Lung cancer cell lines harboring MET gene amplification are dependent on Met for growth and survival

The Met receptor tyrosine kinase: a key player in oncogenesis and drug resistance

The Met receptor tyrosine kinase (RTK) is an attractive oncology therapeutic target. Met and its ligand, HGF, play a central role in signaling pathways that are exploited during the oncogenic process, including regulation of cell proliferation, invasion, angiogenesis, and cancer stem cell regulation. Elevated Met and HGF as well as numerous Met genetic alterations have been reported in human cancers and correlate with poor outcome. Alterations of pathways that regulate Met, such as the ubiquitin ligase c-Cbl are also likely to activate Met in the oncogenic setting. Moreover, interactive crosstalk between Met and other receptors such as EGFR, HER2 and VEGFR, underlies a key role for Met in resistance to other RTK-targeted therapies. A large body of preclinical and clinical data exists that supports the use of either antibodies or small molecule inhibitors that target Met or HGF as oncology therapeutics. The prognostic potential of Met expression has been suggested from studies in numerous cancers including lung, renal, liver, head and neck, stomach, and breast. Clinical trials using Met inhibitors indicate that the level of Met expression is a determinant of trial outcome, a finding that is actively under investigation in multiple clinical scenarios. Research in Met prognostics and predictors of drug response is now shifting toward more sophisticated methodologies suitable for development as validated and effective biomarkers that can be partnered with therapeutics to improve patient survival.

New treatment strategy for patients with EGFR-mutant lung cancer

SUMMARY Activating EGFR mutations in non-small-cell lung cancer were discovered in 2004. Patients harboring these mutations, who have been treated with EGFR–tyrosine kinase inhibitor (TKI), are expected to live longer than 2 years. However, lung cancer eventually progresses and the patients die of the disease. Thus, alternative treatments are needed for EGFR-mutated lung cancer. Here, we review the alternative treatments for patients with activating EGFR mutation. Combinations of available EGFR–TKIs (gefitinib or erlotinib) with chemotherapy and newer EGFR–TKIs (second-generation or third-generation EGFR–TKIs) have been developed as treatments for obtaining a more durable response or overcoming the acquired resistance to current EGFR–TKIs. In addition, new drugs other than EGFR–TKIs have also been developed. Their targets include EGFR itself and downstream signals of EGFR pathway, among others. However, these therapies cannot reach clinically striking effects so far. Greater efforts are needed to achieve an increased response, overcome resistance and prolong overall survival.

The effect of deposition Se on the mRNA expression levels of GPxs in goats from a Se-enriched county of China

Previous studies revealed that Se was an important regulatory factor for glutathione peroxidase (GPx) genes. However, the relationship between Se concentrations and mRNA expression levels of GPxs were unclear in goats, especially the goats living in natural Se-enriched area. Thus, the aim of this study was to determine the Se concentrations and the mRNA expression levels of GPx-1, GPx-2, GPx-3, and GPx-4 in goats from Ziyang County (ZY-H and ZY-L goats) and Baoji City (BJ-P goats), which were Se-rich region and Se-poor region in China, respectively. Atomic fluorescence spectrometry was used as an essential method to determine the Se concentrations in heart, liver, spleen, lung, kidney, longissimus, biceps femoris, and serum, and the gene expressions were quantified in mRNA samples extracted from the above tissues by real-time quantitative reverse transcription-polymerase chain reaction. We found that the Se concentrations in ZY-H and ZY-L goats were higher than that in BJ-P goats significantly (P < 0.05), and the pertinence relations of Se levels between serum and heart, liver, spleen, and kidney were significant (P < 0.05). The mRNA levels of GPx-1 in ZY-H and ZY-L goats were higher than that in BJ-P goats very significantly (P < 0.01) except for longissimus (P < 0.05). Our results indicated a significant trend for GPx-2 in the direction of increasing mRNA levels with increasing Se concentrations in goats but had no statistical significance (P > 0.05) in our experimental conditions. As to GPx-3, its mRNA expression in spleen, lung, and kidney (P < 0.05) were upregulated and were consensual to high Se contents in ZY-H goats, but no significant effects were observed in heart, liver, longissimus, and biceps femoris among our three groups (P > 0.05). The mRNA levels of GPx-4 in heart, liver, lung, and kidney of ZY-H and ZY-L goats were higher than that of BJ-P goats (P < 0.05), and the difference was very significant in lung especially (P < 0.01), but no change in spleen, longissimus, and biceps femoris (P > 0.05). In summary, these data suggested that the goats living in Ziyang County were rich in Se, and the deposition Se played important roles in the mRNA expression of GPx-1, GPx-3, and GPx-4 in certain tissues of goats differentially.

Evidence that depletion of the sorting nexin 1 by siRNA promotes HGF-induced MET endocytosis and MET phosphorylation in a gefitinib-resistant human lung cancer cell line

The receptor tyrosine kinase MET and its ligand HGF are known to be overexpressed in malignant tumor cells, and they have been implicated in gefitinib resistance in lung cancer cells. We recently found that sorting nexin 1 (SNX1), a protein that interacts with EGFR, exhibited negative regulation of EGFR trafficking out of early to late endosomes in gefitinib-resistant NSCLC cell lines. To investigate the role of SNX1 on HGF-stimulated MET endocytosis and its downregulation via the early/late endocytic pathway, we examined the effect of depletion of SNX1 expression by siRNA in NSCLC cells. Using immunofluorescence, we found that the silencing of SNX1 by siRNA caused a dramatic change in the intracellular distribution of plasma membrane-associated MET and that the resultant MET staining was spread throughout the cytoplasm, and it co-localized well with the endocytosed Texas red-labeled transferrin in the siRNA-SNX1-transfected cells. We also found efficient MET phosphorylation and rapid endocytic delivery of phosphorylated MET from early endosomes to late endosomes in the siRNA-SNX1-transfected cells. By contrast, the siRNA-control transfected cells showed inefficient endocytic delivery of phosphorylated MET from early endosomes to late endosomes. Furthermore, large amounts of phosphorylated MET that had accumulated in late endosomes were seen even after 60 min of HGF-stimulation in the presence of bafilomycin A1, indicating that degradation of phosphorylated MET proceeds in a late endosome/lysosome pathway. Western blot analysis revealed that depletion of SNX1 by siRNA induced a maximal and dramatic increase in phosphorylated MET at 60 min, followed by an accelerated degradation of phosphorylated MET after HGF stimulation in the cells. Taken together, we suggest that SNX1 plays a suppressive role in the regulation of HGF-stimulated MET/phosphorylated MET endocytosis and downregulation via the early/late endocytic pathway in the gefitinib-resistant NSCLC cells.

Caspase-generated fragment of the Met receptor favors apoptosis via the intrinsic pathway independently of its tyrosine kinase activity

The receptor tyrosine kinase Met and its ligand, the hepatocyte growth factor, are essential to embryonic development, whereas the deregulation of Met signaling is associated with tumorigenesis. While ligand-activated Met promotes survival, caspase-dependent generation of the p40 Met fragment leads to apoptosis induction - hallmark of the dependence receptor. Although the survival signaling pathways induced by Met are well described, the pro-apoptotic signaling pathways are unknown. We show that, although p40 Met contains the entire kinase domain, it accelerates apoptosis independently of kinase activity. In cell cultures undergoing apoptosis, the fragment shows a mitochondrial localization, required for p40 Met-induced cell death. Fulminant hepatic failure induced in mice leads to the generation of p40 Met localized also in the mitochondria, demonstrating caspase cleavage of Met in vivo. According to its localization, the fragment induces mitochondrial permeabilization, which is inhibited by Bak silencing and Bcl-xL overexpression. Moreover, Met silencing delays mitochondrial permeabilization induced by an apoptotic treatment. Thus, the Met-dependence receptor in addition to its well-known role in survival signaling mediated by its kinase activity, also participates in the intrinsic apoptosis pathway through the generation of p40 Met - a caspase-dependent fragment of Met implicated in the mitochondrial permeabilization process.

Targeted therapy by gene transfer of a monovalent antibody fragment against the Met oncogenic receptor

Due to the key role played in critical sub-populations, Met is considered a relevant therapeutic target for glioblastoma multiforme and lung cancers. The anti-Met DN30 antibody, engineered to a monovalent Fab (Mv-DN30), proved to be a potent antagonist, inducing physical removal of Met receptor from the cell surface. In this study, we designed a gene therapy approach, challenging Mv-DN30 in preclinical models of Met-driven human glioblastoma and lung carcinoma. Mv-DN30 was delivered by a Tet-inducible-bidirectional lentiviral vector. Gene therapy solved the limitations dictated by the short half-life of the low molecular weight form of the antibody. In vitro, upon doxycycline induction, the transgene: (1) drove synthesis and secretion of the correctly assembled Mv-DN30; (2) triggered the displacement of Met receptor from the surface of target cancer cells; (3) suppressed the Met-mediated invasive growth phenotype. Induction of transgene expression in cancer cells-transplanted either subcutaneously or orthotopically in nude mice-resulted in inhibition of tumor growth. Direct Mv-DN30 gene transfer in nude mice, intra-tumor or systemic, was followed by a therapeutic response. These results provide proof of concept for a gene transfer immunotherapy strategy by a Fab fragment and encourage clinical studies targeting Met-driven cancers with Mv-DN30.

KEY MESSAGE

Gene transfer allows the continuous in vivo production of therapeutic Fab fragments. Mv-DN30 is an excellent tool for the treatment of Met-driven cancers. Mv-DN30 gene therapy represents an innovative route for Met targeting.

Genetic alterations defining NSCLC subtypes and their therapeutic implications

Lung cancer is the leading cause of cancer death worldwide, accounting for more deaths than breast, prostate and colon cancer combined. While treatment decisions are determined primarily by stage, therapeutically non small cell lung cancer (NSCLC) has traditionally been treated as a single disease. However, recent findings have led to the recognition of histology and molecular subtypes as important determinants in treatment selection. Identifying the genetic differences that define these molecular and histological subtypes has the potential to impact treatment and as such is currently the focus of much research. Microarray and genomic sequencing efforts have provided unparalleled insight into the genomes of lung cancer subtypes, specifically adenocarcinoma (AC) and squamous cell carcinoma (SqCC), revealing subtype specific genomic alterations and molecular subtypes as well as differences in cell signaling pathways. In this review, we discuss the recurrent genomic alterations characteristic of AC and SqCC (including molecular subtypes), their therapeutic implications and emerging clinical practices aimed at tailoring treatments based on a tumor's molecular alterations with the hope of improving patient response and survival.

Targeted therapy for NSCLC with driver mutations

INTRODUCTION

Activating mutations of the epidermal growth factor receptor (EGFR) gene and rearrangement of anaplastic lymphoma kinase (ALK) gene best illustrate the therapeutic relevance of molecular characterization in non-small cell lung cancer (NSCLC) patients. Several genetic aberrations with a potential prognostic or predictive role have been identified, mainly in adenocarcinoma subtype, including ROS1, RET, MET, HER2, BRAF and KRAS. More recently oncogenic drivers, such as DDR2, FGFR1 and PI3KCA, have been characterized in squamous cell lung carcinoma (SCC) and target agents are currently under evaluation. The aim of this review is to summarize the growing scenario of new targetable oncogenes in NSCLC.

AREAS COVERED

For this review article all published data on NSCLC genomic alterations, including the techniques employed for oncogenic drivers identification, the prevalence of each one in lung cancer subtypes, the preclinical data corroborating their role in tumorigenesis and the potential biological tailored agents tested and under evaluation were collected and analyzed using PubMed.

EXPERT OPINION

Oncogenic products represent reliable targets for drug therapy and the expanding knowledge of molecular pathways involved in lung tumorigenesis is resulting in a dramatic change of treatment strategies leading to an improvement in disease and symptom control, extending life duration and improving quality of life.

Population pharmacokinetic analysis from phase I and phase II studies of the humanized monovalent antibody, onartuzumab (MetMAb), in patients with advanced solid tumors

Onartuzumab is a unique, humanized, monovalent (one-armed) monoclonal antibody (mAb) against the MET receptor. The intravenous (IV) pharmacokinetics (PK) of onartuzumab were investigated in a phase I study and a phase II study in recurrent non-small cell lung cancer (NSCLC) patients. The potential for drug-drug interaction (DDI) was assessed during co-administration of IV onartuzumab with oral erlotinib, by measuring the PK of both drugs. The concentration-time profiles of onartuzumab were adequately described using a two-compartment model with linear clearance (CL) at doses between 4 and 30 mg/kg. The estimates for CL, central compartment volume (V1 ), and median terminal half-life were 0.439 L/day, 2.77 L, and 13.4 days, respectively. Statistically significant covariates included creatinine clearance (CrCL) on clearance, weight and gender on V1 , and weight on peripheral compartment volume (V2 ), but the clinical relevance of these covariates needs to be further evaluated. The current analysis did not indicate obvious DDI between onartuzumab and erlotinib. MET diagnostic status did not impact the exposure of either agent. Despite the slightly faster clearance compared with typical bivalent mAbs, the PK of onartuzumab support dosing regimens of 15 mg/kg every 3 weeks or doses equivalent to achieve the target minimum tumoristatic concentration in patients.

Targeting genomic alterations in squamous cell lung cancer

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

Targeting MET: why, where and how?

Despite the initial skepticism, targeted therapies represent a new perspective in the treatment of cancer. Tyrosine kinases, and in particular receptor tyrosine kinases (RTKs), are considered ideal targets for this type of therapy. MET, the tyrosine kinase receptor for the Hepatocyte Growth Factor (HGF), has recently become a very interesting and studied target in oncology. In this review we discuss firstly 'why' the MET/HGF pathway can be considered a target in human tumors; secondly 'where' MET/HGF inhibition can be useful in cancer treatment and finally 'how' MET and HGF can be inhibited using either monoclonal antibodies or tyrosine kinase inhibitors. We also highlight some questions in the anti-MET/HGF targeted therapy field that are still waiting for an answer.

MET overexpression and gene amplification in NSCLC: a clinical perspective

The transmembrane tyrosine kinase mesenchymal-epidermal transition (MET) receptor and its ligand, hepatocyte growth factor, also known as scatter factor, have recently been identified as novel promising targets in several human malignancies, including non-small cell lung cancer (NSCLC). Amplification, mutation, or overexpression of the MET gene can result in aberrant activation of the MET axis, leading to migration, invasion, proliferation, metastasis, and neoangiogenesis of cancer cells, suggesting that interfering with the MET/hepatocyte growth factor pathway could represent a potential antitumor strategy. While the role of MET mutations in NSCLC is not as yet fully understood, retrospective studies have shown that an increased MET gene copy number is a negative prognostic factor. In NSCLC, amplification of the MET gene is a relatively rare event, occurring in approximately 4% of patients not previously exposed to systemic therapies and in up to 20% of patients with acquired resistance to epidermal growth factor receptor tyrosine kinase inhibitors. In preclinical models, the presence of MET amplification is a predictor of high sensitivity to anti-MET compounds, and several agents have entered in clinical trials for patients having advanced disease, with promising results. The aim of the present review is to summarize available data on the role of MET in NSCLC and to describe therapeutic strategies under investigation.

[A new drug in thoracic oncology: MetMab (onartuzumab)]

Met pathway is activated in many solid cancers. In advanced non-small cell lung cancer (NSCLC), Met amplification is involved in 5 to 20% of acquired resistance to EGFR tyrosine kinase inhibitors (TKI) in tumors with initially sensitive EGFR mutation. MetMab (onartuzumab) is a monoclonal single-arm humanized anti-Met antibody. Its fixation on the Met receptor prevents the binding of the ligand (Hepatocyte Growth factor [HGF]) and the signal transduction. After promising results in preclinical and phase I trials, a randomized phase II trial has been conducted in advanced NSCLC in 2nd or 3rd line treatment. One hundred and twenty-eight patients have been randomized between an association of erlotinib+placebo and erlotinib+MetMab (15mg/kg IV every 3 weeks) until progression or toxicity. Patients with overexpression of Met in immunohistochemistry (IHC) had a progression-free survival (PFS) and an overall survival (OS) two-fold (median 1.5 versus 2.9 months; HR=0.53; P=0.04) and three-fold (median 3.8 versus 12.6 months; HR=0.37; P=0.002) longer, respectively, than patients with negative IHC score. The erlotinib+MetMab association had a worse effect on SSP and OS than the control arm in patients with negative IHC. The toxicity profile of MetMab is very good, and the main adverse effect is the occurrence of peripheral edemas, most of the time of low grade. A randomized phase III is on going to validate these results.

Strengthening context-dependent anticancer effects on non-small cell lung carcinoma by inhibition of both MET and EGFR

The MET and EGFR receptor tyrosine kinases (RTK) are often coexpressed and may cross-talk in driving the development and progression of non-small cell lung carcinoma (NSCLC). In addition, MET amplification is an alternative resistance mechanism for escaping EGFR-targeted therapy. To assess the benefits of combined targeting of MET and EGFR for treating NSCLCs, we investigated the activities of these two RTK pathways in NSCLC cell lines and evaluated their responses to SGX523 and erlotinib, the small-molecule kinase inhibitors of MET and EGFR, respectively. We showed that MET interacts with and cross-activates EGFR in MET-amplified or -overexpressed cells. The inhibition of both MET and EGFR results in maximal suppression of downstream signaling and of cell proliferation when their ligands are present. Furthermore, we showed that SGX523 plus erlotinib strengthens anticancer activity in vivo in a cellular context-dependent manner. The combination led to the regression of H1993 tumors by enhancing the suppression of proliferation and inducing apoptosis, whereas H1373 tumor growth was significantly reduced by the combination via suppression of proliferation without inducing apoptosis. SGX523 alone was sufficient to achieve near-complete regression of EBC-1 tumors; its combination with erlotinib strongly inhibited the viability of a population of insensitive cells emerging from an SGX523-treated EBC-1 tumor recurrence. Our data suggest that inhibition of both MET and EGFR can enhance anticancer effects against NSCLCs in a context-dependent manner and thus provide a strong rationale for combining MET and EGFR inhibitors in treating NSCLCs.

EMD 1214063 and EMD 1204831 constitute a new class of potent and highly selective c-Met inhibitors

PURPOSE

The mesenchymal-epithelial transition factor (c-Met) receptor, also known as hepatocyte growth factor receptor (HGFR), controls morphogenesis, a process that is physiologically required for embryonic development and tissue repair. Aberrant c-Met activation is associated with a variety of human malignancies including cancers of the lung, kidney, stomach, liver, and brain. In this study, we investigated the properties of two novel compounds developed to selectively inhibit the c-Met receptor in antitumor therapeutic interventions.

EXPERIMENTAL DESIGN

The pharmacologic properties, c-Met inhibitory activity, and antitumor effects of EMD 1214063 and EMD 1204831 were investigated in vitro and in vivo, using human cancer cell lines and mouse xenograft models.

RESULTS

EMD 1214063 and EMD 1204831 selectively suppressed the c-Met receptor tyrosine kinase activity. Their inhibitory activity was potent [inhibitory 50% concentration (IC50), 3 nmol/L and 9 nmol/L, respectively] and highly selective, when compared with their effect on a panel of 242 human kinases. Both EMD 1214063 and EMD 1204831 inhibited c-Met phosphorylation and downstream signaling in a dose-dependent fashion, but differed in the duration of their inhibitory activity. In murine xenograft models, both compounds induced regression of human tumors, regardless of whether c-Met activation was HGF dependent or independent. Both drugs were well tolerated and induced no substantial weight loss after more than 3 weeks of treatment.

CONCLUSIONS

Our results indicate selective c-Met inhibition by EMD 1214063 and EMD 1204831 and strongly support clinical testing of these compounds in the context of molecularly targeted anticancer strategies.

A novel inhibitor of c-Met and VEGF receptor tyrosine kinases with a broad spectrum of in vivo antitumor activities

The c-Met receptor tyrosine kinase and its ligand, hepatocyte growth factor (HGF), are dysregulated in a wide variety of human cancers and are linked with tumorigenesis and metastatic progression. VEGF also plays a key role in tumor angiogenesis and progression by stimulating the proangiogenic signaling of endothelial cells via activation of VEGF receptor tyrosine kinases (VEGFR). Therefore, inhibiting both HGF/c-Met and VEGF/VEGFR signaling may provide a novel therapeutic approach for treating patients with a broad spectrum of tumors. Toward this goal, we generated and characterized T-1840383, a small-molecule kinase inhibitor that targets both c-Met and VEGFRs. T-1840383 inhibited HGF-induced c-Met phosphorylation and VEGF-induced VEGFR-2 phosphorylation in cancer epithelial cells and vascular endothelial cells, respectively. It also inhibited constitutively activated c-Met phosphorylation in c-met-amplified cancer cells, leading to suppression of cell proliferation. In addition, T-1840383 potently blocked VEGF-dependent proliferation and capillary tube formation of endothelial cells. Following oral administration, T-1840383 showed potent antitumor efficacy in a wide variety of human tumor xenograft mouse models, along with reduction of c-Met phosphorylation levels and microvessel density within tumor xenografts. These results suggest that the efficacy of T-1840383 is produced by direct effects on tumor cell growth and by an antiangiogenic mechanism. Furthermore, T-1840383 showed profound antitumor activity in a gastric tumor peritoneal dissemination model. Collectively, our findings indicate the therapeutic potential of targeting both c-Met and VEGFRs simultaneously with a single small-molecule inhibitor for the treatment of human cancers.

Tivantinib (ARQ197) displays cytotoxic activity that is independent of its ability to bind MET

PURPOSE

MET, the high-affinity receptor for hepatocyte growth factor, is frequently deregulated in human cancer. Tivantinib (ARQ197; Arqule), a staurosporine derivative that binds to the dephosphorylated MET kinase in vitro, is being tested clinically as a highly selective MET inhibitor. However, the mechanism of action of tivantinib is still unclear.

EXPERIMENTAL DESIGN

The activity of tivantinib was analyzed in multiple cellular models, including: cells displaying c-MET gene amplification, strictly 'addicted' to MET signaling; cells with normal c-MET gene copy number, not dependent on MET for growth; cells not expressing MET; somatic knockout cells in which the ATP-binding cleft of MET, where tivantinib binds, was deleted by homologous recombination; and a cell system 'poisoned' by MET kinase hyperactivation, where cells die unless cultured in the presence of a specific MET inhibitor.

RESULTS

Tivantinib displayed cytotoxic activity independently of c-MET gene copy number and regardless of the presence or absence of MET. In both wild-type and isogenic knockout cells, tivantinib perturbed microtubule dynamics, induced G2/M arrest, and promoted apoptosis. Tivantinib did not rescue survival of cells 'poisoned' by MET kinase hyperactivation, but further incremented cell death. In all cell models analyzed, tivantinib did not inhibit HGF-dependent or -independent MET tyrosine autophosphorylation.

CONCLUSIONS

We conclude that tivantinib displays cytotoxic activity via molecular mechanisms that are independent from its ability to bind MET. This notion has a relevant impact on the interpretation of clinical results, on the design of future clinical trials, and on the selection of patients receiving tivantinib treatment.

MET as a possible target for non-small-cell lung cancer

Lung cancer is a heterogeneous group of disorders that is now being subdivided into molecular subtypes with dedicated targeted therapies. The MET receptor tyrosine kinase has been identified as aberrantly overexpressed, potentially having activating mutations, and amplified in certain subsets of lung cancers. The ligand hepatocyte growth factor (HGF) can also be overexpressed in lung cancer or expressed in stroma, and both the MET receptor and the HGF ligand can be targets for therapeutics, especially in lung cancer. Activation of MET leads to a plethora of biochemical and biologic changes both in normal and cancerous cells. Preclinically, it has been shown that silencing or inactivating MET leads to decreased viability of cancer cells. There are a number of compounds against MET/HGF in clinical trials that have been shown to be active in lung cancers. This review will summarize the biology of MET as well as its therapeutic inhibition in lung cancer.

The role of MET receptor tyrosine kinase in non-small cell lung cancer and clinical development of targeted anti-MET agents

A better understanding of the pathophysiology and evolution of non-small cell lung cancer (NSCLC) has identified a number of molecular targets and spurred development of novel targeted therapeutic agents. The MET receptor tyrosine kinase and its ligand hepatocyte growth factor (HGF) are implicated in tumor cell proliferation, migration, invasion, and angiogenesis in a broad spectrum of human cancers, including NSCLC. Amplification of MET has been reported in approximately 5%-22% of lung tumors with acquired resistance to small-molecule inhibitors of the epidermal growth factor receptor (EGFR). Resistance to EGFR inhibitors is likely mediated through downstream activation of the phosphoinositide 3-kinase /AKT pathway. Simultaneous treatment of resistant tumors with a MET inhibitor plus an EGFR inhibitor can abrogate activation of downstream effectors of cell growth, proliferation, and survival, thereby overcoming acquired resistance to EGFR inhibitors. Development and preclinical testing of multiple agents targeting the HGF-MET pathway, including monoclonal antibodies targeting HGF or the MET receptor and small-molecule inhibitors of the MET tyrosine kinase, have confirmed the crucial role of this pathway in NSCLC. Several agents are now in phase III clinical development for the treatment of NSCLC. This review summarizes the role of MET in the pathophysiology of NSCLC and in acquired resistance to EGFR inhibitors and provides an update on progress in the clinical development of inhibitors of MET for treatment of NSCLC.

Drug Resistance Mechanisms in Non-Small Cell Lung Carcinoma

Lung cancer is the most commonly diagnosed cancer in the world. “Driver” and “passenger” mutations identified in lung cancer indicate that genetics play a major role in the development of the disease, progression, metastasis and response to therapy. Survival rates for lung cancer treatment have remained stagnant at ~15% over the past 40 years in patients with disseminated disease despite advances in surgical techniques, radiotherapy and chemotherapy. Resistance to therapy; either intrinsic or acquired has been a major hindrance to treatment leading to great interest in studies seeking to understand and overcome resistance. Genetic information gained from molecular analyses has been critical in identifying druggable targets and tumor profiles that may be predictors of therapeutic response and mediators of resistance. Mutated or overexpressed epidermal growth factor receptor (EGFR) and translocations in the echinoderm microtubule-associated protein-like 4 (EML4)-anaplastic lymphoma kinase (ALK) genes (EML4-ALK) are examples of genetic aberrations resulting in targeted therapies for both localized and metastatic disease. Positive clinical responses have been noted in patients harboring these genetic mutations when treated with targeted therapies compared to patients lacking these mutations. Resistance is nonetheless a major factor contributing to the failure of targeted agents and standard cytotoxic agents. In this review, we examine molecular mechanisms that are potential drivers of resistance in non-small cell lung carcinoma, the most frequently diagnosed form of lung cancer. The mechanisms addressed include resistance to molecular targeted therapies as well as conventional chemotherapeutics through the activity of multidrug resistance proteins.

The Blocking of c-Met Signaling Induces Apoptosis through the Increase of p53 Protein in Lung Cancer

Purpose

c-Met is an attractive potential target for novel therapeutic inhibition of human cancer, and c-Met tyrosine kinase inhibitors (TKIs) are effective growth inhibitors of various malignancies. However, their mechanisms in anticancer effects are not clear. In the present study, we investigated the possibility that blocking c-Met signaling induces p53-mediated growth inhibition in lung cancer.

Materials and Methods

The growth inhibitory effects of c-Met TKI (SU11274) on lung cancer cells and a xenograft model were assessed using the MTT assay, flow cytometry, and terminal deoxyribonucleotide transferase-mediated nick-end labeling staining. The role of p53 protein in the sensitivity of c-Met TKI (SU11274) was examined by Western blot analysis and immunohistochemistry.

Results

SU11274 significantly induced apoptosis in A549 cells with wild-type p53, compared with that in Calu-1 cells with null-type p53. SU11274 increased p53 protein by enhancing the stability of p53 protein. Increased p53 protein by SU11274 induced up-regulation of Bax and PUMA expression and down-regulation of Bcl-2 expression, subsequently activating caspase 3. In p53 knock-out and knock-in systems, we confirmed that SU11274 caused apoptosis through the p53-mediated apoptotic pathway. Likewise, in the A549 xenograft model, SU11274 effectively shrank tumor volume and induced apoptosis via increased p53 protein expression. Blocking c-Met signaling increased the level of p53 protein.

Conclusion

Our finding suggested that p53 plays an important role in SU11274-induced apoptosis, and p53 status seems to be related to the sensitivity to SU11274 in lung cancer.

First- and second-line treatment of non-small-cell lung cancer patients withEGFRmutation-positive tumors

SUMMARY EGFR is a mediator of cell proliferation and is targeted by EGFR tyrosine kinase inhibitors (TKIs) to treat non-small-cell lung cancer (NSCLC). Efficacy of EGFR TKIs (specifically erlotinib and gefitinib) is influenced by mutations in EGFR. We review the evidence for targeted use of EGFR TKIs in the first-line treatment of EGFR mutation-positive NSCLC, considering epidemiology and timing/methodology of diagnosis. First- and second-generation TKIs, and other investigational drugs, also have a role in the second-line treatment of EGFR mutation-positive NSCLC; we discuss this in the context of disease progression and drug resistance. Patients with EGFR mutation-positive tumors should be considered as a separate subpopulation within NSCLC, which is the first step towards individualized treatment of this disease.

EGFR and c-Met Cross Talk in Glioblastoma and Its Regulation by Human Cord Blood Stem Cells

Receptor tyrosine kinases (RTK) and their ligands control critical biologic processes, such as cell proliferation, migration, and differentiation. Aberrant expression of these receptor kinases in tumor cells alters multiple downstream signaling cascades that ultimately drive the malignant phenotype by enhancing tumor cell proliferation, invasion, metastasis, and angiogenesis. As observed in human glioblastoma (hGBM) and other cancers, this dysregulation of RTK networks correlates with poor patient survival. Epidermal growth factor receptor (EGFR) and c-Met, two well-known receptor kinases, are coexpressed in multiple cancers including hGBM, corroborating that their downstream signaling pathways enhance a malignant phenotype. The integration of c-Met and EGFR signaling in cancer cells indicates that treatment regimens designed to target both receptor pathways simultaneously could prove effective, though resistance to tyrosine kinase inhibitors continues to be a substantial obstacle. In the present study, we analyzed the antitumor efficacy of EGFR inhibitors erlotinib and gefitinib and c-Met inhibitor PHA-665752, along with their respective small hairpin RNAs (shRNAs) alone or in combination with human umbilical cord blood stem cells (hUCBSCs), in glioma cell lines and in animal xenograft models. We also measured the effect of dual inhibition of EGFR/c-Met pathways on invasion and wound healing. Combination treatments of hUCBSC with tyrosine kinase inhibitors significantly inhibited invasion and wound healing in U251 and 5310 cell lines, thereby indicating the role of hUCBSC in inhibition of RTK-driven cell behavior. Further, the EGFR and c-Met localization in glioma cells and hGBM clinical specimens indicated that a possible cross talk exists between EGFR and c-Met signaling pathway.

miRNA-34 prevents cancer initiation and progression in a therapeutically resistant K-ras and p53-induced mouse model of lung adenocarcinoma

Lung cancer is the leading cause of cancer deaths worldwide, and current therapies fail to treat this disease in the vast majority of cases. The RAS and p53 pathways are two of the most frequently altered pathways in lung cancers, with such alterations resulting in loss of responsiveness to current therapies and decreased patient survival. The microRNA-34 (mir-34) gene family members are downstream transcriptional targets of p53, and miR-34 expression is reduced in p53 mutant tumors; thus, we hypothesized that treating mutant Kras;p53 tumors with miR-34 would represent a powerful new therapeutic to suppress lung tumorigenesis. To this end we examined the therapeutically resistant Kras(LSL-G12D)(/+);Trp53(LSL-R172H)(/+) mouse lung cancer model. We characterized tumor progression in these mice following lung-specific transgene activation and found tumors as early as 10 weeks postactivation, and severe lung inflammation by 22 weeks. Tumors harvested from these lungs have elevated levels of oncogenic miRNAs, miR-21 and miR-155; are deficient for p53-regulated miRNAs; and have heightened expression of miR-34 target genes, such as Met and Bcl-2. In the presence of exogenous miR-34, epithelial cells derived from these tumors show reduced proliferation and invasion. In vivo treatment with miR-34a prevented tumor formation and progression in Kras(LSL-G12D)(/+);Trp53(LSL-R172H)(/+) mice. Animals infected with mir-34a-expressing lentivirus at the same time as transgene activation had little to no evidence of tumorigenesis, and lentivirus-induced miR-34a also prevented further progression of preformed tumors. These data support the use of miR-34 as a lung tumor-preventative and tumor-static agent.

c-MET as a potential therapeutic target and biomarker in cancer

The receptor tyrosine kinase c-MET and its ligand, hepatocyte growth factor (HGF), regulate multiple cellular processes that stimulate cell proliferation, invasion and angiogenesis. This review provides an overview of the evidence to support c-MET or the HGF/c-MET signaling pathway as relevant targets for personalized cancer treatment based on high frequencies of c-MET and/or HGF overexpression, activation, amplification in non-small cell lung carcinoma (NSCLC), gastric, ovarian, pancreatic, thyroid, breast, head and neck, colon and kidney carcinomas. Additionally, the current knowledge of small molecule inhibitors (tivantinib [ARQ 197]), c-MET/HGF antibodies (rilotumumab and MetMAb) and mechanisms of resistance to c-MET-targeted therapies are discussed.

An overview of the c-MET signaling pathway

c-MET is a receptor tyrosine kinase that, after binding with its ligand, hepatocyte growth factor, activates a wide range of different cellular signaling pathways, including those involved in proliferation, motility, migration and invasion. Although c-MET is important in the control of tissue homeostasis under normal physiological conditions, it has also been found to be aberrantly activated in human cancers via mutation, amplification or protein overexpression. This paper provides an overview of the c-MET signaling pathway, including its role in the development of cancers, and provides a rationale for targeting the pathway as a possible treatment option.

Higher levels of c-Met expression and phosphorylation identify cell lines with increased sensitivity to AMG-458, a novel selective c-Met inhibitor with radiosensitizing effects

PURPOSE

c-Met is overexpressed in some non-small cell lung cancer (NSCLC) cell lines and tissues. Cell lines with higher levels of c-Met expression and phosphorylation depend on this receptor for survival. We studied the effects of AMG-458 on 2 NSCLC cell lines.

METHODS AND MATERIALS

3-(4,5-Dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assays assessed the sensitivities of the cells to AMG-458. Clonogenic survival assays illustrated the radiosensitizing effects of AMG-458. Western blot for cleaved caspase 3 measured apoptosis. Immunoblotting for c-Met, phospho-Met (p-Met), Akt/p-Akt, and Erk/p-Erk was performed to observe downstream signaling.

RESULTS

AMG-458 enhanced radiosensitivity in H441 but not in A549. H441 showed constitutive phosphorylation of c-Met. A549 expressed low levels of c-Met, which were phosphorylated only in the presence of exogenous hepatocyte growth factor. The combination of radiation therapy and AMG-458 treatment was found to synergistically increase apoptosis in the H441 cell line but not in A549. Radiation therapy, AMG-458, and combination treatment were found to reduce p-Akt and p-Erk levels in H441 but not in A549. H441 became less sensitive to AMG-458 after small interfering RNA knockdown of c-Met; there was no change in A549. After overexpression of c-Met, A549 became more sensitive, while H441 became less sensitive to AMG-458.

CONCLUSIONS

AMG-458 was more effective in cells that expressed higher levels of c-Met/p-Met, suggesting that higher levels of c-Met and p-Met in NSCLC tissue may classify a subset of tumors that are more sensitive to molecular therapies against this receptor.

JAK2-related pathway induces acquired erlotinib resistance in lung cancer cells harboring an epidermal growth factor receptor-activating mutation

Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors, such as gefitinib and erlotinib, are effective for non-small cell lung cancer with activating EGFR mutations. However, even in patients with an initial dramatic response to such a drug, acquired resistance develops after 6-12 months. A secondary mutation of T790M in EGFR and amplification of the MET gene account for this resistance; however, the mechanism(s) of approximately 30% of acquired resistance cases remain unknown. We established an erlotinib-resistant lung cancer cell line named PC-9/ER3 that harbors an EGFR mutation after continuously exposing PC-9 cells to erlotinib. PC-9/ER3 cells were 136-fold more resistant to erlotinib than the parental cells. Although the PC-9/ER3 cells did not carry the T790M mutation or MET amplification and had similar levels of phosphorylated (p) STAT3, pJAK2 increased in the resistant cells. It was found in the present study that 3-12 h of exposure to erlotinib in both cell lines did not affect pJAK2 expression, but did result in increased pSTAT3 expression. pAkt in PC-9/ER3 cells was less suppressed than in PC-9 cells, although pEGFR and pMAPK were markedly suppressed in both cell lines. The combined treatment of erlotinib plus a JAK2 inhibitor (JSI-124) suppressed pAkt in PC-9/ER3 cells. Similarly, the combination of erlotinib plus JSI-124 or siRNA against JAK2 restored sensitivity to erlotinib in PC-9/ER3 cells. The combination of erlotinib plus JSI-124 was also effective for reducing PC-9/ER3 tumors in a murine xenograft model. Our results suggest that the activation of JAK2 partially accounts for acquired erlotinib resistance.

A novel SND1-BRAF fusion confers resistance to c-Met inhibitor PF-04217903 in GTL16 cells through [corrected] MAPK activation

Targeting cancers with amplified or abnormally activated c-Met (hepatocyte growth factor receptor) may have therapeutic benefit based on nonclinical and emerging clinical findings. However, the eventual emergence of drug resistant tumors motivates the pre-emptive identification of potential mechanisms of clinical resistance. We rendered a MET amplified gastric cancer cell line, GTL16, resistant to c-Met inhibition with prolonged exposure to a c-Met inhibitor, PF-04217903 (METi). Characterization of surviving cells identified an amplified chromosomal rearrangement between 7q32 and 7q34 which overexpresses a constitutively active SND1-BRAF fusion protein. In the resistant clones, hyperactivation of the downstream MAPK pathway via SND1-BRAF conferred resistance to c-Met receptor tyrosine kinase inhibition. Combination treatment with METi and a RAF inhibitor, PF-04880594 (RAFi) inhibited ERK activation and circumvented resistance to either single agent. Alternatively, treatment with a MEK inhibitor, PD-0325901 (MEKi) alone effectively blocked ERK phosphorylation and inhibited cell growth. Our results suggest that combination of a c-Met tyrosine kinase inhibitor with a BRAF or a MEK inhibitor may be effective in treating resistant tumors that use activated BRAF to escape suppression of c-Met signaling.

Elevated expression of Fn14 in non-small cell lung cancer correlates with activated EGFR and promotes tumor cell migration and invasion

Lung cancer is the leading cause of cancer deaths worldwide; approximately 85% of these cancers are non-small cell lung cancer (NSCLC). Patients with NSCLC frequently have tumors harboring somatic mutations in the epidermal growth factor receptor (EGFR) gene that cause constitutive receptor activation. These patients have the best clinical response to EGFR tyrosine kinase inhibitors (TKIs). Herein, we show that fibroblast growth factor-inducible 14 (Fn14; TNFRSF12A) is frequently overexpressed in NSCLC tumors, and Fn14 levels correlate with p-EGFR expression. We also report that NSCLC cell lines that contain EGFR-activating mutations show high levels of Fn14 protein expression. EGFR TKI treatment of EGFR-mutant HCC827 cells decreased Fn14 protein levels, whereas EGF stimulation of EGFR wild-type A549 cells transiently increased Fn14 expression. Furthermore, Fn14 is highly expressed in EGFR-mutant H1975 cells that also contain an EGFR TKI-resistance mutation, and high TKI doses are necessary to reduce Fn14 levels. Constructs encoding EGFRs with activating mutations induced Fn14 expression when expressed in rat lung epithelial cells. We also report that short hairpin RNA-mediated Fn14 knockdown reduced NSCLC cell migration and invasion in vitro. Finally, Fn14 overexpression enhanced NSCLC cell migration and invasion in vitro and increased experimental lung metastases in vivo. Thus, Fn14 may be a novel therapeutic target for patients with NSCLC, in particular for those with EGFR-driven tumors who have either primary or acquired resistance to EGFR TKIs.

Activation of multiple cancer pathways and tumor maintenance function of the 3q amplified oncogene FNDC3B

FNDC3B was recently identified in an oncogenomic screen for amplified oncogenes in hepatocellular carcinoma. It is located at 3q26 and is amplified in over 20% of cancers, usually as part of a broad amplified region encompassing the entire 3q arm. Consistent with an oncogenic role in multiple cancer types, we show here that overexpression of FNDC3B is capable of malignantly transforming mammary and kidney epithelial cells in addition to hepatocytes. To explore how FNDC3B transforms cells, we determined the cellular localization of its gene product and the cancer pathways that it activates. We found that the FNDC3B oncoprotein localizes to the Golgi network, and that its correct localization is essential for its transforming function. We found that overexpression of FNDC3B induces the epithelial-to-mesenchymal transition (EMT) and activates several cancer pathways, including PI3-kinase/Akt, Rb1 and TGFβ signaling. For TGFβ signaling, we analyzed the point in the pathway at which FNDC3B operates and obtained evidence that it induces expression of all three TGFβ ligands and also promotes TGFBR1 cell-surface localization. We found that RNAi-mediated knockdown of FNDC3B in cancer cells with 3q amplification suppressed their clonogenicity and tumorigenicity, but that the same RNAi knockdown had no effect on single-copy 3q cancer cells. These results indicate that FNDC3B is an important oncogenic driver gene of the 3q amplicon, adding to the growing list of oncogenic drivers within this commonly amplified region.

Rationale and design of MARQUEE: a phase III, randomized, double-blind study of tivantinib plus erlotinib versus placebo plus erlotinib in previously treated patients with locally advanced or metastatic, nonsquamous, non-small-cell lung cancer

We present the rationale and design for MARQUEE, a phase III, randomized, double-blind, placebo-controlled study of ARQ 197 plus erlotinib versus placebo plus erlotinib in previously treated subjects with locally advanced or metastatic, nonsquamous, non-small-cell lung cancer (NSCLC). The design of MARQUEE is based on preclinical data, the current understanding of the role of cellular N-methyl-N'-nitroso-guanidine human osteosarcoma (MNNG HOS) transforming gene (MET) in NSCLC, and clinical data from a randomized phase II study. The available evidence suggests that dual inhibition of MET and the epidermal growth factor receptor (EGFR) may overcome resistance to EGFR inhibitors. In the phase II study, the combination of tivantinib plus erlotinib significantly improved progression-free survival (PFS) and overall survival (OS) compared with placebo plus erlotinib in the subset of patients with nonsquamous histology, a population enriched for MET overexpression. The primary endpoint in MARQUEE is OS. Secondary and exploratory objectives include determination of PFS, OS in molecular subgroups (defined by EGFR and KRAS mutation status, amplification or overexpression of MET, and serum hepatocyte growth factor), and safety. All patients will be tested for biomarkers, and the results will provide a wealth of information on the role of tivantinib in treating nonsquamous NSCLC.

Squamous cell carcinoma of the lung: molecular subtypes and therapeutic opportunities

Lung cancer is the leading cause of cancer-related deaths worldwide. Next to adenocarcinoma, squamous cell carcinoma (SCC) of the lung is the most frequent histologic subtype in non-small cell lung cancer. Encouraging new treatments (i.e., bevacizumab, EGFR tyrosine kinase inhibitors, and ALK inhibitors) have afforded benefits to patients with adenocarcinoma, but unfortunately the same is not true for SCC. However, many genomic abnormalities are present in SCC, and there is growing evidence of their biologic significance. Thus, in the short term, the molecular characterization of patients with SCC in modern profiling platforms will probably be as important as deciphering the molecular genetics of adenocarcinoma. Patients with SCC of the lung harboring specific molecular defects that are actionable (e.g., fibroblast growth factor receptor 1 amplification, discoidin domain receptor 2 mutation, and phosphoinositide 3-kinase amplification) should be enrolled in prospective clinical trials targeting such molecular defects.

Sensitivity of selected human tumor models to PF-04217903, a novel selective c-Met kinase inhibitor

The c-Met pathway has been implicated in a variety of human cancers for its critical role in tumor growth, invasion, and metastasis. PF-04217903 is a novel ATP-competitive small-molecule inhibitor of c-Met kinase. PF-04217903 showed more than 1,000-fold selectivity for c-Met compared with more than 150 kinases, making it one of the most selective c-Met inhibitors described to date. PF-04217903 inhibited tumor cell proliferation, survival, migration/invasion in MET-amplified cell lines in vitro, and showed marked antitumor activity in tumor models harboring either MET gene amplification or a hepatocyte growth factor (HGF)/c-Met autocrine loop at well-tolerated dose levels in vivo. Antitumor efficacy of PF-04217903 was dose-dependent and showed a strong correlation with inhibition of c-Met phosphorylation, downstream signaling, and tumor cell proliferation/survival. In human xenograft models that express relatively high levels of c-Met, complete inhibition of c-Met activity by PF-04217903 only led to partial tumor growth inhibition (38%-46%) in vivo. The combination of PF-04217903 with Recepteur d'origine nantais (RON) short hairpin RNA (shRNA) knockdown in the HT29 model that also expresses activated RON kinase-induced tumor cell apoptosis and resulted in enhanced antitumor efficacy (77%) compared with either PF-04217903 (38%) or RON shRNA alone (56%). PF-04217903 also showed potent antiangiogenic properties in vitro and in vivo. Furthermore, PF-04217903 strongly induced phospho-PDGFRβ (platelet-derived growth factor receptor) levels in U87MG xenograft tumors, indicating a possible oncogene switching mechanism in tumor cell signaling as a potential resistance mechanism that might compromise tumor responses to c-Met inhibitors. Collectively, these results show the use of highly selective inhibition of c-Met and provide insight toward targeting tumors exhibiting different mechanisms of c-Met dysregulation.

MET tyrosine kinase inhibitor crizotinib (PF-02341066) shows differential antitumor effects in non-small cell lung cancer according to MET alterations

INTRODUCTION

Tyrosine kinase inhibitors (TKIs) targeted to MET are undergoing clinical trials in patients with solid tumors, but the precise mechanism of the antitumor activity of these drugs remains unclear. We examined the antitumor action of the MET-TKI crizotinib (PF-02341066) in lung cancer cells that are positive or negative for MET amplification or mutation.

METHODS

The antitumor action of crizotinib was evaluated on the basis of signal transduction, cell proliferation, apoptosis, and progression of tumor xenografts.

RESULTS

Inhibition of MET signaling by crizotinib or by RNA interference-mediated MET depletion resulted in the induction of apoptosis accompanied by inhibition of AKT and extracellular signal-regulated kinase phosphorylation in lung cancer cells with MET amplification but not in cells with a MET mutation or in those without amplification or mutation of MET. These results suggest that MET signaling is essential for the survival of cells with MET amplification but not for that of cells without this genetic change, including those with a MET mutation. Crizotinib up-regulated the expression of BIM, a proapoptotic member of the Bcl-2 family, and down-regulated that of survivin, a member of the inhibitor of apoptosis protein family, in cells with MET amplification. Forced depletion of BIM and expression of survivin each inhibited crizotinib-induced apoptosis, suggesting that both up-regulation of BIM and down-regulation of survivin contribute to the proapoptotic effect of crizotinib.

CONCLUSIONS

Crizotinib shows a marked antitumor action in MET amplification-positive lung cancer cells but not in cells without MET amplification, including those with a MET mutation.

Antitumor activity of SNX-2112, a synthetic heat shock protein-90 inhibitor, in MET-amplified tumor cells with or without resistance to selective MET Inhibition

PURPOSE

Heat shock protein-90 (HSP-90), a molecular chaperone required by numerous oncogenic kinases [e.g., HER-2, epidermal growth factor receptor (EGFR), Raf-1, v-Src, and AKT] for conformational stability, has attracted wide interest as a novel target for cancer therapy. HSP-90 inhibition induces degradation of HSP-90 client proteins, leading to a combinatorial inhibition of multiple oncogenic signaling pathways with consecutive growth arrest and apoptosis. MET, a tyrosine kinase that is constitutively active in tumor cells with MET oncogene amplification, has recently been identified as another HSP-90 client.

EXPERIMENTAL DESIGN

The aim of our study was to assess the efficacy of SNX-2112, a synthetic HSP-90 inhibitor, in 3 different MET-amplified tumor cell lines (GTL-16, MKN-45, and EBC-1) as well as PR-GTL-16 cells, a GTL-16 subline selected for resistance to the highly selective MET kinase inhibitor PHA-665752.

RESULTS

In all cell lines, SNX-2112 led to degradation of MET, HER-2, EGFR, and AKT, as well as abrogation of Ras/Raf/MEK/MAPK and PI3K/AKT signaling, followed by complete cell cycle arrest. SNX-5542, an orally bioavailable prodrug of SNX-2112, displayed significant antitumor efficacy in vivo in nude mice bearing MET-amplified tumor xenografts. Importantly, HSP-90 inhibition maintained its antitumor efficacy in PR-GTL-16 cells both in vitro and in vivo, suggesting that HSP-90 inhibition could be a particularly valuable strategy in MET-amplified tumors that have acquired resistance to MET kinase inhibition.

CONCLUSIONS

Our study provides evidence for the efficacy of HSP-90 inhibition in MET-amplified cancer cells, particularly when MET kinase inhibitor resistance has emerged.

Carbon nanotubes and pleural damage: perspectives of nanosafety in the light of asbestos experience

Carbon nanotubes are molecular-scale one-dimensional manufactured materials which display several potential applications in engineering and materials science. Burgeoning evidence demonstrates that carbon nanotubes and asbestos share comparable physical properties. Therefore carbon nanotubes might display toxic effects and the extent of the toxicity is more specifically directed to lung and pleura. These effects are related to properties of carbon nanotubes, such as their structure, length, aspects ratio, surface area, degree of aggregation, extent of oxidation, bound functional group, method of manufacturing, concentration and dose. At the present there is no global agreement about the risk of carbon nanotubes on human health and in particular on their transformation capacity. Safety concerns regarding carbon nanotubes can be ameliorated. In this context, it is important to put the known hazards of carbon nanotubes into perspective. Here is presented an overview about toxicity issues in the application of carbon nanotubes to biological systems, taking into consideration the already known asbestos-induced mechanisms of biological damages.

Novel therapeutic target for head and neck squamous cell carcinoma: HGF-MET signaling pathway

Head and neck squamous cell carcinoma (HNSCC) represents a devastating type of malignancy characterized by its high incidence of regional and distant metastases at the time of diagnosis. Vital physiological functions in the upper aerodigestive tract are often impaired as a result of the disease and treatment for the disease, giving rise to severe morbidity in patients suffering from this type of cancer. It is crucial to delineate the aberrant growth signaling pathways in HNSCC cells and develop specific target therapies for the disease to improve the treatment outcome. Although the epidermal growth factor receptor pathway has been extensively studied in HNSCC and anti-epidermal growth factor receptor therapy has already shown promise in treating HNSCC in phase III clinical trials, the signaling pathway that accounts for the highly invasive phenotype of HNSCC needs to be defined and also therapeutically targeted. The hepatocyte growth factor-MET signaling pathway has been studied extensively over the past two decades and it is now clear that it plays an important role in mediating invasive growth of many types of cancer. Here, we review comprehensively the evidence on hepatocyte growth factor-MET cascade being a key in the signaling pathway in mediating invasive growth of HNSCC and the potential of this signaling pathway to be a therapeutic target for the treatment of HNSCC.

Differential roles of trans-phosphorylated EGFR, HER2, HER3, and RET as heterodimerisation partners of MET in lung cancer with MET amplification

Background:

MET is a receptor tyrosine kinase (RTK) whose gene is amplified in various tumour types. We investigated the roles and mechanisms of RTK heterodimerisation in lung cancer with MET amplification.

Methods:

With the use of an RTK array, we identified phosphorylated RTKs in lung cancer cells with MET amplification. We examined the roles and mechanisms of action of these RTKs with immunoprecipitation, annexin V binding, and cell migration assays.

Results:

We identified epidermal growth factor receptor (EGFR), human EGFR (HER)2, HER3, and RET in addition to MET as highly phosphorylated RTKs in lung cancer cells with MET amplification. Immunoprecipitation revealed that EGFR, HER2, HER3, and RET each formed a heterodimer exclusively with MET and that these associations were markedly reduced in extent by treatment with a MET kinase inhibitor. RNA interference-mediated depletion of EGFR, HER2, or HER3 induced apoptosis in association with inhibition of AKT and ERK signalling pathways, whereas depletion of HER2 or RET inhibited both cell migration and STAT3 signalling.

Conclusion:

Our data suggest that heterodimers of MET with EGFR, HER2, HER3, or RET have differential roles in tumour development, and they provide new insight into the function of trans-phosphorylated RTKs as heterodimerisation partners of MET in lung cancer with MET amplification.

MET phosphorylation predicts poor outcome in small cell lung carcinoma and its inhibition blocks HGF-induced effects in MET mutant cell lines

Background:

Small cell lung carcinoma (SCLC) has poor prognosis and remains orphan from targeted therapy. MET is activated in several tumour types and may be a promising therapeutic target.

Methods:

To evaluate the role of MET in SCLC, MET gene status and protein expression were evaluated in a panel of SCLC cell lines. The MET inhibitor PHA-665752 was used to study effects of pathway inhibition in basal and hepatocyte growth factor (HGF)-stimulated conditions. Immunohistochemistry for MET and p-MET was performed in human SCLC samples and association with outcome was assessed.

Results:

In MET mutant SCLC cells, HGF induced MET phosphorylation, increased proliferation, invasiveness and clonogenic growth. PHA-665752 blocked MET phosphorylation and counteracted HGF-induced effects. In clinical samples, total MET and p-MET overexpression were detected in 54% and 43% SCLC tumours (n=77), respectively. MET phosphorylation was associated with poor median overall survival (132 days) vs p-MET negative cases (287 days)(P<0.001). Phospho-MET retained its prognostic value in a multivariate analysis.

Conclusions:

MET activation resulted in a more aggressive phenotype in MET mutant SCLC cells and its inhibition by PHA-665752 reversed this phenotype. In patients with SCLC, MET activation was associated with worse prognosis, suggesting a role in the adverse clinical behaviour in this disease.

Marsdenia tenacissima extract restored gefitinib sensitivity in resistant non-small cell lung cancer cells

Most non-small cell lung cancer (NSCLC) patients responding to gefitinib harbor activating mutations in the epidermal growth factor receptor (EGFR). However, the responsive cases eventually develop the resistance to gefitinib. Besides, K-ras mutations were identified as the primary resistance to gefitinib. We investigated whether Marsdenia tenacissima extract (MTE, trade name: Xiao-Ai-Ping injection) combined with gefitinib could overcome the resistance of NSCLC cells to gefitinib. NSCLC cell lines with different sensitivities to gefitinib were studied. Cell growth and apoptosis were evaluated by MTT assay and flow cytometry, respectively. The EGFR-related signaling molecule phosphorylation was assessed by Western blotting. We found that MTE inhibited cell growth in gefitinib-sensitive and -resistant cells. In gefitinib-resistant cells, the MTE→MTE+gefitinib (M→M+G) treatment was most potent over the concurrent administration of MTE and gefitinib (M+G) or gefitinib→gefitinib+MTE (G→G+M) treatment in cell growth inhibition and apoptosis induction. The M→M+G treatment significantly reduced the phosphorylation of EGFR downstream signaling molecules PI3K/Akt/mTOR and ERK, on which MTE and gefitinib alone had no obvious effects on the resistant cells. The M→M+G treatment attenuated c-Met phosphorylation in H460 and H1975 as well. Thus, we found that the M→M+G treatment improved the sensitivity of resistant NSCLC cells carrying T790M or K-ras mutations to gefitinib, suggesting that the M→M+G treatment may be a promising therapeutic strategy to overcome gefitinib resistance in NSCLC.

MET/PKCbeta expression correlate with metastasis and inhibition is synergistic in lung cancer

Background:

Treatment of non-small cell lung cancer (NSCLC) remains a difficult task in oncology. Targeted inhibition of oncogenic proteins is promising. In this study, we evaluate the expression of MET and PKCß and in vitro effects of their inhibition using SU11274 and enzastaurin (LY317615.HCl) respectively.

Materials and Methods:

Patient samples were analyzed by immunohistochemistry for expression of PKCß and MET, utilizing tissue microarrays under an IRB-approved protocol. Expression of PKCß and MET was evaluated in cell lines by immunoblotting. Treatment with SU1174 against MET and enzastaurin against PKCß was performed in H1993 and H358 cell lines, and cell proliferation and downstream signaling (phosphorylation of MET, AKT, FAK, and GSK3ß) were evaluated by immunoblotting. Statistical analysis was performed using SPSS 16.0.

Results:

Expression of MET positively correlated with lymph node metastases (p=.0004), whereas PKCß showed no correlation (p=0.204). MET and PKCß expression were also strongly correlated (p<0.001). Expression of MET was observed in 5/8 cell lines (H358, H1703, A549, H1993, H2170; absent from H522, H661, or SW1573), whereas PKCß expression was observed in 8/8 cell lines. Cell proliferation was significantly impaired by treatment with SU11274 and enzastaurin, and their effects were synergistic in combination (CI=0.32 and 0.09). Phosphorylation of MET, FAK, AKT, and GSK3ß were strongly inhibited with both agents in combination.

Conclusions:

Concomitant inhibition of MET and PKCß significantly increased cytotoxicity in vitro against NSCLC, disrupting important downstream signaling pathways. Further evaluation in animal models is warranted.

A drug resistance screen using a selective MET inhibitor reveals a spectrum of mutations that partially overlap with activating mutations found in cancer patients

The emergence of drug resistance is a primary concern in any cancer treatment, including with targeted kinase inhibitors as exemplified by the appearance of Bcr-Abl point mutations in chronic myeloid leukemia (CML) patients treated with imatinib. In vitro approaches to identify resistance mutations in Bcr-Abl have yielded mutation spectra that faithfully recapitulated clinical observations. To predict resistance mutations in the receptor tyrosine kinase MET that could emerge during inhibitor treatment in patients, we conducted a resistance screen in BaF3 TPR-MET cells using the novel selective MET inhibitor NVP-BVU972. The observed spectrum of mutations in resistant cells was dominated by substitutions of tyrosine 1230 but also included other missense mutations and partially overlapped with activating MET mutations that were previously described in cancer patients. Cocrystallization of the MET kinase domain in complex with NVP-BVU972 revealed a key role for Y1230 in binding of NVP-BVU972, as previously reported for multiple other selective MET inhibitors. A second resistance screen in the same format with the MET inhibitor AMG 458 yielded a distinct spectrum of mutations rich in F1200 alterations, which is consistent with a different predicted binding mode. Our findings suggest that amino acid substitutions in the MET kinase domain of cancer patients need to be carefully monitored before and during treatment with MET inhibitors, as resistance may preexist or emerge. Compounds binding in the same manner as NVP-BVU972 might be particularly susceptible to the development of resistance through mutations in Y1230, a condition that may be addressed by MET inhibitors with alternative binding modes.