chimeric antigen receptors (CARs) couple the HLA-independent binding of a cell surface target to the delivery of a tailored T-cell activating signal. Here, we evaluated the anti-tumor activity of MET re-targeted CAR T-cells against mesothelioma. Using immunohistochemistry, MET was detected in 67% of malignant pleural mesotheliomas, most frequently of epithelioid or biphasic subtype. The presence of MET did not influence patient survival. Candidate MET-specific CARs were engineered in which a CD28+CD3ζ endodomain was fused to one of 3 peptides derived from the N and K1 domains of hepatocyte growth factor (HGF), which represents the minimum MET binding element present in this growth factor. Using an NIH3T3-based artificial antigen-presenting cell system, we found that all 3 candidate CARs demonstrated high specificity for MET. By contrast, these CARs did not mediate T-cell activation upon engagement of other HGF binding partners, namely CD44v6 or heparan sulfate proteoglycans, including Syndecan-1. NK1-targeted CARs demonstrated broadly similar in vitro potency, indicated by destruction of MET-expressing mesothelioma cell lines, accompanied by cytokine release. In vivo anti-tumor activity was demonstrated following intraperitoneal delivery to mice with an established mesothelioma xenograft. Progressive tumor regression occurred without weight loss or other clinical indicators of toxicity. These data confirm the frequent expression of MET in malignant pleural mesothelioma and demonstrate that this can be targeted effectively and safely using a CAR T-cell immunotherapeutic strategy.

Malignant peritoneal mesothelioma: a review

Mesothelioma is a malignancy of serosal membranes. It is most commonly encountered in the visceral pleura with the second most common location in the peritoneum. The diagnosis is very rare and has been linked to toxic exposure to industrial pollutants, especially asbestos. Malignant peritoneal mesothelioma (MPM) commonly presents with diffuse, extensive spread throughout the abdomen with rare metastatic spread beyond the abdominal cavity. Due to its rarity and nonspecific symptoms, it is usually diagnosed late when the disease burden is extensive. Because pleural mesothelioma is more common than MPM, most research has been on the pleural variant and extrapolated for MPM. While treatment advances have been made for MPM, the disease is universally fatal from either abdominal complications secondary to the spread of disease or starvation. Untreated, the life expectancy is less than a year. Cytoreductive surgery (CRS) with heated intraperitoneal chemotherapy (HIPEC) has become the mainstay of therapy with systemic therapies still being developed. We will review the epidemiology of MPM and discuss diagnostic and treatment strategies.

PIK3CA hotspot mutations differentially impact responses to MET targeting in MET-driven and non-driven preclinical cancer models

Background

The MET receptor tyrosine kinase represents a promising target in cancer. PIK3CA activating mutations are common in several tumor types and can potentially confer resistance to anti-receptor tyrosine kinase therapy.

Methods

MET and/or PI3K pathway inhibition was assessed in NIH3T3 cells harboring MET-activating point mutation with or without ectopic expression of PIK3CA^E545K and PIK3CA^H1047R, as well as in MET-expressing head and neck cancer cells with endogenous PIK3CA mutations. Endpoints included PI3K pathway activation, cell proliferation, colony-forming ability, cell death, wound-healing, and an in vivo model.

Results

PIK3CA^E545K and PIK3CA^H1047R confer resistance to MET inhibition in MET-driven models. PIK3CA^H1047R was more potent than PIK3CA^E545K at inducing resistance in PI3K pathway activation, cell proliferation, colony-forming ability, induction of cell death and wound-healing upon MET inhibition. Resistance to MET inhibition could be synergistically overcome by co-targeting PI3K. Furthermore, combined MET/PI3K inhibition led to enhanced anti-tumor activity in vivo in tumors harboring PIK3CA^H1047R. In head and neck cancer cells the combination of MET/PI3K inhibitors led to more-than-additive effects.

Conclusions

PIK3CA mutations can lead to resistance to MET inhibition, supporting future clinical evaluation of combinations of PI3K and MET inhibitors in common scenarios of malignant neoplasms featuring aberrant MET expression and PIK3CA mutations.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-017-0660-5) contains supplementary material, which is available to authorized users.

PI3 Kinase Pathway and MET Inhibition is Efficacious in Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) is an aggressive cancer that is commonly associated with prior asbestos exposure. Receptor tyrosine kinases (RTKs) such as MET and its downstream target PI3K are overexpressed and activated in a majority of MPMs. Here, we studied the combinatorial therapeutic efficacy of the MET/ALK inhibitor crizotinib, with either a pan-class I PI3K inhibitor, BKM120, or with a PI3K/mTOR dual inhibitor, GDC-0980, in mesothelioma. Cell viability results showed that MPM cells were highly sensitive to crizotinib, BKM120 and GDC-0980 when used individually and their combination was more effective in suppressing growth. Treatment of MPM cells with these inhibitors also significantly decreased cell migration, and the combination of them was synergistic. Treatment with BKM120 alone or in combination with crizotinib induced G2-M arrest and apoptosis. Both crizotinib and BKM120 strongly inhibited the activity of MET and PI3K as evidenced by the decreased phosphorylation of MET, AKT and ribosomal S6 kinase. Using a PDX mouse model, we showed that a combination of crizotinib with BKM120 was highly synergetic in inhibiting MPM tumor growth. In conclusion our findings suggest that dual inhibition of PI3K and MET pathway is an effective strategy in treating MPM as compared to a single agent.

The resistance related to targeted therapy in malignant pleural mesothelioma: Why has not the target been hit yet?

Malignant pleural mesothelioma (MPM) is an aggressive tumor of the pleura with a poor prognosis. The most active first-line regimens are platinum compounds and pemetrexed. There is no standard second-line treatment in MPM. Advances in the understanding of tumor molecular biology have led to the development of several targeted treatments, which have been evaluated in clinical trials. Unfortunately none of the explored targeted treatments can currently be recommended as routine treatment in MPM. We reviewed the biological pathways involved in MPM, the clinical trials about targeted therapy, and possible related mechanisms of resistance. We suggest that specific genetic markers are needed as targets of selective therapy. By this way the selection of patients based on the molecular profile may facilitate a therapeutic strategy that allows the use of the most appropriate drug for each patient.

New therapeutic strategies for malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is a rare and aggressive malignant disease affecting the mesothelium, commonly associated to asbestos exposure. Therapeutic actions are limited due to the late stage at which most patients are diagnosed and the intrinsic chemo-resistance of the tumor. The recommended systemic therapy for MPM is cisplatin/pemetrexed regimen with a mean overall survival of about 12months and a median progression free survival of less than 6months. Considering that the incidence of this tumor is expected to increase in the next decade and that its prognosis is poor, novel therapeutic approaches are urgently needed. For some tumors, such as lung cancer and breast cancer, druggable oncogenic alterations have been identified and targeted therapy is an important option for these patients. For MPM, clinical guidelines do not recommend biological targeted therapy, mainly because of poor target definition or inappropriate trial design. Further studies are required for a full comprehension of the molecular pathogenesis of MPM and for the development of new target agents. This review updates pre-clinical and clinical data on the efficacy of targeted therapy and immune checkpoint inhibition in the treatment of mesothelioma. Finally, future perspectives in this deadly disease are also discussed.

A randomized, placebo-controlled, phase 1/2 study of tivantinib (ARQ 197) in combination with irinotecan and cetuximab in patients with metastatic colorectal cancer with wild-type KRAS who have received first-line systemic therapy

Cetuximab in combination with an irinotecan-containing regimen is a standard treatment in patients with KRAS wild-type (KRAS WT), metastatic colorectal cancer (mCRC). We investigated the addition of the oral MET inhibitor tivantinib to cetuximab + irinotecan (CETIRI) based on preclinical evidence that activation of the MET pathway may confer resistance to anti-EGFR therapy. Previously treated patients with KRAS WT advanced or mCRC were enrolled. The phase 1, open-label 3 + 3, dose-escalation study evaluated the safety and maximally tolerated dose of tivantinib plus CETIRI. The phase 2, randomized, double-blinded, placebo-controlled study of biweekly CETIRI plus tivantinib or placebo was restricted to patients who had received only one prior line of chemotherapy. The phase 2 primary endpoint was progression-free survival (PFS). The recommended phase 2 dose was tivantinib (360 mg/m(2) twice daily) with biweekly cetuximab (500 mg/m(2)) and irinotecan (180 mg/m(2)). Among 117 patients evaluable for phase 2 analysis, no statistically significant PFS difference was observed: 8.3 months on tivantinib vs. 7.3 months on placebo (HR, 0.85; 95% confidence interval, 0.55-1.33; P = 0.38). Subgroup analyses trended in favor of tivantinib in patients with MET-High tumors by immunohistochemistry, PTEN-Low tumors, or those pretreated with oxaliplatin, but subgroups were too small to draw conclusions. Neutropenia, diarrhea, nausea and rash were the most frequent severe adverse events in tivantinib-treated patients. The combination of tivantinib and CETIRI was well tolerated but did not significantly improve PFS in previously treated KRAS WT mCRC. Tivantinib may be more active in specific subgroups.

Unique fractal evaluation and therapeutic implications of mitochondrial morphology in malignant mesothelioma

Malignant mesothelioma (MM), is an intractable disease with limited therapeutic options and grim survival rates. Altered metabolic and mitochondrial functions are hallmarks of MM and most other cancers. Mitochondria exist as a dynamic network, playing a central role in cellular metabolism. MM cell lines display a spectrum of altered mitochondrial morphologies and function compared to control mesothelial cells. Fractal dimension and lacunarity measurements are a sensitive and objective method to quantify mitochondrial morphology and most importantly are a promising predictor of response to mitochondrial inhibition. Control cells have high fractal dimension and low lacunarity and are relatively insensitive to mitochondrial inhibition. MM cells exhibit a spectrum of sensitivities to mitochondrial inhibitors. Low mitochondrial fractal dimension and high lacunarity correlates with increased sensitivity to the mitochondrial inhibitor metformin. Lacunarity also correlates with sensitivity to Mdivi-1, a mitochondrial fission inhibitor. MM and control cells have similar sensitivities to cisplatin, a chemotherapeutic agent used in the treatment of MM. Neither oxidative phosphorylation nor glycolytic activity, correlated with sensitivity to either metformin or mdivi-1. Our results suggest that mitochondrial inhibition may be an effective and selective therapeutic strategy in mesothelioma, and identifies mitochondrial morphology as a possible predictor of response to targeted mitochondrial inhibition.

Diagnosis and management of patients with malignant peritoneal mesothelioma

Malignant peritoneal mesothelioma (MPM) is a rare neoplastic condition that arises, usually diffusely, from the serosal membranes of the abdominal cavity. MPM represents about 7% to 10% of all mesothelioma diagnoses and this translates into approximately 800 cases per year in the United States. The disease has variable tumor biology but progression, when it occurs, is almost always within the abdominal cavity. Although many patients can be successfully treated at initial presentation, the disease is almost always fatal in time. It afflicts men and women almost equally and the median age at presentation is 50 years. The diagnosis is made when a diffuse malignant process within the abdominal cavity is observed and a tissue sample reveals the characteristic histopathology and immunohistochemical profile of mesothelioma. Initial staging is usually via a cross sectional imaging study of the abdomen and pelvis making sure that the lower thorax is also assessed. If the disease burden and distribution is favorable then operative exploration, cytoreduction, and hyperthermic intraperitoneal chemotherapy (HIPEC) are considered first line treatment in selected patients. Systemic pemetrexed and cisplatin (or gemcitabine) have modest response rates that are of limited duration. Research advances with novel systemic or intraperitoneal agents hold promise.

Latest developments in our understanding of the pathogenesis of mesothelioma and the design of targeted therapies

Malignant mesothelioma is an aggressive cancer whose pathogenesis is causally linked to occupational exposure to asbestos. Familial clusters of mesotheliomas have been observed in settings of genetic predisposition. Mesothelioma incidence is anticipated to increase worldwide in the next two decades. Novel treatments are needed, as current treatment modalities may improve the quality of life, but have shown modest effects in improving overall survival. Increasing knowledge on the molecular characteristics of mesothelioma has led to the development of novel potential therapeutic strategies, including: molecular targeted approaches, that is the inhibition of vascular endothelial growth factor with bevacizumab; immunotherapy with chimeric monoclonal antibody, immunotoxin, antibody drug conjugate, vaccine and viruses; inhibition of asbestos-induced inflammation, that is aspirin inhibition of HMGB1 activity may decrease or delay mesothelioma onset and/or growth. We elaborate on the rationale behind new therapeutic strategies, and summarize available preclinical and clinical results, as well as efforts still ongoing.

Autophagy Correlates with the Therapeutic Responsiveness of Malignant Pleural Mesothelioma in 3D Models

Malignant pleural mesothelioma is a highly chemoresistant solid tumor. We have studied this apoptotic resistance using in vitro and ex vivo three-dimensional models, which acquire a high level of chemoresistance that can be reduced by PI3K/mTOR inhibitors. Here, we investigate the activity of GDC-0980, a novel dual PI3K/mTOR inhibitor, which has been proposed to be effective in mesothelioma. In this work, we aimed to identify mechanisms and markers of efficacy for GDC-0980 by utilizing 3D models of mesothelioma, both in vitro multicellular spheroids and ex vivo tumor fragment spheroids grown from patient tumor samples. We found that a subset of mesothelioma spheroids is sensitive to GDC-0980 alone and to its combination with chemotherapy. Unexpectedly, this sensitivity did not correlate with the activation of the Akt/mTOR pathway. Instead, sensitivity to GDC-0980 correlated with the presence of constitutive ATG13 puncta, a feature of autophagy, a cellular program that supports cells under stress. In tumor fragment spheroids grown from 21 tumors, we also found a subset (n = 11) that was sensitive to GDC-0980, a sensitivity that also correlated with the presence of ATG13 puncta. Interference with autophagy by siRNA of ATG7, an essential autophagic protein, increased the response to chemotherapy, but only in the sensitive multicellular spheroids. In the spheroids resistant to GDC-0980, autophagy appeared to play no role. In summary, we show that GDC-0980 is effective in mesothelioma 3D models that display ATG13 puncta, and that blockade of autophagy increases their response to chemotherapy. For the first time, we show a role for autophagy in the response to chemotherapy of 3D models of mesothelioma and propose ATG13 as a potential biomarker of the therapeutic responsiveness of mesothelioma.

Temsirolimus targets multiple hallmarks of cancer to impede mesothelioma growth in vivo

BACKGROUND AND OBJECTIVE

The mechanistic target of rapamycin (mTOR) promotes cancer cell proliferation and survival, transduces pro-angiogenic signals and regulates immune cell differentiation and function. We hypothesized that temsirolimus, an mTOR inhibitor, would curtail experimental mesothelioma progression in vivo by limiting tumour cell growth, abrogating tumour angiogenesis and modulating immune/inflammatory tumour milieu.

METHODS

We produced flank and pleural syngeneic murine mesotheliomas by delivering AE17 and AB1 murine mesothelioma cells into the right flank or the pleural space of C57BL/6 and BALB/c mice, respectively. Animals were given five times/week intraperitoneal injections of 20 mg/kg temsirolimus or vehicle and were sacrificed on day 26 (flank) or on day 15 (pleural) post-tumour cell propagation.

RESULTS

Temsirolimus limited mesothelioma growth in vivo by stimulating tumour cell apoptosis, inhibiting tumour angiogenesis, enhancing tumour lymphocyte abundance and blocking pro-tumour myeloid cell recruitment. Pleural fluid accumulation was significantly mitigated in AE17 but not in AB1 mesotheliomas. In vitro, temsirolimus hindered mesothelioma cell growth, NF-kappaB activation and macrophage migration.

CONCLUSIONS

In conclusion, temsirolimus apart from inducing tumour cell apoptosis, targets tumour angiogenesis and influences inflammatory tumour microenvironment to halt experimental mesothelioma growth in vivo.

Phase III Multinational, Randomized, Double-Blind, Placebo-Controlled Study of Tivantinib (ARQ 197) Plus Erlotinib Versus Erlotinib Alone in Previously Treated Patients With Locally Advanced or Metastatic Nonsquamous Non-Small-Cell Lung Cancer

PURPOSE

Tivantinib, a MET receptor tyrosine kinase inhibitor, demonstrated increased anticancer activity in preclinical and early clinical studies when combined with erlotinib. Our study aimed to confirm efficacy and safety of the combination in previously treated patients with non-small-cell lung cancer (NSCLC).

PATIENTS AND METHODS

Patients with advanced nonsquamous NSCLC previously treated with one to two systemic regimens, including a platinum doublet, were randomly assigned at a 1:1 ratio to receive erlotinib 150 mg daily plus oral tivantinib 360 mg twice daily (E + T) or erlotinib plus placebo (E + P) until disease progression. Tumor specimens were evaluated for EGFR and KRAS mutations, MET expression, and MET gene amplification. The primary end point was overall survival (OS). Secondary and exploratory objectives included progression-free survival (PFS), OS in molecular subgroups, and safety.

RESULTS

The study enrolled 1,048 patients and was discontinued for futility at the interim analysis. OS did not improve with E + T versus E + P (median OS, 8.5 v 7.8 months, respectively; hazard ratio [HR], 0.98; 95% CI, 0.84 to 1.15; P = .81), even though PFS increased (median PFS, 3.6 v 1.9 months; HR, 0.74; 95% CI, 0.62 to 0.89; P < .001). Exploratory subgroup analyses suggested OS improvement in patients with high MET expression (HR, 0.70; 95% CI, 0.49 to 1.01). Most common adverse events occurring with E + T versus E + P were rash (33.1% v 37.3%, respectively), diarrhea (34.6% v 41.0%), asthenia or fatigue (43.5% v 38.1%), and neutropenia (grade 3 to 4; 8.5% v 0.8%).

CONCLUSION

E + T was well tolerated and increased PFS but did not improve OS in the overall nonsquamous NSCLC population.

Inhibition of autophagy sensitizes malignant pleural mesothelioma cells to dual PI3K/mTOR inhibitors

Malignant pleural mesothelioma (MPM) originates in most of the cases from chronic inflammation of the mesothelium due to exposure to asbestos fibers. Given the limited effect of chemotherapy, a big effort is being made to find new treatment options. The PI3K/mTOR pathway was reported to be upregulated in MPM. We tested the cell growth inhibition properties of two dual PI3K/mTOR inhibitors NVP-BEZ235 and GDC-0980 on 19 MPM cell lines. We could identify resistant and sensitive lines; however, there was no correlation to the downregulation of PI3K/mTOR activity markers. As a result of mTOR inhibition, both drugs efficiently induced long-term autophagy but not cell death. Autophagy blockade by chloroquine in combination with the dual PI3K/mTOR inhibitors significantly induced caspase-independent cell death involving RIP1 in the sensitive cell line SPC212. Cell death in the resistant cell line Mero-82 was less pronounced, and it was not induced via RIP1-dependent mechanism, suggesting the involvement of RIP1 downstream effectors. Cell death induction was confirmed in 3D systems. Based on these results, we identify autophagy as one of the main mechanisms of cell death resistance against dual PI3K/mTOR inhibitors in MPM. As PI3K/mTOR inhibitors are under investigation in clinical trials, these results may help interpreting their outcome and suggest ways for intervention.

Mechano-growth factor accelerates the proliferation and osteogenic differentiation of rabbit mesenchymal stem cells through the PI3K/AKT pathway

BACKGROUND

Mesenchymal stem cells (MSCs) can differentiate into chondroblasts, adipocytes, or osteoblasts under appropriate stimulation. Mechano-growth factor (MGF) reportedly displays a neuroprotective effect in cerebral regions that were exposed to ischemia and is expressed in stromal cells of the eutopic endometrium and in glandular cells of the ectopic endometrium.

RESULTS

This study sought to understand the potential involvement of phosphatidylinositol-3-kinase (PI3K)/protein kinase B (AKT) in MGF-induced growth of rabbit MSCs (rMSCs). We applied various concentrations of MGF to cultured rMSCs and observed the growth rate of the cells, the changes in the phosphorylation state of AKT and mammalian target of rapamycin (mTOR), and the expression levels of alkaline phosphatase and osteocalcin. We found that the growth and osteogenic differentiation of MGF-induced rMSCs were promoted primarily by phosphorylated AKT, and that this phosphorylation, as well mTOR phosphorylation, was mediated by the MGF receptor.

CONCLUSION

Our study suggests that MGF promotes the growth and osteogenic differentiation of rMSCs primarily through the PI3K/AKT pathway.