Novel mutation in the ATP-binding site of the MET oncogene tyrosine kinase in a HPRCC family

Quantification and clinical validation of the selective MET kinase inhibitor DO-2 and its metabolites DO-5 and M3 in human plasma

DO-2 is a highly selective MNNG HOS transforming (MET) inhibitor. This deuterated drug is thought to diminish the formation of the Aldehyde Oxidase 1 inactive metabolite M3. For various reasons, quantification of DO-2 and its metabolites M3 and DO-5 is highly relevant. In this study, we present an ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method to quantify DO-2, M3 and DO-5. Rolipram served as the internal standard. Aliquots of 25 µL were mixed with 100 µL internal standard consisting of 10 ng/mL rolipram in acetonitrile. Separation of the analytes was achieved on an Acquity UPLC ® HSS T3 column, utilizing gradient elution with water/formic acid and acetonitrile/formic acid at a flow-rate of 0.400 mL/min. Calibration curves were linear in the range of 1.00 - 1000 ng/mL for DO-2 and DO-5, and 2.00 - 2000 ng/mL for M3 in human plasma. The within-run and between-run precisions of DO-2, DO-5 and M3, also at the level of the LLQ, were within 12.1%, while the accuracy ranged from 89.5 to 108.7%. All values for accuracy, within-run and between-run precisions met the criteria set by the Food and Drug Administration. The method was effectively employed in the analysis of samples obtained from a clinical trial.

MET variants with activating N-lobe mutations identified in hereditary papillary renal cell carcinomas still require ligand stimulation

In hereditary papillary renal cell carcinoma (HPRCC), the MET receptor tyrosine kinase (RTK) mutations recorded to date are located in the kinase domain and lead to constitutive MET activation. This contrasts with MET mutations recently identified in non-small cell lung cancer (NSCLC), which lead to exon 14 skipping and deletion of a regulatory domain: in this latter case, the mutated receptor still requires ligand stimulation. Sequencing of MET in samples from 158 HPRCC and 2808 NSCLC patients revealed ten uncharacterized mutations. Four of these, all found in HPRCC and leading to amino acid substitutions in the N-lobe of the MET kinase, proved able to induce cell transformation, further enhanced by HGF stimulation: His1086Leu, Ile1102Thr, Leu1130Ser, and Cis1125Gly. Similar to the variant resulting in MET exon14 skipping, the two N-lobe MET variants His1086Leu, Ile1102Thr further characterized were found to require stimulation by HGF in order to strongly activate downstream signaling pathways and epithelial cell motility. The Ile1102Thr mutation displayed also transforming potential, promoting tumor growth in a xenograft model. In addition, the N-lobe-mutated MET variants were found to trigger a common HGF-stimulation-dependent transcriptional program, consistent with an observed increase in cell motility and invasion. Altogether, this functional characterization revealed that N-lobe variants still require ligand stimulation, in contrast to other RTK variants. This suggests that HGF expression in the tumor microenvironment is important for tumor growth. The sensitivity of these variants to MET TKIs opens the way for use of targeted therapies for patients harboring the corresponding mutations.

A pharmacokinetic-pharmacodynamic model for the MET tyrosine kinase inhibitor, savolitinib, to explore target inhibition requirements for anti-tumour activity

BACKGROUND AND PURPOSE

Savolitinib (AZD6094, HMPL-504, volitinib) is an oral, potent, and highly MET receptor TK inhibitor. This series of studies aimed to develop a pharmacokinetic-pharmacodynamic (PK/PD) model to link inhibition of MET phosphorylation (pMET) by savolitinib with anti-tumour activity.

EXPERIMENTAL APPROACH

Cell line-derived xenograft (CDX) experiments using human lung cancer (EBC-1) and gastric cancer (MKN-45) cells were conducted in athymic nude mice using a variety of doses and schedules of savolitinib. Tumour pMET changes and growth inhibition were calculated after 28 days. Population PK/PD techniques were used to construct a PK/PD model for savolitinib.

KEY RESULTS

Savolitinib showed dose- and dose frequency-dependent anti-tumour activity in the CDX models, with more frequent, lower dosing schedules (e.g., twice daily) being more effective than intermittent, higher dosing schedules (e.g., 4 days on/3 days off or 2 days on/5 days off). There was a clear exposure-response relationship, with maximal suppression of pMET of >90%. Data from additional CDX and patient-derived xenograft (PDX) models overlapped, allowing calculation of a single EC₅₀ of 0.38 ng·ml^-1 . Tumour growth modelling demonstrated that prolonged, high levels of pMET inhibition (>90%) were required for tumour stasis and regression in the models.

CONCLUSION AND IMPLICATIONS

High and persistent levels of MET inhibition by savolitinib were needed for optimal monotherapy anti-tumour activity in preclinical models. The modelling framework developed here can be used to translate tumour growth inhibition from the mouse to human and thus guide choice of clinical dose and schedule.

Case of Hereditary Papillary Renal Cell Carcinoma Type I in a Patient With a Germline MET Mutation in Russia

Hereditary papillary renal carcinoma (HPRC) is a rare autosomal dominant disease characterized by the development of multiple papillary type I renal cell carcinomas. This hereditary kidney cancer form is caused by activating mutations in MET. Descriptions of patients with HPRC are scarce in the world literature, and no cases have been described in open sources in Russia. Here, we describe a 28-year-old female Russian patient with 7 and 10 primary papillary renal cell carcinomas in the left and right kidneys, respectively. The patient did not have a family history of any of the known hereditary cancer syndromes. A comprehensive medical examination was performed in 2016 including computed tomography and pathomorphological analysis. The observed tumors were resected in a two-step surgical treatment. In February 2019, no sign of disease progression was detected in follow-up medical examination. Molecular genetic analysis revealed the germline heterozygous missense variant in MET: c.3328G>A (p.V1110I; CM990852). We have discussed the biological effects of the detected mutation and the utility of DNA diagnostics for treating patients with HPRC.

Meta-analysis of functional expression and mutational analysis of c-Met in various cancers

Comprehensive genomic profiling is expected to revolutionize cancer therapy. c-Met signaling is responsible for tumorigenesis in various cancers. In this prospective, we present the prevalence of c-Met mutations and copy number alterations across various solid tumors. We used major databases like cBioportal, PubMed, and COSMIC for c-Met mutation and amplification data collection from various cancers. Our result shows complete details about c-Met mutation and its clinical data of various cancers. Hotspot mutation of human c-Met protein reveals that repeatedly and most mutated regions and these hotspots may be a diagnostic tool for cancer confirmation. Amino acid and nucleotide changes and their prevalence were reported in a number of individual cancers. However, we collectively present the amino acid and nucleotide changes in various cancers in this review. Our collection of data for c-Met mutation and its distribution in different cancer tissue is showing that the missense mutation is the major one in all type of cancers. Copy number variation data showing amplification and deletion of human c-Met from various tumor types, lung and central nervous system tumors showing high amplification comparatively other types.

C-Met as a Key Factor Responsible for Sustaining Undifferentiated Phenotype and Therapy Resistance in Renal Carcinomas

C-Met tyrosine kinase receptor plays an important role under normal and pathological conditions. In tumor cells’ overexpression or incorrect activation of c-Met, this leads to stimulation of proliferation, survival and increase of motile activity. This receptor is also described as a marker of cancer initiating cells. The latest research shows that the c-Met receptor has an influence on the development of resistance to targeted cancer treatment. High c-Met expression and activation in renal cell carcinomas is associated with the progression of the disease and poor survival of patients. C-Met receptor has become a therapeutic target in kidney cancer. However, the therapies used so far using c-Met tyrosine kinase inhibitors demonstrate resistance to treatment. On the other hand, the c-Met pathway may act as an alternative target pathway in tumors that are resistant to other therapies. Combination treatment together with c-Met inhibitor reduces tumor growth, vascularization and pro-metastatic behavior and results in suppressed mesenchymal phenotype and vascular endothelial growth factor (VEGF) secretion. Recently, it has been shown that the acquirement of mesenchymal phenotype or lack of cell differentiation might be related to the presence of the c-Met receptor and is consequently responsible for therapy resistance. This review presents the results from recent studies identifying c-Met as an important factor in renal carcinomas being responsible for tumor growth, progression and metastasis, indicating the role of c-Met in resistance to antitumor therapy and demonstrating the pivotal role of c-Met in supporting mesenchymal cell phenotype.

Circulating tumor DNA profiling by next generation sequencing reveals heterogeneity of crizotinib resistance mechanisms in a gastric cancer patient with MET amplification

Crizotinib has been used to counter MET gene amplification in a number of different human malignancies. Transient response to crizotinib in MET-amplified gastric cancer has been reported, but the mechanisms of resistance are not well studied. Here, we reported a stage IV gastric cancer patient with high levels of MET amplification. The implementation of crizotinib treatment led to significant symptomatic improvement in the first 2 months, but was followed by rapid disease progression. Periodic mutation profiling of patient's circulating tumor DNA (ctDNA) by next generation sequencing (NGS) revealed a number of genetic alterations including re-occurrence of MET amplification, multiple secondary MET mutations, a dramatic increase of FGFR2 gene relative copy number as well as mutations in other downstream and bypassing elements, which may collectively related to the patient's cancer progression. Our results illustrate the complex and heterogeneous molecular mechanisms for crizotinib resistance in this patient, and demonstrate the great potential of ctDNA profiling for treatment decision-making and prognosis in clinical practice.

MicroRNA-34a: A Key Regulator in the Hallmarks of Renal Cell Carcinoma

Renal cell carcinoma (RCC) incidence has increased over the past two decades. Recent studies reported microRNAs as promising biomarkers for early cancer detection, accurate prognosis, and molecular targets for future treatment. This study aimed to evaluate the expression levels of miR-34a and 11 of its bioinformatically selected target genes and proteins to test their potential dysregulation in RCC. Quantitative real-time PCR for miR-34a and its targets; MET oncogene; gene-regulating apoptosis (TP53INP2 and DFFA); cell proliferation (E2F3); and cell differentiation (SOX2 and TGFB3) as well as immunohistochemical assay for VEGFA, TP53, Bcl2, TGFB1, and Ki67 protein expression have been performed in 85 FFPE RCC tumor specimens. Clinicopathological parameter correlation and in silico network analysis have also implicated. We found RCC tissues displayed significantly higher miR-34a expression level than their corresponding noncancerous tissues, particularly in chromophobic subtype. MET and E2F3 were significantly upregulated, while TP53INP2 and SOX2 were downregulated. ROC analysis showed high diagnostic performance of miR-34a (AUC = 0.854), MET (AUC = 0.765), and E2F3 (AUC = 0.761). The advanced pathological grade was associated with strong TGFB1, VEGFA, and Ki67 protein expression and absent Tp53 staining. These findings indicate miR-34a along with its putative target genes could play a role in RCC tumorigenesis and progression.

Establishing Dual Resistance to EGFR-TKI and MET-TKI in Lung Adenocarcinoma Cells In Vitro with a 2-step Dose-escalation Procedure

Drug resistance is a major challenge in cancer therapy. The generation of resistant sublines in vitro is necessary for discovering novel mechanisms to overcome this challenge. Here, a 2-step dose-escalation method for establishing dual-resistance to an epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitor (TKI), gefitinib, and a MET-TKI, PHA665752, is described. This method is based on simple stepwise dose-escalation of inhibitors for inducing acquired resistance in cell lines. The alternate method for generating resistant sublines involves exposing the cells to high concentrations of the inhibitor in one step. The stepwise dose-escalation method has a higher possibility of successfully inducing acquired resistance than this method. Activating EGFR mutations are biomarkers of a response to treatment with EGFR-TKI, which is an applied first-line treatment for non-small cell lung cancers (NSCLC) that harbor these mutations. However, despite reports of effective responses, the use of EGFR-TKI is limited because tumors inevitably acquire resistance. The major mechanisms behind EGFR-TKI resistance include a secondary mutation at the gatekeeper site, T790M in exon 20 of EGFR, and a bypass signal of MET. Thus, a potential solution for this issue would be a combination of EGFR-TKI and MET-TKI. This combined treatment has been shown to be effective in an in vitro study model. Acquired gefitinib-resistance was established through MET-amplification by stepwise dose-escalation of gefitinib for 12 months, and a cell line named PC-9MET1000 was generated in a previous study. To further investigate the mechanisms of acquired MET-TKI and EGFR-TKI resistance, a MET-TKI, PHA665752, was administered to these cells with stepwise dose-escalation in the presence of gefitinib for 12 months. This protocol has also been successfully applied for a number of combination therapies to establish acquired resistance to other inhibitor molecules.

Risk of Subsequent Primary Kidney Cancer After Another Malignancy: A Population-based Study

BACKGROUND

Population-based data on the development of kidney cancer as a second malignant neoplasm following the diagnosis of other common malignancies are rare. This clinical scenario has been evaluated within the Surveillance, Epidemiology, and End Results (SEER) database.

MATERIALS AND METHODS

The SEER-9 database (1973-2013) was queried using the SEER*Stat program to determine the standardized incidence ratios (SIRs) of kidney cancer development following each one of 10 common invasive malignancies (colorectal, breast, prostate, lung, thyroid, corpus uteri, urinary bladder, kidney/renal pelvis, cutaneous melanoma, and non-Hodgkin lymphoma). The following data were collected for patients with a second renal cancer: age at diagnosis of the second renal cancer; gender, race, and histology of the second primary renal cancer; SEER historic stage of the second primary renal cancer; and method of diagnostic confirmation of the second primary cancer.

RESULTS

A total of 10,145 kidney cancers were observed. Elevated SIRs for kidney cancer were noted for all 10 evaluated malignancies in the initial 12 months after diagnosis. The SIRs remained elevated 12 to 59 months after diagnosis for all cancers except breast and prostate cancers. Increased risks persisted 60 to 119 months beyond diagnosis for renal cancer (SIR, 4.13), thyroid cancer (SIR, 2.30), and non-Hodgkin lymphoma (SIR, 1.40); and 120+ months for renal cancer (SIR, 3.60), thyroid cancer (SIR, 1.90), and non-Hodgkin lymphoma (SIR, 1.27). Increased kidney cancer risk after non-Hodgkin lymphoma was not related to radiation therapy. Papillary renal cell carcinoma has the highest SIRs for subsequent kidney cancers.

CONCLUSION

Many common cancers are associated with an increased risk of kidney cancer development within the first 5 years after their diagnosis. Although this can be partly interpreted by increased rates of surveillance tests, radiotherapy effects, or genetic associations for some cancers, additional research is required to explain the persistently increased risk beyond 5 years associated with some cancers.

A novel antagonist anti-cMet antibody with antitumor activities targeting both ligand-dependent and ligand-independent c-Met receptors

c-Met is a prototypic member of a sub-family of RTKs. Inappropriate c-Met activation plays a crucial role in tumor formation, proliferation and metastasis. Using a key c-Met dimerization assay, a set of 12 murine whole IgG1 monoclonal antibodies was selected and a lead candidate, m224G11, was humanized by CDR-grafting and engineered to generate a divalent full antagonist humanized IgG1 antibody, hz224G11. Neither m224G11 nor hz224G11 bind to the murine c-Met receptor. Their antitumor activity was investigated in vitro in a set of experiments consistent with the reported pleiotropic effects mediated by c-Met and, in vivo, using several human tumor xenograft models. Both m224G11 and hz224G11 exhibited nanomolar affinities for the receptor and inhibited HGF binding, c-Met phosphorylation, and receptor dimerization in a similar fashion, resulting in a profound inhibition of all c-Met functions in vitro. These effects were presumably responsible for the inhibition of c-Met's major functions including cell proliferation, migration, invasion scattering, morphogenesis and angiogenesis. In addition to these in vitro properties, hz224G11 dramatically inhibits the growth of autocrine, partially autophosphorylated and c-Met amplified cell lines in vivo. Pharmacological studies performed on Hs746T gastric cancer xenografts demonstrate that hz224G11 strongly downregulates c-Met expression and phosphorylation. It also decreases the tumor mitotic index (Ki67) and induces apoptosis. Taken together, the in vitro and in vivo data suggest that hz224G11 is a promising candidate for the treatment of tumors. This antibody, now known as ABT-700 and currently in Phase I clinical trials, may provide a novel therapeutic approach to c-Met-expressing cancers.

Regulation of the MET oncogene: molecular mechanisms

The MET oncogene is a predictive biomarker and an attractive therapeutic target for various cancers. Its expression is regulated at multiple layers via various mechanisms. It is subject to epigenetic modifications, i.e. DNA methylation and histone acetylation. Hypomethylation and acetylation of the MET gene have been associated with its high expression in some cancers. Multiple transcription factors including Sp1 and Ets-1 govern its transcription. After its transcription, METmRNA is spliced into multiple species in the nucleus before being transported to the cytoplasm where its translation is modulated by at least 30 microRNAs and translation initiation factors, e.g. eIF4E and eIF4B. METmRNA produces a single chain pro-Met protein of 170 kDa which is cleaved into α and β chains. These two chains are bound together through disulfide bonds to form a heterodimer which undergoes either N-linked or O-linked glycosylation in the Golgi apparatus before it is properly localized in the membrane. Upon interactions with its ligand, i.e. hepatocyte growth factor (HGF), the activity of Met kinase is boosted through various phosphorylation mechanisms and the Met signal is relayed to downstream pathways. The phosphorylated Met is then internalized for subsequent degradation or recycle via proteasome, lysosome or endosome pathways. Moreover, the Met expression is subject to autoregulation and activation by other EGFRs and G-protein coupled receptors. Since deregulation of the MET gene leads to cancer and other pathological conditions, a better understanding of the MET regulation is critical for Met-targeted therapeutics.

Diagnosis and Management of Hereditary Renal Cell Cancer

Renal cell cancer (RCC) is the common denominator for a heterogeneous group of diseases. The subclassification of these tumours is based on histological type and molecular pathogenesis. Insight into molecular pathogenesis has led to the development of targeted systemic therapies. Genetic susceptibility is the principal cause of RCC in about 2-4% of cases. Hereditary RCC is the umbrella term for about a dozen different conditions, the most frequent of which is von Hippel-Lindau disease . Here, we describe the main hereditary RCC syndromes, consider criteria for referral of RCC patients for clinical genetic assessment and discuss management options for patients with hereditary RCC and their at-risk relatives.

Papillary renal cell carcinoma with a somatic mutation in MET in a patient with autosomal dominant polycystic kidney disease

Autosomal-dominant polycystic kidney disease (ADPKD) is caused by mutations in PKD1 and PKD2 and is characterized by proliferation of renal tubular epithelium and progressive chronic kidney disease. Derangements in similar cellular signaling pathways occur in ADPKD and renal malignancies, although an association of these disorders has not been established. Herein, we present a case of papillary RCC (pRCC) incidentally discovered in a patient with ADPKD following bilateral native nephrectomy during renal transplantation. Whole exome sequencing of the pRCC found a somatic missense mutation in MET proto-oncogene, p.Val1110Ile, not present in kidney cyst epithelium or non-cystic tissue. RNA sequencing demonstrated increased mRNA expression of MET and pathway-related genes, but no significant copy number variation of MET was detected. Genetic analysis of PKD genes from peripheral blood lymphocytes and renal cyst epithelium identified a constitutional PKD1 germline mutation, p.Trp1582Ser, predicted to be pathogenic. Unique somatic mutations in PKD1 were also detected in 80% of the renal cysts analyzed, but not in the pRCC. These results suggest that, in this patient, the pRCC utilized a signaling pathway involving MET that was distinct from the pathogenesis of ADPKD. This is the first report of PKD1 mutations and a somatic mutation of the MET oncogene in a pRCC in ADPKD.

Biology of MET: a double life between normal tissue repair and tumor progression

MNNG HOS transforming gene (MET) is a class IV receptor tyrosine kinase, expressed on the surface of epithelial cells. The interaction with the hepatocyte grow factor (HGF) induces MET dimerization and the activation of multiple intracellular pathways leading to cell proliferation, anti-apoptosis, morphogenic differentiation, motility, invasion, and angiogenesis. Knock out mice have demonstrated that MET is necessary for normal embryogenesis including the formation of striate muscles, liver and trophoblastic structures. The overexpression of MET and HGF are common in solid tumors and contribute to determine their growth. Indeed, MET has been cloned as a transforming gene from a chemically induced human osteosarcoma cell line and therefore is considered a proto-oncogene. Germline MET mutations are characteristic of hereditary papillary kidney cancers and MET amplification is observed in tumors including lung and gastric adenocarcinomas. The inhibition of MET signaling is the target for specific drugs that are raising exciting expectation for medical treatment of cancer.

Prognostic and predictive value of MET deregulation in non-small cell lung cancer

Recent progress in cancer biology has led to the discovery of increasing number of oncogene alterations that have dramatically changed the paradigm of lung cancer treatment. MET is a tyrosine kinase receptor for the hepatocyte growth factor (HGF) that is deregulated in several malignancies, including non-small cell lung cancer (NSCLC). Abnormal MET-HGF signaling pathway activation can occur via different mechanisms, including HGF and/or MET overexpression, MET gene amplification, mutations or rearrangements. MET protein overexpression and increased MET gene number have been identified as poor prognostic factors in several series of surgically resected NSCLC making this receptor an attractive target for cancer treatment. Several clinical trials have recently evaluated the activity of a variety of anti-MET strategies in NSCLC patients with or without molecular selection with a variable degree of success, underscoring the need of establishing the best predictive biomarker for the identification of responding patients.

MET is a potential target across all papillary renal cell carcinomas: result from a large molecular study of pRCC with CGH array and matching gene expression array

PURPOSE

Papillary renal cell carcinomas (pRCC) are the most common nonclear cell RCC subtype. Germline mutations of the MET oncogene at 7q31 have been detected in patients with hereditary type I pRCC and in 13% of sporadic type I pRCC. Recent report of MET inhibition strengthened the role of c-Met inhibition across pRCC.

EXPERIMENTAL DESIGN

We collected 220 frozen samples of sporadic pRCC through the French RCC Network and quality controlled for percentage of malignant cells >70%. Gene expression was assessed on 98 pRCC using human whole-genome Agilent 8 × 60K arrays. Copy number alterations were analyzed using Agilent Human 2 × 400K and 4× 180K array for type II pRCC and comparative genomic microarray analysis method for type I pRCC. MET gene sequencing was performed on type I pRCC.

RESULTS

MET expression level was high across all pRCC. We identified copy number alterations (gain) in 46% of type II pRCC and in 81% of type I pRCC. Correlation between DNA copy number alterations and mRNA expression level was highly significant. Eleven somatic mutations of MET gene were identified amongst 51 type I pRCC (21.6%), including 4 new mutations. We validated LRRK2 cokinase as highly correlated to MET expression.

CONCLUSION

The present report expands the role of MET activation as a potential target across all pRCC subtypes. These data support investigating MET inhibitors in pRCC in correlation with MET activation status.

Analysis of MET genetic aberrations in patients with breast cancer at MD Anderson Phase I unit

BACKGROUND

c-MET is a receptor tyrosine kinase whose phosphorylation activates important proliferation pathways. MET amplification and mutation have been described in various malignancies, including breast cancer (BC), and c-MET overexpression is associated with worse survival outcomes in patients with BC. We describe MET mutation and amplification rates in a BC cohort of patients referred to a Phase I Unit.

METHODS

We reviewed the electronic medical records of all patients with advanced BC tested for MET amplification, mutation, or both who were referred to the Department of Investigational Cancer Therapeutics at MD Anderson.

RESULTS

A total of 107 patients with advanced BC were analyzed for MET mutation/variant (88 patients) or amplification (63 patients). Of these, 49 were tested for both genetic abnormalities. Three of 63 patients (4.7%) demonstrated MET gene amplification by fluorescence in situ hybridization (2 in primary tissue; 1 in metastatic site). MET mutation/variant was detected in 8 of 88 patients (9%). High-grade tumors were characteristic of all patients harboring MET amplification and were present in 7 of 8 (87.5%) of those with MET mutation. Metastatic sites were greater in MET-amplified compared with wild-type patients (median of 7 vs. 3 sites). Five of 8 patients (62.5%) with MET mutations had triple negative BC compared with 46% in controls. In addition, patients with positive test results for MET aberrations (n = 11) had inferior overall survival (OS) from Phase I consult compared with wild-type patients (n = 37), although this was not statistically significant (median OS = 9 vs. 15 months, P = .43).

CONCLUSIONS

In this cohort of patients with BC who were referred to our Phase I Department, MET aberrations were associated with higher metastatic burden and high-grade histology. We could not demonstrate differences in survival outcomes because of a small sample size.

Genetic unraveling of colorectal cancer

Colorectal cancer is a common disease in both men and women (being the third most common cancer in men and the second most common among women) and thus represents an important and serious public health issue, especially in the western world. Although it is a well-established fact that cancers of the large intestine produce symptoms relatively earlier at a stage that can be easily cured by resection, a large number of people lose their lives to this deadly disease each year. Recent times have seen an important change in the incidence of colorectal cancer in different parts of the world. The etiology of colorectal cancer is multifactorial and is likely to involve the actions of genes at multiple levels along the multistage carcinogenesis process. Exhaustive efforts have been made out in the direction of unraveling the role of various environmental factors, gene mutations, and polymorphisms worldwide (as well as in Kashmir-"a valley of gastrointestinal cancers") that have got a role to play in the development of this disease so that antitumor drugs could be developed against this cancer, first, and, finally, the responsiveness or resistance to these agents could be understood for combating this global issue.

cMET as a potential therapeutic target in gastric cancer (Review)

Gastric cancer is one of the most common malignancies worldwide. Despite improvements in surgery and chemotherapy, the outcomes in patients with advanced gastric cancer remain poor. cMET is a member of the receptor tyrosine kinase family, and plays a key role in tumor survival, growth, angiogenesis and metastasis. cMET overexpression and/or gene amplification occurs in a significant proportion of gastric cancers. cMET is associated with a high tumor stage and poor prognosis. Several cMET inhibitors have been investigated in clinical trials, and the initial results are encouraging. It has become increasingly apparent that cMET is a promising therapeutic target in gastric cancer. In this review, we summarize the development of cMET inhibitors in the preclinical and clinical environment. In addition, we discuss the challenges of cMET-targeted therapy in gastric cancer and explore possible solutions.

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

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

An overview of the c-MET signaling pathway

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

Molecular genetic analysis of the hepatocyte growth factor/MET signaling pathway in pediatric medulloblastoma

The hepatocyte growth factor (HGF)/MET pathway plays a critical role in the development of the nervous system and has been implicated in medulloblastoma pathogenesis. Recent studies have shown a role for gene amplification of activators of this pathway, as well as silencing of its inhibitors in medulloblastoma pathogenesis. We analyzed exon array data from a cohort of 103 primary medulloblastomas to show that HGF/MET pathway elements are dysregulated in tumors compared to normal cerebellum. To determine if mutation of HGF/MET pathway genes is a mechanism for pathway dysregulation, we conducted a mutational analysis by exon resequencing of three key components of this pathway, including serine protease inhibitor Kunitz-type 1 (SPINT1), serine protease inhibitor Kunitz-type 2 (SPINT2), and MET, in 32 primary human medulloblastoma specimens. From this analysis, we identified multiple coding synonymous and nonsynonymous single nucleotide polymorphisms in these genes among the 32 tumor samples. Interestingly, we also discovered two unreported sequence variants in SPINT1 and SPINT2 in two tumors that resulted in Arginine to Histidine amino acid substitutions at codons 418 and 233, respectively. However, conservation assessment and functional assays of these two variants indicate that they involve nonconserved residues and that they do not affect the function of SPINT1 and SPINT2 as tumor suppressor genes. In conclusion, our data suggest that mutation alone plays a minor role in causing aberrancies of the HGF/MET pathway in medulloblastoma in comparison with other malignancies such as breast, hepatocellular, renal, and lung carcinomas.

MET and KRAS gene amplification mediates acquired resistance to MET tyrosine kinase inhibitors

The establishment of the role of MET in human cancer has led to the development of small-molecule inhibitors, many of which are currently in clinical trials. Thus far, nothing is known about their therapeutic efficacy and the possible emergence of resistance to treatment, a problem that has been often observed with other receptor tyrosine kinase (RTK) inhibitors. To predict mechanisms of acquired resistance, we generated resistant cells by treating MET-addicted cells with increasing concentrations of the MET small-molecule inhibitors PHA-665752 or JNJ38877605. Resistant cells displayed MET gene amplification, leading to increased expression and constitutive phosphorylation of MET, followed by subsequent amplification and overexpression of wild-type (wt) KRAS. Cells harboring KRAS amplification progressively lost their MET dependence and acquired KRAS dependence. Our results suggest that MET and KRAS amplification is a general mechanism of resistance to specific MET inhibitors given that similar results were observed with two small inhibitors and in different cell lines of different histotypes. To our knowledge, this is the first report showing that overexpression of wt KRAS can overcome the inhibitory effect of a RTK inhibitor. In view of the fact that cellular models of resistance to inhibitors targeting other tyrosine kinases have predicted and corroborated clinical findings, our results provide insights into strategies for preventing and/or overcoming drug resistance.

Safety, pharmacokinetics, and pharmacodynamics of AMG 102, a fully human hepatocyte growth factor-neutralizing monoclonal antibody, in a first-in-human study of patients with advanced solid tumors

PURPOSE

The aims were to assess the safety, pharmacokinetics, maximum tolerated dose, and antitumor activity of AMG 102, a fully human hepatocyte growth factor/scatter factor (HGF/SF)-neutralizing monoclonal antibody, in patients with solid tumors.

EXPERIMENTAL DESIGN

Patients (N = 40) with refractory advanced solid tumors were enrolled into six sequential dose-escalation cohorts (0.5, 1, 3, 5, 10, or 20 mg/kg AMG 102 i.v. every 2 weeks) and a dose-expansion cohort (20 mg/kg AMG 102 every 2 weeks). Safety, anti-AMG 102 antibody formation, pharmacokinetics, tumor response, and exploratory biomarkers were assessed.

RESULTS

AMG 102 was well tolerated up to the planned maximum dose of 20 mg/kg, and the maximum tolerated dose was not reached. Treatment-related adverse events were generally mild and included fatigue (13%), constipation (8%), nausea (8%), vomiting (5%), anorexia (5%), myalgia (5%), and hypertension (5%). Two patients experienced dose-limiting toxicities: one patient (0.5 mg/kg cohort) experienced grade 3 hypoxia and grade 3 dyspnea and one patient (1 mg/kg cohort) experienced grade 3 upper gastrointestinal hemorrhage. No anti-AMG 102 antibodies were detected, and AMG 102 had linear pharmacokinetics within the dose range investigated. Sixteen of 23 (70%) evaluable patients had a best response of stable disease with progression-free survival ranging from 7.9 to 40 weeks. Circulating levels of the biomarker HGF/SF (bound and unbound) increased in a dose-dependent manner, whereas soluble c-Met concentrations were generally similar across doses.

CONCLUSIONS

AMG 102 is safe and well tolerated, has a favorable pharmacokinetic profile, and will be further investigated as a monotherapy and in combination with other agents.

met oncogene activation qualifies spontaneous canine osteosarcoma as a suitable pre-clinical model of human osteosarcoma

The Met receptor tyrosine kinase (RTK) is aberrantly expressed in human osteosarcoma and is an attractive molecular target for cancer therapy. We studied spontaneous canine osteosarcoma (OSA) as a potential pre-clinical model for evaluation of Met-targeted therapies. The canine MET oncogene exhibits 90% homology compared with human MET, indicating that cross-species functional studies are a viable strategy. Expression and activation of the canine Met receptor were studied utilizing immunohistochemical techniques in 39 samples of canine osteosarcoma, including 35 primary tumours and four metastases. Although the Met RTK is barely detectable in primary culture of canine osteoblasts, high expression of Met protein was observed in 80% of canine osteosarcoma samples acquired from various breeds. Met protein overexpression was also concordant with its activation as indicated by phosphorylation of critical tyrosine residues. In addition, Met was expressed and constitutively activated in canine osteosarcoma cell lines. OSA cells expressing high levels of Met demonstrated activation of downstream transducers, elevated spontaneous motility, and invasiveness which were impaired by both a small molecule inhibitor of Met catalytic activity (PHA-665752) and met-specific, stable RNA interference obtained by means of lentiviral vector. Similar to observations in human OSA, these data suggest that Met is commonly overexpressed and activated in canine OSA and that inhibition of Met impairs the invasive and motogenic properties of canine OSA cells. These data implicate Met as a potentially important factor for canine OSA progression and indicate that it represents a viable model to study Met-targeted therapies.

c-Met inhibitors with novel binding mode show activity against several hereditary papillary renal cell carcinoma-related mutations

c-Met is a receptor tyrosine kinase often deregulated in human cancers, thus making it an attractive drug target. One mechanism by which c-Met deregulation leads to cancer is through gain-of-function mutations. Therefore, small molecules capable of targeting these mutations could offer therapeutic benefits for affected patients. SU11274 was recently described and reported to inhibit the activity of the wild-type and some mutant forms of c-Met, whereas other mutants are resistant to inhibition. We identified a novel series of c-Met small molecule inhibitors that are active against multiple mutants previously identified in hereditary papillary renal cell carcinoma patients. AM7 is active against wild-type c-Met as well as several mutants, inhibits c-Met-mediated signaling in MKN-45 and U-87 MG cells, and inhibits tumor growth in these two models grown as xenografts. The crystal structures of AM7 and SU11274 bound to unphosphorylated c-Met have been determined. The AM7 structure reveals a novel binding mode compared with other published c-Met inhibitors and SU11274. The molecule binds the kinase linker and then extends into a new hydrophobic binding site. This binding site is created by a significant movement of the C-helix and so represents an inactive conformation of the c-Met kinase. Thus, our results demonstrate that it is possible to identify and design inhibitors that will likely be active against mutants found in different cancers.

[Molecular biology of the clear cell renal cell carcinoma: principles for a selective treatment]

Renal cell carcinoma (RCC) and its most frequent subtype, the clear cell hystology type, has shown resistance to chemotherapy and radiotherapy treatment when disease was already spread in patients. Recently, a huge advance in the molecular biology of this tumor has been performed. This fact allowed a deeper and better knowledge of the disease and the development of new drugs that work against the growth factors involved in tumor origin. In this review article it is summarized the molecular milestones that are involved in the development of clear cell renal cell carcinomas.

Genetic targeting of the kinase activity of the Met receptor in cancer cells

The development of kinase inhibitors is revolutionizing cancer treatment. Assessing the oncogenic potential of individual kinase activities and ensuring that a drug of interest acts by direct inhibition of its putative target kinase are clear priorities. We developed a genetic strategy to selectively inactivate the catalytic activity of kinases. This approach generates isogenic cells in which a given kinase gene is expressed but is devoid of enzymatic activity. As a model to test this approach, we chose the MET receptor, which is involved in multiple cancers and is the focus of several therapeutic efforts. The exon encoding the ATP-binding site of MET was deleted from the genome of colorectal, bladder, and endometrial cancer cells. The derivative isogenic cells expressed a kinase-inactive Met (MET-KD) and were completely unresponsive to its ligand hepatocyte growth factor (HGF), indicating the exclusivity of this ligand-receptor axis. The in vivo tumorigenic potential of MET-KD cells was reduced but could be partially restored by HGF, suggesting that concomitant targeting of the receptor and its ligand should be therapeutically exploited. A reportedly selective Met-kinase inhibitor (SU-11274) markedly affected the growth of MET-KD cancer cells, indicating this compound exerts its effects not only through the intended target. The genetic strategy presented here is not limited to kinase genes but could be broadly applicable to any drug/protein combination in which the target enzymatic domain is known.

The therapeutic potential of hepatocyte growth factor to sensitize ovarian cancer cells to cisplatin and paclitaxel in vivo

PURPOSE

Advanced ovarian cancers are initially responsive to combinatorial chemotherapy with platinum drugs and taxanes but, in most cases, develop drug resistance. We recently showed that, in vitro, hepatocyte growth factor (HGF) enhances death of human ovarian cancer cell lines treated with cisplatin (CDDP) and paclitaxel. The present study addresses whether in vivo HGF makes ovarian carcinoma cells more responsive to these chemotherapeutics.

EXPERIMENTAL DESIGN

Using Lentiviral vectors carrying the HGF transgene, we transduced SK-OV-3 and NIH:OVCAR-3 ovarian carcinoma cell lines to obtain stable autocrine and paracrine HGF receptor activation. In vitro, we assayed growth, motility, invasiveness, and the response to CDDP and paclitaxel of the HGF-secreting bulk unselected cell populations. In vivo, we tested the cytotoxic effects of the drugs versus s.c. tumors formed by the wild-type and HGF-secreting cells in immunocompromised mice. Tumor-bearing mice were treated with CDDP (i.p.) and paclitaxel (i.v.), combined in different schedules and doses.

RESULTS

In vitro, HGF-secreting cells did not show altered proliferation rates and survival but were strongly sensitized to the death triggered by CDDP and paclitaxel, alone or in combination. In vivo, we found a therapeutic window in which autocrine/paracrine HGF made tumors sensitive to low doses of the drugs, which were ineffective on their own.

CONCLUSIONS

These data provide the proof-of-concept that in vivo gene therapy with HGF might be competent in sensitizing ovarian cancer cells to conventional chemotherapy.

Specific Grb2-mediated interactions regulate clathrin-dependent endocytosis of the cMet-tyrosine kinase

Lysosomal degradation of the receptor-tyrosine kinase cMet requires receptor ubiquitination by the E3 ubiquitin ligase Cbl followed by clathrin-dependent internalization. A role for Cbl as an adaptor for cMet internalization has been previously reported. However, the requirement for Cbl ubiquitin ligase activity in this process and its mode of recruitment to cMet has yet to be determined. Cbl can directly bind cMet at phosphotyrosine 1003 or indirectly via Grb2 to phosphotyrosine 1356 in the multisubstrate binding domain of cMet. The direct binding of Cbl with cMet is critical for receptor degradation and not receptor internalization. Here we show a strict requirement for Grb2 and the ubiquitin ligase activity of Cbl for cMet endocytosis. Receptor internalization was impaired by small interfering RNA depletion of Grb2, overexpression of dominant negative Grb2 mutants, and point mutations in the cMet multisubstrate docking site that inhibits the direct association of Grb2 with cMet. The requirement for Grb2 was specific and did not involve the multiadaptor Gab1. cMet internalization was impaired in cells expressing an ubiquitin ligase-deficient Cbl mutant or conjugation-deficient ubiquitin but was unaffected in cells expressing a Cbl mutant that is unable to bind cMet directly. Expression of a Cbl-Grb2 chimera rescued impaired cMet endocytosis in cells depleted of endogenous Grb2. These results indicate that the ubiquitin ligase activity of Cbl is critical for clathrin-dependent cMet internalization and suggest a role for Grb2 as an intermediary linking Cbl ubiquitin ligase activity to this process.

Targeting the c-Met signaling pathway in cancer

On binding to the cell surface receptor tyrosine kinase (TK) known as c-Met, hepatocyte growth factor (HGF) stimulates mitogenesis, motogenesis, and morphogenesis in a wide range of cellular targets including, epithelial and endothelial cells, hematopoietic cells, neurons, melanocytes, and hepatocytes. These pleiotropic actions are fundamentally important during development, homeostasis, and tissue regeneration. HGF signaling also contributes to oncogenesis and tumor progression in several human cancers and promotes aggressive cellular invasiveness that is strongly linked to tumor metastasis. Our present understanding of c-Met oncogenic signaling supports at least three avenues of pathway selective anticancer drug development: antagonism of ligand/receptor interaction, inhibition of TK catalytic activity, and blockade of intracellular receptor/effector interactions. Potent and selective preclinical drug candidates have been developed using all three strategies, and human clinical trials in two of the three areas are now under way.

Structural characterization of autoinhibited c-Met kinase produced by coexpression in bacteria with phosphatase

Protein kinases are a large family of cell signaling mediators undergoing intensive research to identify inhibitors or modulators useful for medicine. As one strategy, small-molecule compounds that bind the active site with high affinity can be used to inhibit the enzyme activity. X-ray crystallography is a powerful method to reveal the structures of the kinase active sites, and thus aid in the design of high-affinity, selective inhibitors. However, a limitation still exists in the ability to produce purified kinases in amounts sufficient for crystallography. Furthermore, kinases exist in different conformation states as part of their normal regulation, and the ability to prepare crystals of kinases in these various states also remains a limitation. In this study, the c-Abl, c-Src, and c-Met kinases are produced in high yields in Escherichia coli by using a bicistronic vector encoding the PTP1B tyrosine phosphatase. A 100-fold lower dose of the inhibitor, Imatinib, was observed to inhibit the unphosphorylated form of c-Abl kinase prepared by using this vector, compared to the phosphorylated form produced without PTP1B, consistent with the known selectivity of this inhibitor for the unactivated conformation of the enzyme. Unphosphorylated c-Met kinase produced with this vector was used to obtain the crystal structure, at 2.15-A resolution, of the autoinhibited form of the kinase domain, revealing an intricate network of interactions involving c-Met residues documented previously to cause dysregulation when mutated in several cancers.

Regulation of the Wild-Type and Y1235D Mutant Met Kinase Activation

Met receptor tyrosine kinase plays a crucial role in the regulation of a large number of cellular processes and, when deregulated by overexpression or mutations, leads to tumor growth and invasion. The Y1235D mutation identified in metastases was shown to induce constitutive activation and a motile-invasive phenotype on transduced carcinoma cells. Wild-type Met activation requires phosphorylation of both Y1234 and Y1235 in the activation loop. We mapped the major phosphorylation sites in the kinase domain of a recombinant Met protein and identified the known residues Y1234 and Y1235 as well as a new phosphorylation site at Y1194 in the hinge region. Combining activating and silencing mutations at these sites, we characterized in depth the mechanism of activation of wild-type and mutant Met proteins. We found that the phosphotyrosine mimetic mutation Y1235D is sufficient to confer constitutive kinase activity, which is not influenced by phosphorylation at Y1234. However, the specific activity of this mutant was lower than that observed for fully activated wild-type Met and induced less phosphorylation of Y1349 in the signaling site, indicating that this mutation cannot entirely compensate for a phosphorylated tyrosine at this position. The Y1194F silencing mutation yielded an enzyme that could be activated to a similar extent as the wild type but with significantly slower activation kinetics, underlying the importance of this residue, which is conserved among different tyrosine kinase receptors. Finally, we observed different interactions of wild-type and mutant Met with the inhibitor K252a that may have therapeutic implications for the selective inhibition of this kinase.

Met receptor dynamics and signalling

The receptor for hepatocyte growth factor (HGF), Met, controls a programme of invasive growth that combines proliferation with various moto- and morphogenetic processes. This process is important for development and organ regeneration, but dysregulation in transformed tissues can contribute to cancer progression and metastasis. Acute stimulation of tissue culture cells with HGF leads to Met downregulation via degradation through an endocytic mechanism that also requires proteasome activity. Perturbation of Met trafficking on the endocytic pathway, either at the level of the internalisation step or during sorting at the early endosome, leads to altered signalling outputs. Ubiquitination of Met through the E3-ligase Cbl is required for receptor downregulation, and a mutant receptor defective in Cbl binding is able to transform cells. We discuss the hypothesis that some naturally occurring Met mutants implicated in cancer may transform cells owing to defects in their trafficking along the endosomal degradation pathway.

Inhibition of Hepatocyte Growth Factor Induction in Human Dermal Fibroblasts by Tryptanthrin

In addition to regulation of normal cell functions, hepatocyte growth factor (HGF) has also been shown to be involved in malignant cell transformation and in growth, invasion and metastasis in cancer cells. Inhibitors of HGF production have a potential for interfering with malignant cell transformation and progression of tumors. We found that tryptanthrin, one of the major compounds extracted from the medicinal plant Polygonum tinctorium, which is known for its antitumor activity, strongly inhibited HGF production stimulated by various HGF inducers in human dermal fibroblasts. HGF production induced by phorbol 12-myristate 13-acetate (PMA) was potently inhibited by tryptanthrin without any appreciable cytotoxic effect. Tryptanthrin also inhibited HGF production induced by epidermal growth factor (EGF) and platelet-derived growth factor. Moreover, proliferation of the fibroblasts induced by the two growth factors was potently suppressed by tryptanthrin to the level of proliferation of unstimulated fibroblasts. However, tryptanthrin did not inhibit HGF production induced by the protein kinase A-activating agents cholera toxin and 8-bromo-cAMP. These effects of tryptanthrin were different from the effects of transforming growth factor beta1 and dexamethasone, both of which inhibit HGF production induced by all the above inducers. Upregulations of HGF gene expression by PMA and EGF were also inhibited by tryptanthrin. Activation of the mitogen-activated protein kinase (MAPK) signaling pathway is crucial for PMA-induced HGF production, but tryptanthrin did not attenuate phosphorylation of MAPK induced by PMA. These results indicate that tryptanthrin potently inhibited induction of HGF production probably through events downstream of MAPK activation.

Early onset hereditary papillary renal carcinoma: germline missense mutations in the tyrosine kinase domain of the met proto-oncogene

PURPOSE

Hereditary papillary renal carcinoma (HPRC) is characterized by a predisposition to multiple, bilateral papillary type 1 renal tumors caused by inherited activating missense mutations in the tyrosine kinase domain of the MET proto-oncogene. In the current study we evaluated the clinical phenotype and germline MET mutation of 3 new HPRC families. We describe the early onset clinical features of HPRC.

MATERIALS AND METHODS

We identified new HPRC families of Italian (family 177), Spanish (family 223) and Cuban (family 268) descent. We evaluated their clinical features, performed MET mutation analysis by denaturing high performance liquid chromatography and DNA sequencing, and estimated age dependent penetrance and survival using Kaplan-Meier analysis. We characterized renal tumors by histology and fluorescence in situ hybridization.

RESULTS

Identical germline MET c.3522G --> A mutations (V1110I) were identified in families 177 and 268 but no evidence of a founder effect was found. Affected members of family 223 carried a germline c.3906G --> C.3522G --> A MET mutation (V1238I). Age dependent penetrance but not survival was significantly earlier for the c.3522G -->A mutation than for the c.3906G --> A mutation in these HPRC families. Trisomy of chromosome 7 and papillary renal carcinoma type 1 histology were detected in papillary renal tumors.

CONCLUSIONS

HPRC can occur in an early onset form. The median age for renal tumor development in these 3 HPRC families was 46 to 63 years. HPRC associated papillary renal tumors may be aggressive and metastasize, leading to mortality. Median survival age was 60 to 70 years. Families with identical germline mutations in MET do not always share a common ancestor. HPRC is characterized by germline mutations in MET and papillary type 1 renal tumor histology.

The met receptor degradation pathway: requirement for Lys48-linked polyubiquitin independent of proteasome activity

Acute stimulation of the receptor for the hepatocyte growth factor/scatter factor Met leads to receptor monoubiquitination and down-regulation through the lysosomal degradation pathway. We have determined that the Met receptor undergoes multiple monoubiquitination as opposed to the appendage of polyubiquitin chains. Nevertheless, overexpression of ubiquitin in HEK293T cells enhances the rate of Met receptor degradation, in contrast to a point mutant of ubiquitin (K48R) that cannot form Lys(48)-linked polyubiquitin chains. Furthermore, an enhancement of Met degradation is also seen under conditions where the proteasome is inhibited by lactacystin. We propose that this reflects polyubiquitin-dependent sorting of Met, as the overexpression of ubiquitin but not K48R ubiquitin also restores hepatocyte growth factor-dependent phosphorylation of the endosomal coat protein Hrs from inhibition by lactacystin. Our data indicate a requirement for K48R-linked polyubiquitin for Met endosomal trafficking independent of its canonical function of targeting for proteasomal degradation.

Truncated RON tyrosine kinase drives tumor cell progression and abrogates cell-cell adhesion through E-cadherin transcriptional repression

RON is a tyrosine kinase receptor that triggers scattering of normal cells and invasive growth of cancer cells on ligand binding. We identified a short RON mRNA, which is expressed in human lung, ovary, tissues of the gastrointestinal tract, and also in several human cancers, including ovarian carcinomas and cell lines from pancreatic carcinomas and leukemias. This transcript encodes a truncated protein (short-form RON; sf-RON), lacking most of the RON receptor extracellular domain but retaining the whole transmembrane and intracellular domains. Sf-RON shows strong intrinsic tyrosine kinase activity and is constitutively phosphorylated. Epithelial cells transduced with sf-RON display an aggressive phenotype; they shift to a nonepithelial morphology, are unable to form aggregates, grow faster in monolayer cultures, show anchorage-independent growth, and become motile. We show that in these cells, E-cadherin expression is lost through a dominant transcriptional repression pathway likely mediated by the transcriptional factor SLUG. Altogether, these data show that expression of a naturally occurring, constitutively active truncated RON kinase results in loss of epithelial phenotype and aggressive behavior and, thus, it might contribute to tumor progression.

The Sema domain of Met is necessary for receptor dimerization and activation

Hepatocyte growth factor (HGF) binds the extracellular domain and activates the Met receptor to induce mitogenesis, morphogenesis, and motility. The extracellular domain of Met is comprised of Sema, PSI, and four IPT subdomains. We investigated the contribution of these subdomains to Met receptor dimerization. Our observations indicate that the Sema domain is necessary for dimerization in addition to HGF binding. Treatment of Met-overexpressing tumor cells with recombinant Sema in the presence or absence of HGF results in decreased Met-mediated signal transduction, cell motility, and migration, behaving in a manner similar to an antagonistic anti-Met Fab. These data suggest that the Sema domain of Met may not only represent a novel anticancer therapeutic target but also acts as a biotherapeutic itself.

Activation of c-Met in colorectal carcinoma cells leads to constitutive association of tyrosine-phosphorylated beta-catenin

Increased expression and/or activity of c-Met, the receptor protein tyrosine kinase for hepatocyte growth factor/scatter factor, occurs commonly during colon tumor progression. To examine potential roles for c-Met in promoting metastasis, we compared the colon tumor cell line KM12C with low metastatic potential to the isogenic variants KM,12L4 and KM12SM with high metastatic potential. KM12C cells express c-Met with low levels of tyrosine phosphorylation in the absence of HGF. The high metastatic cells express a c-Met that is constitutively tyrosine phosphorylated, they have increased colony formation, and are minimally responsive to HGF relative to the parental cells. Tyrosine-phosphorylated beta-catenin was constitutively associated with c-Met in the more metastatic cells, but was inducible only after HGF addition in the less metastatic cells. Functions mediated by beta-catenin, including cell-cell adhesion and migration, and activation of the tcf (T-cell factor) family of transcription factors, were also elevated in the more metastatic KM12SM and L4 cells. Furthermore, analysis of the known tcf transcriptional target genes, cyclin D1, c-Myc, and uPAR, demonstrated increased expression in the high metastatic cells, correlating with the levels of tcf activity. Collectively, these results suggest that endogenous activation of c-Met in highly metastatic KM12SM CRC cells results in increased survival and growth under anchorage independent conditions, increased in vitro migration, and elevated levels of tcf target genes. Thus, beta-catenin association with activated c-Met may contribute to a more aggressive liver metastatic phenotype of these cells.

Role of the MET/HGF receptor in proliferation and invasive behavior of osteosarcoma

Signal transduction downstream HGF receptor (MET) activation involves multiple pathways that account for mitogenesis, motility and morphogenesis in a cell type-dependent fashion. MET receptor is aberrantly expressed in almost 100% of human osteosarcomas. We analyzed the effect of the MET receptor activation in five human osteosarcoma cell lines evaluating the levels of HGF-dependent activation of MAPK and PKB/AKT as biochemical readouts of mitogenic and invasive responses, respectively. All the cell lines tested expressed high levels of the MET proto-oncogene. Four cell lines showed activation of the MAPK cascade upon HGF stimulation, suggesting that this growth factor serves a common proliferative function in osteosarcomas. Two lines showed activation of PKB/AKT that is known to be involved in migration mediated by HGF receptor. Accordingly, cell lines where MAPK cascade was activated responded to HGF with increased proliferation, while induction and inhibition of PKB/AKT activity corresponded to acquisition or block of the invasive-motile response to HGF, respectively. Both the HGF dependent responses were reverted by the specific MET inhibitor K252a. These data show that HGF activates both the mitogen and motogen machinery in osteosarcoma cells and suggest that HGF might promote their malignant behavior by concomitant activation of different pathways and biological functions.