Lung cancer cell lines harboring MET gene amplification are dependent on Met for growth and survival

Fibroblast growth factor (FGF) and FGF receptor-mediated autocrine signaling in non-small-cell lung cancer cells

Despite widespread expression of epidermal growth factor (EGF) receptors (EGFRs) and EGF family ligands in non-small-cell lung cancer (NSCLC), EGFR-specific tyrosine kinase inhibitors (TKIs) such as gefitinib exhibit limited activity in this cancer. We propose that autocrine growth signaling pathways distinct from EGFR are active in NSCLC cells. To this end, gene expression profiling revealed frequent coexpression of specific fibroblast growth factors (FGFs) and FGF receptors (FGFRs) in NSCLC cell lines. It is noteworthy that FGF2 and FGF9 as well as FGFR1 IIIc and/or FGFR2 IIIc mRNA and protein are frequently coexpressed in NSCLC cell lines, especially those that are insensitive to gefitinib. Specific silencing of FGF2 reduced anchorage-independent growth of two independent NSCLC cell lines that secrete FGF2 and coexpress FGFR1 IIIc and/or FGFR2 IIIc. Moreover, a TKI [(+/-)-1-(anti-3-hydroxy-cyclopentyl)-3-(4-methoxy-phenyl)-7-phenylamino-3,4-dihydro-1H-pyrimido-[4,5-d]pyrimidin-2-one (RO4383596)] that targets FGFRs inhibited basal FRS2 and extracellular signal-regulated kinase phosphorylation, two measures of FGFR activity, as well as proliferation and anchorage-independent growth of NSCLC cell lines that coexpress FGF2 or FGF9 and FGFRs. By contrast, RO4383596 influenced neither signal transduction nor growth of NSCLC cell lines lacking FGF2, FGF9, FGFR1, or FGFR2 expression. Thus, FGF2, FGF9 and their respective high-affinity FGFRs comprise a growth factor autocrine loop that is active in a subset of gefitinib-insensitive NSCLC cell lines.

Hepatocyte growth factor induces gefitinib resistance of lung adenocarcinoma with epidermal growth factor receptor-activating mutations

Lung cancer with epidermal growth factor receptor (EGFR)-activating mutations responds favorably to the EGFR tyrosine kinase inhibitors gefitinib and erlotinib. However, 25% to 30% of patients with EGFR-activating mutations show intrinsic resistance, and the responders invariably acquire resistance to gefitinib. Here, we showed that hepatocyte growth factor (HGF), a ligand of MET oncoprotein, induces gefitinib resistance of lung adenocarcinoma cells with EGFR-activating mutations by restoring the phosphatidylinositol 3-kinase/Akt signaling pathway via phosphorylation of MET, but not EGFR or ErbB3. Strong immunoreactivity for HGF in cancer cells was detected in lung adenocarcinoma patients harboring EGFR-activating mutations, but no T790M mutation or MET amplification, who showed intrinsic or acquired resistance to gefitinib. The findings indicate that HGF-mediated MET activation is a novel mechanism of gefitinib resistance in lung adenocarcinoma with EGFR-activating mutations. Therefore, inhibition of HGF-MET signaling may be a considerable strategy for more successful treatment with gefitinib.

Expression and mutational analysis of MET in human solid cancers

MET receptor tyrosine kinase and its ligand hepatocyte growth factor (HGF) regulate a variety of cellular functions, many of which can be dysregulated in human cancers. Activated MET signaling can lead to cell motility and scattering, angiogenesis, proliferation, branching morphogenesis, invasion, and eventual metastasis. We performed systematic analysis of the expression of the MET receptor and its ligand HGF in tumor tissue microarrays (TMA) from human solid cancers. Standard immunohistochemistry (IHC) and a computerized automated scoring system were used. DNA sequencing for MET mutations in both nonkinase and kinase domains was also performed. MET was differentially overexpressed in human solid cancers. The ligand HGF was widely expressed in both tumors, primarily intratumoral, and nonmalignant tissues. The MET/HGF likely is functional and may be activated in autocrine fashion in vivo. MET and stem cell factor (SCF) were found to be positively stained in the bronchioalevolar junctions of lung tumors. A number of novel mutations of MET were identified, particularly in the extracellular semaphorin domain and the juxtamembrane domain. MET-HGF pathway can be assayed in TMAs and is often overexpressed in a wide variety of human solid cancers. MET can be activated through overexpression, mutation, or autocrine signaling in malignant cells. Mutations in the nonkinase regions of MET might play an important role in tumorigenesis and tumor progression. MET would be an important therapeutic antitumor target to be inhibited, and in lung cancer, MET may represent a cancer early progenitor cell marker.

HER kinase activation confers resistance to MET tyrosine kinase inhibition in MET oncogene-addicted gastric cancer cells

Tumor cells with genomic amplification of MET display constitutive activation of the MET tyrosine kinase, which renders them highly sensitive to MET inhibition. Several MET inhibitors have recently entered clinical trials; however, as with other molecularly targeted agents, resistance is likely to develop. Therefore, elucidating possible mechanisms of resistance is of clinical interest. We hypothesized that collateral growth factor receptor pathway activation can overcome the effects of MET inhibition in MET-amplified cancer cells by reactivating key survival pathways. Treatment of MET-amplified GTL-16 and MKN-45 gastric cancer cells with the highly selective MET inhibitor PHA-665752 abrogated MEK/mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K)/AKT signaling, resulting in cyclin D1 loss and G(1) arrest. PHA-665752 also inhibited baseline phosphorylation of epidermal growth factor receptor (EGFR) and HER-3, which are transactivated via MET-driven receptor cross-talk in these cells. However, MET-independent HER kinase activation using EGF (which binds to and activates EGFR) or heregulin-beta1 (which binds to and activates HER-3) was able to overcome the growth-inhibitory effects of MET inhibition by restimulating MEK/MAPK and/or PI3K/AKT signaling, suggesting a possible escape mechanism. Importantly, dual inhibition of MET and HER kinase signaling using PHA-665752 in combination with the EGFR inhibitor gefitinib or in combination with inhibitors of MEK and AKT prevented the above rescue effects. Our results illustrate that highly targeted MET tyrosine kinase inhibition leaves MET oncogene-"addicted" cancer cells vulnerable to HER kinase-mediated reactivation of the MEK/MAPK and PI3K/AKT pathways, providing a rationale for combined inhibition of MET and HER kinase signaling in MET-amplified tumors that coexpress EGFR and/or HER-3.

MET increased gene copy number and primary resistance to gefitinib therapy in non-small-cell lung cancer patients

BACKGROUND

MET amplification has been detected in approximately 20% of non-small-cell lung cancer patients (NSCLC) with epidermal growth factor receptor (EGFR) mutations progressing after an initial response to tyrosine kinase inhibitor (TKI) therapy.

PATIENTS AND METHODS

We analyzed MET gene copy number using FISH in two related NSCLC cell lines, one sensitive (HCC827) and one resistant (HCC827 GR6) to gefitinib therapy and in two different NSCLC patient populations: 24 never smokers or EGFR FISH-positive patients treated with gefitinib (ONCOBELL cohort) and 182 surgically resected NSCLC not exposed to anti-EGFR agents.

RESULTS

HCC827 GR6-resistant cell line displayed MET amplification, with a mean MET copy number >12, while sensitive HCC827 cell line had a mean MET copy number of 4. In the ONCOBELL cohort, no patient had gene amplification and MET gene copy number was not associated with outcome to gefitinib therapy. Among the surgically resected patients, MET was amplified in 12 cases (7.3%) and only four (2.4%) had a higher MET copy number than the resistant HCC827 GR6 cell line.

CONCLUSIONS

MET gene amplification is a rare event in patients with advanced NSCLC. The development of anti-MET therapeutic strategies should be focused on patients with acquired EGFR-TKI resistance.

Nonredundant functions for tumor protein D52-like proteins support specific targeting of TPD52

PURPOSE

Tumor protein D52 (TPD52 or D52) is frequently overexpressed in breast and other cancers and present at increased gene copy number. It is, however, unclear whether D52 amplification and overexpression target specific functional properties of the encoded protein.

EXPERIMENTAL DESIGN

The expression of D52-like genes and MAL2 was compared in breast tissues using quantitative reverse transcription-PCR. The functions of human D52 and D53 genes were then compared by stable expression in BALB/c 3T3 fibroblasts and transient gene knockdown in breast carcinoma cell lines. In situ D52 and MAL2 protein expression was analyzed in breast tissue samples using tissue microarray sections.

RESULTS

The D52 (8q21.13), D54 (20q13.33), and MAL2 (8q24.12) genes were significantly overexpressed in breast cancer tissue (n = 95) relative to normal breast (n = 7; P </= 0.005) unlike the D53 gene (6q22.31; P = 0.884). Subsequently, D52-expressing but not D53-expressing 3T3 cell lines showed increased proliferation and anchorage-independent growth capacity, and reduced D52 but not D53 expression in SK-BR-3 cells significantly increased apoptosis. High D52 but not MAL2 expression was significantly associated with reduced overall survival in breast carcinoma patients (log-rank test, P < 0.001; n = 357) and was an independent predictor of survival (hazard ratio, 2.274; 95% confidence interval, 1.228-4.210; P = 0.009; n = 328).

CONCLUSION

D52 overexpression in cancer reflects specific targeting and may contribute to a more proliferative, aggressive tumor phenotype in breast cancer.

Heat shock protein 90 inhibition in lung cancer

The heat shock protein 90 (Hsp90) chaperone is required for the conformational maturation and stability of multiple oncogenic kinases that drive signal transduction and proliferation of lung cancer cells. The recent demonstration that mutant epidermal growth factor receptor is an Hsp90 client, irrespective of the presence of the secondary threonine-to-methionine amino acid substitution mutation at position 790 mediating anilinoquinazoline resistance, suggests Hsp90 inhibition as a novel strategy against this group of lung cancers. The rarer epidermal growth factor receptors harboring exon 20 insertions and vIII mutations are also Hsp90 clients. Lung cancers may also be driven by mutant ErbB2, mutant B-Raf, or mutant or overexpressed c-Met, all of which are also degraded on Hsp90 inhibition. Hsp90 inhibitors may be synergistic with other drugs that disrupt chaperone function, including inhibitors of histone deacetylase 6 and the proteasome and agents that inhibit Hsp70 function. Hsp90 plays a unique antiapoptotic role in small cell lung cancer cells, so that Hsp90 inhibition results in substantial cell death in both chemosensitive and chemoresistant small cell lung cancer cell lines. Clinically, the geldanamycin compounds are the most mature, with manageable toxic effects. Several new classes of Hsp90 inhibitors are emerging, including purines and pyrazoles that have entered phase 1 trials. The available data suggest that Hsp90 inhibitors should be evaluated in multiple lung cancer subsets.

Role of cMET expression in non-small-cell lung cancer patients treated with EGFR tyrosine kinase inhibitors

BACKGROUND

Approximately 10% of unselected non-small-cell lung cancer (NSCLC) patients responded to the epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) treatment. However, resistance mechanisms are not well understood. We evaluated several potential biological markers of intrinsic EGFR-TKIs-resistance in NSCLC.

MATERIALS AND METHODS

pAKT, pERK, cSRC, E-cadherin, cMET[pY1003], cMET[pY1230/1234/1235], and cMET[pY1349] immunohistochemistry, cMET FISH analysis, and EGFR-, KRAS-, and cMET mutation analysis were carried out on tumor samples from 51 gefitinib-treated NSCLC patients. Biological parameters and survival end points were compared by univariate and multivariate analyses. cMET expression was also investigated in two additional series of patients. The in vitro antiproliferative activity of gefitinib alone or in combination with hepatocyte growth factor and the cMET antibody DN-30 was assessed in NSCLC cells.

RESULTS

EGFR19 deletion and pAKT expression were significantly associated with response (P < 0.0001) and longer time to progression (TTP) (P = 0.007), respectively. Strong cMET[pY1003] membrane immunoreactivity was expressed in 6% of 149 tumors analyzed and was significantly associated with progressive disease (P = 0.019) and shorter TTP (P = 0.041). In vitro, the DN-30 combination synergistically (CI < 1) enhanced gefitinib-induced growth inhibition in all cMET[pY1003]-expressing cell lines studied.

CONCLUSIONS

Activated cMET[pY1003] appears to be a marker of primary gefitinib resistance in NSCLC patients. cMET may be a target in treatment of NSCLC.

MET as a target for treatment of chest tumors

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

Drug development of MET inhibitors: targeting oncogene addiction and expedience

The MET tyrosine kinase stimulates cell scattering, invasion, protection from apoptosis and angiogenesis, thereby acting as a powerful expedient for cancer dissemination. MET can also be genetically selected for the long-term maintenance of the primary transformed phenotype, and some tumours appear to be dependent on (or 'addicted' to) sustained MET activity for their growth and survival. Because of its dual role as an adjuvant, pro-metastatic gene for some tumour types and as a necessary oncogene for others, MET is a versatile candidate for targeted therapeutic intervention. Here we discuss recent progress in the development of molecules that inhibit MET function and consider their application in a subset of human tumours that are potentially responsive to MET-targeted therapies.

MET gene copy number in non-small cell lung cancer: molecular analysis in a targeted tyrosine kinase inhibitor naïve cohort

INTRODUCTION

Recent clinical success of epidermal growth factor (EGFR)-tyrosine kinase inhibitors (TKIs) in non-small cell lung cancer (NSCLC) have raised hopes that targeting other deregulated growth factor signaling, such as the hepatocyte growth factor/MET pathway, will lead to new therapeutic options for NSCLC. Furthermore, NSCLC present secondary EGFR-TKIs resistance related to exons 20 and 19 EGFR mutations or more recently to MET amplification. The aim of this study was to determine MET copy number related to EGFR copy number and K-Ras mutations in a targeted TKI naive NSCLC cohort.

METHODS

We investigated 106 frozen tumors from surgically resected NSCLC patients. Genes copy number of MET and EGFR were assessed by quantitative relative real-time polymerase chain reaction and K-Ras mutations by sequencing.

RESULTS

MET is amplified in 22 cases (21%) and deleted in nine cases (8.5%). EGFR is amplified in 31 cases (29%). K-Ras is mutated in 11 cases (10.5%). As observed for EGFR amplification, MET amplification is never associated with K-Ras mutation. MET amplification could be associated with EGFR amplification. MET amplification is not related to clinical and pathologic features. MET amplification and EGFR amplification showed a trend toward poor prognosis in adenocarcinomas.

CONCLUSION

In EGFR-TKIs naive NSCLC patients, MET amplification is a frequent event, which could be associated with EGFR amplification, but not with K-Ras mutation. MET amplification may identify a subset of NSCLC for new targeted therapy. It will also be important to evaluate MET copy number to properly interpret future clinical trials.

MicroRNA miR-199a* regulates the MET proto-oncogene and the downstream extracellular signal-regulated kinase 2 (ERK2)

MicroRNAs (miRNAs) constitute a class of small noncoding RNAs that play important roles in a variety of biological processes including development, apoptosis, proliferation, and differentiation. Here we show that the expression of miR-199a and miR-199a* (miR-199a/a*), which are processed from the same precursor, is confined to fibroblast cells among cultured cell lines. The fibroblast-specific expression pattern correlated well with methylation patterns: gene loci on chromosome 1 and 19 were fully methylated in all examined cell lines but unmethylated in fibroblasts. Transfection of miR-199a and/or -199a* mimetics into several cancer cell lines caused prominent apoptosis with miR-199a* being more pro-apoptotic. The mechanism underlying apoptosis induced by miR-199a was caspase-dependent, whereas a caspase-independent pathway was involved in apoptosis induced by miR-199a* in A549 cells. By employing microarray and immunoblotting analyses, we identified the MET proto-oncogene as a target of miR-199a*. Studies with a luciferase reporter fused to the 3'-untranslated region of the MET gene demonstrated miR-199a*-mediated down-regulation of luciferase activity through a binding site of miR-199a*. Interestingly, extracellular signal-regulated kinase 2 (ERK2) was also down-regulated by miR-199a*. Coordinated down-regulation of both MET and its downstream effector ERK2 by miR-199a* may be effective in inhibiting not only cell proliferation but also motility and invasive capabilities of tumor cells.

c-Met gene amplification is associated with advanced stage colorectal cancer and liver metastases

The c-Met proto-oncogene encodes a receptor tyrosine kinase (TK) that promotes invasive tumor growth and metastasis. Recent studies show that the presence of c-Met gene amplification is predictive for selective c-Met TK inhibitors in gastric cancer and lung cancer. In this study, we utilized a highly quantitative PCR/ligase detection reaction technique to quantify c-Met gene copy number in primary colorectal cancer (CRC) (N=247), liver metastases (N=147), and paired normal tissues. We identified no differences in c-Met gene copy number between normal colonic mucosa and liver tissue. However, mean c-Met gene copy number was significantly elevated in CRC compared with normal mucosa (P<0.001), and in liver metastases compared with normal liver (P<0.001). Furthermore, a significant increase in c-Met was seen in liver metastases compared with primary CRC (P<0.0001). c-Met gene amplification was observed in 2% (3/177) of localized cancers, 9% (6/70) of cancers with distant metastases (P<0.02), and 18% (25/147) of liver metastases (P<0.01). Among patients treated by liver resection, there was a trend toward poorer 3-year survival in association with c-Met gene amplification (P=0.07). Slight increases in c-Met copy number can be detected in localized CRCs, but gene amplification is largely restricted to Stage IV primary cancers and liver metastases. c-Met gene amplification is linked to metastatic progression, and is a viable target for a significant subset of advanced CRC.

The Met tyrosine kinase receptor in development and cancer

Met is a tyrosine kinase receptor, encoded by an oncogene, whose crucial role has been elucidated during the last two decades. The complex biological program triggered by Met has been dissected and its biological relevance in both physiology and pathology has been proven. Met supports a morphogenetic program, known as invasive growth, taking place both during embryogenesis and adulthood. In tumors Met is often aberrantly activated, giving rise to the pathological counterpart of the invasive growth program: cancer progression towards metastasis. Several approaches have been recently developed to interfere with the tumorigenic and metastatic processes triggered by Met.

Showering c-MET-dependent cancers with drugs

The receptor tyrosine kinase, c-MET and its ligand hepatocyte growth factor/scatter factor (HGF/SF) have become leading candidates for targeted cancer therapies. Inappropriate c-MET signaling through autocrine, paracrine, amplification, and mutational activation occurs in virtually all types of solid tumors (http://www.vai.org/met), contributing to one or a combination of proliferative, invasive, survival, or angiogenic cancer phenotypes. c-MET and HGF/SF participate in all stages of malignant progression and represent promising drug targets in a variety of cancer types, including carcinomas, sarcomas, and brain tumors. While many are in pre-clinical testing, a few inhibitors have entered clinical trials. With hundreds of thousands of potential responding cancers that express c-MET, the interest in this molecule as a drug target is not surprising. However, the cognate c-MET diagnostic tests lag behind. In addition, despite the great enthusiasm based on response rates in phase I trials, there is a need for caution. It is almost without question that combination therapies with c-MET-HGF/SF inhibitors will be required for most cancers to achieve a cytotoxic tumor response.

Global survey of phosphotyrosine signaling identifies oncogenic kinases in lung cancer

Despite the success of tyrosine kinase-based cancer therapeutics, for most solid tumors the tyrosine kinases that drive disease remain unknown, limiting our ability to identify drug targets and predict response. Here we present the first large-scale survey of tyrosine kinase activity in lung cancer. Using a phosphoproteomic approach, we characterize tyrosine kinase signaling across 41 non-small cell lung cancer (NSCLC) cell lines and over 150 NSCLC tumors. Profiles of phosphotyrosine signaling are generated and analyzed to identify known oncogenic kinases such as EGFR and c-Met as well as novel ALK and ROS fusion proteins. Other activated tyrosine kinases such as PDGFRalpha and DDR1 not previously implicated in the genesis of NSCLC are also identified. By focusing on activated cell circuitry, the approach outlined here provides insight into cancer biology not available at the chromosomal and transcriptional levels and can be applied broadly across all human cancers.

MET amplification occurs with or without T790M mutations in EGFR mutant lung tumors with acquired resistance to gefitinib or erlotinib

In human lung adenocarcinomas harboring EGFR mutations, a second-site point mutation that substitutes methionine for threonine at position 790 (T790M) is associated with approximately half of cases of acquired resistance to the EGFR kinase inhibitors, gefitinib and erlotinib. To identify other potential mechanisms that contribute to disease progression, we used array-based comparative genomic hybridization (aCGH) to compare genomic profiles of EGFR mutant tumors from untreated patients with those from patients with acquired resistance. Among three loci demonstrating recurrent copy number alterations (CNAs) specific to the acquired resistance set, one contained the MET proto-oncogene. Collectively, analysis of tumor samples from multiple independent patient cohorts revealed that MET was amplified in tumors from 9 of 43 (21%) patients with acquired resistance but in only two tumors from 62 untreated patients (3%) (P = 0.007, Fisher's Exact test). Among 10 resistant tumors from the nine patients with MET amplification, 4 also harbored the EGFR(T790M) mutation. We also found that an existing EGFR mutant lung adenocarcinoma cell line, NCI-H820, harbors MET amplification in addition to a drug-sensitive EGFR mutation and the T790M change. Growth inhibition studies demonstrate that these cells are resistant to both erlotinib and an irreversible EGFR inhibitor (CL-387,785) but sensitive to a multikinase inhibitor (XL880) with potent activity against MET. Taken together, these data suggest that MET amplification occurs independently of EGFR(T790M) mutations and that MET may be a clinically relevant therapeutic target for some patients with acquired resistance to gefitinib or erlotinib.

Identification of genotype-correlated sensitivity to selective kinase inhibitors by using high-throughput tumor cell line profiling

Kinase inhibitors constitute an important new class of cancer drugs, whose selective efficacy is largely determined by underlying tumor cell genetics. We established a high-throughput platform to profile 500 cell lines derived from diverse epithelial cancers for sensitivity to 14 kinase inhibitors. Most inhibitors were ineffective against unselected cell lines but exhibited dramatic cell killing of small nonoverlapping subsets. Cells with exquisite sensitivity to EGFR, HER2, MET, or BRAF kinase inhibitors were marked by activating mutations or amplification of the drug target. Although most cell lines recapitulated known tumor-associated genotypes, the screen revealed low-frequency drug-sensitizing genotypes in tumor types not previously associated with drug susceptibility. Furthermore, comparing drugs thought to target the same kinase revealed striking differences, predictive of clinical efficacy. Genetically defined cancer subsets, irrespective of tissue type, predict response to kinase inhibitors, and provide an important preclinical model to guide early clinical applications of novel targeted inhibitors.

The MET receptor tyrosine kinase in invasion and metastasis

Various cytokines and soluble growth factors upon interaction with their membrane receptors are responsible for inducing cellular proliferation, differentiation, movement, and protection from anoikis (a planned suicide activated by normal cells in absence of attachment to neighboring cells or extracellular matrix (EMC)). Among those soluble factors a major position is exerted by hepatocyte growth factor (HGF) together with its receptor MET and macrophage-stimulating protein (MSP) in cooperation with its receptor RON.