Activation of c-Met (hepatocyte growth factor receptor) in human gastric cancer tissue

Research progress on the development of hepatocyte growth factor/c-Met signaling pathway in gastric cancer: A review

Hepatocyte growth factor (HGF) and its receptor, c-Met, play important roles in the occurrence, development, and treatment of gastric cancer (GC). This review explored the function of the HGF/c-Met signaling pathway in GC and its potential targeted therapeutic mechanisms. As one of the most common malignant tumors worldwide, GC has a complex pathogenesis and limited therapeutic options. Therefore, a thorough understanding of the molecular mechanism of GC is very important for the development of new therapeutic methods. The HGF/c-Met signaling pathway plays an important role in the proliferation, migration, and invasion of GC cells and has become a new therapeutic target. This review summarizes the current research progress on the role of HGF/c-Met in GC and discusses targeted therapeutic strategies targeting this signaling pathway, providing new ideas and directions for the treatment of GC.

Ferroptosis regulating lipid peroxidation metabolism in the occurrence and development of gastric cancer

BACKGROUND

Gastric cancer is one of the most common malignant tumors in the world, and its occurrence and development involve complex biological processes. Iron death, as a new cell death mode, has attracted wide attention in recent years. However, the regulatory mechanism of iron death in gastric cancer and its effect on lipid peroxidation metabolism remain unclear.

AIM

To explore the role of iron death in the development of gastric cancer, reveal its relationship with lipid peroxidation, and provide a new theoretical basis for revealing the molecular mechanism of the occurrence and development of gastric cancer.

METHODS

The process of iron death in gastric cancer cells was simulated by cell culture model, and the occurrence of iron death was detected by fluorescence microscopy and flow cytometry. The changes of gene expression related to iron death and lipid peroxidation metabolism were analyzed by high-throughput sequencing technology. In addition, a mouse model of gastric cancer was established, and the role of iron death in vivo was studied by histology and immunohistochemistry, and the level of lipid peroxidation was detected. These methods comprehensively and deeply reveal the regulatory mechanism of iron death on lipid peroxidation metabolism in the occurrence and development of gastric cancer.

RESULTS

Iron death was significantly activated in gastric cancer cells, and at the same time, associated lipid peroxidation levels increased significantly. Through high-throughput sequencing analysis, it was found that iron death regulated the expression of several genes related to lipid metabolism. In vivo experiments demonstrated that increased iron death in gastric cancer mice was accompanied by a significant increase in lipid peroxidation.

CONCLUSION

This study confirmed the important role of iron death in regulating lipid peroxidation metabolism in the occurrence and development of gastric cancer. The activation of iron death significantly increased lipid peroxidation levels, revealing its regulatory mechanism inside the cell.

Targeted dual inhibition of c-Met/VEGFR2 signalling by foretinib improves antitumour effects of nanoparticle paclitaxel in gastric cancer models

Elevated expression of multiple growth factors and receptors including c‐Met and VEGFR has been reported in gastric adenocarcinoma (GAC) and thus provides a potentially useful therapeutic target. The therapeutic efficacy of foretinib, a c‐Met/VEGFR2 inhibitor, was determined in combination with nanoparticle paclitaxel (NPT) in GAC. Animal studies were conducted in NOD/SCID mice in subcutaneous and peritoneal dissemination xenografts. The mechanism of action was assessed by Immunohistochemical and Immunoblot analyses. In c‐Met overexpressing MKN‐45 cell‐derived xenografts, NPT and foretinib demonstrated inhibition in tumour growth, while NPT plus foretinib showed additive effects. In c‐Met low‐expressing SNU‐1 or patient‐derived xenografts, the foretinib effect was smaller, while NPT had a similar effect compared with MKN‐45, as NPT plus foretinib still exhibited an additive response. Median mice survival was markedly improved by NPT (83%), foretinib (100%) and NPT plus foretinib (230%) in peritoneal dissemination xenografts. Subcutaneous tumour analyses exhibited that foretinib increased cancer cell death and decreased cancer cell proliferation and tumour vasculature. NPT and foretinib suppressed the proliferation of GAC cells in vitro and had additive effects in combination. Further, foretinib caused a dramatic decrease in phosphorylated forms of c‐Met, ERK, AKT and p38. Foretinib led to a decrease in Bcl‐2, and an increase in p27, Bax, Bim, cleaved PARP‐1 and cleaved caspase‐3. Thus, these findings highlight the antitumour impact of simultaneous suppression of c‐Met and VEGFR2 signalling in GAC and its potential to enhance nanoparticle paclitaxel response. This therapeutic approach might lead to a clinically beneficial combination to increase GAC patients’ survival.

New Preclinical Development of a c-Met Inhibitor and Its Combined Anti-Tumor Effect in c-Met-Amplified NSCLC

c-Met is a receptor tyrosine kinase with no commercially available product despite being a pivotal target in cancer progression. Unlike other c-Met inhibitors that fail clinically, ABN401 is a newly synthesized c-Met inhibitor that is not potentially degraded by aldehyde oxidase (AO) in human liver cytosol. This study aimed to determine the physicochemical stability, pharmacokinetics in beagle dogs, and therapeutic effect of ABN401 in a c-Met-amplified non-small-cell lung cancer (NSCLC) patient-derived xenograft (PDX) model. ABN401 was found to be a weak basic compound, with pKa and log P values of 7.49 and 2.46, respectively. It is poorly water-soluble but soluble at acidic pH. The accelerated storage stability is dependent on temperature, but the purity remains at over 97% after 6 months. The bioavailability is approximately 30% in dogs and it is highly efficient in the PDX model, achieving around 90% tumor growth inhibition in combination with erlotinib. These observations indicate that the compound is acceptable for the next phase of trials.

Tailoring subtractive cell biopanning to identify diffuse gastric adenocarcinoma-associated antigens via human scFv antibodies

Among various solid tumours, gastric cancer (GC) is one of the leading causes of cancer-related deaths worldwide. Expansion into the peritoneal cavity, which results from dissemination of diffuse cancer cells, is the main cause of mortality in gastric adenocarcinoma patients. Therefore, investigation of putative biomarkers involved in metastasis is prerequisite for GC management. In an effort to discover potential tumour markers associated with peritoneal metastasis of GC, a semi-synthetic human scFv library (Tomlinson I) was used to isolate novel antibody fragments recognizing MKN-45, a poorly differentiated diffuse gastric adenocarcinoma cell line. Four rounds of subtractive selection each consisting of extensive pre-absorption of phage library with NIH-3T3 murine embryonic fibroblasts and AGS (a well-differentiated intestinal gastric adenocarcinoma) cell line were carried out prior to positive selection on MKN-45 target cells. ELISA-based screening of 192 phage-displayed scFv clones indicated 21 high-affinity binders with specific staining of MKN-45 compared with AGS cells. Diversity analysis of the selected phage-scFvs resulted in five distinct sequences with multiple frequency. Further analysis by ELISA and flow cytometry verified three clones that specifically recognized MKN-45 cells. Liquid chromatography-mass spectrometry analysis of the scFv-immunoprecipitated proteins has led to identification of c-Met, HSP90 α and HSP90 β as candidate biomarkers associated with diffuse GC. Immunohistochemistry revealed the capability of purified scFvs to differentiate diffuse and intestinal gastric adenocarcinoma. Taken together, the isolated MKN-45-specific scFv fragments and their cognate antigens would be beneficial in screening and management as well as targeting and therapy of the diffuse gastric adenocarcinoma.

Suppressive impact of metronomic chemotherapy using UFT and/or cyclophosphamide on mediators of breast cancer dissemination and invasion

Metronomic chemotherapy using the 5-FU prodrug uracil-tegafur (UFT) and cyclophosphamide (CTX) was previously shown to only modestly delay primary tumor growth, but nevertheless markedly suppressed the development of micro-metastasis in an orthotopic breast cancer xenograft model, using the metastatic variant of the MDA-MB-231 cell line, 231/LM2-4. Furthermore, a remarkable prolongation of survival, with no toxicity, was observed in a model of postsurgical advanced metastatic disease. A question that has remained unanswered is the seemingly selective anti-metastatic mechanisms of action responsible for this treatment. We assessed the in vivo effect of metronomic UFT, CTX or their combination, on vascular density, collagen deposition and c-Met (cell mediators or modulators of tumor cell invasion or dissemination) via histochemistry/immunohistochemistry of primary tumor sections. We also assessed the effect of continuous exposure to low and non-toxic doses of active drug metabolites 5-fluorouracil (5-FU), 4-hydroperoxycyclophosphamide (4-HC) or their combination, on 231/LM2-4 cell invasiveness in vitro. In the in vivo studies, a significant reduction in vascular density and p-Met[Y1003] levels was associated with UFT+CTX treatment. All treatments reduced intratumoral collagen deposition. In the in vitro studies, a significant reduction of collagen IV invasion by all treatments was observed. The 3D structures formed by 231/LM2-4 on Matrigel showed a predominantly Mass phenotype under treated conditions and Stellate phenotype in untreated cultures. Taken together, the results suggest the low-dose metronomic chemotherapy regimens tested can suppress several mediators of tumor invasiveness highlighting a new perspective for the anti-metastatic efficacy of metronomic chemotherapy.

Hepatocyte growth factor-induced mesenchymal-epithelial transition factor activation leads to insulin-like growth factor 1 receptor inhibitor unresponsiveness in gastric cancer cells

Insulin-like growth factor 1 receptor (IGF-1R) inhibitors have been developed as potential therapeutics for cancer treatment; however, the phase III trials have not produced promising overall survival rates. Therefore, understanding the mechanism underlying intrinsic resistance to IGF-1R-targeted agents is urgently required. A number of studies have revealed that activation of alternative receptor tyrosine kinases can mediate resistance to IGF-1R-targeted therapy. The present study investigated whether activated mesenchymal-epithelial transition factor (MET; also known as c-Met and hepatocyte growth factor receptor) confers resistance to an IGF-1R inhibitor (NVP-AEW541) of gastric cancer (GC) cells. NCI-N87 and MGC-803 cells were treated with varying concentrations and combinations of NVP-AEW541, hepatocyte growth factor (HGF) and MET small interfering (si)-RNA or crizotinib (a MET inhibitor). The effects of these agents on cell proliferation and pro-apoptotic events were assessed by Cell Counting Kit-8 assays and flow cytometry. Receptor activation and the downstream signaling pathway were examined using western blot analysis. Expression and/or activation of MET and IGF-1R in 156 GC specimens were evaluated by immunohistochemistry. The results demonstrated that NVP-AEW541 inhibited cell growth, with dephosphorylation of IGF-1R and protein kinase B (AKT), in NCI-N87 and MGC-803 cells. Application of HGF activated MET and the downstream AKT signaling pathways, decreased apoptotic events and restored cell proliferation, which were reversed by MET inhibition via crizotinib or siRNA knockdown. Furthermore, combination therapy of NVP-AEW541 and crizotinib exhibited an enhanced effectiveness in vitro. In addition, >40% of IGF-1R overexpressed GC specimens showed MET expression and activation. In conclusion, HGF-induced MET activation may represent a novel mechanism conferring unresponsiveness to IGF-1R-targeted agents in GC, and inhibition of MET may improve the efficacy of IGF-1R inhibitors.

Aberrant methylation and silencing of the SPINT2 gene in high-grade gliomas

Hepatocyte growth factor activator inhibitor type 2 (HAI‐2), encoded by the SPINT2 gene, is a membrane‐anchored protein that inhibits proteases involved in the activation of hepatocyte growth factor (HGF), a ligand of MET receptor. Epigenetic silencing of the SPINT2 gene has been reported in a human glioblastoma cell line (U87) and glioblastoma‐derived cancer stem cells. However, the incidence of SPINT2 methylation in tumor tissues obtained from glioma patients is unknown. In this study, we analyzed the methylation status of the SPINT2 gene of eight human glioblastoma cell lines and surgically resected glioma tissues of different grades (II, III, and IV) by bisulfite sequence analysis and methylation‐specific PCR. Most glioblastoma lines (7/8) showed methylation of the SPINT2 gene with a significantly reduced level of SPINT2mRNA compared to cultured astrocytes and normal brain tissues. However, all glioblastoma lines expressed mRNA for HGF activator (HGFAC), a target protease of HAI‐2/SPINT2. Forced expression of SPINT2 reduced MET phosphorylation of U87 glioblastoma cells both in vitro and in intracranial xenografts in nude mice. Methylation‐specific PCR analysis of the resected glioma tissues indicated notable methylation of the SPINT2 gene in 33.3% (2/6), 71.4% (10/14), and 74.3% (26/35) of grade II, III, and IV gliomas, respectively. Analysis of RNA sequencing data in a public database indicated an increased HGFAC/SPINT2 expression ratio in high‐grade compared to low‐grade gliomas (P = .01). In summary, aberrant methylation of the SPINT2 gene is frequently observed in high‐grade gliomas and might confer MET signaling in the glioma cells.

Current advances of targeting HGF/c-Met pathway in gastric cancer

Despite the advances in systemic chemotherapy, gastric adenocarcinoma (GC) remains the third most common cause of cancer-related deaths with poor prognosis. The heterogeneity of GC indicates that novel biomarkers should be established in order to further classify tumors and develop individual targeted therapies. High-quality preclinical and clinical research has demonstrated that growth factor (HGF)-hepatocyte growth factor receptor (c-Met) pathway plays a pivotal role on the growth, survival and invasiveness of GC. In particular, aberrant activation of HGF/c-Met signaling pathway has been associated with poor clinical outcomes, suggesting the therapeutic potential of c-Met. This has stimulated the development and evaluation of a number of c-Met targeted agents in an advance disease setting. In this review, we summarize the current state of the art in the advances on the inhibition of c-Met pathway, with particular emphasis on the clinical testing of c-Met targeted therapeutic agents. Furthermore, we discuss the challenges facing the incorporation of c-Met targeted agents in randomized trials, with the idea that the definition of the appropriate genetic and molecular context for the use of these agents remains the priority.

The association among HER2, MET and FOXP3 expression and tumor regression grading in gastric adenocarcinoma

Although the introduction of the perioperative chemotherapy on the management of gastric cancer has improved patients survival, heterogeneity of clinical outcomes has been evidenced in parallel to different histopathological regression pattern of gastric cancer cells. Thus, this study evaluated the tumor regression grading (TRG) in a series of post-treatment gastric tumors and its associations with HER2, MET, and FOXP3 expression. Material of 54 gastric cancer samples was available for TRG evaluation and immunohistochemistry. We found that total and subtotal pathologic response were significantly associated to the intestinal subtype (p = 0.04) and that well-differentiated tumors were significantly correlated with total or partial response (p = 0.019). Although not associated with the TRG, FOXP3 expression in gastric tumors was associated to poorly differentiated tumors (p = 0.03), to the diffuse and mixed subtypes together (p = 0.04) and to the presence of vascular infiltration (p = 0.04), while HER2 overexpression was associated to better differentiated cases (p = 0.04) and to the absence of vascular infiltration (p = 0.02). MET expression, however, showed no association with the analyzed clinicopathological factors. This study highlights the role of tissue differentiation on pathological response to neoadjuvant chemotherapy in gastric cancer and shows no impact between FOXP3, HER2 and MET expression in terms of TRG.

MET4 expression predicts poor prognosis of gastric cancers with Helicobacter pylori infection

The role of HGF/SF‐MET signaling is important in cancer progression, but its relation with Helicobacter pylori‐positive gastric cancers remains to be elucidated. In total, 201 patients with primary gastric carcinoma who underwent curative or debulking resection without preoperative chemotherapy were studied. MET4 and anti‐HGF/SF mAbs were used for immunohistochemical analysis. Survival of gastric cancer patients was estimated by Kaplan–Meier method and compared with log‐rank. Cox proportional hazards models were fit to determine the independent association of MET‐staining status with outcome. The effect of live H. pylori bacteria on cell signaling and biological behaviors was evaluated using gastric cancer cell lines. MET4‐positive gastric cancers showed poorer prognosis than MET4‐negative cases (overall survival, P = 0.02; relapse‐free survival, P = 0.06). Positive staining for MET4 was also a statistically significant factor to predict poor prognosis in H. pylori‐positive cases (overall survival, P < 0.01; relapse‐free survival, P = 0.01) but not in H. pylori‐negative cases. Gastric cancers positively stained with both HGF/SF and MET4 showed a tendency of the worst prognosis. Stimulation of MET‐positive gastric cancer cells with live H. pylori bacteria directly upregulated MET phosphorylation and activated MET downstream signals such as p44/42MAPK and Akt, conferring cell proliferation and anti‐apoptotic activity. In conclusion, positive staining for MET4 was useful for predicting poor prognosis of gastric cancers with H. pylori infection. Helicobacter pylori stimulated MET‐positive gastric cancers and activated downstream signaling, thereby promoting cancer proliferation and anti‐apoptotic activity. These results support the importance of H. pylori elimination from gastric epithelial surface in clinical therapy.

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.

Preclinical Evaluation of AMG 337, a Highly Selective Small Molecule MET Inhibitor, in Hepatocellular Carcinoma

Aberrant hepatocyte growth factor (HGF)/MET signaling has been implicated in hepatocarcinogenesis, suggesting that MET may serve as an attractive therapeutic target in hepatocellular carcinoma. We sought to investigate the in vitro and in vivo antitumor activity of AMG 337, a potent and highly selective small molecule MET kinase inhibitor, in preclinical models of hepatocellular carcinoma. The antiproliferative activity of AMG 337 was evaluated across a panel of hepatocellular carcinoma cell lines in a viability assay. Daily oral administration was used to evaluate the in vivo antitumor activity of AMG 337 in two patient-derived xenograft (PDX) models of hepatocellular carcinoma (LI0612 and LI1078). AMG 337 exerted potent antiproliferative activity against 2 of 40 hepatocellular carcinoma cell lines, namely, MHCC97H (IC50, 0.015 μmol/L) and HCCLM3 (IC50, 0.025 μmol/L). Both sensitive cell lines showed MET amplification (MET/CEN-7 >2.0) assessed by FISH, and high MET expression (3+ IHC) assessed by IHC. AMG 337 potently inhibited p-MET in all cell lines with detectable levels of total MET. However, the dose-dependent inhibition of downstream effectors of HGF/MET signaling, including p-GAB1, p-AKT, and p-ERK, was limited to those cell lines sensitive to AMG 337 in a viability assay (MHCC97H and HCCLM3). AMG 337 significantly inhibited tumor growth at all doses tested in the MET-amplified and MET-high-expressing hepatocellular carcinoma PDX model LI0612 and had no effect on tumor growth in the non-MET-amplified and MET-low-expressing hepatocellular carcinoma PDX model LI1078. AMG 337 represents a promising and novel therapeutic strategy for targeting hepatocellular carcinomas with a dependence on HGF/MET signaling. Mol Cancer Ther; 15(6); 1227-37. ©2016 AACR.

Detection of MET Gene Copy Number in Cancer Samples Using the Droplet Digital PCR Method

PURPOSE

The analysis of MET gene copy number (CN) has been considered to be a potential biomarker to predict the response to MET-targeted therapies in various cancers. However, the current standard methods to determine MET CN are SNP 6.0 in the genomic DNA of cancer cell lines and fluorescence in situ hybridization (FISH) in tumor models, respectively, which are costly and require advanced technical skills and result in relatively subjective judgments. Therefore, we employed a novel method, droplet digital PCR (ddPCR), to determine the MET gene copy number with high accuracy and precision.

METHODS

The genomic DNA of cancer cell lines or tumor models were tested and compared with the MET gene CN and MET/CEN-7 ratio determined by SNP 6.0 and FISH, respectively.

RESULTS

In cell lines, the linear association of the MET CN detected by ddPCR and SNP 6.0 is strong (Pearson correlation = 0.867). In tumor models, the MET CN detected by ddPCR was significantly different between the MET gene amplification and non-amplification groups according to FISH (mean: 15.4 vs 2.1; P = 0.044). Given that MET gene amplification is defined as MET CN >5.5 by ddPCR, the concordance rate between ddPCR and FISH was 98.0%, and Cohen's kappa coefficient was 0.760 (95% CI, 0.498-1.000; P <0.001).

CONCLUSIONS

The results demonstrated that the ddPCR method has the potential to quantify the MET gene copy number with high precision and accuracy as compared with the results from SNP 6.0 and FISH in cancer cell lines and tumor samples, respectively.

Recent developments in receptor tyrosine kinases targeted anticancer therapy

Novel concepts and understanding of receptors lead to discoveries and optimization of many small molecules and antibodies as anti-cancerous drugs. Receptor tyrosine kinases (RTKs) are such a promising class of receptors under the investigation in past three decades. RTKs are one of the essential mediators of cell signaling mechanism for various cellular processes. Transformations such as overexpression, dysregulation, or mutations of RTKs may result into malignancy, and thus are an important target for anticancer therapy. Numerous subfamilies of RTKs, such as epidermal growth factor receptor, vascular endothelial growth factor receptor, fibroblast growth factor receptors, insulin-like growth factor receptor, and hepatocyte growth factor receptor, have been being investigated in recent years as target for anticancer therapy. The present review focuses several small molecules drugs as well as monoclonal antibodies targeting aforesaid subfamilies either approved or under investigation to treat the various cancers.

State of the art management of metastatic gastroesophageal cancer

The anatomical locations of upper gastrointestinal (GI) tumors have changed remarkably in the western world and reflect the increasing impact of obesity and gastroesophageal (GE) reflux rather than infectious etiologies. Incidence rates of GE tumors are rising rapidly and survival rates for patients with metastatic disease remain poor. Traditionally, cytotoxic chemotherapy has had some survival advantages but increasingly complex combination regimens are limited by toxicities. The advent of molecularly targeted therapy has provided additional options for patients with advanced disease including trastuzumab and ramucirumab. There has also been detailed molecular characterization of upper GI tumors which hopefully will result in improved tailoring of clinical trial design accounting for the heterogeneity inherent in GE tumors. While numerous targeted therapies are currently being studied in clinical trials, there is much excitement regarding the role of immunotherapy in GE cancers. Although further investigation is warranted, it represents a promising avenue for patients with advanced GE tumors.

Overexpression of PI3K p110α contributes to acquired resistance to MET inhibitor, in MET-amplified SNU-5 gastric xenografts

Gastric cancer is one of the most virulent malignant diseases and is the second leading cause of cancer mortality in the world. The receptor tyrosine kinase MET is constitutively activated in many gastric cancers and its expression is strictly required for survival of some gastric cancer cells. Targeting gastric cancers with amplified or abnormally activated MET may have therapeutic benefit based on nonclinical and emerging clinical findings. However, one of the major problems of therapies targeting tyrosine kinases is that many tumors are not responsive to treatment or eventually develop resistance to the drugs. This study aims to understand the mechanisms of MET resistance in gastric SNU-5 xenografts which developed resistance to PHA665752, a MET inhibitor, through long-period tyrosine kinase inhibitor exposure. In the current study, we found that PI3K p110α is overexpressed in PHA665752-resistant SNU-5 xenografts. These findings showed that high PI3K p110α expression contributes to tyrosine kinase inhibitor resistance. In addition, we reported the development of a carcinogen-induced gastric cancer model that recapitulates PI3K p110α expression in human disease, which will serve as a useful model to study PI3K p110α's biology and its effectiveness as a novel biomarker and a molecular target for gastric cancer. Ultimately, PI3K p110α represents a novel target for gastric cancer.

Tumor MET Expression and Gene Amplification in Chinese Patients with Locally Advanced or Metastatic Gastric or Gastroesophageal Junction Cancer

MET and its sole ligand, hepatocyte growth factor (HGF), are promising targets in gastric and gastroesophageal junction cancer. We evaluated whether MET protein expression or MET gene amplification is prognostic for overall survival (OS) in Chinese patients with advanced gastric or gastroesophageal junction cancer. Archival formalin-fixed, paraffin-embedded tumor samples from patients with unresectable locally advanced or metastatic gastric or gastroesophageal junction cancer enrolled in clinical trials at Peking University Cancer Hospital from 2008 to 2010 were assessed for MET and phospho-MET (p-MET) expression by immunohistochemistry and MET amplification by FISH. MET-positive expression was defined as membrane protein staining in ≥25% of tumor cells. MET amplification was defined as MET:centromere 7 ratio >2.0. We tested the association of MET status with clinical characteristics and OS, and also evaluated the association between expression and amplification. One hundred sixty-eight patients were eligible. Of the evaluable samples, 53 of 137 (39%) were MET positive, eight of 134 (6%) were p-MET positive, and eight of 113 (7%) were MET amplified. Neither MET expression nor MET amplification were associated with clinical characteristics, except Lauren classification (P = 0.04); MET amplification was associated with diffuse type. No significant OS difference was observed between MET-positive and MET-negative populations, regardless of first-line chemotherapy received. In 95 evaluable patients, MET expression was significantly associated with MET amplification (P < 0.001); all MET-amplified tumor samples showed some MET expression. In 96 evaluable patients, p-MET positivity was significantly associated with MET amplification (P < 0.001). Further evaluation in larger and independent sample sets is warranted to confirm our findings.

Improved diagnostics targeting c-MET in non-small cell lung cancer: expression, amplification and activation?

BACKGROUND

Several c-MET targeting inhibitory molecules have already shown promising results in the treatment of patients with Non-small Cell Lung Cancer (NSCLC). Combination of EGFR- and c-MET-specific molecules may overcome EGFR tyrosine kinase inhibitor (TKI) resistance. The aim of this study was to allow for the identification of patients who might benefit from TKI treatments targeting MET and to narrow in on the diagnostic assessment of MET.

METHODS

222 tumor tissues of patients with NSCLC were analyzed concerning c-MET expression and activation in terms of phosphorylation (Y1234/1235 and Y1349) using a microarray format employing immunohistochemistry (IHC). Furthermore, protein expression and MET activation was correlated with the amplification status by Fluorescence in Situ Hybridization (FISH).

RESULTS

Correlation was observed between phosphorylation of c-MET at Y1234/1235 and Y1349 (spearman correlation coefficient rs = 0.41; p < 0.0001). No significant correlation was shown between MET expression and phosphorylation (p > 0.05). c-MET gene amplification was detected in eight of 214 patients (3.7%). No significant association was observed between c-MET amplification, c-MET protein expression and phosphorylation.

CONCLUSION

Our data indicate, that neither expression of c-MET nor the gene amplification status might be the best way to select patients for MET targeting therapies, since no correlation with the activation status of MET was observed. We propose to take into account analyzing the phosphorylation status of MET by IHC to select patients for MET targeting therapies. Signaling of the receptor and the activation of downstream molecules might be more crucial for the benefit of therapeutics targeting MET receptor tyrosine kinases than expression levels alone.

c-Met targeting in advanced gastric cancer: An open challenge

Despite significant improvements in systemic chemotherapy over the last two decades, the prognosis of patients with advanced gastric and gastroesophageal junction adenocarcinoma (GC) remains poor. Because of molecular heterogeneity, it is essential to classify tumors based on the underlying oncogenic pathways and to develop targeted therapies acting on individual tumors. High-quality research and advances in technology have contributed to the elucidation of molecular pathways underlying disease progression and have stimulated many clinical studies testing target therapies in an advanced disease setting. In particular, strong preclinical evidence for the aberrant activation of the HGF/c-Met signaling pathways in GC cancers exists. This review will cover the c-Met pathway, the mechanisms of c-Met activation and the different strategies of its inhibition. Next, we will focus on the current state of the art in the clinical evaluation of c-Met-targeted therapies and the description of ongoing randomized trials with the idea that in this disease, high quality translational research to identify and validate biomarkers is a priority task.

From molecular classification to targeted therapeutics: the changing face of systemic therapy in metastatic gastroesophageal cancer

Histological classification of adenocarcinoma or squamous cell carcinoma for esophageal cancer or using the Lauren classification for intestinal and diffuse type gastric cancer has limited clinical utility in the management of advanced disease. Germline mutations in E-cadherin (CDH1) or mismatch repair genes (Lynch syndrome) were identified many years ago but given their rarity, the identification of these molecular alterations does not substantially impact treatment in the advanced setting. Recent molecular profiling studies of upper GI tumors have added to our knowledge of the underlying biology but have not led to an alternative classification system which can guide clinician's therapeutic decisions. Recently the Cancer Genome Atlas Research Network has proposed four subtypes of gastric cancer dividing tumors into those positive for Epstein-Barr virus, microsatellite unstable tumors, genomically stable tumors, and tumors with chromosomal instability. Unfortunately to date, many phase III clinical trials involving molecularly targeted agents have failed to meet their survival endpoints due to their use in unselected populations. Future clinical trials should utilize molecular profiling of individual tumors in order to determine the optimal use of targeted therapies in preselected patients.

Volitinib, a potent and highly selective c-Met inhibitor, effectively blocks c-Met signaling and growth in c-MET amplified gastric cancer patient-derived tumor xenograft models

PURPOSE

To investigate the incidence of cMET gene copy number changes and protein overexpression in Chinese gastric cancer (GC) and to preclinically test the hypothesis that the novel, potent and selective cMET small-molecule inhibitor volitinib, will deliver potent anti-tumor activity in cMET-dysregulated GC patient-derived tumor xenograft (PDX) models.

EXPERIMENTAL DESIGN

A range of assays were used and included; in vitro cell line panel screening and pharmacodynamic (PD) analysis, cMET fluorescence in-situ hybridization (FISH) and immunohistochemical (IHC) tissue microarray (TMA) analysis of Chinese GC (n = 170), and anti-tumor efficacy testing and PD analysis of gastric PDX models using volitinib.

RESULTS

The incidence of cMET gene amplification and protein overexpression within Chinese patient GC tumors was 6% and 13%, respectively. Volitinib displayed a highly selective profile across a gastric cell line panel, potently inhibiting cell growth only in those lines with dysregulated cMET (EC50 values 0.6 nM/L-12.5 nM/L). Volitinib treatment led to pharmacodynamic modulation of cMET signaling and potent tumor stasis in 3/3 cMET-dysregulated GC PDX models, but had negligible activity in a GC control model.

CONCLUSIONS

This study provides an assessment of tumor cMET gene copy number changes and protein overexpression incidence in a cohort of Chinese GC patients. To our knowledge, this is the first study to demonstrate anti-tumor efficacy in a panel of cMET-dysregulated gastric cancer PDX models, using a novel selective cMET-inhibitor (volitinib). Thus, the translational science presented here provides strong rationale for the investigation of volitinib as a therapeutic option for patients with GC tumors harboring amplified cMET.

Targeting receptor tyrosine kinases in gastric cancer

Molecularly targeted therapeutic agents are constantly being developed and have been shown to be effective in various clinical trials. One group of representative targeted oncogenic kinases, the receptor tyrosine kinases (RTKs), has been associated with gastric cancer development. Trastuzumab, an inhibitor of ERBB2, has been approved for the treatment of gastric cancer, although other receptor tyrosine kinases, such as epidermal growth factor receptor, vascular endothelial growth factor, platelet-derived growth factor receptor, c-Met, IGF-1R and fibroblast growth factor receptor 2, are also activated in gastric cancer. The promising results of the trastuzumab clinical trial for gastric cancer resulted in the approval of trastuzumab-based therapy as a first-line treatment for human epidermal growth factor receptor 2-positive patients. On the other hand, the trial examining bevacizumab in combination with conventional chemotherapy did not meet its primary goal of increasing the overall survival time of gastric cancer patients; however, a significantly higher response rate and a longer progression-free survival were observed in the bevacizumab arm of the trial. Other clinical trials, especially phase III trials that have tested drugs targeting RTKs, such as cetuximab, panitumumab, gefitinib, erlotinib, figitumumab, sorafenib, sunitinib and lapatinib, have shown that these drugs have modest effects against gastric cancer. This review summarizes the recent results from the clinical trials of molecularly targeted drugs and suggests that further improvements in the treatment of advanced gastric cancer can be achieved through the combination of conventional drugs with the new molecularly targeted therapies.

Role of the tumor microenvironment in the pathogenesis of gastric carcinoma

Gastric carcinoma (GC) is the 4^th most prevalent cancer and has the 2^nd highest cancer-related mortality rate worldwide. Despite the incidence of GC has decreased over the past few decades, it is still a serious health problem. Chronic inflammatory status of the stomach, caused by the infection of Helicobacter pylori (H. pylori) and through the production of inflammatory mediators within the parenchyma is suspected to play an important role in the initiation and progression of GC. In this review, the correlation between chronic inflammation and H. pylori infection as an important factor for the development of GC will be discussed. Major components, including tumor-associated macrophages, lymphocytes, cancer-associated fibroblasts, angiogenic factors, cytokines, and chemokines of GC microenvironment and their mechanism of action on signaling pathways will also be discussed. Increasing our understanding of how the components of the tumor microenviroment interact with GC cells and the signaling pathways involved could help identify new therapeutic and chemopreventive targets.

Paracrine activation of MET promotes peritoneal carcinomatosis in scirrhous gastric cancer

Scirrhous gastric cancer is associated with abundant stroma and frequently develops into peritoneal carcinomatosis with malignant ascites. Although malignant ascites is among the most deadly diseases worldwide, its molecular pathogenesis is poorly understood. We investigated the role of hepatocyte growth factor (HGF) in the production of peritoneal carcinomatosis with malignant ascites. We examined three scirrhous and three non-scirrhous human gastric cancer cell lines for the production of peritoneal carcinomatosis in vivo and responses to HGF in vitro. Furthermore, clinical scirrhous gastric cancer specimens were examined for HGF production. Among the six cell lines examined, only two scirrhous cell lines (NUGC4 and GCIY) produced peritoneal carcinomatosis with massive ascites after intraperitoneal injection in nude mice. Their proliferation was stimulated by exogenous HGF in vitro. On the other hand, a non-scirrhous cell line, MKN45, with MET amplification generated peritoneal tumors but not ascites. MET tyrosine kinase inhibitors, crizotinib and TAS-115, inhibited HGF-stimulated proliferation of NUGC4 and GCIY as well as constitutive proliferation of MKN45. Furthermore, crizotinib and TAS-115 prolonged the survival of mice bearing established tumors by NUGC4 or MKN45. In clinical specimens, HGF was markedly produced by stromal fibroblasts. Malignant ascitic fluids from patients with peritoneal carcinomatosis contained high levels of HGF. Our results strongly suggest that paracrine HGF-induced activation of MET-mediated signaling pathways plays an important role in the pathogenesis of peritoneal carcinomatosis in scirrhous gastric cancer. Thus, MET signaling pathway may be a potential therapeutic target for peritoneal carcinomatosis of gastric cancer, even without MET amplification.

C-Met as a prognostic marker in gastric cancer: a systematic review and meta-analysis

BACKGROUND

c-Met has been recognized as an important therapeutic target in gastric cancer, but the prognostic property of the c-Met status is still unclear. We aimed to characterize the prognostic effect of c-Met by systematic review and meta-analysis.

METHODS

We identified 15 studies assessing survival in gastric cancer by c-Met status. Effect measure of interest was hazard ratio (HR) for survival. Meta-regression was performed to estimate the relationship between HR and disease stage. Random-effects meta-analyses were used to account for heterogeneity.

RESULTS

15 eligible studies provided outcome data stratified by c-Met status in 2210 patients. Meta-analysis of the HRs indicated a significantly poorer Os in patients with high c-Met expression (average HR=2.112, 95%CI: 1.622-2.748). Subgroup analysis showed the prognostic effect of c-Met was identical in protein-level and gene-level based methodology. The same effect was also seen in Asian and Western ethnicity subgroup analysis. Meta-regression showed HR was not associated with disease stage.

CONCLUSIONS

Patients with tumors that harbor high c-Met expression are more likely to have a worse Os, with this prognostic effect independent of disease stage. c-Met status should be evaluated in clinical prognosis.

A c-Met inhibitor increases the chemosensitivity of cancer stem cells to the irinotecan in gastric carcinoma

Background:

Cancer stem cells (CSCs) may be postulated mediators of the chemoresistance. This study aimed to determine an effective signal inhibitor with effects on the proliferation of CSCs in combination with anticancer drugs.

Methods:

We used three gastric cancer cell lines and three side population (SP)-enriched CSC cell lines. We examined the combined effects of inhibitors against stemness signals, including c-Met inhibitor SU11274, and five anticancer drugs on the CSC proliferation and mRNA expression of chemoresistance-associated genes.

Results:

The IC₅₀ of irinotecan in SP-enriched CSC was 10.5 times higher than parent OCUM-2M cells, whereas that of oxaliplatin, taxol, gemcitabine, and 5-fluorouracil was 2.0, 2.8, 2.0, and 1.2, respectively. The SP cell lines had higher expression levels of UGT1A1, ABCG2, and ABCB1 than their parent cell lines. There was a synergistic antiproliferative effect with a combination of SU11274 and SN38 in SP cells, but not other inhibitors. The SU11274 significantly decreased the expression of UGT1A1, but not ABCG2 and ABCB1. The SN38 plus SU11274 group more effectively suppressed in vivo tumour growth by OCUM-2M/SP cells than either group alone.

Conclusion:

Cancer stem cells have chemoresistance to irinotecan. The c-Met inhibitor may be a promising target molecule for irinotecan-based chemotherapy of gastric cancer.

Expression of ST3GAL4 leads to SLe(x) expression and induces c-Met activation and an invasive phenotype in gastric carcinoma cells

Sialyl-Lewis X (SLe(x)) is a sialylated glycan antigen expressed on the cell surface during malignant cell transformation and is associated with cancer progression and poor prognosis. The increased expression of sialylated glycans is associated with alterations in the expression of sialyltransferases (STs). In this study we determined the capacity of ST3GAL3 and ST3GAL4 sialyltransferases to synthesize the SLe(x) antigen in MKN45 gastric carcinoma cells and evaluated the effect of SLe(x) overexpression in cancer cell behavior both in vitro and in vivo using the chicken chorioallantoic membrane (CAM) model. The activation of tyrosine kinase receptors and their downstream molecular targets was also addressed. Our results showed that the expression of ST3GAL4 in MKN45 gastric cancer cells leads to the synthesis of SLe(x) antigens and to an increased invasive phenotype both in vitro and in the in vivo CAM model. Analysis of phosphorylation of tyrosine kinase receptors showed a specific increase in c-Met activation. The characterization of downstream molecular targets of c-Met activation, involved in the invasive phenotype, revealed increased phosphorylation of FAK and Src proteins and activation of Cdc42, Rac1 and RhoA GTPases. Inhibition of c-Met and Src activation abolished the observed increased cell invasive phenotype. In conclusion, the expression of ST3GAL4 leads to SLe(x) antigen expression in gastric cancer cells which in turn induces an increased invasive phenotype through the activation of c-Met, in association with Src, FAK and Cdc42, Rac1 and RhoA GTPases activation.

SB365, Pulsatilla saponin D, targets c-Met and exerts antiangiogenic and antitumor activities

SB365, Pulsatilla saponin D isolated from the root of Pulsatilla koreana, has exhibited potential beneficial effects as a chemopreventive agent for critical health conditions including cancer. However, the molecular mechanisms underlying the activity of SB365 remain unknown. Here, we examined anticancer efficacy of SB365 against gastric cancer and its mechanism of action. SB365 effectively inhibited the growth of gastric cancer cells. Its apoptotic effect was accompanied by increased evidence of cleaved caspase-3 and poly(ADP ribose) polymerase. To elucidate the anticancer mechanism of SB365, we used an array of 42 different receptor tyrosine kinases (RTKs). Of the 42 different phospho-RTKs, SB365 strongly inhibited expression of activated c-mesenchymal-epithelial transition factor (c-Met) in gastric cancer cells. Also, the activation of the c-Met signal cascade components, including Akt and mammalian target of rapamycin, was inhibited by SB365 in a dose-dependent manner. In angiogenesis studies, SB365 inhibited tube formation in hepatocyte growth factor (HGF)-induced human umbilical vein endothelial cells and suppressed microvessel sprouting from the rat aortic ring, ex vivo, and blood vessel formation in the Matrigel plug assay in mice. In xenograft animal models, SB365 significantly delayed tumor growth in a dose-dependent manner. In tumor tissue, SB365 suppressed c-Met signaling, proliferation and angiogenesis and induced apoptosis. These findings suggest that SB365 docks at an allosteric site on c-Met and thereby targets c-Met signaling pathway, cell growth/angiogenesis inhibition and apoptosis induction. Therefore, SB365 may be a novel drug candidate for the treatment of gastric cancer.

Hepatocyte growth factor activator inhibitor type 1 is a suppressor of intestinal tumorigenesis

Hepatocyte growth factor activator inhibitor type 1 (HAI-1/SPINT1) is a membrane-bound serine protease inhibitor expressed on the surface of epithelial cells. Although HAI-1/SPINT1 is abundantly expressed in the intestinal epithelium, its role in intestinal tumorigenesis is not known. In this study, we investigated the role of Hai-1/Spint1 in intestinal tumorigenesis using mouse models. The membranous Hai-1/Spint1 immunoreactivity was decreased in murine Apc(Min/+) tumors and also in carcinogen (azoxymethane treatment followed by dextran sodium sulfate administration)-induced colon tumors compared with the adjacent non-neoplastic epithelium. The decreased immunoreactivity appeared to be due to sheddase activity of membrane-type 1 matrix metalloprotease. Then, we examined the effect of intestine-specific deletion of Spint1 gene on Apc(Min/+) mice. The loss of Hai-1/Spint1 significantly accelerated tumor formation in Apc(Min/+) mice and shortened their survival periods. Activation of HGF was enhanced in Hai-1/Spint1-deficient Apc(Min/+) intestine. Gene expression profiling revealed upregulation of the Wnt/β-catenin signaling circuit, claudin-2 expression, and angiogenesis not only in tumor tissue but also in the background mucosa without macroscopic tumors in Hai-1/Spint1-deficient Apc(Min/+) intestine. Intestinal deletion of Spint1 also enhanced the susceptibility to carcinogen-induced colon tumorigenicity of wild-type Apc mice. Our findings suggest that HAI-1/SPINT1 has a crucial role in suppressing intestinal tumorigenesis, which implies a novel link between epithelial cell surface serine protease inhibitors and protection from carcinogenic stimuli.

Loss of HGF activator inhibits foveolar hyperplasia induced by oxyntic atrophy without altering gastrin levels

Spasmolytic polypeptide/trefoil family factor 2 expressing metaplasia (SPEM) is induced by oxyntic atrophy and is known as a precancerous or paracancerous lesion. We now have sought to determine whether hepatocyte growth factor (HGF) influences the development of SPEM and oxyntic atrophy. DMP-777, a parietal cell ablating reagent, was administered to HGF activator (HGFA)-deficient mice and wild-type mice. Gastric mucosal lineage changes were analyzed in the DMP-777 treatment phase and recovery phase. Both wild-type and HGFA knockout mice showed SPEM, and there was no difference in SPEM development. However, after cessation of DMP-777, HGFA-deficient mice showed delayed recovery from SPEM compared with wild-type mice. Foveolar cell hyperplasia and the increase in proliferating cells after parietal cell loss were reduced in HGFA-deficient mice. The HGFA does not affect emergence of SPEM. However, the absence of HGFA signaling causes a delay in the recovery from SPEM to normal glandular composition. HGFA also promotes foveolar cell hyperplasia and mucosal cell proliferation in acute oxyntic injury.

Bioinformatics analysis with graph-based clustering to detect gastric cancer-related pathways

Despite a dramatic reduction in incidence and mortality rates, gastric cancer still remains one of the most common malignant tumors worldwide, especially in China. We sought to identify a set of discriminating genes that could be used for characterization and prediction of response to gastric cancer. Using bioinformatics analysis, two gastric cancer datasets, GSE19826 and GSE2685, were merged to find novel target genes and domains to explain pathogenesis; we selected differentially expressed genes in these two datasets and analyzed their correlation in order to construct a network. This network was examined to find graph clusters and related significant pathways. We found that ALDH2 and CCNB1 were associated with gastric cancer. We also mined for the underlying molecular mechanisms involving these differently expressed genes. We found that ECM-receptor interaction, focal adhesion, and cell cycle were among the significantly associated pathways. We were able to detect genes and pathways that were not considered in previous research on gastric cancer, indicating that this approach could be an improvement on the investigative mechanisms for finding genetic associations with disease.

MET: a promising anticancer therapeutic target

The MET pathway is dysregulated in many human cancers and promotes tumour growth, invasion and dissemination. Abnormalities in MET signalling have been reported to correlate with poor clinical outcomes and drug resistance in patients with cancer. Thus, MET has emerged as an attractive target for cancer therapy. Several MET inhibitors have been introduced into the clinic, and are currently in all phases of clinical trials. In general, initial results from these studies indicate only a modest benefit in unselected populations. In this Review, we discuss current challenges in developing MET inhibitors--including identification of predictive biomarkers--as well as the most-efficient ways to combine these drugs with other targeted agents or with classic chemotherapy or radiotherapy.

Genetic susceptibility on CagA-interacting molecules and gene-environment interaction with phytoestrogens: a putative risk factor for gastric cancer

OBJECTIVES

To evaluate whether genes that encode CagA-interacting molecules (SRC, PTPN11, CRK, CRKL, CSK, c-MET and GRB2) are associated with gastric cancer risk and whether an interaction between these genes and phytoestrogens modify gastric cancer risk.

METHODS

In the discovery phase, 137 candidate SNPs in seven genes were analyzed in 76 incident gastric cancer cases and 322 matched controls from the Korean Multi-Center Cancer Cohort. Five significant SNPs in three genes (SRC, c-MET and CRK) were re-evaluated in 386 cases and 348 controls in the extension phase. Odds ratios (ORs) for gastric cancer risk were estimated adjusted for age, smoking, H. pylori seropositivity and CagA strain positivity. Summarized ORs in the total study population (462 cases and 670 controls) were presented using pooled- and meta-analysis. Plasma concentrations of phytoestrogens (genistein, daidzein, equol and enterolactone) were measured using the time-resolved fluoroimmunoassay.

RESULTS

SRC rs6122566, rs6124914, c-MET rs41739, and CRK rs7208768 showed significant genetic effects for gastric cancer in both the pooled and meta-analysis without heterogeneity (pooled OR = 3.96 [95% CI 2.05-7.65], 1.24 [95% CI = 1.01-1.53], 1.19 [95% CI = 1.01-1.41], and 1.37 [95% CI = 1.15-1.62], respectively; meta OR = 4.59 [95% CI 2.74-7.70], 1.36 [95% CI = 1.09-1.70], 1.20 [95% CI = 1.00-1.44], and 1.32 [95% CI = 1.10-1.57], respectively). Risk allele of CRK rs7208768 had a significantly increased risk for gastric cancer at low phytoestrogen levels (p interaction<0.05).

CONCLUSIONS

Our findings suggest that SRC, c-MET and CRK play a key role in gastric carcinogenesis by modulating CagA signal transductions and interaction between CRK gene and phytoestrogens modify gastric cancer risk.

Targeted therapy in the management of advanced gastric cancer: are we making progress in the era of personalized medicine?

BACKGROUND

Gastric cancer is one of the leading causes of cancer death. With greater understanding of the molecular basis of carcinogenesis, targeted agents have led to a modest improvement in the outcome of advanced gastric cancer (AGC) patients.

METHODS AND RESULTS

We conducted an overview of the published evidence regarding the use of targeted therapy in AGC patients. Thus far, the human epidermal growth factor receptor (HER) pathway, angiogenic pathway, and phosphatidylinositol-3-kinase (PI3K)-Akt-mammalian target of rapamycin pathway have emerged as potential avenues for targeted therapy in AGC patients. The promising efficacy results of the Trastuzumab for Gastric Cancer trial led to the approved use of trastuzumab-based therapy as first-line treatment for patients with HER-2+ AGC. On the other hand, the Avastin® in Gastric Cancer trial evaluating bevacizumab in combination with chemotherapy did not meet its primary endpoint of a longer overall survival duration despite a significantly higher response rate and longer progression-free survival time in patients in the bevacizumab arm. Phase III data are awaited for other targeted agents, including cetuximab, panitumumab, lapatinib, and everolimus.

CONCLUSION

Recent progress in targeted therapy development for AGC has been modest. Further improvement in the outcome of AGC patients will depend on the identification of biomarkers in different patient populations to facilitate the understanding of gastric carcinogenesis, combining different targeted agents with chemotherapy, and unraveling new molecular targets for therapeutic intervention.

Targeting MET in cancer: rationale and progress

Uncontrolled cell survival, growth, angiogenesis and metastasis are essential hallmarks of cancer. Genetic and biochemical data have demonstrated that the growth and motility factor hepatocyte growth factor/scatter factor (HGF/SF) and its receptor, the tyrosine kinase MET, have a causal role in all of these processes, thus providing a strong rationale for targeting these molecules in cancer. Parallel progress in understanding the structure and function of HGF/SF, MET and associated signalling components has led to the successful development of blocking antibodies and a large number of small-molecule MET kinase inhibitors. In this Review, we discuss these advances, as well as results from recent clinical studies that demonstrate that inhibiting MET signalling in several types of solid human tumours has major therapeutic value.

c-Met upregulates aquaporin 3 expression in human gastric carcinoma cells via the ERK signalling pathway

Aquaporin 3 (AQP3) and c-Met are both overexpressed in human gastric carcinoma and highly associated with its metastasis and invasion. However, it still remains unknown whether c-Met and AQP3 correlate with each other. Herein, we demonstrated that c-Met expression in gastric cancer tissues significantly correlated with differentiation, lymph node metastasis and lymphovascular invasion, and c-Met exhibited marked association with AQP3 expression. Immunoblotting assays showed that hHGF phosphorylated c-Met in SGC7901 and AGS cells and upregulated AQP3 expression in a dose- or time-dependent way. RNAi against c-Met reduced total c-Met levels by about two thirds in both AGS and SGC7901 cells and attenuated hHGF-induced AQP3 expression significantly. In vitro migration and proliferation assays showed that siRNA against AQP3 noticeably restrained HGF-promoted migration and proliferation of these cells. Furthermore, Immunoblotting studies revealed that HGF induced phosphorylation of ERK, and pre-treatment with U0126, a MAPK/ERK inhibitor, partially inhibited hHGF-induced increase in AQP3 expression. Together, these data provide initial evidence that c-Met regulates the expression of AQP3 via the ERK signalling pathway in gastric carcinoma. These findings assist in understanding the mechanism of growth and invasion of gastric carcinoma, and provide a possible strategy for the inhibition of gastric tumor metastasis.

MET activation mediates resistance to lapatinib inhibition of HER2-amplified gastric cancer cells

HER2 amplification is found in more than 15% of gastric cancers and is associated with poor clinical outcome. Lapatinib, a dual HER2 and epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor, has shown promising in vitro results in treating HER2(+) cancer cells. However, several studies have shown that activation of alternative receptor tyrosine kinases can mediate resistance to HER-targeted therapy. Here, we investigated whether activated MET can confer resistance to lapatinib inhibition of gastric cancer cells. A panel of gastric cancer cell lines was treated with lapatinib, and we observed that cell proliferation was reduced by 70% and that the degree of HER2 amplification corresponds to sensitivity to lapatinib. Immunoblotting analysis indicated that phosphorylation of HER2, EGFR, MET, AKT, and extracellular signal-regulated kinase was inhibited by lapatinib and presumably led to cell-cycle arrest as observed with flow cytometry. Hepatocyte growth factor (HGF) activation of MET receptors rescued cells from lapatinib-induced growth inhibition by restimulating the downstream pathways and restoring normal cell-cycle progression. This rescue effect could be abrogated by inhibiting MET with PHA-665752 (a highly specific MET inhibitor) or downregulating MET expression with short interfering RNA. No synergy in growth inhibition was observed when cells were treated with a combination of lapatinib and PHA-665752. Repeat studies using insulin-like growth factor 1 and fibroblast growth factor 3 could not uniformly rescue the lapatinib-treated gastric cancer cells. In conclusion, HGF/MET-mediated resistance to lapatinib is a novel mechanism of resistance to HER2-targeted agents in gastric cancer cells. Development of inhibitors targeting multiple receptors or common downstream signaling proteins merits further investigation.

Molecular targeted agents for gastric and gastroesophageal junction cancer

Despite recent improvements in surgical techniques and chemotherapy, advanced cancers of the stomach and gastroesophageal junction (GEJ) continue to have poor clinical outcomes. However, molecules intimately related to cancer cell proliferation, invasion, and metastasis have been studied as candidates for molecular targeted agents. Target molecules, such as the epidermal growth factor receptor, vascular endothelial growth factor receptor, and P13k/Akt/mTor pathway, as well as the insulin-like growth factor receptor, c-Met pathways, fibroblast growth factor receptor, and other pathways are considered to be promising candidates for molecular targeted therapy for gastric and GEJ cancer. In this review we focus on the recent developments in targeting relevant pathways in these types of cancer.

Genetic activation of the MET pathway and prognosis of patients with high-risk, radically resected gastric cancer

PURPOSE

To investigate whether prognosis of patients with high-risk gastric cancer may depend on MET copy number gain (CNG) or an activating truncation within a deoxyadenosine tract element (DATE) in the promoter region of the MET ligand HGF.

PATIENTS AND METHODS

A single-institution cohort of 230 patients with stage II/III gastric cancer was studied. Formalin-fixed paraffin-embedded tumor specimens were used for DNA extraction. Quantitative polymerase chain reaction (qPCR) for MET CNG and sequencing for HGF DATE truncation (< 25 deoxyadenosines instead of 30) were used. Results were analyzed for association with disease-free survival (DFS) and overall survival (OS). To assess the reliability of the qPCR measurement, a random sample of cases was reanalyzed using an alternative assay (fluorescent in situ hybridization [FISH]) with calculation of the intracorrelation coefficient (ICC).

RESULTS

In 216 assessable patients, MET CNG five or more copies and homozygous HGF-truncated DATE occurred in 21 patients (10%) and 30 patients (13%), respectively. Patients with MET CNG five or more copies (MET-positive) showed significantly worse prognosis with multivariate hazard ratio (HR) of 3.02 (95% CI, 1.71 to 5.33; P < .001) for DFS and multivariate HR of 2.91 (95% CI, 1.65 to 5.11; P < .001) for OS. The agreement between qPCR and FISH was high, with ICC = 0.9% (95% CI, 0.81% to 0.95%; the closer the ICC is to 1, the greater is the agreement). HGF-truncated DATE did not show relevant prognostic effect.

CONCLUSION

In this study, qPCR revealed approximately 10% of white patients with gastric cancer harboring MET CNG of five or more copies. This marker was significantly associated with unfavorable prognosis. This information is relevant to the current clinical development of anti-MET compounds.

Regulation of microRNA expression by hepatocyte growth factor in human head and neck squamous cell carcinoma

Hepatocyte growth factor (HGF) is a multifunctional molecule that acts as mitogen, motogen, and/or morphogen in a variety of cells. MET, a specific receptor tyrosine kinase for HGF, is upregulated in various tumors including squamous cell carcinoma of the human head and neck (HNSCC), but how HGF affects the expression of downstream functional genes has not yet been elucidated in detail. In the present study, we examined the expression of microRNA (miRNA), non-coding small RNA that regulate cell proliferation and functions by interfering with the translation of target mRNA, with or without HGF stimulation in HNSCC cell line HSC3. Among several miRNAs, in which the expression was altered after HGF stimulation, we focused on miR-200c and miR-27b, both of which were drastically downregulated after HGF stimulation. Expression of ZEB1, a target mRNA for miR-200c, was upregulated 3 and 6 h after HGF stimulation, and that of E-cadherin, a downstream molecule of ZEB1, was downregulated 12 h after HGF stimulation. Expression of ST14/matriptase, an enzyme for extracellular matrix (ECM) degradation and HGF activation and a target mRNA for miR-27b, was drastically upregulated in the protein level after HGF stimulation, although it was not statistically altered in the mRNA level. These results suggest that miR-200c and miR-27b downregulated by HGF might play an important role in epithelial-mesenchymal transition mediated by ZEB1/E-cadherin and ECM degradation and HGF autoactivation mediated by ST14/matriptase, respectively. Altered expression of miRNA directly regulated by HGF might contribute enhanced progressive and invasive characteristics of HNSCC by regulating the translation of HGF-induced functional molecules.

Co-overexpression of Met and hepatocyte growth factor promotes systemic metastasis in NCI-H460 non-small cell lung carcinoma cells

Complete resection of early-stage non-small cell lung cancer (NSCLC) is potentially curative, yet approximately 50% of patients are at risk for developing metastatic recurrence. Met, the receptor for hepatocyte growth factor (HGF) is a receptor tyrosine kinase with demonstrated roles in regulating cellular proliferation, motility, morphogenesis, and apoptosis. Met receptor and its ligand, HGF, are commonly overexpressed in NSCLC, and their overexpression has been associated with poor prognosis, which could potentially involve a paracrine and/or autocrine activation loop. However, there is as yet no direct evidence that HGF-Met signaling directly promotes metastasis in NSCLC cells. Using retroviral transduction, we overexpressed the human c-met and hgf complementary DNA, alone or in combination in the NCI-H460 human large cell carcinoma cell line. The HGF/Met co-overexpressing (H460-HGF/Met) cells demonstrated enhanced tumorigenicity in xenograft SCID mice. When these cells are implanted orthotopically into the lungs of nude rats, only the H460-HGF/Met cells showed higher spontaneous metastases to distant organs including bone, brain, and kidney. These results provide evidence that autocrine overactivation of the Met- HGF loop enhances systemic metastases in NSCLC. Targeted interference of this loop may potentially be an effective adjuvant therapy to improve survival of early-stage NSCLC patients.

Gastric cancer in the era of molecularly targeted agents: current drug development strategies

Gastric cancer is the second most common cause of cancer death worldwide with approximately one million cases diagnosed annually. Despite considerable improvements in surgical techniques, innovations in clinical diagnostics and the development of new chemotherapy regimens, the clinical outcome for patients with advanced gastric cancer and cancer of the GEJ is generally poor with 5-year survival rates ranging between 5 and 15%. The understanding of cancer relevant events has resulted in new therapeutic strategies, particularly in developing of new molecular targeted agents. These agents have the ability to target a variety of cancer relevant receptors and downstream pathways including the epidermal growth factor receptor (EGFR), the vascular endothelial growth factor receptor (VEGFR), the insulin-like growth factor receptor (IGFR), the c-Met pathway, cell-cycle pathways, and down-stream signalling pathways such as the Akt-PI3k-mTOR pathway. In the era of new molecularly targeted agents this review focuses on recent developments of targeting relevant pathways involved in gastric cancer and cancer of the GEJ.

Phosphorylated hepatocyte growth factor receptor/c-Met is associated with tumor growth and prognosis in patients with bladder cancer: correlation with matrix metalloproteinase-2 and -7 and E-cadherin

Hepatocyte growth factor receptor/c-Met is associated with malignant aggressiveness and survival in various cancers including bladder cancer. Although phosphorylation of hepatocyte growth factor receptor/c-Met is essential for its function, the pathologic significance of phosphorylated hepatocyte growth factor receptor/c-Met in bladder cancer remains elusive. We investigated the clinical significance of its expression, and its correlation with cancer cell progression-related molecules. The expression levels of 2 tyrosine residues of hepatocyte growth factor receptor/c-Met (pY1234/1235 and pY1349) were examined immunohistochemically in 133 specimens with nonmetastatic bladder cancer. We also investigated their correlation with matrix metalloproteinase-1, -2, -7, and -14; urokinase-type plasminogen activator; E-cadherin; CD44 standard, variant 3, and variant 6; and vascular endothelial growth factor. Expression of phosphorylated hepatocyte growth factor receptor/c-Met was detected in cancer cells, but was rare in normal urothelial cells. Although hepatocyte growth factor receptor/c-Met, pY1234/1235 hepatocyte growth factor receptor/c-Met, and pY1349 hepatocyte growth factor receptor/c-Met were associated with pT stage, multivariate analysis identified pY1349 hepatocyte growth factor receptor/c-met expression only as a significant factor for high pT stage. Expression of pY1349 hepatocyte growth factor receptor/c-Met was a marker of metastasis and (P = .001) and cause-specific survival (P = .003). Expressions of matrix metalloproteinase-2, matrix metalloproteinase-7, and E-cadherin correlated with pY1349 hepatocyte growth factor receptor/c-Met expression. Our results demonstrated that pY1349 hepatocyte growth factor receptor/c-Met plays an important role in tumor development, and its expression is a significant predictor of metastasis and survival of patients with bladder cancer. The results suggest that these activities are mediated, at least in part, by matrix metalloproteinase-2, matrix metalloproteinase-7, and E-cadherin.