Met in urological cancers

Met is a tyrosine kinase receptor that is considered to be a proto-oncogene. The hepatocyte growth factor (HGF)-Met signaling system plays an important role in tumor growth, invasion, and metastasis in many types of malignancies. Furthermore, Met expression has been reported to be a useful predictive biomarker for disease progression and patient survival in these malignancies. Many studies have focused on the clinical significance and prognostic role of Met in urological cancers, including prostate cancer (PCa), renal cell carcinoma (RCC), and urothelial cancer. Several preclinical studies and clinical trials are in progress. In this review, the current understanding of the pathological role of Met in cancer cell lines, its clinical significance in cancer tissues, and its predictive value in patients with urological cancers are summarized. In particular, Met-related malignant behavior in castration-resistant PCa and the different pathological roles Met plays in papillary RCC and other histological types of RCC are the subjects of focus. In addition, the pathological significance of phosphorylated Met in these cancers is shown. In recent years, Met has been recognized as a potential therapeutic target in various types of cancer; therapeutic strategies used by Met-targeted agents in urological cancers are summarized in this review.

Genomic alterations in advanced esophageal cancer may lead to subtype-specific therapies

The development of targeted agents for metastatic esophageal or gastroesophageal junction (GEJ) tumors has been limited when compared with that for other common tumors. To date, the anti-human epidermal growth factor receptor-2 (HER-2) antibody, trastuzumab, in combination with chemotherapy, is the only approved novel agent for these cancers, and its use is limited to the small population of patients whose tumors overexpress HER-2. Despite recent progress in the field, median overall survival remains only 8-12 months for patients with stage IV esophageal or GEJ cancer. In this article, we examine the molecular aberrations thought to drive the development and spread of esophageal cancer and identify promising targets for specific tumor inhibition. Data from clinical studies of targeted agents are reviewed, including epidermal growth factor receptor antibodies, tyrosine kinase inhibitors, HER-2, and vascular endothelial growth factor-directed therapy. Current and future targets include MET, fibroblast growth factor receptor, and immune-based therapies. Evidence from trials to date suggests that molecularly unselected patient cohorts derive minimal benefit from most target-specific agents, suggesting that future collaborative investigation should focus on preselected molecular subgroups of patients with this challenging heterogeneous disease.

The role of the c-Met pathway in lung cancer and the potential for targeted therapy

Hepatocyte growth factor receptor (HGFR), the product of the MET gene, plays an important role in normal cellular function and oncogenesis. In cancer, HGFR has been implicated in cellular proliferation, cell survival, invasion, cell motility, metastasis and angiogenesis. Activation of HGFR can occur through binding to its ligand, hepatocyte growth factor (HGF), overexpression/amplification, mutation, and/or decreased degradation. Amplification of HGFR can occur de novo or in resistance to therapy. Mutations of HGFR have been described in the tyrosine kinase domain, juxtamembrane domain, or semaphorin domain in a number of tumors. These mutations appear to have gain of function, and also reflect differential sensitivity to therapeutic inhibition. There have been various drugs developed to target HGFR, including antibodies to HGFR/HGF, small-molecule inhibitors against the tyrosine kinase domain of HGFR and downstream targets. Different HGFR inhibitors are currently in clinical trials in lung cancer and a number of solid tumors. Several phase I trials have already been completed, and two specific trials have been reported combining HGFR with epidermal growth factor receptor (EGFR) inhibition in non-small cell lung cancer. In particular, trials involving MetMAb and ARQ197 (tivantinib) have gained interest. Ultimately, as individualized therapies become a reality for cancers, HGFR will be an important molecular target.

A phase I dose-escalation study of Tivantinib (ARQ 197) in adult patients with metastatic solid tumors

BACKGROUND

Tivantinib, an oral, non-ATP competitive, selective c-MET inhibitor, exhibited antitumor activity in preclinical models. This open-label, phase I, dose-escalation study evaluated the safety, tolerability, pharmacokinetics, and pharmacodynamics of tivantinib in patients with advanced or metastatic solid tumors refractory to standard therapy.

METHODS

Thirteen dose levels of tivantinib ranging from 10 to 360 mg twice a day were administered to patient cohorts in 21-day cycles (14 days on/7 days off); three active pharmaceutical ingredient forms of tivantinib (amorphous, crystalline A, and crystalline B) were also investigated. Treatment was continued until the occurrence of unacceptable toxicity, tumor progression, patient withdrawal, or death.

RESULTS

A total of 79 patients with advanced solid tumors were enrolled. A maximum tolerated dose was not determined. Tivantinib was well tolerated, with mild to moderate toxicities. Two patients discontinued the study drug due to treatment-emergent adverse events. Dose-limiting grade of 3 or more toxicities including leukopenia, neutropenia, thrombocytopenia, vomiting, and dehydration, were observed in 2 patients treated with tivantinib 360 mg twice a day. The rate of absorption of tivantinib peaked approximately 2 to 4 hours after initial dosing, followed by a linear decrease in plasma concentrations. Increases in tivantinib exposure were not dose proportional. There was significant interpatient pharmacokinetic variability; however the clinical safety of tivantinib seemed unaffected. Three patients (3.8%) achieved a partial response and 40 patients (50.6%) maintained stable disease for a median of 19.9 weeks.

CONCLUSIONS

Tivantinib 360 mg twice a day was well tolerated in patients with refractory advanced solid tumors. The results of this trial warrant further clinical investigation. Clin Cancer Res; 17(24); 7754-64. ©2011 AACR.

Early clinical development of ARQ 197, a selective, non-ATP-competitive inhibitor targeting MET tyrosine kinase for the treatment of advanced cancers

Expression of the receptor tyrosine kinase c-MET (MET, mesenchymal-epithelial transition factor) in many cancers, and its participation in multiple signal transduction pathways involved in malignant tumor growth, suggest a wide therapeutic potential for MET inhibition in human cancer. Here we describe the discovery and early clinical development of ARQ 197, a novel, selective, non-ATP-competitive inhibitor of MET. Phase I studies demonstrate that ARQ 197 has a predictable pharmacokinetics and favorable safety profile, making it a potentially ideal partner for combination with cytotoxic chemotherapies and targeted anticancer agents. Results from phase I and phase II trials demonstrate preliminary evidence of anticancer activity. New data from a global phase II randomized trial comparing a combination of ARQ 197 plus erlotinib with erlotinib/placebo, in endothelial growth factor receptor inhibitor-naïve patients with locally advanced/metastatic non-small cell lung cancer, demonstrate improvement in progression-free and overall survival with combined therapy. Results were especially pronounced for patients with non-squamous lung cancer histologies, and in particular molecularly defined subgroups including KRAS mutations. These and other data from ARQ 197 clinical trials in hepatocellular, germ-cell, pancreatic (in combination with gemcitabine), and colorectal (in combination with cetuximab and irinotecan) cancers further highlight the potential role of ARQ 197 in existing and emerging anticancer therapeutic regimens.

Multiple mutations and bypass mechanisms can contribute to development of acquired resistance to MET inhibitors

Therapies targeting receptor tyrosine kinases have shown efficacy in molecularly defined subsets of cancers. Unfortunately, cancers invariably develop resistance, and overcoming or preventing resistance will ultimately be key to unleashing their full therapeutic potential. In this study, we examined how cancers become resistant to MET inhibitors, a class of drugs currently under clinical development. We utilized the highly sensitive gastric carcinoma cell line, SNU638, and two related MET inhibitors PHA-665752 and PF-2341066. To our surprise, we observed at least two mechanisms of resistance that arose simultaneously. Both resulted in maintenance of downstream PI3K (phosphoinositide 3-kinase)-AKT and MEK (MAP/ERK kinase)-ERK signaling in the presence of inhibitor. One mechanism, observed by modeling resistance both in vitro and in vivo, involved the acquisition of a mutation in the MET activation loop (Y1230). Structural analysis indicates that this mutation destabilizes the autoinhibitory conformation of MET and abrogates an important aromatic stacking interaction with the inhibitor. The other cause of resistance was activation of the epidermal growth factor receptor (EGFR) pathway due to increased expression of transforming growth factor α. Activation of EGFR bypassed the need for MET signaling to activate downstream signaling in these cells. This resistance could be overcome by combined EGFR and MET inhibition. Thus, therapeutic strategies that combine MET inhibitors capable of inhibiting Y1230 mutant MET in combination with anti-EGFR-based therapies may enhance clinical benefit for patients with MET-addicted cancers. Importantly, these results also underscore the notion that a single cancer can simultaneously develop resistance induced by several mechanisms and highlight the daunting challenges associated with preventing or overcoming resistance.

Preclinical absorption, distribution, metabolism, excretion, and pharmacokinetic-pharmacodynamic modelling of N-(4-(3-((3S,4R)-1-ethyl-3-fluoropiperidine-4-ylamino)-1H-pyrazolo[3,4-b]pyridin-4-yloxy)-3-fluorophenyl)-2-(4-fluorophenyl)-3-oxo-2,3-dihydropyridazine-4-carboxamide, a novel MET kinase inhibitor

GNE-A (AR00451896; N-(4-(3-((3S,4R)-1-ethyl-3-fluoropiperidine-4-ylamino)-1H-pyrazolo[3,4-b]pyridin-4-yloxy)-3-fluorophenyl)-2-(4-fluorophenyl)-3-oxo-2,3-dihydropyridazine-4-carboxamide) is a potent, selective MET kinase inhibitor being developed as a potential drug for the treatment of human cancers. Plasma clearance was low in mice and dogs (15.8 and 2.44 mL/min/kg, respectively) and moderate in rats and monkeys (36.6 and 13.9 mL/min/kg, respectively). The volume of distribution ranged from 2.1 to 9.0 L/kg. The mean terminal elimination half-life ranged from 1.67 h in rats to 16.3 h in dogs. Oral bioavailability in rats, mice, monkeys, and dogs were 11.2%, 88.0%, 72.4%, and 55.8%, respectively. Allometric scaling predicted a clearance of 1.3-7.4 mL/min/kg and a volume of distribution of 4.8-11 L/kg in human. Plasma protein binding was high (96.7-99.0% bound). Blood-to-plasma concentration ratios (0.78-1.46) indicated that GNE-A did not preferentially distribute into red blood cells. Transporter studies in MDCKI-MDR1 and MDCKII-Bcrp1 cells suggested that GNE-A is likely a substrate for MDR1 and BCRP. Pharmacokinetic-pharmacodynamic modelling of tumour growth inhibition in MET-amplified EBC-1 human non-small cell lung carcinoma tumour xenograft mice projected oral doses of 5.6 and 13 mg/kg/day for 50% and 90% tumour growth inhibition, respectively. Overall, GNE-A exhibited favourable preclinical properties and projected human dose estimates.

Targeting the MET oncogene in cancer and metastases

IMPORTANCE OF THE FIELD

'Invasive growth' is a genetic program involved in embryonic development and adult organ regeneration and usurped by cancer cells. Although its control is complex, tumor- and context-specific and regulated by several cytokines and growth factors, the role played by the MET oncogene is well documented. In human cancers the contribution of MET to invasive growth is mainly through overexpression, driven by unfavorable microenvironmental conditions. MET activation confers a selective advantage to neoplastic cells in tumor progression and drug resistance. A subset of tumors feature alterations of the MET gene and a consequent MET-addicted phenotype.

AREAS COVERED IN THIS REVIEW

The molecular basis and rationale of MET inhibition in cancer and metastases are discussed. A number of molecules designed to block MET signaling are under development and several Phase II trials are ongoing.

WHAT THE READER WILL GAIN

Knowledge of the state of the art of anti-MET targeted approaches and the molecular basis and strategies to select patients eligible for treatment with MET inhibitors.

TAKE HOME MESSAGE

Due to its versatile functions MET is a promising candidate for cancer therapy. Understanding molecular mechanisms of sensitization and resistance to MET inhibitors is a priority to guide tailored therapies and select patients that are most likely to achieve a clinical benefit.

Selection criteria for c-Met-targeted therapies: emerging evidence for biomarkers

Extensive development of targeted therapies emphasize the critical need for biomarkers and major efforts have been engaged to identify screening, prognostic, stratification and therapy-monitoring markers. One of the challenges in translating preclinical studies into effective clinical therapies remains the accurate identification of a responsive subsets of patients. Studies on trastuzumab demonstrated that patient response could be specifically correlated with the amplification of the Her2 gene. However, for the EGF receptor, it has been more difficult to find the right stratification biomarker and recent data demonstrate that genetic alterations for the EGF receptor have to be considered. Taken together, these data underline the need for a deeper understanding of both targeted receptor and human disease to determine pathways that might be investigated during early clinical trials in order to define relevant biomarkers for patient selection. This article, dealing with the c-Met tyrosine kinase receptor, provides an overview of c-Met alterations observed in cancer and proposes approaches for stratification biomarker selection.

The evolving role of monoclonal antibodies in colorectal cancer: early presumptions and impact on clinical trial development

Targeted biologic agents have an established role in treating metastatic colorectal cancer (mCRC). Bevacizumab, a recombinant monoclonal antibody against the vascular endothelial growth factor ligand is approved by the U.S. Food and Drug Administration (FDA) for bevacizumab-naïve patients. Cetuximab, a chimeric monoclonal antibody (mAb) against the epidermal growth factor receptor (EGFR) is FDA approved as a single agent, or in combination with irinotecan, in both irinotecan-naïve and refractory patients, and has additional efficacy in combination with oxaliplatin. Panitumumab, a fully human EGFR mAb, is FDA approved as a single agent in refractory patients but has additional efficacy in combination with chemotherapy. After reaching a temporary therapeutic plateau of FDA-approved agents for the treatment of mCRC, pivotal results have developed that critically affect the care for these patients. Correlative data from randomized trials of EGFR inhibitors across disease settings have demonstrated higher response rates, specifically for patients with wild-type K-RAS tumors. The interpretation of the B-RAF mutation and other molecular markers may further define the appropriateness of anti-EGFR therapy. Recent literature revealed that the first-line use of combined anti-EGFR therapy plus bevacizumab resulted in inferior outcomes and additional toxicities. Furthermore, the role of biologic agents for locally advanced colon cancer cannot be advocated at this time. With impending changes in the health care system, the economic impact of mAbs will continue to be scrutinized. Hence, as the significance of molecular markers continues to develop, their role as it pertains to the appropriate use of biologic agents in the treatment of mCRC will continue to evolve.

Targeted therapy for metastatic renal cell carcinoma: current treatment and future directions

An understanding of vascular endothelial growth factor (VEGF) and mammalian target of rapamycin (mTOR) pathways has greatly changed the way metastatic renal cell carcinoma (RCC) is treated. Based on available phase III randomized trials, anti-VEGF agents such as sunitinib, sorafenib, bevacizumab-based therapy, and mTOR-targeted agents such as temsirolimus and everolimus have been used in the treatment armamentarium for this disease. Now that agents directed against these pathways have largely replaced immunotherapy as the standard of care, new questions have emerged and are the subject of ongoing clinical trials. The development of new targeted therapies including axitinib, pazopanib, cediranib, volociximab, tivozanib (AV-951), BAY 73-4506, and c-met inhibitors such as GSK1363089 and ARQ197 may potentially expand the list of treatment options. Sequential and combination targeted therapies are currently under investigation in advanced disease as are adjuvant and neo-adjuvant approaches around nephrectomy.

EGFRvIII and c-Met pathway inhibitors synergize against PTEN-null/EGFRvIII+ glioblastoma xenografts

Receptor tyrosine kinase (RTK) systems, such as hepatocyte growth factor (HGF) and its receptor c-Met, and epidermal growth factor receptor (EGFR), are responsible for the malignant progression of multiple solid tumors. Recent research shows that these RTK systems comodulate overlapping and dynamically adaptable oncogenic downstream signaling pathways. This study investigates how EGFRvIII, a constitutively active EGFR deletion mutant, alters tumor growth and signaling responses to RTK inhibition in PTEN-null/HGF(+)/c-Met(+) glioma xenografts. We show that a neutralizing anti-HGF monoclonal antibody (L2G7) potently inhibits tumor growth and the activation of Akt and mitogen-activated protein kinase (MAPK) in PTEN-null/HGF(+)/c-Met(+)/EGFRvIII(-) U87 glioma xenografts (U87wt). Isogenic EGFRvIII(+) U87 xenografts (U87-EGFRvIII), which grew five times more rapidly than U87-wt xenografts, were unresponsive to EGFRvIII inhibition by erlotinib and were only minimally responsive to anti-HGF monoclonal antibodies. EGFRvIII expression diminished the magnitude of Akt inhibition and completely prevented MAPK inhibition by L2G7. Despite the lack of response to L2G7 or erlotinib as single agents, their combination synergized to produce substantial antitumor effects (inhibited tumor cell proliferation, enhanced apoptosis, arrested tumor growth, prolonged animal survival), against subcutaneous and orthotopic U87-EGFRvIII xenografts. The dramatic response to combining HGF:c-Met and EGFRvIII pathway inhibitors in U87-EGFRvIII xenografts occurred in the absence of Akt and MAPK inhibition. These findings show that combining c-Met and EGFRvIII pathway inhibitors can generate potent antitumor effects in PTEN-null tumors. They also provide insights into how EGFRvIII and c-Met may alter signaling networks and reveal the potential limitations of certain biochemical biomarkers to predict the efficacy of RTK inhibition in genetically diverse cancers.

Pancreatic cancer: molecular pathogenesis and new therapeutic targets

Patients with pancreatic cancer normally present with advanced disease that is lethal and notoriously difficult to treat. Survival has not improved dramatically despite routine use of chemotherapy and radiotherapy; this situation signifies an urgent need for novel therapeutic approaches. Over the past decade, a large number of studies have been published that aimed to target the molecular abnormalities implicated in pancreatic tumor growth, invasion, metastasis, angiogenesis and resistance to apoptosis. This research is of particular importance, as data suggest that a large number of genetic alterations affect only a few major signaling pathways and processes involved in pancreatic tumorigenesis. Although laboratory results of targeted therapies have been impressive, until now only erlotinib, an epidermal growth factor receptor tyrosine kinase inhibitor, has demonstrated modest survival benefit in combination with gemcitabine in a phase III clinical trial. Whilst the failures of targeted therapies in the clinical setting are discouraging, lessons have been learnt and new therapeutic targets that hold promise for the future management of the disease are continuously emerging. This Review describes some of the important developments and targeted agents for pancreatic cancer that have been tested in clinical trials.

The MET axis as a therapeutic target

The MET receptor tyrosine kinase and its ligand hepatocyte growth factor (HGF) have been implicated in transformation of a variety of malignancies. Chronic or dysregulated activation of the MET/HGF pathway may lead to increased cell growth, invasion, angiogenesis, and metastasis, reduced apoptosis, altered cytoskeletal functions and other biological changes. It has been suggested that ligand activated MET stimulation can be sufficient for a transforming phenotype. In addition, amplification and activation mutations (germline and/or somatic) within the tyrosine kinase domain, juxtamembrane domain, or semaphorin domain have been identified for MET. MET gain-of-function mutations lead to either deregulated or prolonged tyrosine kinase activity, which are instrumental to its transforming activity. A number of therapeutic strategies targeting ligand-dependent activation or the kinase domain have been employed to inhibit MET. The different structural requirements for activation of signaling events and biological functions regulated by MET will be summarized. Therapeutic targets and current pre-clinical and clinical approaches will be described. Targeting the HGF/MET pathway, alone or in combination with standard therapies, is likely to improve present therapies in MET-dependent malignancies.

Novel therapeutic inhibitors of the c-Met signaling pathway in cancer

A wide variety of human malignancies exhibit sustained c-Met stimulation, overexpression, or mutation, including carcinomas of the breast, liver, lung, ovary, kidney, and thyroid. Notably, activating mutations in c-Met have been positively identified in patients with a particular hereditary form of papillary renal cancer, directly implicating c-Met in human tumorigenesis. Aberrant signaling of the c-Met signaling pathway due to dysregulation of the c-Met receptor or overexpression of its ligand, hepatocyte growth factor (HGF), has been associated with an aggressive phenotype. Extensive evidence that c-Met signaling is involved in the progression and spread of several cancers and an enhanced understanding of its role in disease have generated considerable interest in c-Met and HGF as major targets in cancer drug development. This has led to the development of a variety of c-Met pathway antagonists with potential clinical applications. The three main approaches of pathway-selective anticancer drug development have included antagonism of ligand/receptor interaction, inhibition of the tyrosine kinase catalytic activity, and blockade of the receptor/effector interaction. Several c-Met antagonists are now under clinical investigation. Preliminary clinical results of several of these agents, including both monoclonal antibodies and small-molecule tyrosine kinase inhibitors, have been encouraging. Several multitargeted therapies have also been under investigation in the clinic and have demonstrated promise, particularly with regard to tyrosine kinase inhibition.

Biological approaches to therapy of pancreatic cancer

Pancreatic cancer is a lethal disease and notoriously difficult to treat. Only a small proportion is curative by surgical resection, whilst standard chemotherapy for patients with advanced disease has only modest effect with substantial toxicity. Clearly there is a need for the continual development of novel therapeutic agents to improve the current situation. Improvement of our understanding of the disease has generated a large number of studies on biological approaches targeting the molecular abnormalities of pancreatic cancer, including gene therapy and signal transduction inhibition, antiangiogenic and matrix metalloproteinase inhibition, oncolytic viral therapy and immunotherapy. This article provides a review of these approaches, both investigated in the laboratories and in subsequent clinical trials.

MET as a target for treatment of chest tumors

The receptor tyrosine kinase MET has been studied of a large variety of human cancers, including lung and mesothelioma. The MET receptor and its ligand HGF (hepatocyte growth factor) play important roles in cell growth, survival and migration, and dysregulation of the HGF-MET pathway leads to oncogenic changes including tumor proliferation, angiogenesis and metastasis. In small cell lung cancer (SCLC), non-small cell lung cancer (NSCLC), and malignant pleural mesothelioma (MPM), MET is dysregulated via overexpression, constitutive activation, gene amplification, ligand-dependent activation, mutation or epigenetic mechanisms. New drugs targeted against MET and HGF are currently being investigated in vitro and in vivo, with promising results. These drugs function at a variety of steps within the HGF-MET pathway, including MET expression at the RNA or protein level, the ligand-receptor interaction, and tyrosine kinase function. This paper will review the structure, function, mechanisms of tumorigenesis, and potential for therapeutic inhibition of the MET receptor in lung cancer and mesothelioma.