Targeting receptor tyrosine kinase MET in cancer: small molecule inhibitors and clinical progress

Met tyrosine kinase inhibitor, PF-2341066, suppresses growth and invasion of nasopharyngeal carcinoma

Purpose

We explored the effect of hepatocyte growth factor (HGF)/Met signaling pathway on nasopharyngeal carcinoma (NPC) cells in vitro and in vivo, and investigated the ability of Met tyrosine kinase inhibitor (TKI) to block HGF-induced biological signaling.

Experimental design

Met TKI inhibitor PF-2341066 alone, or in combination with cisplatin, was investigated for its ability to block HGF-induced signaling and biological effects in vitro and in vivo. HGF/Met expression and activation of signaling in NPC cells were detected by using Western blot and immunohistochemistry. Biological evaluation, including wound healing, cell proliferation, and invasion of NPC cells, was also examined, and the correlation between HGF/Met expression of primary and metastatic tumor in NPC patients and clinical prognosis were also analyzed.

Results

Met TKI inhibitor, PF-2341066, inhibited growth of NPC cells in vivo with half maximal inhibitory concentration of 0.79±0.21 μmol/L, and suppressed invasion and migration of NPC cells; also, the inhibition of PF-2341066 was synergized with cisplatin treatment. Compared with the control group, Met TKI inhibited metastasis of transplanted NPC in nude mice (the number of live metastases [mean ± SD]: 5.8±2.2 versus 11.8±2.2, P=0.03; the number of lung metastases: 2.3±1.5 versus 5.3±0.9, P=0.06). HGF was widely expressed in both primary and metastatic lesions while Met expression of metastatic lesions was higher than that of primary lesions (primary lesions: 24.7%; liver metastases: 40%; lung metastases: 29%; lymph node metastases: 29%, P<0.05), and overall survival of NPC patients with higher expression of Met was shorter (P=0.13).

Conclusion

Our results demonstrated that HGF/Met signaling promoted NPC growth, further resulting in metastasis and poor prognosis. Met TKI, PF-2341066, showed potent antitumor activity in vivo and in vitro which was enhanced by combination with cisplatin. Our study implied that HGF/Met signaling was the potential therapeutic target in NPC, and blockage of the signaling could prevent growth and metastasis of NPC and derive clinical benefit.

The hepatocyte growth factor receptor as a potential therapeutic target for dedifferentiated liposarcoma

Dedifferentiated liposarcomas (DDLPS) are highly resistant to conventional chemo- and radiotherapies, with surgical resection remaining the classic treatment strategy; therefore, there is a pressing need for novel anti-DDLPS-targeted chemotherapeutics. Hepatocyte growth factor receptor (Met) expression is elevated in DDLPS, but the functional role of Met signaling in this disease is not known. We found that the in vitro stimulation of DDLPS cells with hepatocyte growth factor (HGF) elevated the degree of PI3K/AKT and MAPK pathway signaling, and that pro-tumorigenic phenotypes such as cell proliferation, invasion, and migration were significantly enhanced. Conversely, Met knockdown using shRNA-mediated interference decreased HGF-induced Met signaling, the invasive and migratory nature of DDLPS cells in vitro, and the tumorigenicity of DDLPS cells in vivo. These data strongly support the role for Met as a DDLPS therapeutic target. To that end, using EMD1214063, an ATP-competitive kinase inhibitor that targets Met more specifically than other kinases, inhibited Met-dependent signaling, reduced the oncogenicity of DDLPS cells in vitro, and significantly increased the survival of nude mice bearing subcutaneous DDLPS xenografts. These findings support further investigations of HGF-induced Met signaling inhibition in DDLPS, as a potential strategy to enhance clinical outcomes for this disease.

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

PURPOSE

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

PATIENTS AND METHODS

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

RESULTS

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

CONCLUSION

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

The tumour microenvironment after radiotherapy: mechanisms of resistance and recurrence

Radiotherapy plays a central part in curing cancer. For decades, most research on improving treatment outcomes has focused on modulating radiation-induced biological effects on cancer cells. Recently, we have better understood that components within the tumour microenvironment have pivotal roles in determining treatment outcomes. In this Review, we describe vascular, stromal and immunological changes that are induced in the tumour microenvironment by irradiation and discuss how these changes may promote radioresistance and tumour recurrence. We also highlight how this knowledge is guiding the development of new treatment paradigms in which biologically targeted agents will be combined with radiotherapy.

Inhibition of ligand-independent constitutive activation of the Met oncogenic receptor by the engineered chemically-modified antibody DN30

An awesome number of experimental and clinical evidences indicate that constitutive activation of the Met oncogenic receptor plays a critical role in the progression of cancer toward metastasis and/or resistance to targeted therapies. While mutations are rare, the common mechanism of Met activation is overexpression, either by gene amplification ('addiction') or transcriptional activation ('expedience'). In the first instance ligand-independent kinase activation plays a major role in sustaining the transformed phenotype. Anti-Met antibodies directed against the receptor binding site behave essentially as ligand (Hepatocyte Growth Factor, HGF) antagonists and are ineffective to counteract ligand-independent activation. The monovalent chimeric MvDN30 antibody fragment, PEGylated to extend its half-life, binds the fourth IPT domain and induces 'shedding' of the Met extracellular domain, dramatically reducing both the number of receptors on the surface and their phosphorylation. Downstream signaling is thus inhibited, both in the absence or in the presence of the ligand. In vitro, MvDN30 is a strong inhibitor not only of ligand-dependent invasive growth, sustained by both paracrine and autocrine HGF, but notably, also of ligand-independent growth of 'Met-addicted' cells. In immunocompromised mice, lacking expression of Hepatocyte Growth Factor cross-reacting with the human receptor - thus providing, by definition, a model of 'ligand-independent' Met activation - PEGylated MvDN30 impairs growth of Met 'addicted' human gastric carcinoma cells. In a Met-amplified patient-derived colo-rectal tumor (xenopatient) MvDN30-PEG overcomes the resistance to EGFR targeted therapy (Cetuximab). The PEGylated MvDN30 is thus a strong candidate for targeting tumors sustained by ligand-independent Met oncogenic activation.

Dysregulation of the Met pathway in non-small cell lung cancer: implications for drug targeting and resistance

The receptor tyrosine kinase, Met, orchestrates a complex signalling network that physiologically drives a programme of 'invasive growth'. In cancer however, this process may be co-opted to promote proliferation, survival and metastasis of cancer cells. Met is thus a key therapeutic target, not least in non-small cell lung cancer (NSCLC) where it is one of the most commonly dysregulated driver oncogenes. Identifying robust biomarkers that allow the selection of patients most likely to respond to Met targeted therapies will however be essential to realising their potential. This has been underlined recently by the early termination of three pivotal phase III trials investigating Met targeted agents in NSCLC, all of which failed to show clinical benefit. In contrast to these trials, which were relatively unselective, a couple of early phase trials have recently been instigated that select patients on the basis of Met amplification. While still at an early stage, interim results are relatively encouraging and strengthen the rationale for using Met amplifaction as a biomarker. Here we will discuss this and other aberrations in Met signalling in relation to their significance in the therapeutic targeting of Met.

Activation of MET via diverse exon 14 splicing alterations occurs in multiple tumor types and confers clinical sensitivity to MET inhibitors

Focal amplification and activating point mutation of the MET gene are well-characterized oncogenic drivers that confer susceptibility to targeted MET inhibitors. Recurrent somatic splice site alterations at MET exon 14 (METex14) that result in exon skipping and MET activation have been characterized, but their full diversity and prevalence across tumor types are unknown. Here, we report analysis of tumor genomic profiles from 38,028 patients to identify 221 cases with METex14 mutations (0.6%), including 126 distinct sequence variants. METex14 mutations are detected most frequently in lung adenocarcinoma (3%), but also frequently in other lung neoplasms (2.3%), brain glioma (0.4%), and tumors of unknown primary origin (0.4%). Further in vitro studies demonstrate sensitivity to MET inhibitors in cells harboring METex14 alterations. We also report three new patient cases with METex14 alterations in lung or histiocytic sarcoma tumors that showed durable response to two different MET-targeted therapies. The diversity of METex14 mutations indicates that diagnostic testing via comprehensive genomic profiling is necessary for detection in a clinical setting.

SIGNIFICANCE

Here we report the identification of diverse exon 14 splice site alterations in MET that result in constitutive activity of this receptor and oncogenic transformation in vitro. Patients whose tumors harbored these alterations derived meaningful clinical benefit from MET inhibitors. Collectively, these data support the role of METex14 alterations as drivers of tumorigenesis, and identify a unique subset of patients likely to derive benefit from MET inhibitors.

Design and optimization of a series of 1-sulfonylpyrazolo[4,3-b]pyridines as selective c-Met inhibitors

c-Met has emerged as an attractive target for targeted cancer therapy because of its abnormal activation in many cancer cells. To identify high potent and selective c-Met inhibitors, we started with profiling the potency and in vitro metabolic stability of a reported hit 7. By rational design, a novel sulfonylpyrazolo[4,3-b]pyridine 9 with improved DMPK properties was discovered. Further elaboration of π-π stacking interactions and solvent accessible polar moieties led to a series of highly potent and selective type I c-Met inhibitors. On the basis of in vitro and in vivo pharmacological and pharmacokinetics studies, compound 46 was selected as a preclinical candidate for further anticancer drug development.

Src protein-tyrosine kinase structure, mechanism, and small molecule inhibitors

The physiological Src proto-oncogene is a protein-tyrosine kinase that plays key roles in cell growth, division, migration, and survival signaling pathways. From the N- to C-terminus, Src contains a unique domain, an SH3 domain, an SH2 domain, a protein-tyrosine kinase domain, and a regulatory tail. The chief phosphorylation sites of human Src include an activating pTyr419 that results from phosphorylation in the kinase domain by an adjacent Src molecule and an inhibitory pTyr530 in the regulatory tail that results from phosphorylation by C-terminal Src kinase (Csk) or Chk (Csk homologous kinase). The oncogenic Rous sarcoma viral protein lacks the equivalent of Tyr530 and is constitutively activated. Inactive Src is stabilized by SH2 and SH3 domains on the rear of the kinase domain where they form an immobilizing and inhibitory clamp. Protein kinases including Src contain hydrophobic regulatory and catalytic spines and collateral shell residues that are required to assemble the active enzyme. In the inactive enzyme, the regulatory spine contains a kink or a discontinuity with a structure that is incompatible with catalysis. The conversion of inactive to active Src is accompanied by electrostatic exchanges involving the breaking and making of distinct sets of kinase domain salt bridges and hydrogen bonds. Src-catalyzed protein phosphorylation requires the participation of two Mg(2+) ions. Although nearly all protein kinases possess a common K/E/D/D signature, each enzyme exhibits its unique variations of the protein-kinase reaction template. Bosutinib, dasatinib, and ponatinib are Src/multikinase inhibitors that are approved by the FDA for the treatment of chronic myelogenous leukemia and vandetanib is approved for the treatment of medullary thyroid cancer. The Src and BCR-Abl inhibitors saracatinib and AZD0424, along with the previous four drugs, are in clinical trials for a variety of solid tumors including breast and lung cancers. Both ATP and targeted therapeutic Src protein kinase inhibitors such as dasatinib and ponatinib make hydrophobic contacts with catalytic spine residues and form hydrogen bonds with hinge residues connecting the small and large kinase lobes.

Registered report: Tumour micro-environment elicits innate resistance to RAF inhibitors through HGF secretion

The Reproducibility Project: Cancer Biology seeks to address growing concerns about reproducibility in scientific research by conducting replications of 50 papers in the field of cancer biology published between 2010 and 2012. This Registered Report describes the proposed replication plan of key experiments from ‘Tumour micro-environment elicits innate resistance to RAF inhibitors through HGF secretion’ by Straussman and colleagues, published in Nature in 2012 (Straussman et al., 2012). The key experiments being replicated in this study are from Figure 2A, C, and D (and Supplemental Figure 11) and Figure 4C (and Supplemental Figure 19) (Straussman et al., 2012). Figure 2 demonstrates resistance to drug sensitivity conferred by co-culture with some stromal cell lines and identifies the secreted factor responsible as HGF. In Figure 4, Straussman and colleagues show that blocking the HGF receptor MET abrogates HGF’s rescue of drug sensitivity. The Reproducibility Project: Cancer Biology is a collaboration between the Center for Open Science and Science Exchange, and the results of the replications will be published by eLife.

DOI:http://dx.doi.org/10.7554/eLife.04034.001

Discovery and SAR study of c-Met kinase inhibitors bearing an 3-amino-benzo[d]isoxazole or 3-aminoindazole scaffold

A series of 3-amino-benzo[d]isoxazole-/3-aminoindazole-based compounds were designed, synthesized and pharmacologically evaluated as tyrosine kinase c-Met inhibitors. The SAR study was conducted leading to identification of nine compounds (8d, 8e, 12, 28a-d, 28h and 28i) with IC50s less than 10nM against c-Met. Compound 28a stood out as the most potent c-Met inhibitor displaying potent inhibitory effects both at enzymatic (IC50=1.8 nM) and cellular (IC50=0.18 μM on EBC-1 cells) levels. In addition, 28a had a relatively good selectivity compared to a panel of our in-house 14 RTKs.

Multitarget inhibitors derived from crosstalk mechanism involving VEGFR2

Seven VEGFR small-molecule inhibitors have been approved by the US FDA as anticancer drugs, which confirms the therapeutic value of angiogenesis inhibitors. However, much more evidence indicates that VEGFR inhibition alone is usually not sufficient to block the tumor progress. The potential of some agents targeting VEGFR owes partially to the simultaneous inhibition of additional targets in other signaling pathways. In this review, the crosstalk between VEGFR2 and the additional targets in other signaling pathways, such as EGFR, MET, FGFR, PDGFR, c-Kit, Raf, PI3K and HDAC, and the synergistic effects derived from multitarget activities against these crosstalks are discussed. We also briefly describe the multitarget inhibitors in clinical trials or reported in the literature and patents under the different multitarget categories involving VEGFR2.

Small molecule tyrosine kinase inhibitors of ErbB2/HER2/Neu in the treatment of aggressive breast cancer

The human epidermal growth factor receptor 2 (HER2) is a member of the erbB class of tyrosine kinase receptors. These proteins are normally expressed at the surface of healthy cells and play critical roles in the signal transduction cascade in a myriad of biochemical pathways responsible for cell growth and differentiation. However, it is widely known that amplification and subsequent overexpression of the HER2 encoding oncogene results in unregulated cell proliferation in an aggressive form of breast cancer known as HER2-positive breast cancer. Existing therapies such as trastuzumab (Herceptin®) and lapatinib (Tyverb/Tykerb®), a monoclonal antibody inhibitor and a dual EGFR/HER2 kinase inhibitor, respectively, are currently used in the treatment of HER2-positive cancers, although issues with high recurrence and acquired resistance still remain. Small molecule tyrosine kinase inhibitors provide attractive therapeutic targets, as they are able to block cell signaling associated with many of the proposed mechanisms for HER2 resistance. In this regard we aim to present a review on the available HER2 tyrosine kinase inhibitors, as well as those currently in development. The use of tyrosine kinase inhibitors as sequential or combinatorial therapeutic strategies with other HER family inhibitors is also discussed.

Molecular modeling of exquisitely selective c-Met inhibitors through 3D-QSAR and molecular dynamics simulations

c-Met has been considered as an attractive target for developing antitumor agents. The highly selective c-Met inhibitors provide invaluable opportunities for the combination with other therapies safely to achieve the optimal efficacy. In this work, a series of triazolopyrazine c-Met inhibitors with exquisitely selectivity were investigated using a combination of molecular docking, three-dimensional quantitative structure-activity relationship (3D-QSAR), and molecular dynamics simulation. Comparative molecular field analysis (CoMFA) and comparative molecular similarity index analysis (CoMSIA) models were developed to reveal the structural determinants for c-Met inhibition. Both models were validated to have high reliability and predictability, and contour map analysis suggested feature requirements for different substituents on the scaffold. It is worth noting that an important hydrogen bond rich region was identified in the unique narrow channel, which is distinct from other kinases. Molecular dynamics simulations and binding free energy calculations provided further support that suitable groups in this hydrogen bond rich region made great contributions to the binding of ligands. Moreover, hydrogen bonds with residues of the narrow channel were also indicated to be essential to improve the activity and selectivity. This study will facilitate the discovery and optimization of novel c-Met inhibitors with higher activity and selectivity.