Somatic mutations of the MET oncogene are selected during metastatic spread of human HNSC carcinomas

c-MET pathway in human malignancies and its targeting by natural compounds for cancer therapy

BACKGROUND

c-MET is a receptor tyrosine kinase which is classically activated by HGF to activate its downstream signaling cascades such as MAPK, PI3K/Akt/mTOR, and STAT3. The c-MET modulates cell proliferation, epithelial-mesenchymal transition (EMT), immune response, morphogenesis, apoptosis, and angiogenesis. The c-MET has been shown to serve a prominent role in embryogenesis and early development. The c-MET pathway is deregulated in a broad range of malignancies, due to overexpression of ligands or receptors, genomic amplification, and MET mutations. The link between the deregulation of c-MET signaling and tumor progression has been well-documented. Overexpression or overactivation of c-MET is associated with dismal clinical outcomes and acquired resistance to targeted therapies. Since c-MET activation results in the triggering of oncogenic pathways, abrogating the c-MET pathway is considered to be a pivotal strategy in cancer therapeutics. Herein, an analysis of role of the c-MET pathway in human cancers and its relevance in bone metastasis and therapeutic resistance has been undertaken. Also, an attempt has been made to summarize the inhibitory activity of selected natural compounds towards c-MET signaling in cancers.

METHODS

The publications related to c-MET pathway in malignancies and its natural compound modulators were obtained from databases such as PubMed, Scopus, and Google Scholar and summarized based on PRISMA guidelines. Some of the keywords used for extracting relevant literature are c-MET, natural compound inhibitors of c-MET, c-MET in liver cancer, c-MET in breast cancer, c-MET in lung cancer, c-MET in pancreatic cancer, c-MET in head and neck cancer, c-MET in bone metastasis, c-MET in therapeutic resistance, and combination of c-MET inhibitors and chemotherapeutic agents. The chemical structure of natural compounds was verified in PubChem database.

RESULTS

The search yielded 3935 publications, of which 195 reference publications were used for our analysis. Clinical trials were referenced using ClinicalTrials.gov identifier. The c-MET pathway has been recognized as a prominent target to combat the growth, metastasis, and chemotherapeutic resistance in cancers. The key role of the c-MET in bone metastasis as well as therapeutic resistance has been elaborated. Also, suppressive effect of selected natural compounds on the c-MET pathway in clinical/preclinical studies has been discussed.

An Observatory for the MET Oncogene: A Guide for Targeted Therapies

The MET proto-oncogene encodes a pivotal tyrosine kinase receptor, binding the hepatocyte growth factor (HGF, also known as scatter factor, SF) and governing essential biological processes such as organogenesis, tissue repair, and angiogenesis. The pleiotropic physiological functions of MET explain its diverse role in cancer progression in a broad range of tumors; genetic/epigenetic alterations of MET drive tumor cell dissemination, metastasis, and acquired resistance to conventional and targeted therapies. Therefore, targeting MET emerged as a promising strategy, and many efforts were devoted to identifying the optimal way of hampering MET signaling. Despite encouraging results, however, the complexity of MET's functions in oncogenesis yields intriguing observations, fostering a humbler stance on our comprehension. This review explores recent discoveries concerning MET alterations in cancer, elucidating their biological repercussions, discussing therapeutic avenues, and outlining future directions. By contextualizing the research question and articulating the study's purpose, this work navigates MET biology's intricacies in cancer, offering a comprehensive perspective.

Identification of Novel MET Exon 14 Skipping Variants in Non-Small Cell Lung Cancer Patients: A Prototype Workflow Involving in Silico Prediction and RT-PCR

Background and aims: The MET exon 14 skipping (METex14) is an oncogenic driver mutation that provides a therapeutic opportunity in non-small cell lung cancer (NSCLCs) patients. This event often results from sequence changes at the MET canonical splicing sites. We characterize two novel non-canonical splicing site variants of MET that produce METex14. Materials and Methods: Two variants were identified in three advanced-stage NSCLC patients in a next-generation sequencing panel. The potential impact on splicing was predicted using in silico tools. METex14 mutation was confirmed using reverse transcription (RT)-PCR and a Sanger sequencing analysis on RNA extracted from stained cytology smears. Results: The interrogated MET (RefSeq ID NM_000245.3) variants include a single nucleotide substitution, c.3028+3A>T, in intron 14 and a deletion mutation, c.3012_3028del, in exon 14. The in silico prediction analysis exhibited reduced splicing strength in both variants compared with the MET normal transcript. The RT-PCR and subsequent Sanger sequencing analyses confirmed METex14 skipping in all three patients carrying these variants. Conclusion: This study reveals two non-canonical MET splice variants that cause exon 14 skipping, concurrently also proposes a clinical workflow for the classification of such non-canonical splicing site variants detected by routine DNA-based NGS test. It shows the usefulness of in silico prediction to identify potential METex14 driver mutation and exemplifies the opportunity of routine cytology slides for RNA-based testing.

Targeting of c-MET and AXL by cabozantinib is a potential therapeutic strategy for patients with head and neck cell carcinoma

Local or metastatic relapse following surgery, radiotherapy, and cisplatin is the leading cause of death in patients with head and neck squamous cell carcinoma (HNSCC). Our study shows overexpression of c-MET and AXL in HNSCC cells and patients resistant to radiotherapy and cisplatin. We demonstrate that cabozantinib, an inhibitor of vascular endothelial growth factor receptor (VEGFR), c-MET, and AXL, decreases migration, invasion, and proliferation and induces mitotic catastrophe and apoptotic cell death of naive and radiotherapy- and cisplatin-resistant HNSCC cells. Cabozantinib inhibits the growth and metastatic spread of experimental HNSCC in zebrafish and the growth of experimental HNSCC in mice by blocking tumor cell proliferation and angiogenesis. The efficacy of cabozantinib is also confirmed on viable sections of surgically removed specimens of human HNSCC and on a patient who relapses after five lines of treatment. These results suggest that cabozantinib is relevant for the treatment of patients with HNSCC after relapse under radiotherapy and cisplatin.

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AXL and c-MET are overexpressed in radiotherapy- and cisplatin-resistant HNSCC

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Overexpression of AXL and c-MET contributes to tumor aggressiveness and poor prognosis

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Cabozantinib has anti-tumor and anti-metastatic efficacy in mice and zebrafish models

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Cabozantinib efficacy is shown on HNSCC biopsies and in one patient after several relapses

Anti-cancer therapeutic strategies based on HGF/MET, EpCAM, and tumor-stromal cross talk

As an intelligent disease, tumors apply several pathways to evade the immune system. It can use alternative routes to bypass intracellular signaling pathways, such as nuclear factor-κB (NF-κB), Wnt, and mitogen-activated protein (MAP)/phosphoinositide 3-kinase (PI3K)/mammalian target of rapamycin (mTOR). Therefore, these mechanisms lead to therapeutic resistance in cancer. Also, these pathways play important roles in the proliferation, survival, migration, and invasion of cells. In most cancers, these signaling pathways are overactivated, caused by mutation, overexpression, etc. Since numerous molecules share these signaling pathways, the identification of key molecules is crucial to achieve favorable consequences in cancer therapy. One of the key molecules is the mesenchymal-epithelial transition factor (MET; c-Met) and its ligand hepatocyte growth factor (HGF). Another molecule is the epithelial cell adhesion molecule (EpCAM), which its binding is hemophilic. Although both of them are involved in many physiologic processes (especially in embryonic stages), in some cancers, they are overexpressed on epithelial cells. Since they share intracellular pathways, targeting them simultaneously may inhibit substitute pathways that tumor uses to evade the immune system and resistant to therapeutic agents.

Imaging Endocytosis Dynamics in Health and Disease

Endocytosis is a critical process for cell growth and viability. It mediates nutrient uptake, guarantees plasma membrane homeostasis, and generates intracellular signaling cascades. Moreover, it plays an important role in dead cell clearance and defense against external microbes. Finally, endocytosis is an important cellular route for the delivery of nanomedicines for therapeutic treatments. Thus, it is not surprising that both environmental and genetic perturbation of endocytosis have been associated with several human conditions such as cancer, neurological disorders, and virus infections, among others. Over the last decades, a lot of research has been focused on developing advanced imaging methods to monitor endocytosis events with high resolution in living cells and tissues. These include fluorescence imaging, electron microscopy, and correlative and super-resolution microscopy. In this review, we outline the major endocytic pathways and briefly discuss how defects in the molecular machinery of these pathways lead to disease. We then discuss the current imaging methodologies used to study endocytosis in different contexts, highlighting strengths and weaknesses.

The Occurrence of MET Ectodomain Shedding in Oral Cancer and Its Potential Impact on the Use of Targeted Therapies

Simple Summary

Head and neck cancer is the sixth most common cancer type worldwide, comprising tumors of the upper aero/digestive tract. Approximately 50% of these cancers originate in the oral cavity. Depending on disease stage, oral cancer patients are treated with single-modality surgery, or in combination with radiotherapy with or without chemotherapy. Despite advances in these modalities, the 5-year survival rate is merely 50%. Therefore, implementation of targeted therapies, directed against signaling molecules, has gained attention. One potential target is the MET protein, which can be present on the surface of cancer cells, orchestrating aggressive behavior. As cancer cells can shed the extracellular part of MET from their surface, it is important to identify for MET positive patients whether they possess the entire and/or only the intracellular part of the receptor to assess whether targeted therapies directed against the extracellular, intracellular, or both parts of MET need to be implemented.

Abstract

The receptor tyrosine kinase MET has gained attention as a therapeutic target. Although MET immunoreactivity is associated with progressive disease, use of targeted therapies has not yet led to major survival benefits. A possible explanation is the lack of companion diagnostics (CDx) that account for proteolytic processing. During presenilin-regulated intramembrane proteolysis, MET’s ectodomain is shed into the extracellular space, which is followed by γ-secretase-mediated cleavage of the residual membranous C-terminal fragment. The resulting intracellular fragment is degraded by the proteasome, leading to downregulation of MET signaling. Conversely, a membrane-bound MET fragment lacking the ectodomain (MET-EC^-) can confer malignant potential. Use of C- and N-terminal MET monoclonal antibodies (moAbs) has illustrated that MET-EC^- occurs in transmembranous C-terminal MET-positive oral squamous cell carcinoma (OSCC). Here, we propose that ectodomain shedding, resulting from G-protein-coupled receptor transactivation of epidermal growth factor receptor signaling, and/or overexpression of ADAM10/17 and/or MET, stabilizes and possibly activates MET-EC^- in OSCC. As MET-EC^- is associated with poor prognosis in OSCC, it potentially has impact on the use of targeted therapies. Therefore, MET-EC^- should be incorporated in the design of CDx to improve patient stratification and ultimately prolong survival. Hence, MET-EC^- requires further investigation seen its oncogenic and predictive properties.

Molecular mechanism(s) of regulation(s) of c-MET/HGF signaling in head and neck cancer

Head and neck cancer is the sixth most common cancer across the globe. This is generally associated with tobacco and alcohol consumption. Cancer in the pharynx majorly arises through human papillomavirus (HPV) infection, thus classifying head and neck squamous cell carcinoma (HNSCC) into HPV-positive and HPV-negative HNSCCs. Aberrant, mesenchymal-epithelial transition factor (c-MET) signal transduction favors HNSCC progression by stimulating proliferation, motility, invasiveness, morphogenesis, and angiogenesis. c-MET upregulation can be found in the majority of head and neck squamous cell carcinomas. c-MET pathway acts on several downstream effectors including phospholipase C gamma (PLCγ), cellular Src kinase (c-Src), phosphotidylinsitol-3-OH kinase (PI3K), alpha serine/threonine-protein kinase (Akt), mitogen-activated protein kinase (MAPK), and wingless-related integration site (Wnt) pathways. c-MET also establishes a crosstalk pathway with epidermal growth factor receptor (EGFR) and contributes towards chemoresistance in HNSCC. In recent years, the signaling communications of c-MET/HGF in metabolic dysregulation, tumor-microenvironment and immune modulation in HNSCC have emerged. Several clinical trials have been established against c-MET/ hepatocyte growth factor (HGF) signaling network to bring up targeted and effective therapeutic strategies against HNSCC. In this review, we discuss the molecular mechanism(s) and current understanding of c-MET/HGF signaling and its effect on HNSCC.

Graphical abstract

The Emerging Role of c-Met in Carcinogenesis and Clinical Implications as a Possible Therapeutic Target

Background

c-MET is a receptor tyrosine kinase receptor (RTK) for the hepatocyte growth factor (HGF). The binding of HGF to c-MET regulates several cellular functions: differentiation, proliferation, epithelial cell motility, angiogenesis, and epithelial-mesenchymal transition (EMT). Moreover, it is known to be involved in carcinogenesis. Comprehension of HGF-c-MET signaling pathway might have important clinical consequences allowing to predict prognosis, response to treatment, and survival rates based on its expression and dysregulation. Discussion. c-MET represents a useful molecular target for novel engineered drugs. Several clinical trials are underway for various solid tumors and the development of new specific monoclonal antibodies depends on the recent knowledge about the definite c-MET role in each different malignance. Recent clinical trials based on c-MET molecular targets result in good safety profile and represent a promising therapeutic strategy for solid cancers, in monotherapy or in combination with other target drugs.

Conclusion

The list of cell surface receptors crosslinking with the c-MET signaling is constantly growing, highlighting the importance of this pathway for personalized target therapy. Research on the combination of c-MET inhibitors with other drugs will hopefully lead to discovery of new effective treatment options.

Molecular Pathways and Druggable Targets in Head and Neck Squamous Cell Carcinoma

Head and neck cancers are a heterogeneous group of neoplasms, affecting an ever increasing global population. Despite advances in diagnostic technology and surgical approaches to manage these conditions, survival rates have only marginally improved and this has occurred mainly in developed countries. Some improvements in survival, however, have been a result of new management and treatment approaches made possible because of our ever-increasing understanding of the molecular pathways triggered in head and neck oncogenesis, and the growing understanding of the abundant heterogeneity of this group of cancers. Some important pathways are common to other solid tumours, but their impact on reducing the burden of head and neck disease has been less than impressive. Other less known and little-explored pathways may hold the key to the development of potential druggable targets. The extensive work carried out over the last decade, mostly utilising next generation sequencing has opened up the development of many novel approaches to head and neck cancer treatment. This paper explores our current understanding of the molecular pathways of this group of tumours and outlines associated druggable targets which are deployed as therapeutic approaches in head and neck oncology with the ultimate aim of improving patient outcomes and controlling the personal and economic burden of head and neck cancer.

Pharmacokinetics of capmatinib in participants with hepatic impairment: A phase 1, open-label, single-dose, parallel-group study

Aims

Capmatinib, a mesenchymal–epithelial transition factor tyrosine kinase inhibitor, is metabolized by cytochrome P450 (CYP) 3A4 and aldehyde oxidase. In individuals with hepatic impairment, alterations in hepatobiliary excretion and metabolism could lead to higher capmatinib exposure. We compared the pharmacokinetics of a single oral dose of capmatinib 200 mg administered to participants with varying degrees of hepatic impairment vs. matched controls with normal hepatic function.

Methods

This phase 1, multicentre, open‐label, parallel‐group study enrolled adult participants with normal hepatic function and mild, moderate and severe hepatic impairments. Eligible participants received a single oral dose of 200 mg capmatinib. The pharmacokinetic parameters of capmatinib were analysed and compared across participants with impaired and normal hepatic function.

Results

Of 31 enrolled participants, 29 had an evaluable pharmacokinetic profile: normal (n = 9); mild (n = 6); moderate (n = 8); severe (n = 6). Compared with the normal group, geometric mean (GM) maximum (peak) observed plasma drug concentration after single‐dose administration decreased by 27.6% in the mild group (GM ratio [GMR] = 0.724; 90% confidence interval [CI]: 0.476–1.10), by 17.2% in the moderate group (GMR = 0.828; 90% CI: 0.563–1.22) and remained unchanged in the severe group (GMR = 1.02; 90% CI: 0.669–1.55). Compared with the normal group, GM area under the plasma concentration–time curve from time zero to infinity decreased by 23.3% in the mild group (GMR = 0.767; 90% CI: 0.532–1.11), by 8.6% in the moderate group (GMR = 0.914; 90% CI: 0.652–1.28) and increased by 24% in the severe group (GMR = 1.24; 90% CI: 0.858–1.78).

Conclusion

Mild, moderate and severe hepatic impairment did not have a clinically relevant impact on capmatinib pharmacokinetics. No new safety findings are reported in this study.

Lung Cancer with MET exon 14 Skipping Mutation: Genetic Feature, Current Treatments, and Future Challenges

MET exon 14 skipping mutation (MET∆ex14) is present about 3% of non-small cell lung cancers (NSCLCs). NSCLC patients with MET∆ex14 are characterized by an average age of over 70 years at diagnosis, a smoking history and a higher frequency in pleomorphic carcinoma and adenosquamous cell carcinoma than in adenocarcinoma. It has also been reported that NSCLCs with MET∆ex14 often have codriver alterations such as EGFR amplification (6–28%), FGFR1 alterations (5–17%), KRAS alterations (~8%), BRAF alterations (~21%), or PIK3CA mutation/amplification (~14%). In 2020, the approval of two MET-tyrosine kinase inhibitors (TKIs), capmatinib and tepotinib, for NSCLCs carrying MET∆ex14 dawned a new era for MET-targeted therapy. These drugs yielded progression-free survival of 5.4−12.4 months in clinical trials; however, it has also been reported that one-third to half of patients show inherent resistance to MET-TKIs. In addition, the emergence of acquired resistance to MET-TKIs is inevitable. In this review, we summarize the clinical and molecular characteristics of NSCLCs with MET∆ex14, the efficacy and safety of capmatinib and tepotinib, the inherent and acquired resistance mechanisms to MET-TKIs, and new treatment strategies for NSCLCs with MET∆ex14 in the near future.

Effect of capmatinib on the pharmacokinetics of digoxin and rosuvastatin administered as a 2-drug cocktail in patients with MET-dysregulated advanced solid tumours: A phase I, multicentre, open-label, single-sequence drug-drug interaction study

Aims

Capmatinib, an orally bioavailable, highly potent and selective MET inhibitor, was recently approved to treat adult patients with metastatic nonsmall cell lung cancer with METex14 skipping mutations. The study investigated the effect of capmatinib on the pharmacokinetics of a single oral dose of digoxin and rosuvastatin in patients with MET‐dysregulated advanced solid tumours.

Methods

This was a multicentre, open‐label, single‐sequence study. An oral drug cocktail containing 0.25 mg digoxin and 10 mg rosuvastatin was administered to adult patients with MET‐dysregulated advanced solid tumours on Day 1, and then on Day 22 with capmatinib. Between Days 11 and 32, capmatinib 400 mg was administered twice daily to ensure the attainment of steady state for drug–drug interaction assessment. Pharmacokinetics of cocktail drugs and safety of capmatinib were evaluated.

Results

Thirty‐two patients were enrolled. Compared to digoxin alone, the geometric mean ratios (90% confidence interval) of area under the concentration–time curve from time zero to infinity and maximum concentration for digoxin plus capmatinib were 1.47 (1.28, 1.68) and 1.74 (1.43, 2.13), respectively. Compared to rosuvastatin alone, the geometric mean ratios (90% confidence interval) of area under the curve to infinity and maximum concentration for rosuvastatin plus capmatinib were 2.08 (1.56, 2.76) and 3.04 (2.36, 3.92), respectively. Most frequent adverse events (≥25% for all grades) were nausea, asthenia, constipation, vomiting, peripheral oedema and pyrexia. Most frequent Grade 3/4 adverse events (≥5%) were anaemia, pulmonary embolism, asthenia, dyspnoea, nausea and vomiting.

Conclusion

This study demonstrated that capmatinib is an inhibitor of P‐gp and BCRP transporters, with clinically relevant drug–drug interaction potential. Capmatinib was well‐tolerated and no unexpected safety concerns were observed.

Co-stimulatory and co-inhibitory immune markers in solid tumors with MET alterations

The implication of MET alterations in solid tumors and the immune microenvironment remains elusive. Formalin-fixed, paraffin-embedded samples of 21 patients with solid tumors harboring MET alterations were used for immunohistochemical staining. Extracted RNA was analyzed with the NanoString nCounter human PanCancer immune profiling panel (NanoString Technologies, Inc., WA, USA). Patients were diagnosed with lung (n = 10), breast (n = 5), genitourinary (n = 3) or colorectal cancer (n = 3). Eleven had a MET missense mutation, four had an exon 14 splice site mutation and six had MET amplification. CD6, CCL19, CD40LG, XCR1, MAGEA1, ATM and CCL19 genes were significantly differentially expressed in MET-altered cancers. MET alterations may have a role in various solid tumors as potential therapeutic targets and combination therapy candidates with immune checkpoint inhibitors.

MET is a receptor for growth signals that keeps cells alive and healthy. However, some tumors have changes in MET that allow for uncontrollable cell growth. Patients with MET-altered tumors may benefit from treatments targeting this gene, but eventually they become resistant to the treatments. Thus, there is a need to identify additional therapies for this patient population. The authors tested immune gene expression in tumors with MET alterations to determine if these patients would benefit from a new class of treatments called immunotherapies and found that patients with and without MET changes had differences in immune gene expression.

Brn3a/Pou4f1 Functions as a Tumor Suppressor by Targeting c-MET/STAT3 Signaling in Thyroid Cancer

BACKGROUND

Brn3a/Pou4f1 is a class IV POU domain-containing transcription factor and has been found to be expressed in a variety of cancers. However, the mechanism and action of Brn3a in thyroid cancer has not been investigated.

PURPOSE

To investigate the role of Brn3a in thyroid cancer progression and its clinical implication.

METHODS

We examined Brn3a expression status in patients with thyroid cancer and analyzed relationships between Brn3a expression and clinicopathological findings using The Cancer Genome Atlas (TCGA) database. For functional in vitro analysis, proliferation, migration, invasion assay, and Western blotting were performed after overexpression or suppression of Brn3a.

RESULTS

The promoter hypermethylation of Brn3a was found in patients with aggressive thyroid cancer and Brn3a was downregulated in tissues of patients with thyroid cancer. In TCGA database, the low-Brn3a-expression group revealed a more aggressive phenotype, including T stage and extrathyroid extension when compared with the high-Brn3a-expression group. Overexpression of Brn3a suppressed cell migration and invasion via regulation of epithelial-mesenchymal transition (EMT)-associated proteins in thyroid cancer cell lines. Brn3a overexpression also downregulated signal transducer and activator of transcription 3 (STAT3) signaling through suppression of tyrosine-protein kinase Met (c-MET). In contrast, knockdown of Brn3a by small interfering ribonucleic acid (siRNA) significantly increased cell migration and invasion through upregulation of c-MET/STAT3. These results imply that Brn3a suppresses tumor metastasis via c-MET/STAT3 inhibition and EMT suppression in thyroid cancer.

CONCLUSIONS

Our findings show that Brn3a is a potential tumor suppressor that leads to reduced cancer cell migration and invasion in thyroid cancer. Elucidation of the Brn3a-regulated cancer pathways may therefore provide novel therapeutic strategies to control thyroid cancer metastasis.

MET receptor in oncology: From biomarker to therapeutic target

First discovered in the 1984, the MET receptor tyrosine kinase (RTK) and its ligand hepatocyte growth factor or HGF (also known as scatter factor or SF) are implicated as key players in tumor cell migration, proliferation, and invasion in a variety of cancers. This pathway also plays a key role during embryogenesis in the development of muscular and nervous structures. High expression of the MET receptor has been shown to correlate with poor prognosis and resistance to therapy. MET exon 14 splicing variants, initially identified by us in lung cancer, is actionable through various tyrosine kinase inhibitors (TKIs). For this reason, this pathway is of interest as a therapeutic target. In this chapter we will be discussing the history of MET, the genetics of this RTK, and give some background on the receptor biology. Furthermore, we will discuss directed therapeutics, mechanisms of resistance, and the future of MET as a therapeutic target.

Metastatic disease in head & neck oncology

The head and neck district represents one of the most frequent sites of cancer, and the percentage of metastases is very high in both loco-regional and distant areas. Prognosis refers to several factors: a) stage of disease; b) loco-regional relapses; c) distant metastasis. At diagnosis, distant metastases of head and neck cancers are present in about 10% of cases with an additional 20-30% developing metastases during the course of their disease. Diagnosis of distant metastases is associated with unfavorable prognosis, with a median survival of about 10 months. The aim of the present review is to provide an update on distant metastasis in head and neck oncology. Recent achievements in molecular profiling, interaction between neoplastic tissue and the tumor microenvironment, oligometastatic disease concepts, and the role of immunotherapy have all deeply changed the therapeutic approach and disease control. Firstly, we approach topics such as natural history, epidemiology of distant metastases and relevant pathological and radiological aspects. Focus is then placed on the most relevant clinical aspects; particular attention is reserved to tumours with distant metastasis and positive for EBV and HPV, and the oligometastatic concept. A substantial part of the review is dedicated to different therapeutic approaches. We highlight the role of immunotherapy and the potential effects of innovative technologies. Lastly, we present ethical and clinical perspectives related to frailty in oncological patients and emerging difficulties in sustainable socio-economical governance.

MET targeting: time for a rematch

MET, the receptor tyrosine kinase (RTK) for hepatocyte growth factor, is a proto-oncogene involved in embryonic development and throughout life in homeostasis and tissue regeneration. Deregulation of MET signaling has been reported in numerous malignancies, prompting great interest in MET targeting for cancer therapy. The present review offers a summary of the biology of MET and its known functions in normal physiology and carcinogenesis, followed by an overview of the most relevant MET-targeting strategies and corresponding clinical trials, highlighting both past setbacks and promising future prospects. By placing their efforts on a more precise stratification strategy through the genetic analysis of tumors, modern trials such as the NCI-MATCH trial could revive the past enthusiasm for MET-targeted therapy.

The Function of the HGF/c-Met Axis in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most common malignancies worldwide, leading to a large global cancer burden. Hepatocyte growth factor (HGF) and its high-affinity receptor, mesenchymal epithelial transition factor (c-Met), are closely related to the onset, progression, and metastasis of multiple tumors. The HGF/c-Met axis is involved in cell proliferation, movement, differentiation, invasion, angiogenesis, and apoptosis by activating multiple downstream signaling pathways. In this review, we focus on the function of the HGF/c-Met axis in HCC. The HGF/c-Met axis promotes the onset, proliferation, invasion, and metastasis of HCC. Moreover, it can serve as a biomarker for diagnosis and prognosis, as well as a therapeutic target for HCC. In addition, it is closely related to drug resistance during HCC treatment.

Targeting cancer stem cells in squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is a highly aggressive tumor and the sixth most common cancer worldwide. Current treatment strategies for HNSCC are surgery, radiotherapy, chemotherapy, immunotherapy or combinatorial therapies. However, the overall 5-year survival rate of HNSCC patients remains at about 50%. Cancer stem cells (CSCs), a small population among tumor cells, are able to self-renew and differentiate into different tumor cell types in a hierarchical manner, similar to normal tissue. In HNSCC, CSCs are proposed to be responsible for tumor initiation, progression, metastasis, drug resistance, and recurrence. In this review, we discuss the molecular and cellular characteristics of CSCs in HNSCC. We summarize current approaches used in the literature for identification of HNSCC CSCs, and mechanisms required for CSC regulation. We also highlight the role of CSCs in treatment failure and therapeutic targeting options for eliminating CSCs in HNSCC.

MET Inhibitors in Small Cell Lung Cancer: From the Bench to the Bedside

Small cell lung cancer (SCLC) is the most aggressive type of lung cancer. The different systemic treatment approaches attempted in the last 35 years have not improved overall survival in the advanced stage. Targeted therapies assessed in clinical trials have failed to show efficacy against SCLC. Within the potentially interesting targets, the hepatocyte growth factor (HGF)/mesenchymal-epithelial transition (MET) pathway activation is associated with worse survival and chemoresistance in SCLC. Preclinical data suggest that the inhibition of the MET pathway can revert chemoresistance and prevent tumor growth. Recently, immunotherapy has shown modest but relevant activity in SCLC. Interestingly, MET modulation seems to be involved in increasing the efficacy of standard checkpoint inhibitors. Here, we review the preclinical and clinical data of MET inhibition in SCLC, and the role of this pathway in the immune response.

Phosphatase of regenerating liver sensitizes MET to functional activation by hepatocyte growth factor

Phosphatase of regenerating liver (PRL) is overexpressed in metastatic cancers and actively drives their malignant progression. Many studies on cultured cancer cells have implied PRL overexpression as a stimulant for cellular signaling involved in cell proliferation. However, its role in the tightly adhered and polarized epithelial cells remains largely uncharacterized. In this study, we show that inducible expression of PRL in MDCK normal epithelial cells sensitized MET, the receptor for hepatocyte growth factor (HGF), to functional activation by HGF. We found that PRL expression amplified tyrosine phosphorylation levels of various proteins, among which MET was identified to be the most abundant. This phosphorylation occurred selectively at Y1234/1235 in the activation loop of MET, whereas phosphorylation of Y1349 in the effector-binding site, which is directly involved in downstream signaling, was almost undetectable. Consistently, PRL overexpression by itself did not cause observable alterations at the cellular level. However, when cells were stimulated with HGF, phosphorylation of Y1349 was much more strongly induced in PRL-expressing cells than in control cells. This resulted in robust cell scattering and tubulogenesis, even with low levels of HGF. Collectively, these results demonstrate a unique role of PRL in regulating MET function, which is known to be crucial for remodeling of epithelial tissues and malignant progression of cancers.

MET/HGF Co-Targeting in Pancreatic Cancer: A Tool to Provide Insight into the Tumor/Stroma Crosstalk

The ‘onco-receptor’ MET (Hepatocyte Growth Factor Receptor) is involved in the activation of the invasive growth program that is essential during embryonic development and critical for wound healing and organ regeneration during adult life. When aberrantly activated, MET and its stroma-secreted ligand HGF (Hepatocyte Growth Factor) concur to tumor onset, progression, and metastasis in solid tumors, thus representing a relevant target for cancer precision medicine. In the vast majority of tumors, wild-type MET behaves as a ‘stress-response’ gene, and relies on ligand stimulation to sustain cancer cell ‘scattering’, invasion, and protection form apoptosis. Moreover, the MET/HGF axis is involved in the crosstalk between cancer cells and the surrounding microenvironment. Pancreatic cancer (namely, pancreatic ductal adenocarcinoma, PDAC) is an aggressive malignancy characterized by an abundant stromal compartment that is associated with early metastases and resistance to conventional and targeted therapies. Here, we discuss the role of the MET/HGF axis in tumor progression and dissemination considering as a model pancreatic cancer, and provide a proof of concept for the application of dual MET/HGF inhibition as an adjuvant therapy in pancreatic cancer patients.

HGF/MET and the Immune System: Relevance for Cancer Immunotherapy

An overactivation of hepatocyte growth factor (HGF)/mesenchymal-epithelial transition factor (MET) axis promotes tumorigenesis and tumor progression in various cancer types. Research data recently evidenced that HGF/MET signaling is also involved also in the immune response, mainly modulating dendritic cells functions. In general, the pathway seems to play an immunosuppressive role, thus hypothesizing that it could constitute a mechanism of primary and acquired resistance to cancer immunotherapy. Recently, some approaches are being developed, including drug design and cell therapy to combine MET and programmed cell death receptor-1 (PD-1)/programmed cell death receptor-ligand 1 (PD-L1) inhibition. This approach could represent a new weapon in cancer therapy in the future.

Expression and prognostic value of c-met in canine mammary tumours

C-met is a receptor normally expressed on epithelial cells and dysregulated in human breast cancers. Mammary tumours are the most common tumour in female dogs. The aims of this study were to detect the expression of c-met in canine mammary tumours (CMTs) and evaluate the correlations between c-met expression and clinicopathological features. A total of 240 specimens of canine mammary tissues composed of 30 normal glands, 30 hyperplastic ones, 90 benign tumours and 90 carcinomas obtained from 127 bitches were examined by immunohistochemical staining. Positive c-met immunoreactivity was demonstrated in the cytoplasm of mammary epithelial cells at variable levels, and in malignant CMTs, higher c-met expression was found in carcinomas whose grade, stage and mitotic index were low, and metastasis was absent. The median survival time was shorter in dogs with malignant CMTs with a maximum diameter ≥5 cm, regional lymph node or distant metastasis, and a high histologic grade. However, the 2-year survival rate was higher in dogs with malignant CMTs of higher c-met expression than those of low c-met expression (80.1% vs 57%). C-met expression could be used as a valuable positive prognostic factor for the clinical outcomes of dogs with malignant CMTs.

Known and novel roles of the MET oncogene in cancer: a coherent approach to targeted therapy

The MET oncogene encodes an unconventional receptor tyrosine kinase with pleiotropic functions: it initiates and sustains neoplastic transformation when genetically altered ('oncogene addiction') and fosters cancer cell survival and tumour dissemination when transcriptionally activated in the context of an adaptive response to adverse microenvironmental conditions ('oncogene expedience'). Moreover, MET is an intrinsic modulator of the self-renewal and clonogenic ability of cancer stem cells ('oncogene inherence'). Here, we provide the latest findings on MET function in cancer by focusing on newly identified genetic abnormalities in tumour cells and recently described non-mutational MET activities in stromal cells and cancer stem cells. We discuss how MET drives cancer clonal evolution and progression towards metastasis, both ab initio and under therapeutic pressure. We then elaborate on the use of MET inhibitors in the clinic with a critical appraisal of failures and successes. Ultimately, we advocate a rationale to improve the outcome of anti-MET therapies on the basis of thorough consideration of the entire spectrum of MET-mediated biological responses, which implicates adequate patient stratification, meaningful biomarkers and appropriate clinical end points.

Met Receptor Tyrosine Kinase and Chemoprevention of Oral Cancer

Background

We have previously shown that gene expression profiles of oral leukoplakia (OL) may improve the prediction of oral cancer (OC) risk. To identify new targets for prevention, we performed a systematic survey of transcripts associated with an increased risk of oral cancer and overexpressed in OC vs normal mucosa (NM).

Methods

We used gene expression profiles of 86 patients with OL and available outcomes from a chemoprevention trial of OC and NM. MET expression was evaluated using immunohistochemistry in 120 OL patients, and its association with OC development was tested in multivariable analysis. Sensitivity to pharmacological Met inhibition was tested invitro in premalignant and OC cell lines (n = 33) and invivo using the 4-NQO model of oral chemoprevention (n = 20 mice per group). All statistical tests were two-sided.

Results

The overlap of 693 transcripts associated with an increased risk of OC with 163 transcripts overexpressed in OC compared with NM led to the identification of 23 overlapping transcripts, including MET. MET overexpression in OL was associated with a hazard ratio of 3.84 (95% confidence interval = 1.59 to 9.27, P = .003) of developing OC. Met activation was found in OC and preneoplastic cell lines. Crizotinib activity in preneoplastic and OC cell lines was comparable. ARQ 197 was more active in preneoplastic compared with OC cell lines. In the 4-NQO model, squamous cell carcinoma, dysplasia, and hyperkeratosis were observed in 75.0%, 15.0%, and 10.0% in the control group, and in 25.0%, 70.0%, and 5.0% in the crizotinib group (P < .001).

Conclusion

Together, these data suggest that MET activation may represent an early driver in oral premalignancy and a target for chemoprevention of OC.

Simm530, a novel and highly selective c-Met inhibitor, blocks c-Met-stimulated signaling and neoplastic activities

The aberrant c-Met activation has been implicated in a variety of human cancers for its critical role in tumor growth, metastasis and tumor angiogenesis. Thus, c-Met axis presents as an attractive therapeutic target. Notably, most of these c-Met inhibitors currently being evaluated in clinical trials lack selectivity and target multiple kinases, often accounting for the undesirable toxicities. Here we described Simm530 as a potent and selective c-Met inhibitor. Simm530 demonstrated >2,000 fold selectivity for c-Met compared with other 282 kinases, making it one of the most selective c-Met inhibitors described to date. This inhibitor significantly blocked c-Met signaling pathways regardless of mechanistic complexity implicated in c-Met activation. As a result, Simm530 led to substantial inhibition of c-Met-promoted cell proliferation, migration, invasion, ECM degradation, cell scattering and invasive growth. In addition, Simm530 inhibited primary human umbilical vascular endothelial cell (HUVEC) proliferation, decreased intratumoral CD31 expression and plasma pro-angiogenic factor interleukin-8 secretion, suggesting its significant anti-angiogenic properties. Simm530 resulted in dose-dependent inhibition of c-Met phosphorylation and tumor growth in c-Met-driven lung and gastric cancer xenografts. And, the inhibitor is well tolerated even at doses that achieve complete tumor regression. Together, Simm530 is a potent and highly selective c-Met kinase inhibitor that may have promising therapeutic potential in c-Met-driven cancer treatment.

Activated HGF-c-Met Axis in Head and Neck Cancer

Head and neck squamous cell carcinoma (HNSCC) is a highly morbid disease. Recent developments including Food and Drug Administration (FDA) approved molecular targeted agent’s pembrolizumab and cetuximab show promise but did not improve the five-year survival which is currently less than 40%. The hepatocyte growth factor receptor; also known as mesenchymal–epithelial transition factor (c-Met) and its ligand hepatocyte growth factor (HGF) are overexpressed in head and neck squamous cell carcinoma (HNSCC); and regulates tumor progression and response to therapy. The c-Met pathway has been shown to regulate many cellular processes such as cell proliferation, invasion, and angiogenesis. The c-Met pathway is involved in cross-talk, activation, and perpetuation of other signaling pathways, curbing the cogency of a blockade molecule on a single pathway. The receptor and its ligand act on several downstream effectors including phospholipase C gamma (PLCγ), cellular Src kinase (c-Src), phosphotidylinsitol-3-OH kinase (PI3K) alpha serine/threonine-protein kinase (Akt), mitogen activate protein kinase (MAPK), and wingless-related integration site (Wnt) pathways. They are also known to cross-talk with other receptors; namely epidermal growth factor receptor (EGFR) and vascular endothelial growth factor receptor (VEGFR) and specifically contribute to treatment resistance. Clinical trials targeting the c-Met axis in HNSCC have been undertaken because of significant preclinical work demonstrating a relationship between HGF/c-Met signaling and cancer cell survival. Here we focus on HGF/c-Met impact on cellular signaling in HNSCC to potentiate tumor growth and disrupt therapeutic efficacy. Herein we summarize the current understanding of HGF/c-Met signaling and its effects on HNSCC. The intertwining of c-Met signaling with other signaling pathways provides opportunities for more robust and specific therapies, leading to better clinical outcomes.

Biological roles of hepatocyte growth factor-Met signaling from genetically modified animals

Hepatocyte growth factor (HGF) is produced by stromal and mesenchymal cells, and it stimulates epithelial cell proliferation, motility, morphogenesis and angiogenesis in various organs via tyrosine phosphorylation of its cognate receptor, Met. The HGF-Met signaling pathway contributes in a paracrine manner to the development of epithelial organs, exerts regenerative effects on the epithelium, and promotes the regression of fibrosis in numerous organs. Additionally, the HGF-Met signaling pathway is correlated with the biology of cancer types, neurons and immunity. In vivo analyses using genetic modification have markedly increased the profound understanding of the HGF-Met system in basic biology and its clinical applications. HGF and Met knockout (KO) mice are embryonically lethal. Therefore, amino acids in multifunctional docking sites of Met have been exchanged with specific binding motifs for downstream adaptor molecules in order to investigate the signaling potential of the HGF-Met signaling pathway. Conditional Met KO mice were generated using Cre-loxP methodology and characterization of these mice indicated that the HGF-Met signaling pathway is essential in regeneration, protection, and homeostasis in various tissue types and cells. Furthermore, the results of studies using HGF-overexpressing mice have indicated the therapeutic potential of HGF for various types of disease and injury. In the present review, the phenotypes of Met gene-modified mice are summarized.

Germacrone derivatives: synthesis, biological activity, molecular docking studies and molecular dynamics simulations

Germacrone is one of the major bioactive components in the Curcuma zedoaria oil product, which is extracted from Curcuma zedoaria Roscoe, known as zedoary. The present study designed some novel germacrone derivatives based on combination principles, synthesized these compounds, and investigated their inhibitions on Bel-7402, HepG2, A549 and HeLa cells. Meanwhile, the study evaluated inhibitions of these derivatives on c-Met kinase, which has been detected in a number of cancers. The results suggested that the majority of the compounds showed stronger inhibitory effect on cancers and c-Met kinase than germacrone. Furthermore, our docking experiments analyzed the results and explained the molecular mechanism. Molecular dynamics simulations were then applied to perform further evaluation of the binding stabilities between compounds and their receptors.

Prognostic value of c-MET in head and neck cancer: A systematic review and meta-analysis of aggregate data

OBJECTIVES

The hepatocyte growth factor (HGF)/mesenchymal-epithelial transition factor (c-MET) ligand/receptor axis has been implicated in pathogenesis of malignant diseases including squamous cell carcinoma of the head and neck (SCCHN). Overexpression of c-MET has been reported as a common molecular abnormality in SCCHN, although its prognostic and predictive value remains to be validated.

METHODS

We systematically searched literature for studies evaluating c-MET expression on immunohistochemistry in newly diagnosed, non-metastatic SCCHN. The c-MET expressing cases were classified into three categories according to predefined cut-off values for positivity. Our aim was to assess the prevalence of c-MET expression and its relationship with selected clinicopathological variables.

RESULTS

Twenty-eight studies with 2019 cases were included. Relative frequencies of c-MET expression above cut-off levels I, II, and III were 81.8%, 63.8%, and 46.2%, respectively. Differences between these three values were statistically significant (p<1.0×10^-6). Above cut-off level II, c-MET positivity was associated with worse overall survival (p=4.0×10^-6), positive nodal status (p=1.0×10^-4), higher disease stage (p=7.0×10^-4), older age (p=2.1×10^-3), disease recurrence (p=2.0×10^-2), and primary tumour localization in the oral cavity (p=2.3×10^-2). Above cut-off level III, c-MET positivity was associated with worse disease-free or progression-free survival (p=9.0×10^-6), p16 negativity (p=2.4×10^-4), worse overall survival (p=4.0×10^-4), positive epidermal growth factor receptor (EGFR) status (p=7.2×10^-4), and larger primary tumours (p=4.6×10^-3).

CONCLUSION

In SCCHN, immunohistochemical overexpression of c-MET above cut-off levels III and particularly II was associated with inferior survival outcomes and advanced disease. Moreover, it represents a promising predictive biomarker for c-MET targeting, yet the optimal scoring method remains to be defined.

Hepatocyte Growth Factor-c-MET Signaling Mediates the Development of Nonsensory Structures of the Mammalian Cochlea and Hearing

The stria vascularis is a nonsensory structure that is essential for auditory hair cell function by maintaining potassium concentration of the scala media. During mouse embryonic development, a subpopulation of neural crest cell-derived melanocytes migrates and incorporates into a subregion of the cochlear epithelium, forming the intermediate cell layer of the stria vascularis. The relation of this developmental process to stria vascularis function is currently unknown. In characterizing the molecular differentiation of developing peripheral auditory structures, we discovered that hepatocyte growth factor (Hgf) is expressed in the future stria vascularis of the cochlear epithelium. Its receptor tyrosine kinase, c-Met, is expressed in the cochlear epithelium and melanocyte-derived intermediate cells in the stria vascularis. Genetic dissection of HGF signaling via c-MET reveals that the incorporation of the melanocytes into the future stria vascularis of the cochlear duct requires c-MET signaling. In addition, inactivation of either the ligand or receptor developmentally resulted in a profound hearing loss at young adult stages. These results suggest a novel connection between HGF signaling and deafness via melanocyte deficiencies.

SIGNIFICANCE STATEMENT

We found the roles of hepatocyte growth factor (HGF) signaling in stria vascularis development for the first time and that lack of HGF signaling in the inner ear leads to profound hearing loss in the mouse. Our findings reveal a novel mechanism that may underlie human deafness DFNB39 and DFNB97. Our findings reveal an additional example of context-dependent c-MET signaling diversity, required here for proper cellular invasion developmentally that is essential for specific aspects of auditory-related organogenesis.

MET in human cancer: germline and somatic mutations

Since the initial discovery of missense MET mutations in hereditary papillary renal carcinoma (HPRC), activating MET mutations have been identified in a diverse range of human cancers. MET mutations have been identified in several functional domains including the kinase, juxtamembrane, and Sema domains. Studies of these mutations have been invaluable for our understanding of the tumor initiating activity of MET, receptor tyrosine kinase (RTK) recycling and regulation, and mechanisms of resistance to kinase inhibition. These studies also demonstrate that mutationally activated MET plays a significant role in a wide range of cancers and RTKs can promote tumor progression through diverse mechanisms. This review will cover the various MET mutations that have been identified, their mechanism of action, and the significant role that mutationally-activated MET plays in tumor initiation, progression, and therapeutic resistance.

The c-Met receptor: Implication for targeted therapies in colorectal cancer

c-Met (mesenchymal–epithelial transition factor) is a tyrosine kinase receptor activated by hepatocyte growth factor and regulates multiple biological processes, such as cell scattering, survival, and proliferation. Aberrant c-Met signaling has been implicated in a variety of cancer types, including colorectal cancer. c-Met is genetically altered through various mechanisms that is associated with colorectal cancer progression and metastasis. Especially, in colorectal cancer, preclinical evidence for the aberrant activation of the c-Met signaling exists. Accordingly, molecular targeting of c-Met receptor could be a promising strategy, in the treatment of colorectal cancer patients. Recently, it was also shown that crosstalk between c-Met and other cell surface receptors attributes to tumorigenesis and development of therapeutic resistance. Characterization of the molecular mechanisms through which c-Met crosstalks with other receptors in favor of tumor formation and progression remains to explore. This review will describe the mechanisms of aberrant c-Met signaling in colorectal cancer and discuss on additional roles for c-Met receptor through crosstalk with other tyrosine kinase receptors and cell surface proteins in colorectal cancer. Novel therapeutic approaches for c-Met pathway targeting will also be discussed.

Hepatocyte Growth Factor/c-Met Signaling in Head and Neck Cancer and Implications for Treatment

Aberrant signaling of the hepatocyte growth factor (HGF)/c-Met pathway has been identified as a promoter of tumorigenesis in several tumor types including head and neck squamous cell carcinoma (HNSCC). Despite a relatively low c-Met mutation frequency, overexpression of HGF and its receptor c-Met has been observed in more than 80% of HNSCC tumors, with preclinical and clinical studies linking overexpression with cellular proliferation, invasion, migration, and poor prognosis. c-Met is activated by HGF through a paracrine mechanism to promote cellular morphogenesis enabling cells to acquire mesenchymal phenotypes in part through the epithelial-mesenchymal transition, contributing to metastasis. The HGF/c-Met pathway may also act as a resistance mechanism against epidermal growth factor receptor (EGFR) inhibition in advanced HNSCC. Furthermore, with the identification of a biologically distinct subset of HNSCC tumors acquired from human papillomavirus (HPV) infection that generally portends a good prognosis, high expression of HGF or c-Met in HPV-negative tumors has been associated with worse prognosis. Dysregulated HGF/c-Met signaling results in an aggressive HNSCC phenotype which has led to clinical investigations for targeted inhibition of this pathway. In this review, HGF/c-Met signaling, pathway alterations, associations with clinical outcomes, and preclinical and clinical therapeutic strategies for targeting HGF/c-Met signaling in HNSCC are discussed.

MET expression and copy number status in clear-cell renal cell carcinoma: prognostic value and potential predictive marker

Multiple targeted therapy for advanced clear-cell renal cell carcinoma (RCC) has substantially improved patient outcome, but complete remission is uncommon and many tumors eventually develop resistance. Mechanistic, preclinical, and early clinical data highlight c-Met / hepatocyte growth factor receptor as a promising target for RCC therapeutic agents.We have examined MET expression, frequency of MET gene copy gains and MET gene mutation in a large, hospital-based series of renal cell carcinomas with long-term follow-up information.Out of a total of 572 clear-cell RCC, only 17% were negative for MET expression whereas 32% showed high protein levels. High MET expression and MET copy number gains were associated with an aggressive phenotype and an unfavorable patient outcome. Elevated protein levels in absence of gene amplification were not attributed to mutations, based on results of targeted next-generation sequencing.Our data reveal that clear-cell RCC with MET upregulation show an aggressive behavior and MET copy number increase is evident in a substantial percentage of patients with high-grade carcinomas and metastatic disease. Diagnostic assessment of MET expression and amplification may be of predictive value to guide targeted therapy against MET signaling in patients with clear-cell RCC.

Novel anti-cancer agents based on germacrone: design, synthesis, biological activity, docking studies and MD simulations

Germacrone is a major activity component found in Curcuma zedoaria oil product, which is extracted from Curcuma zedoaria.

The Met tyrosine kinase receptor as a therapeutic target and a potential cancer stem cell factor responsible for therapy resistance (Review)

The MET tyrosine kinase receptor plays an important role during tumor development and progression being responsible for proliferation, morphogenetic transformation, cell motility and invasiveness. High expression of the MET receptor has been shown to correlate with increased tumor growth and metastasis, poor prognosis and resistance to radiotherapy. Moreover, MET expression and activation has been shown to be associated with therapy resistance. The occurrence of resistance to targeted therapy might be related to the presence of cancer stem cells (CSCs). CSCs are a subpopulation of cells in the tumor that possess the ability of self-renewal, clonogenicity, radioresistance and self-sustained protection from apoptosis. Recently, MET has been postulated as an essential factor supporting the functional stem cell phenotype in some tumors and as a CSC factor is believed to be responsible for therapy resistance. This review presents the results from recent studies identifying MET as a potential marker of CSCs and tumor initiating cells, demonstrating pivotal role of MET in supporting stem cell phenotype and indicating the role of MET in acquiring resistance to antitumor therapy.

Nodal metastasis signatures in breast cancer

Although the molecular taxonomy of invasive breast cancer is based on heterogeneous histologic types, pathologic nodal (pN) stage remains one of the most important independent prognostic factors. Although node-positive number (NPN) has been widely as an accepted staging algorithm of pN stage, the node-positive ratio (NPR) in totally resected axillary nodes has been considered as another reasonable indicator. We aimed to identify signatures to play a predictive role in nodal metastasis for analytic validation between the primary breast cancers with positive node metastasis and those with negative node metastasis. We validated expression profiles of surrogate candidates extracted from the prior 2D MALDI-TOF data for invasive breast cancer using fluorescence/silver in situ hybridization (FISH/SISH) and immunohistochemistry (IHC) in 151 primary breast cancers accompanied with 102 metastatic nodal tissues. Cox proportional hazards regression analyses indicated that event factors (recurrence or metastasis) were significantly more frequent in cases with CCDN1, c-myc gene amplification, IgHA2 low expression. CCDN1 gene amplification (OR: 5.702, p=0.0006), IgHA2 low expression (OR: 0.16, p=0.0184) remained significant factors for events on multivariate analyses. WDR⁺/ERK⁺⁺ was significantly detected in higher pN stage (averaging 6.5 regional nodes or 43% of NPR), while seldom found in pN0-1. In conclusion, both overexpression of WDR1 and p-ERK in the primary breast cancer could play a role in the nodal signature over pN2-3.

Molecular Imaging and Precision Medicine in Head and Neck Cancer

The concept of using tumor genomic profiling information has revolutionized personalized cancer treatment. Head and neck (HN) cancer management is being influenced by recent discoveries of activating mutations in epidermal growth factor receptor and related targeted therapies with tyrosine kinase inhibitors, targeted therapies for Kristen Rat Sarcoma, and MET proto-oncogenes. Molecular imaging using PET plays an important role in assessing the biologic behavior of HN cancer with the goal of delivering individualized cancer treatment. This review summarizes recent genomic discoveries in HN cancer and their implications for functional PET imaging in assessing response to targeted therapies, and drug resistance mechanisms.

Novel c-Met inhibitory olive secoiridoid semisynthetic analogs for the control of invasive breast cancer

Dysregulated receptor tyrosine kinase c-Met and its ligand HGF is valid and attractive molecular target for therapeutic blockade in cancer. Inspired by the chemical structure of the naturally occurring olive secoiridoid (-)-oleocanthal (1) and its documented anticancer activity against c-Met-dependent malignancies, a previous study reported tyrosol sinapate (4) as a c-Met inhibitor hit. This study reports additional semisynthetic optimization and SAR of 4 to improve its selective activity against c-Met-dependent breast cancer by increasing its capacity to inhibit c-Met phosphorylation. Forty-three compounds (5-47) were synthesized, among which the novel analog homovanillyl sinapate (HVS-16) was distinguished for its remarkable activity. HVS-16 substantially impaired c-Met-mediated proliferation, migration, and invasion across human breast cancer cell lines in two- and three-dimensional culture systems, while similar treatment doses were found to have effect neither on the non-tumorigenic human mammary epithelial cell growth nor on the c-Met independent breast cancer cell viability. HVS-16 showed a dose-dependent inhibition of ligand-mediated c-Met activation in human breast cancer cells. Docking studies revealed that HVS-16 fits very well inside c-Met crystal structures, satisfying critical interactions at the ATP binding site. This study identified important structural pharmacophoric features in HVS-16 and correlated its postulated binding pose with c-Met kinase assay data that would guide future olive secoiridoid bioisostere lead design. Results presented herein suggest HVS-16 as a promising c-Met inhibitor validated hit with potential to control invasive breast malignancies with aberrant c-Met activity.

MET-targeted therapy for gastric cancer: the importance of a biomarker-based strategy

The MET protooncogene encodes the receptor tyrosine kinase c-MET (MET). Aberrant activation of MET signaling occurs in a subset of advanced malignancies, including gastric cancer, and promotes tumor cell growth, survival, migration, and invasion as well as tumor angiogenesis, suggesting its potential importance as a therapeutic target. MET can be activated by two distinct pathways that are dependent on or independent of its ligand, hepatocyte growth factor (HGF), with the latter pathway having been attributed mostly to MET amplification in gastric cancer. Preclinical evidence has suggested that interruption of the HGF-MET axis either with antibodies to HGF or with MET tyrosine kinase inhibitors (TKIs) has antitumor effects in gastric cancer cells. Overexpression of MET occurs frequently in gastric cancer and has been proposed as a potential predictive biomarker for anti-MET therapy. However, several factors can trigger such MET upregulation in a manner independent of HGF, suggesting that gastric tumors with MET overexpression are not necessarily MET driven. On the other hand, gastric cancer cells with MET amplification are dependent on MET signaling for their survival and are thus vulnerable to MET TKI treatment. Given the low prevalence of MET amplification in gastric cancer (approximately 8 %), testing for this genetic change would substantially narrow the target population but it might constitute a better biomarker than MET overexpression for MET TKI therapy. We compare aberrant MET signaling dependent on the HGF-MET axis or on MET amplification as well as address clinical issues and challenges associated with the identification of appropriate biomarkers for MET-driven tumors.

HGF/Met Signaling in Head and Neck Cancer: Impact on the Tumor Microenvironment

Studies to date have revealed several major molecular alterations that contribute to head and neck squamous cell carcinoma (HNSCC) initiation, progression, metastatic spread, and therapeutic failure. The EGFR is the only FDA-approved therapeutic target, yet responses to cetuximab have been limited. Activation and cross-talk of cellular receptors and consequent activation of different signaling pathways contribute to limited activity of blockade of a single pathway. The hepatocyte growth factor (HGF) receptor, Met, has been implicated in HNSCC tumorigenesis and EGFR inhibitor resistance. HGF, the sole ligand of Met, is overexpressed in the tumor microenvironment. The role of HGF/Met signaling in proliferation, metastasis, and angiogenesis has been investigated in HNSCC, leading to clinical trials with various Met inhibitors and HGF antibodies. However, the role of the HGF/Met signaling axis in mediating the tumor microenvironment has been relatively understudied in HNSCC. In this review, we discuss the functional roles of Met and HGF in HNSCC with a focus on the tumor microenvironment and the immune system. Clin Cancer Res; 22(16); 4005-13. ©2016 AACR.