Biological and targeting differences between the rare KRAS A146T and canonical KRAS mutants in gastric cancer models

BACKGROUND

Gastric cancer (GC) is the third leading cause of cancer-related death worldwide, with a poor prognosis for patients with advanced disease. Since the oncogenic role of KRAS mutants has been poorly investigated in GC, this study aims to biochemically and biologically characterize different KRAS-mutated models and unravel differences among KRAS mutants in response to therapy.

METHODS

Taking advantage of a proprietary, molecularly annotated platform of more than 200 GC PDXs (patient-derived xenografts), we identified KRAS-mutated PDXs, from which primary cell lines were established. The different mutants were challenged with KRAS downstream inhibitors in in vitro and in vivo experiments.

RESULTS

Cells expressing the rare KRAS A146T mutant showed lower RAS-GTP levels compared to those bearing the canonical G12/13D mutations. Nevertheless, all the KRAS-mutated cells displayed KRAS addiction. Surprisingly, even if the GEF SOS1 is considered critical for the activation of KRAS A146T mutants, its abrogation did not significantly affect cell viability. From the pharmacologic point of view, Trametinib monotherapy was more effective in A146T than in G12D-mutated models, suggesting a vulnerability to MEK inhibition. However, in the presence of mutations in the PI3K pathway, more frequently co-occurrent in A146T models, the association of Trametinib and the AKT inhibitor MK-2206 was required to optimize the response.

CONCLUSION

A deeper genomic and biological characterization of KRAS mutants might sustain the development of more efficient and long-lasting therapeutic options for patients harbouring KRAS-driven GC.

Targeting SMAD3 Improves Response to Oxaliplatin in Esophageal Adenocarcinoma Models by Impeding DNA Repair

PURPOSE

TGFβ signaling is implicated in the progression of most cancers, including esophageal adenocarcinoma (EAC). Emerging evidence indicates that TGFβ signaling is a key factor in the development of resistance toward cancer therapy.

EXPERIMENTAL DESIGN

In this study, we developed patient-derived organoids and patient-derived xenograft models of EAC and performed bioinformatics analysis combined with functional genetics to investigate the role of SMAD family member 3 (SMAD3) in EAC resistance to oxaliplatin.

RESULTS

Chemotherapy nonresponding patients showed enrichment of SMAD3 gene expression when compared with responders. In a randomized patient-derived xenograft experiment, SMAD3 inhibition in combination with oxaliplatin effectively diminished tumor burden by impeding DNA repair. SMAD3 interacted directly with protein phosphatase 2A (PP2A), a key regulator of the DNA damage repair protein ataxia telangiectasia mutated (ATM). SMAD3 inhibition diminished ATM phosphorylation by enhancing the binding of PP2A to ATM, causing excessive levels of DNA damage.

CONCLUSIONS

Our results identify SMAD3 as a promising therapeutic target for future combination strategies for the treatment of patients with EAC.

Increased genomic instability and reshaping of tissue microenvironment underlie oncogenic properties of Arid1a mutations

Oncogenic mutations accumulating in many chromatin-associated proteins have been identified in different tumor types. With a mutation rate from 10 to 57%, ARID1A has been widely considered a tumor suppressor gene. However, whether this role is mainly due to its transcriptional-related activities or its ability to preserve genome integrity is still a matter of intense debate. Here, we show that ARID1A is largely dispensable for preserving enhancer-dependent transcriptional regulation, being ARID1B sufficient and required to compensate for ARID1A loss. We provide in vivo evidence that ARID1A is mainly required to preserve genomic integrity in adult tissues. ARID1A loss primarily results in DNA damage accumulation, interferon type I response activation, and chronic inflammation leading to tumor formation. Our data suggest that in healthy tissues, the increased genomic instability that follows ARID1A mutations and the selective pressure imposed by the microenvironment might result in the emergence of aggressive, possibly immune-resistant, tumors.

Fatty acid synthase as a new therapeutic target for HER2-positive gastric cancer

PURPOSE

Trastuzumab is an HER2-specific agent approved as the gold-standard therapy for advanced HER2-positive (HER2+) gastric cancer (GC), but the high rate and rapid appearance of resistance limit its clinical efficacy, resulting in the need to identify new vulnerabilities. Defining the drivers influencing HER2+ cancer stem cell (CSC) maintenance/survival could represent a clinically useful strategy to counteract tumor growth and therapy resistance. Accumulating evidence show that targeting crucial metabolic hubs, as the fatty acid synthase (FASN), may be clinically relevant.

METHODS

FASN protein and transcript expression were examined by WB and FACS and by qRT-PCR and GEP analyses, respectively, in trastuzumab-sensitive and trastuzumab-resistant HER2+ GC cell lines cultured in adherent (2D) or gastrosphere promoting (3D) conditions. Molecular data were analyzed in silico in public HER2+ GC datasets. The effectiveness of the FASN inhibitor TVB3166 to overcome anti-HER2 therapy resistance was tested in vitro in gastrospheres forming efficiency bioassays and in vivo in mice bearing trastuzumab-resistant GC cells.

RESULTS

We compared the transcriptome profiles of HER2+ GC cells cultured in 2D versus 3D conditions finding a significant enrichment of FASN in 3D cultures. FASN upregulation significantly correlated with high stemness score and poor prognosis in HER2+ GC cases. TVB3166 treatment significantly decreased GCSCs in all cell targets. HER2 and FASN cotargeting significantly decreased the capability to form gastrospheres versus monotherapy and reduced the in vivo growth of trastuzumab-resistant GC cells.

CONCLUSION

Our findings indicate that cotargeting HER2 and FASN increase the benefit of anti-HER2 therapy representing a new opportunity for metabolically combating trastuzumab-resistant HER2+ GC.

BRCA2 Germline Mutations Identify Gastric Cancers Responsive to PARP Inhibitors

Despite negative results of clinical trials conducted on the overall population of patients with gastric cancer, PARP inhibitor (PARPi) therapeutic strategy still might represent a window of opportunity for a subpopulation of patients with gastric cancer. An estimated 7% to 12% of gastric cancers exhibit a mutational signature associated with homologous recombination (HR) failure, suggesting that these patients could potentially benefit from PARPis. To analyze responsiveness of gastric cancer to PARPi, we exploited a gastroesophageal adenocarcinoma (GEA) platform of patient-derived xenografts (PDX) and PDX-derived primary cells and selected 10 PDXs with loss-of-function mutations in HR pathway genes. Cell viability assays and preclinical trials showed that olaparib treatment was effective in PDXs harboring BRCA2 germline mutations and somatic inactivation of the second allele. Olaparib responsive tumors were sensitive to oxaliplatin as well. Evaluation of HR deficiency (HRD) and mutational signatures efficiently stratified responder and nonresponder PDXs. A retrospective analysis on 57 patients with GEA showed that BRCA2 inactivating variants were associated with longer progression-free survival upon platinum-based regimens. Five of 7 patients with BRCA2 germline mutations carried the p.K3326* variant, classified as "benign." However, familial history of cancer, the absence of RAD51 foci in tumor cells, and a high HRD score suggest a deleterious effect of this mutation in gastric cancer. In conclusion, PARPis could represent an effective therapeutic option for BRCA2-mutated and/or high HRD score patients with GEA, including patients with familial intestinal gastric cancer.

SIGNIFICANCE

PARP inhibition is a potential strategy for treating patients with gastric cancer with mutated BRCA2 or homologous repair deficiency, including patients with familial intestinal gastric cancer, for whom BRCA2 germline testing should be recommended.

Identification of a subpopulation of patients with gastric cancer responsive to PARP inhibitors

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Background: Treatment with PARP inhibitors (PARPi) has been approved in some tumors bearing a deficient Homologous Recombination (HR) system. Despite negative results of clinical trials conducted on the overall population of gastric cancer (GC) patients, we wondered whether a PARPi therapeutic strategy might represent a window of opportunity for a subpopulation of these patients. 7-12% of gastric cancers exhibit a mutational signature associated with HR failure, suggesting that these patients might benefit from PARPi. Methods: To analyze responsiveness to PARPi we exploited a proprietary human Gastro-Esophageal Adenocarcinoma (GEA) annotated platform of Patient-Derived Xenografts (PDXs) and PDX-derived primary cells on which we performed in vivo and in vitro experiments. Results: We selected 10 PDXs with loss-of-function mutations in HR pathway genes. Cell viability assays and preclinical trials showed that treatment with PARPi was effective in PDXs harbouring BRCA2 germline mutations and somatic inactivation of the second allele in a microsatellite stable background. PARPi responsive tumors were sensitive to oxaliplatin as well. Evaluation of HR deficiency and mutational signatures efficiently stratified responder vs non-responder PDXs. A retrospective analysis on 57 GEA patients showed that those carrying BRCA2 inactivating variants had longer PFS upon platinum-based regimens (used as proxy). In 5 out of 7 BRCA2 germline mutated patients we identified the p.K3326* variant, currently classified as “benign”. However, familial history of cancer, the absence of RAD51 foci in the tumor cells and a high HR deficiency score suggest a deleterious effect for this mutation in gastric cancer. Conclusions: PARP inhibition could represent a new therapeutic perspective for BRCA2 mutated and/or high HRD score GEA patients, including familial intestinal gastric cancer patients.

HER2 Copy Number and Resistance Mechanisms in Patients with HER2-positive Advanced Gastric Cancer Receiving Initial Trastuzumab-based Therapy in JACOB Trial

PURPOSE

In JACOB trial, pertuzumab added to trastuzumab-chemotherapy did not significantly improve survival of patients with HER2-positive metastatic gastric cancer, despite 3.3 months increase versus placebo. HER2 copy-number variation (CNV) and AMNESIA panel encompassing primary resistance alterations (KRAS/PIK3CA/MET mutations, KRAS/EGFR/MET amplifications) may improve patients' selection for HER2 inhibition.

EXPERIMENTAL DESIGN

In a post hoc analysis of JACOB on 327 samples successfully sequenced by next-generation sequencing (NGS; Oncomine Focus DNA), HER2 CNV, HER2 expression by IHC, and AMNESIA were correlated with overall response rate (ORR), progression-free survival (PFS), and overall survival (OS) by univariable/multivariable models.

RESULTS

Median HER2 CNV was 4.7 (interquartile range, 2.2-16.9). HER2 CNV-high versus low using the median as cutoff was associated with longer median PFS (10.5 vs. 6.4 months; HR = 0.48; 95% confidence interval: 0.38-0.62; P < 0.001) and OS (20.3 vs. 13.0 months; HR = 0.54; 0.42-0.72; P < 0.001). Combining HER2 CNV and IHC improved discriminative ability, with better outcomes restricted to HER2-high/HER2 3+ subgroup. AMNESIA positivity was found in 51 (16%), with unadjusted HR = 1.35 (0.98-1.86) for PFS; 1.43 (1.00-2.03) for OS.In multivariable models, only HER2 CNV status remained significant for PFS (P < 0.001) and OS (P = 0.004). Higher ORR was significantly associated with IHC 3+ [61% vs. 34% in 2+; OR = 3.11 (1.89-5.17)] and HER2-high [59% vs. 43% in HER2-low; OR = 1.84 (1.16-2.94)], with highest OR in the top CNV quartile. These biomarkers were not associated with treatment effect of pertuzumab.

CONCLUSIONS

HER2 CNV-high assessed by NGS may be associated with better ORR, PFS, and OS in a JACOB subgroup, especially if combined with HER2 3+. The negative prognostic role of AMNESIA requires further clinical validation.

hOA-DN30: a highly effective humanized single-arm MET antibody inducing remission of ‘MET-addicted’ cancers

Background

The tyrosine kinase receptor encoded by the MET oncogene is a major player in cancer. When MET is responsible for the onset and progression of the transformed phenotype (MET-addicted cancers), an efficient block of its oncogenic activation results in potent tumor growth inhibition.

Methods

Here we describe a molecular engineered MET antibody (hOA-DN30) and validate its pharmacological activity in MET-addicted cancer models in vitro and in vivo. Pharmacokinetics and safety profile in non-human primates have also been assessed.

Results

hOA-DN30 efficiently impaired MET activation and the intracellular signalling cascade by dose and time dependent removal of the receptor from the cell surface (shedding). In vitro, the antibody suppressed cell growth by blocking cell proliferation and by concomitantly inducing cell death in multiple MET-addicted human tumor cell lines. In mice xenografts, hOA-DN30 induced an impressive reduction of tumor masses, with a wide therapeutic window. Moreover, the antibody showed high therapeutic efficacy against patient-derived xenografts generated from MET-addicted gastric tumors, leading to complete tumor regression and long-lasting effects after treatment discontinuation. Finally, hOA-DN30 showed a highly favorable pharmacokinetic profile and substantial tolerability in Cynomolgus monkeys.

Conclusions

hOA-DN30 unique ability to simultaneously erase cell surface MET and release the ‘decoy’ receptor extracellular region results in a paramount MET blocking action. Its remarkable efficacy in a large number of pre-clinical models, as well as its pharmacological features and safety profile in non-human primates, strongly envisage a successful clinical application of this novel single-arm MET therapeutic antibody for the therapy of MET-addicted cancers.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-022-02320-6.

The importance of being CAFs (in cancer resistance to targeted therapies)

In the last two decades, clinical oncology has been revolutionized by the advent of targeted drugs. However, the efficacy of these therapies is significantly limited by primary and acquired resistance, that relies not only on cell-autonomous mechanisms but also on tumor microenvironment cues. Cancer-associated fibroblasts (CAFs) are extremely plastic cells of the tumor microenvironment. They not only produce extracellular matrix components that build up the structure of tumor stroma, but they also release growth factors, chemokines, exosomes, and metabolites that affect all tumor properties, including response to drug treatment. The contribution of CAFs to tumor progression has been deeply investigated and reviewed in several works. However, their role in resistance to anticancer therapies, and in particular to molecular therapies, has been largely overlooked. This review specifically dissects the role of CAFs in driving resistance to targeted therapies and discusses novel CAF targeted therapeutic strategies to improve patient survival.

A novel strategy for combination of clofarabine and pictilisib is synergistic in gastric cancer

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Drug sensitivity testing identified novel drugs like clofarabine effective in treating gastric cancer.

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mRNA sequencing can be used to identify agents with synergistic activity to a reference compound.

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Pictilisib sensitizes gastric cancer to clofarabine treatment through AKT inhibition.

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The combination of clofarabine and pictilisib inhibits tumor growth in cell lines and PDX models.

Gastric cancer (GC) is frequently characterized by resistance to standard chemotherapeutic regimens and poor clinical outcomes. We aimed to identify a novel therapeutic approach using drug sensitivity testing (DST) and our computational SynerySeq pipeline. DST of GC cell lines was performed with a library of 215 Federal Drug Administration (FDA) approved compounds and identified clofarabine as a potential therapeutic agent. RNA-sequencing (RNAseq) of clofarabine treated GC cells was analyzed according to our SynergySeq pipeline and identified pictilisib as a potential synergistic agent. Clonogenic survival and Annexin V assays demonstrated increased cell death with clofarabine and pictilisib combination treatment (P<0.01). The combination induced double strand breaks (DSB) as indicated by phosphorylated H2A histone family member X (γH2AX) immunofluorescence and western blot analysis (P<0.01). Pictilisib treatment inhibited the protein kinase B (AKT) cell survival pathway and promoted a pro-apoptotic phenotype as evidenced by quantitative real time polymerase chain reaction (qRT-PCR) analysis of the B-cell lymphoma 2 (BCL2) protein family members (P<0.01). Patient derived xenograft (PDX) data confirmed that the combination is more effective in abrogating tumor growth with prolonged survival than single-agent treatment (P<0.01). The novel combination of clofarabine and pictilisib in GC promotes DNA damage and inhibits key cell survival pathways to induce cell death beyond single-agent treatment.

Molecularly Targeted Therapies for Gastric Cancer. State of the Art

Many phase III trials failed to demonstrate a survival benefit from the addition of molecular therapy to conventional chemotherapy for advanced and metastatic gastric cancer, and only three agents were approved by the FDA. We examined the efficacy and safety of novel drugs recently investigated. PubMed, Embase and Cochrane Library were searched for phase III randomized controlled trials published from January 2016 to December 2020. Patients in the experimental arm received molecular therapy with or without conventional chemotherapy, while those in the control arm had conventional chemotherapy alone. The primary outcomes were overall and progression-free survival. The secondary outcomes were the rate of tumor response, severe adverse effects, and quality of life. Eight studies with a total of 4223 enrolled patients were included. The overall and progression-free survival of molecular and conventional therapy were comparable. Most of these trials did not find a significant difference in tumor response rate and in the number of severe adverse effects and related deaths between the experimental and control arms. The survival benefits of molecular therapies available to date for advanced and metastatic gastric cancer are rather unclear, mostly due to inaccurate patient selection, particularly concerning oncogene amplification and copy number.

Optimized EGFR Blockade Strategies in EGFR Addicted Gastroesophageal Adenocarcinomas

PURPOSE

Gastric and gastroesophageal adenocarcinomas represent the third leading cause of cancer mortality worldwide. Despite significant therapeutic improvement, the outcome of patients with advanced gastroesophageal adenocarcinoma is poor. Randomized clinical trials failed to show a significant survival benefit in molecularly unselected patients with advanced gastroesophageal adenocarcinoma treated with anti-EGFR agents.

EXPERIMENTAL DESIGN

We performed analyses on four cohorts: IRCC (570 patients), Foundation Medicine, Inc. (9,397 patients), COG (214 patients), and the Fondazione IRCCS Istituto Nazionale dei Tumori (206 patients). Preclinical trials were conducted in patient-derived xenografts (PDX).

RESULTS

The analysis of different gastroesophageal adenocarcinoma patient cohorts suggests that EGFR amplification drives aggressive behavior and poor prognosis. We also observed that EGFR inhibitors are active in patients with EGFR copy-number gain and that coamplification of other receptor tyrosine kinases or KRAS is associated with worse response. Preclinical trials performed on EGFR-amplified gastroesophageal adenocarcinoma PDX models revealed that the combination of an EGFR mAb and an EGFR tyrosine kinase inhibitor (TKI) was more effective than each monotherapy and resulted in a deeper and durable response. In a highly EGFR-amplified nonresponding PDX, where resistance to EGFR drugs was due to inactivation of the TSC2 tumor suppressor, cotreatment with the mTOR inhibitor everolimus restored sensitivity to EGFR inhibition.

CONCLUSIONS

This study underscores EGFR as a potential therapeutic target in gastric cancer and identifies the combination of an EGFR TKI and a mAb as an effective therapeutic approach. Finally, it recognizes mTOR pathway activation as a novel mechanism of primary resistance that can be overcome by the combination of EGFR and mTOR inhibitors.See related commentary by Openshaw et al., p. 2964.

Microsatellite instability in Gastric Cancer: Between lights and shadows

Gastric cancer (GC) represents an important contributor to the global burden of cancer, being one of the most common and deadly malignancies worldwide. According to TCGA and ACRG classifications, the microsatellite instable (MSI) group represents a significant subset of GCs and is currently in the limelight of many researches due to its favorable survival outcome in resectable stages compared to microsatellite stable tumors. MSI GCs hypermutated phenotype triggers immunosurveillance, making this molecular subgroup a promising candidate for immune checkpoint inhibitors treatment. Conversely, conflicting outcomes have been reported in chemotherapy settings. Due to the clinical relevance of these observations, in this review we report and discuss the molecular, pathological, prognostic, and predictive features of MSI gastric tumors.

Patient-Derived Cancer Models

For many decades, basic and preclinical cancer research has been based on the use of established, commercially available cell lines, originally derived from patients' samples but adapted to grow indefinitely in artificial culture conditions, and on xenograft models developed by injection of these cells in immunocompromised animals [...].

Patient-Derived Orthotopic Xenograft models in gastric cancer: a systematic review

Patient-Derived Xenografts (PDXs) are, so far, the best preclinical model to validate targets and predictors of response to therapy. While subcutaneous implantation very rarely allows metastatic dissemination, orthotopic implantation (Patient-Derived Orthotopic Xenograft-PDOX) increases metastatic capability. Using a modified tool to analyze model validity, we performed a systematic review of Embase, PubMed, and Web of Science up to December 2018 to identify all original publications describing gastric cancer (GC) PDOXs. We identified ten studies of PDOX model validation from January 1981 to December 2018 that fulfilled the inclusion and exclusion criteria. Most models (70%) were derived from human GC cell lines rather than tissue fragments. In 90% of studies, the implantation was performed in the subserosal layer. Tumour engraftment rate ranged from 0 to 100%, despite the technique. Metastases were observed in 40% of PDOX models implanted into the subserosal layer, employing either cell suspension or cell line-derived tumour fragments. According to our modified model validity tool, half of the studies were defined as unclear because one or more validation criteria were not reported. Available GC PDOX models are not adequate according to our model validity tool. There is no demonstration that the submucosal site is more effective than the subserosal layer, and that tissue fragments are better than cell suspensions for successful engraftment and metastatic spread. Further studies should strictly employ model validity tools and large samples with orthotopic implant sites mirroring as much as possible the donor tumour characteristics.

A Comprehensive PDX Gastric Cancer Collection Captures Cancer Cell-Intrinsic Transcriptional MSI Traits

Gastric cancer is the world's third leading cause of cancer mortality. In spite of significant therapeutic improvements, the clinical outcome for patients with advanced gastric cancer is poor; thus, the identification and validation of novel targets is extremely important from a clinical point of view. We generated a wide, multilevel platform of gastric cancer models, comprising 100 patient-derived xenografts (PDX), primary cell lines, and organoids. Samples were classified according to their histology, microsatellite stability, Epstein-Barr virus status, and molecular profile. This PDX platform is the widest in an academic institution, and it includes all the gastric cancer histologic and molecular types identified by The Cancer Genome Atlas. PDX histopathologic features were consistent with those of patients' primary tumors and were maintained throughout passages in mice. Factors modulating grafting rate were histology, TNM stage, copy number gain of tyrosine kinases/KRAS genes, and microsatellite stability status. PDX and PDX-derived cells/organoids demonstrated potential usefulness to study targeted therapy response. Finally, PDX transcriptomic analysis identified a cancer cell-intrinsic microsatellite instability (MSI) signature, which was efficiently exported to gastric cancer, allowing the identification, among microsatellite stable (MSS) patients, of a subset of MSI-like tumors with common molecular aspects and significant better prognosis. In conclusion, we generated a wide gastric cancer PDX platform, whose exploitation will help identify and validate novel "druggable" targets and optimize therapeutic strategies. Moreover, transcriptomic analysis of gastric cancer PDXs allowed the identification of a cancer cell-intrinsic MSI signature, recognizing a subset of MSS patients with MSI transcriptional traits, endowed with better prognosis. SIGNIFICANCE: This study reports a multilevel platform of gastric cancer PDXs and identifies a MSI gastric signature that could contribute to the advancement of precision medicine in gastric cancer.

Increased Lactate Secretion by Cancer Cells Sustains Non-cell-autonomous Adaptive Resistance to MET and EGFR Targeted Therapies

The microenvironment influences cancer drug response and sustains resistance to therapies targeting receptor-tyrosine kinases. However, if and how the tumor microenvironment can be altered during treatment, contributing to resistance onset, is not known. We show that, under prolonged treatment with tyrosine kinase inhibitors (TKIs), EGFR- or MET-addicted cancer cells displayed a metabolic shift toward increased glycolysis and lactate production. We identified secreted lactate as the key molecule instructing cancer-associated fibroblasts to produce hepatocyte growth factor (HGF) in a nuclear factor κB-dependent manner. Increased HGF, activating MET-dependent signaling in cancer cells, sustained resistance to TKIs. Functional or pharmacological targeting of molecules involved in the lactate axis abrogated in vivo resistance, demonstrating the crucial role of this metabolite in the adaptive process. This adaptive resistance mechanism was observed in lung cancer patients progressed on EGFR TKIs, demonstrating the clinical relevance of our findings and opening novel scenarios in the challenge to drug resistance.

Rituximab Treatment Prevents Lymphoma Onset in Gastric Cancer Patient-Derived Xenografts

Patient-Derived Xenografts (PDXs), entailing implantation of cancer specimens in immunocompromised mice, are emerging as a valuable translational model that could help validate biologically relevant targets and assist the clinical development of novel therapeutic strategies for gastric cancer.

More than 30% of PDXs generated from gastric carcinoma samples developed human B-cell lymphomas instead of gastric cancer. These lymphomas were monoclonal, Epstein Barr Virus (EBV) positive, originated tumorigenic cell cultures and displayed a mutational burden and an expression profile distinct from gastric adenocarcinomas. The ability of grafted samples to develop lymphomas did not correlate with patient outcome, nor with the histotype, the lymphocyte infiltration level, or the EBV status of the original gastric tumor, impeding from foreseeing lymphoma onset. Interestingly, lymphoma development was significantly more frequent when primary rather than metastatic samples were grafted.

Notably, the development of such lympho-proliferative disease could be prevented by a short rituximab treatment upon mice implant, without negatively affecting gastric carcinoma engraftment.

Due to the high frequency of human lymphoma onset, our data show that a careful histologic analysis is mandatory when generating gastric cancer PDXs. Such care would avoid misleading results that could occur if testing of putative gastric cancer therapies is performed in lymphoma PDXs. We propose rituximab treatment of mice to prevent lymphoma development in PDX models, averting the loss of human-derived samples.

Biomarkers of Primary Resistance to Trastuzumab in HER2-Positive Metastatic Gastric Cancer Patients: the AMNESIA Case-Control Study

Purpose: Refining the selection of HER2-positive metastatic gastric cancer patient candidates for trastuzumab is a challenge of precision oncology. Preclinical studies have suggested several genomic mechanisms of primary resistance, leading to activation of tyrosine kinase receptors other than HER2 or downstream signaling pathways.Experimental Design: We carried out this multicenter, prospective, case-control study to demonstrate the negative predictive impact of a panel of candidate genomic alterations (AMNESIA panel), including EGFR/MET/KRAS/PI3K/PTEN mutations and EGFR/MET/KRAS amplifications. Hypothesizing a prevalence of candidate alterations of 30% and 0% in resistant and sensitive HER2-positive patients, respectively, 20 patients per group were needed.Results: AMNESIA panel alterations were significantly more frequent in resistant (11 of 20, 55%) as compared with sensitive (0% of 17) patients (P < 0.001), and in HER2 IHC 2⁺ (7 of 13, 53.8%) than 3⁺ (4 of 24, 16.7%) tumors (P = 0.028). Patients with tumors bearing no candidate alterations had a significantly longer median progression-free [5.2 vs. 2.6 months; HR, 0.34; 95% confidence interval (CI), 0.07-0.48; P = 0.001] and overall survival (16.1 vs. 7.6 months; HR, 0.38; 95% CI, 0.09-0.75; P = 0.015). The predictive accuracy of the AMNESIA panel and HER2 IHC was 76% and 65%, respectively. The predictive accuracy of the combined evaluation of the AMNESIA panel and HER2 IHC was 84%.Conclusions: Our panel of candidate genomic alterations may be clinically useful to predict primary resistance to trastuzumab in patients with HER2-positive metastatic gastric cancer and should be further validated with the aim of molecularly stratifying HER2-addicted cancers for the development of novel treatment strategies. Clin Cancer Res; 24(5); 1082-9. ©2017 AACR.

YAP-Dependent AXL Overexpression Mediates Resistance to EGFR Inhibitors in NSCLC

The Yes-associated protein (YAP) is a transcriptional co-activator upregulating genes that promote cell growth and inhibit apoptosis. The main dysregulation of the Hippo pathway in tumors is due to YAP overexpression, promoting epithelial to mesenchymal transition, cell transformation, and increased metastatic ability. Moreover, it has recently been shown that YAP plays a role in sustaining resistance to targeted therapies as well. In our work, we evaluated the role of YAP in acquired resistance to epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors in lung cancer. In EGFR-addicted lung cancer cell lines (HCC4006 and HCC827) rendered resistant to several EGFR inhibitors, we observed that resistance was associated to YAP activation. Indeed, YAP silencing impaired the maintenance of resistance, while YAP overexpression decreased the responsiveness to EGFR inhibitors in sensitive parental cells. In our models, we identified the AXL tyrosine kinase receptor as the main YAP downstream effector responsible for sustaining YAP-driven resistance: in fact, AXL expression was YAP dependent, and pharmacological or genetic AXL inhibition restored the sensitivity of resistant cells to the anti-EGFR drugs. Notably, YAP overactivation and AXL overexpression were identified in a lung cancer patient upon acquisition of resistance to EGFR TKIs, highlighting the clinical relevance of our in vitro results. The reported data demonstrate that YAP and its downstream target AXL play a crucial role in resistance to EGFR TKIs and suggest that a combined inhibition of EGFR and the YAP/AXL axis could be a good therapeutic option in selected NSCLC patients.

Abstract 3851: Targeting HER2 in gastric cancer: Hints from a gastric PDX platform

Introduction: Gastric cancer is the 3rd leading cause of cancer mortality worldwide. Surgery is the only curative treatment strategy and conventional chemotherapy has shown limited efficacy. Trastuzumab (a HER2 mAb), is the only therapy targeting molecular alterations approved so far in gastric cancer, for HER2+ patients with advanced disease. However only a fraction (&lt;20%) of HER2 amplified patients benefits from treatment.

Methods: We have recently generated a molecularly annotated colony of gastro-esophageal PDXs (at the moment, &gt; 70 PDXs). The platform also comprises primary cell lines and 3D-cultured organoids derived from gastric cancer PDXs.

Results and Discussion: At present, we have identified several HER2+ PDXs and generated the corresponding in vitro derivatives. Four HER2+ PDXs, showing 3+ HercepTest score and HER2 amplification &gt; 8 copies (thus theoretically sensitive to Trastuzumab), were selected to undergo ‘xenotrials’ with the following anti-HER2 drugs/combos: Trastuzumab (T); Pertuzumab (P, anti-HER2 mAb); Lapatinib (L, a dual HER2-EGFR tyrosine kinase inhibitor). According to RECIST-like criteria, T induced tumor regression in only 1 out of 4 HER2+ PDXs. Interestingly, in all the tumors but one the combos T+P and T+L were able to bypass resistance to T monotherapy and to induce tumor regression. One tumor was resistant to all the tested therapeutic approaches.

Conclusion: We identified PDXs displaying HER2 gene amplification. Only a minor fraction of them benefited from the anti-HER2 mono-therapy, despite the presence of a strong HER2 gene amplification, while the association of two HER2 inhibiting drugs resulted in intense and prolonged response. This suggests that monotherapy with T might not be the most effective therapeutic approach in gastric cancer patients. We are currently investigating the cause of resistance to anti-HER2 drugs to identify mutations/CNV in tumors showing resistance to Trastuzumab.

Note: This abstract was not presented at the meeting.

Citation Format: Simona Corso, Cristina Migliore, Maria Apicella, Silvia Menegon, Eirini Pectasides, Tania Capeloa, Stefania Durando, Marilisa Cargnelutti, Paola Cassoni, Anna Sapino, Maurizio de Giuli, Adam Bass, Silvia Giordano. Targeting HER2 in gastric cancer: Hints from a gastric PDX platform [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3851. doi:10.1158/1538-7445.AM2017-3851

Targeted therapies for gastric cancer: failures and hopes from clinical trials

Gastric cancer is the third leading cause of cancer mortality worldwide. As surgery is the only curative treatment strategy and conventional chemotherapy has shown limited efficacy -with a median overall survival of 10 months- new treatments are urgently needed. Trastuzumab and Ramucirumab (targeting HER2 and VEGFR2, respectively) are the only targeted therapies approved so far. Indeed, most Phase III clinical trials evaluating molecular drugs in gastric cancer failed. This review will retrace the relevant clinical trials with molecular therapies performed in gastric cancer patients, discussing the possible reasons for their failure and indicating new perspective for a real improvement of the treatment of this disease.

Abstract A04: Combined anti–MET/EGFR treatment results in complete tumor regression and prevents resistance onset in a MET-amplified gastroesophageal xenopatient cohort

Gastric cancer is the world third leading cause of cancer mortality. In spite of the significant therapeutic advances, the overall clinical outcome for patients with advanced gastric cancer is poor, with 5-20% 5-year survival. The only targeted therapy approved so far are trastuzumab, and Ramucirumab which have given unsatisfactory results. Around 50% of gastric tumors bear genetic alterations affecting tyrosine kinase pathways (mainly EGFR, HER3, FGFR2 and MET pathways, besides HER2) but their clinical validation as tumor drivers is missing. The need for new therapeutic options and the possible presence of “druggable” targets prompted us to investigate potential targeted therapies for this disease.

Our project aims at identifying and validating targeted therapeutic strategies in gastric cancer, through the generation of a platform of gastric tumor patient-derived xenografts (PDXs), animal models in which tumor surgical specimens are directly transferred into mice. Upon engraftment, the tumor is split and re-implanted in a cohort of mice, allowing the simultaneous testing of different drugs on the same tumor. Thanks to the establishment of a network of 15 Italian centers for samples collection, we generated around 80 gastric PDXs and successfully derived cell lines and organoids from engrafted tumors. Among the tumors collected so far, we found HER2, EGFR, FGFR2, MET and KRAS amplifications. This gastric PDX platform will be exploited for: 1) Validation of candidate oncogenes as relevant targets and identification of efficient therapeutic strategies 2) Identification of novel molecular targets; 3) identification of genetic predictors of response/resistance.

In the PDX platform we identified one tumor bearing a high level of MET gene amplification (26 gene copies). We thus performed a preclinical study on a cohort of patient-derived xenografts generated from the MET-amplified gastroesophageal tumor. Despite the high amplification level, MET inhibitors induced only a partial response, while the combined anti-MET/EGFR treatment led to complete tumor regression. Most important, the combo treatment also prevented resistance onset. This data represent the proof of concept that a combined anti-MET/EGFR therapy can be more effective than anti-MET treatment alone in MET-amplified gastroesophageal tumors, in the absence of EGFR genetic lesions.

Citation Format: Simona Corso, Maria Apicella, Silvia Menegon, Marilisa Cargnelutti, Maria Stella Scalzo, Rossella Reddavid, Paola Cassoni, Anna Sapino, Maurizio De Giuli, Silvia Giordano. Combined anti–MET/EGFR treatment results in complete tumor regression and prevents resistance onset in a MET-amplified gastroesophageal xenopatient cohort. [abstract]. In: Proceedings of the AACR Special Conference: Patient-Derived Cancer Models: Present and Future Applications from Basic Science to the Clinic; Feb 11-14, 2016; New Orleans, LA. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(16_Suppl):Abstract nr A04.

Abstract 622: Gastric cancer in the age of targeted agents: identification and validation of novel therapeutic strategies through the generation of a patient-derived xenografts platform

Gastric cancer is the world third leading cause of cancer mortality. In spite of the significant therapeutic advances, the overall clinical outcome for patients with advanced gastric cancer is poor, with 5-20% 5-year survival. The only targeted therapy approved so far are trastuzumab, and Ramucirumab which have given unsatisfactory results. Around 50% of gastric tumors bear genetic alterations affecting tyrosine kinase pathways (mainly EGFR, HER3, FGFR2 and MET pathways, besides HER2) but their clinical validation as tumor drivers is missing. The need for new therapeutic options and the possible presence of ‘druggable’ targets prompted us to investigate potential targeted therapies for this disease.

Our project aims at identifying and validating targeted therapeutic strategies in gastric cancer, through the generation of a platform of gastric tumor patient-derived xenografts (PDXs), animal models in which tumor surgical specimens are directly transferred into mice. Upon engraftment, the tumor is split and re-implanted in a cohort of mice, allowing the simultaneous testing of different drugs on the same tumor. Thanks to the establishment of a network of 15 Italian centers for samples collection, we generated around 80 gastric PDXs and successfully derived cell lines and organoids from engrafted tumors. Among the tumors collected so far, we found HER2, EGFR, FGFR2, MET and KRAS amplifications. This gastric PDX platform will be exploited for: 1) Validation of candidate oncogenes as relevant targets and identification of efficient therapeutic strategies 2) Identification of novel molecular targets; 3) identification of genetic predictors of response/resistance.

In the PDX platform we identified one tumor bearing a high level of MET gene amplification (26 gene copies). We thus performed a preclinical study on a cohort of patient-derived xenografts generated from the MET-amplified gastroesophageal tumor. Despite the high amplification level, MET inhibitors induced only a partial response, while the combined anti-MET/EGFR treatment led to complete tumor regression. Most important, the combo treatment also prevented resistance onset. This data represent the proof of concept that a combined anti-MET/EGFR therapy can be more effective than anti-MET treatment alone in MET-amplified gastroesophageal tumors, in the absence of EGFR genetic lesions.

Citation Format: Silvia Menegon, Maria Apicella, Cristina Migliore, Tania Capeloa, Marilisa Cargnelutti, Maurizio Degiuli, Anna Sapino, Paola Cassoni, Michele De Simone, Paolo M. Comoglio, Silvia Marsoni, Simona Corso, Silvia Giordano. Gastric cancer in the age of targeted agents: identification and validation of novel therapeutic strategies through the generation of a patient-derived xenografts platform. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 622.

How Can Gastric Cancer Molecular Profiling Guide Future Therapies?

Gastric cancer is the third greatest global cause of cancer-related deaths. Despite its high prevalence, only recently have comprehensive genomic surveys shed light on its molecular alterations. As surgery is the only curative treatment strategy and chemotherapy has shown limited efficacy, new treatments are urgently needed. Many molecular therapies for gastric cancer have entered clinical trials but-apart from Trastuzumab and Ramucirumab-all have failed. We analyze the current knowledge of the genetic 'landscape' of gastric cancers, elaborating on novel, preclinical approaches. We posit that this knowledge lays the basis for identifying bona fide molecular targets and developing solid therapeutic approaches, requiring accurate patient selection and taking advantage of preclinical models to assist clinical development of novel combination strategies.

Activation of RAS family members confers resistance to ROS1 targeting drugs

The ROS1 tyrosine kinase is activated in lung cancer as a consequence of chromosomal rearrangement. Although high response rates and disease control have been observed in lung cancer patients bearing rearranged ROS1 tumors (ROS1+) treated with the kinase inhibitor crizotinib, many of these patients eventually relapse.To identify mechanisms of resistance to ROS1 inhibitors we generated resistant cells from HCC78 lung cancer cells bearing the SLC34A2-ROS1 rearrangement. We found that activation of the RAS pathway in the HCC78 cell model, due to either KRAS/NRAS mutations or to KRAS amplification, rendered the cells resistant to ROS1 inhibition. These cells were cross-resistant to different ROS1 inhibitors, but sensitive to inhibitors of the RAS signaling pathway. Interestingly, we identified focal KRAS amplification in a biopsy of a tumor from a patient that had become resistant to crizotinib treatment.Altogether our data suggest that the activation of members of the RAS family can confer resistance to ROS1 inhibitors. This has important clinical implications as: (i) RAS genetic alterations in ROS1+ primary tumors are likely negative predictors of efficacy for targeted drugs and (ii) this kind of resistance is unlikely to be overcome by the use of more specific or more potent ROS1 targeting drugs.

Abstract 3606: Increase of MET gene copy number confers resistance to a monovalent MET antibody and establishes drug dependence

The tyrosine kinase receptor encoded by the MET oncogene is one of the most frequently altered oncogenes in human cancer. The relevant role played by the MET oncogene in cancer progression led to the development of specific inhibitors targeting MET, some of which are now in advanced phases of clinical trials.

Previous experience has shown that the main limit to the efficacy of most targeted treatments is the advent of resistance. Mechanisms underlying resistance to MET-specific small tyrosine kinase inhibitors (TKIs) have been already described, while nothing is known about resistance to MET monoclonal antibodies, nor about bypassing resistance to chemical TKIs by antibodies or vice-versa.

A monovalent form of an anti-MET monoclonal antibody (MV-DN30) was previously generated to target MET by promoting receptor “shedding”, inactivation and by inhibiting the MET-mediated invasive growth program both in vitro and in vivo cancer models. In our study EBC1 lung cancer cells that are MET-addicted as a consequence of gene amplification and thus sensitive to MET inhibitors, including the MV-DN30 were used as cell model. Upon prolonged treatment of these cells with the MV-DN30 we generated EBC1 cells resistant to this antibody and found that resistance was due to a further increase of MET gene copy number and a dramatic over-expression of the MET receptor. Such an excess of expression saturated the ‘shedding’ activity of MV-DN30, and prevented both the efficient down-regulation of the MET receptor from the surface and the inhibition of the ensuing constitutive activation.

Notably, antibody-resistant cells became ‘drug-dependent’, since the removal of MV-DN30 led them to death due to an excess of MET signal and a concomitant p38MAPK activation. Moreover, antibody-resistant cells remained MET-’addicted’ and were still sensitive to MET TKIs.

Finally, cells made resistant to MET specific TKIs were still sensitive to treatment with the antibody MV-DN30.

These findings suggest that a discontinuous or combined treatment by antibodies and chemical kinase inhibitors may increase the clinical response and bypass resistance to anti-MET targeted therapies.

Citation Format: Valentina Martin, Simona Corso, Paolo Maria Comoglio, Silvia Giordano. Increase of MET gene copy number confers resistance to a monovalent MET antibody and establishes drug dependence. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3606. doi:10.1158/1538-7445.AM2015-3606

Abstract B12: Understanding the role of the tumor microenvironment in mediating resistance to anti-MET drugs

Resistance to targeted therapy represents a major challenge to the treatment of cancer patients. Many data support the role of tumor stroma in modulating tumor progression, but little is known about its potential role in drug resistance. This is mostly due to the fact that resistance to targeted therapies has been mainly studied in vitro; thus in vivo tumor models that better mimic human tumors are absolutely needed.

Since MET, the tyrosine kinase receptor for Hepatocyte Growth Factor, is frequently implicated in resistance to kinase-targeted therapies and MET Tyrosine kinase inhibitors (TKIs) are currently in advanced phases of clinical trials, our aim was to investigate a possible role of non-cell-autonomous (microenvironment-mediated) mechanisms of resistance to MET-TKIs.

We generated in vivo models of MET-addicted tumors resistant to anti-MET treatment, subcutaneously injecting the non–small cell lung carcinoma cell line-EBC-1 and the gastric carcinoma cells GTL16 in NOD-SCID mice and treating them with MET inhibitors (JNJ-38877605 or CRIZOTINIB) until resistance onset. In parallel, untreated tumors were used as control.

We analyzed both tumors and cells (tumor cells and murine fibroblasts) isolated and put in culture from WT and resistant (RES) tumors. Through cell viability assays we demonstrated that six out of seven xeno-derived tumor cell lines were not or poorly resistant in vitro to MET inhibitors, suggesting a possible involvement of microenvironment in sustaining resistance.

We reasoned that the stroma of the resistant tumors could be qualitatively and/or quantitatively different from that of the wild-type tumors. To support this idea murine-gene arrays showed a significantly different gene expression profile between WT and resistant murine stroma. Gene-annotation enrichment analysis showed that inflammatory pathways and cancer-associated fibroblast (CAF) genes were particularly up-regulated in resistant versus wt tumors.

In order to understand whether the stroma may confer resistance to MET TKIs, we started to perform in vitro- and in vivo- co-colture experiments. In vitro experiments suggest that tumor cells co-cultured with fibroblasts were less sensitive to the MET inhibitors. We also performed preliminary in vivo experiments to demonstrate that the stroma of resistant tumors can induce resistance. We injected wild-type EBC1 cells (highly sensitive to MET inhibitors), transduced with the luciferase gene, into pre-existing wild-type or resistant tumors. Then we treated mice with the MET inhibitor JNJ-38877605 and monitored the luciferase signal. At the end of the experiment, by IVIS imaging analysis, we observed a decrease of the EBC1 luciferase signal (that is death of the WT labeled injected cells) in WT tumors treated with the MET inhibitor, but an increased luciferase signal in the resistant tumors (meaning that luciferase-labeled WT cells did not die in the presence of the MET inhibitor when in the contest of resistant tumors).

All together our experiments suggest that the microenvironment of resistant tumors can induce resistance to targeted therapies, protecting tumor cells from the effect of the drug.

Citation Format: Simona Corso, Maria Apicella, Silvia Giordano. Understanding the role of the tumor microenvironment in mediating resistance to anti-MET drugs. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Drug Sensitivity and Resistance: Improving Cancer Therapy; Jun 18-21, 2014; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(4 Suppl): Abstract nr B12.

Increase of MET gene copy number confers resistance to a monovalent MET antibody and establishes drug dependence

The relevant role in cancer played by the tyrosine kinase receptor encoded by the MET oncogene led to the development of specific inhibitors, some of which are now in advanced phases of clinical trials. Previous experience has shown that the main limit to the efficacy of most targeted treatments is the advent of resistance. Mechanisms underlying resistance to MET-specific small tyrosine kinase inhibitors (TKIs) have been already described, while nothing is known about resistance to MET monoclonal antibodies, nor about bypassing resistance to chemical TKIs by antibodies or vice-versa. EBC1 lung cancer cells are MET-addicted as a consequence of gene amplification and thus sensitive to MET inhibitors, including the monovalent form of a MET monoclonal antibody (MV-DN30). We generated cells resistant to this antibody and found that resistance was due to a further increase of gene copy number and a dramatic overexpression of the MET receptor. Such an excess of expression saturated the 'shedding' activity of MV-DN30, and prevented both the efficient down-regulation of the MET receptor from the surface and the inhibition of the ensuing constitutive activation. Notably, antibody-resistant cells remained MET-'addicted' and were still sensitive to MET TKIs. Moreover, antibody-resistant cells became 'drug-dependent', since the removal of MV-DN30 led them to death due to excess of signal. In the mirror experiment, cells made resistant to MET-specific TKIs were still sensitive to treatment with the antibody MV-DN30. These findings suggest that a discontinuous, combined treatment by antibodies and chemical kinase inhibitors may increase the clinical response and bypass resistance to anti-MET targeted therapies.

Abstract C92: MET amplification and overexpression sustain resistance and drive drug dependency to the DN30Fab antibody in MET-addicted cells

The establishment of the oncogenic role of the tyrosine kinase receptor for hepatocyte growth factor, encoded by the MET gene, led to the development of several specific inhibitors, many of which are currently in clinical trials. Clinical experience has shown that the main limit to the efficacy of targeted treatments is represented by resistance. Although the mechanisms underlying resistance to MET-specific Tyrosine Kinase Inhibitors (TKIs) have been already described, nothing is known, up to now, about the emergence of resistance to treatment with MET monoclonal antibodies (mAbs). To predict the mechanisms of acquired resistance, we generated resistant cells by treating a MET-addicted lung cancer cell line (EBC1) with increasing concentrations of the monovalent form of the DN30mAb (DN30Fab), previously developed as a therapeutic tool to block MET activation. The molecular analyses revealed that resistant cells underwent MET amplification and reached such a level of MET overexpression that DN30Fab was no longer able to efficiently downregulate MET and to abrogate its constitutive activation. However, resistant cells remained MET-addicted as they were still sensitive to MET TKIs. Interestingly, resistant cells acquired drug dependence, since removal of DN30Fab led them to death due to excess of signal. Finally, we also show that cells with acquired resistance to MET TKIs are still sensitive to treatment with DN30Fab and that the two drugs have a synergistic effect on tumor cells. Our findings might have important clinical meaning, since they indicate a combined therapy (mAb plus TKI) and a discontinuous treatment as possible strategies to bypass resistance to anti-MET antibodies.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C92.

Citation Format: Valentina Martin, Simona Corso, Fiorella Petronzelli, Rita De Santis, Paolo M. Comoglio, Silvia Giordano. MET amplification and overexpression sustain resistance and drive drug dependency to the DN30Fab antibody in MET-addicted cells. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C92.

Cell-autonomous and non-cell-autonomous mechanisms of HGF/MET-driven resistance to targeted therapies: from basic research to a clinical perspective

Targeted therapies have opened new perspectives in clinical oncology. However, clinicians have observed a lack of response in a relevant percentage of patients and frequent relapse in patients who initially respond. Therefore, a compelling challenge is to identify mechanisms underlying resistance and strategies to circumvent these hurdles. A growing body of evidence indicates that MET, the tyrosine kinase receptor for hepatocyte growth factor (HGF), is frequently implicated in resistance to targeted therapies. In this review, we highlight cell-autonomous and non-cell-autonomous mechanisms through which MET drives resistance, and we discuss some unsolved issues related to the selection of patients who could benefit from combined therapies.

SIGNIFICANCE

Resistance is, at present, the major limitation to the efficacy of targeted therapies. Inappropriate MET activation is very frequently implicated in the onset of primary and secondary resistance to these therapies. Deciphering the role of the HGF/MET axis in resistance to different drugs could guide the design of new clinical trials based on combinatorial therapies, and it might help to overcome, or possibly prevent, the onset of resistance.

Amplification of the MET receptor drives resistance to anti-EGFR therapies in colorectal cancer

EGF receptor (EGFR)-targeted monoclonal antibodies are effective in a subset of metastatic colorectal cancers. Inevitably, all patients develop resistance, which occurs through emergence of KRAS mutations in approximately 50% of the cases. We show that amplification of the MET proto-oncogene is associated with acquired resistance in tumors that do not develop KRAS mutations during anti-EGFR therapy. Amplification of the MET locus was present in circulating tumor DNA before relapse was clinically evident. Functional studies show that MET activation confers resistance to anti-EGFR therapy both in vitro and in vivo. Notably, in patient-derived colorectal cancer xenografts, MET amplification correlated with resistance to EGFR blockade, which could be overcome by MET kinase inhibitors. These results highlight the role of MET in mediating primary and secondary resistance to anti-EGFR therapies in colorectal cancer and encourage the use of MET inhibitors in patients displaying resistance as a result of MET amplification.

Amplification of the MET receptor to drive resistance to anti-EGFR therapies in colorectal cancer

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Background: The anti EGFR monoclonal antibodies cetuximab and panitumumab are used to treat metastatic colorectal cancer patients but their clinical efficacy is limited by the development of acquired resistance. We recently reported that secondary KRAS mutations are responsible for acquired resistance in approximately 50% of the patients who initially respond to cetuximab or panitumumab (Misale et al., Nature 2012; Diaz et al., Nature 2012). Here we studied the molecular bases of relapse in CRC patients who do not develop KRAS mutations during the course of anti-EGFR therapy. Methods: Next generation sequencing was applied to tumor biopsies to identify genetic alterations associated with relapse to cetuximab and panitumumab in mCRC patients. Detection and quantitation of genetic alterations in circulating tumor DNA was used to monitor the occurrence of KRAS mutations and MET amplification in blood samples. Results: Molecular analyses of tumor biopsies from patients who did not develop KRAS mutations during anti-EGFR therapy revealed high level of amplification of the MET proto-oncogene in 3/5 cases. Quantitative PCR, FISH and IHC analysis confirmed high level of MET amplification in the post-therapy samples but not in the matched pre-treatment tissues. We developed a PCR based assay to detect the presence of the MET amplicon in circulating, cell-free, DNA. We found that MET amplification could be detected in the blood as early as 3 months after initiation of anti EGFR therapy. To functionally evaluate the role of MET amplification on resistance to anti EGFR antibody therapies we exploited patient-derived CRC xenografts (‘xenopatients). We found that (2/2) xenopatients established from MET amplified tumors were completely refractory to cetuximab but showed sensitivity to the Met inhibitor crizotinib. Conclusions: Amplification of the MET proto-oncogene is responsible for acquired acquired resistance to anti-EGFR antibody therapy in a subset of CRCs. The emergence of MET amplification in circulating, cell-free, DNA may be used to select patients most likely to benefit from anti MET therapies.

Conservative management of early-stage epithelial ovarian cancer: results of a large retrospective series

BACKGROUND

To assess the long-term oncological outcome and the fertility of young women with early-stage epithelial ovarian cancer (ES/EOC) treated with fertility-sparing surgery (FSS).

PATIENTS AND METHODS

All patients treated with FSS for ES/EOC in two Italian centers were considered for this analysis. Univariate and multivariate analyses were used to test demographic characteristics and clinical features for the association with overall survival (OS), recurrence-free survival (RFS) and fertility.

RESULTS

From 1982 to 2010, 240 patients with malignant ES/EOC were treated with FSS in two tertiary centers in Italy. At a median follow-up of 9 years, 27 patients had relapsed (11%) and 11 (5%) had died of progressive disease. Multivariate analysis found only grade 3 negatively affected the prognosis of patients [hazard ratio (HR) for recurrence: 4.2, 95% confidence interval (CI): 1.5-11.7, P=0.0067; HR for death: 7.6, 95% CI: 2.0-29.3, P=0.0032]. Grade 3 was also significantly associated with extra-ovarian relapse (P=0.006). Of the 105 patients (45%) who tried to become pregnant, 84 (80%) were successful.

CONCLUSIONS

Conservative treatment can be proposed to all young patients when tumor is limited to the ovaries, as ovarian recurrences can always be managed successfully. Patients with G3 tumors are more likely to have distant recurrences and should be closely monitored.

Only a subset of Met-activated pathways are required to sustain oncogene addiction

Tumor onset and progression require the accumulation of many genetic and epigenetic lesions. In some cases, however, cancer cells rely on only one of these lesions to maintain their malignant properties, and this dependence results in tumor regression upon oncogene inactivation ("oncogene addiction"). Determining which nodes of the many networks operative in the transformed phenotype specifically mediate this response to oncogene neutralization is crucial to identifying the vulnerabilities of cancer. Using the Met receptor as the major model system, we combined multiplex phosphoproteomics, genome-wide expression profiling, and functional assays in various cancer cells addicted to oncogenic receptor tyrosine kinases. We found that Met blockade affected a limited subset of Met downstream signals: Little or no effect was observed for several pathways downstream of Met; instead, only a restricted and pathway-specific signature of transducers and transcriptional effectors downstream of Ras or phosphoinositide 3-kinase (PI3K) was inactivated. An analogous signature was also generated by inhibition of epidermal growth factor receptor in a different cellular context, suggesting a stereotyped response that likely is independent of receptor type or tissue origin. Biologically, Met inhibition led to cell-cycle arrest. Inhibition of Ras-dependent signals and PI3K-dependent signals also resulted in cell-cycle arrest, whereas cells in which Met was inhibited proliferated when Ras or PI3K signaling was active. These findings uncover "dominant" and "recessive" nodes among the numerous oncogenic networks regulated by receptor tyrosine kinases and active in cancer, with the Ras and PI3K pathways as determinants of therapeutic response.

Expression of DNA repair genes in ovarian cancer samples: biological and clinical considerations

The purpose of this study was to investigate retrospectively the mRNA expression of genes involved in different DNA repair pathways implicated in processing platinum-induced damage in 171 chemotherapy-naïve ovarian tumours and correlate the expression of the different genes with clinical parameters. The expression of genes involved in DNA repair pathways (PARP1, ERCC1, XPA, XPF, XPG, BRCA1, FANCA, FANCC, FANCD2, FANCF and PolEta), and in DNA damage transduction (Chk1 and Claspin) was measured by RT-PCR in 13 stage I borderline and 77 stage I and 88 III ovarian carcinomas. ERCC1, XPA, XPF and XPG genes were significantly less expressed in stage III than in stage I carcinoma; BRCA1, FANCA, FANCC, FANCD2 gene expressions were low in borderline tumours, higher in stage I carcinomas and lower in stage III samples. High levels of ERCC1, XPA, FANCC, XPG and PolEta correlated with an increase in Overall Survival (OS) and Progression Free Survival (PFS), whilst high BRCA1 levels were associated with PFS on univariate analysis. With multivariate analyses no genes retained an association when adjusted by stage, grade and residual tumour. A tendency towards a better PFS was observed in patients with the highest level of ERCC1 and BRCA1 after platinum-based therapy than those given both platinum and taxol. The expression of DNA repair genes differed in borderline stage I, stage I and stage III ovarian carcinomas. The role of DNA repair genes in predicting the response in ovarian cancer patients seems far from being established.

Expression of DNA repair genes in ovarian cancer samples: biological and clinical considerations

The purpose of this study was to investigate retrospectively the mRNA expression of genes involved in different DNA repair pathways implicated in processing platinum-induced damage in 171 chemotherapy-naïve ovarian tumours and correlate the expression of the different genes with clinical parameters. The expression of genes involved in DNA repair pathways (PARP1, ERCC1, XPA, XPF, XPG, BRCA1, FANCA, FANCC, FANCD2, FANCF and PolEta), and in DNA damage transduction (Chk1 and Claspin) was measured by RT-PCR in 13 stage I borderline and 77 stage I and 88 III ovarian carcinomas. ERCC1, XPA, XPF and XPG genes were significantly less expressed in stage III than in stage I carcinoma; BRCA1, FANCA, FANCC, FANCD2 gene expressions were low in borderline tumours, higher in stage I carcinomas and lower in stage III samples. High levels of ERCC1, XPA, FANCC, XPG and PolEta correlated with an increase in Overall Survival (OS) and Progression Free Survival (PFS), whilst high BRCA1 levels were associated with PFS on univariate analysis. With multivariate analyses no genes retained an association when adjusted by stage, grade and residual tumour. A tendency towards a better PFS was observed in patients with the highest level of ERCC1 and BRCA1 after platinum-based therapy than those given both platinum and taxol. The expression of DNA repair genes differed in borderline stage I, stage I and stage III ovarian carcinomas. The role of DNA repair genes in predicting the response in ovarian cancer patients seems far from being established.

The tetraspanin CD151 is required for Met-dependent signaling and tumor cell growth

CD151, a transmembrane protein of the tetraspanin family, is implicated in the regulation of cell-substrate adhesion and cell migration through physical and functional interactions with integrin receptors. In contrast, little is known about the potential role of CD151 in controlling cell proliferation and survival. We have previously shown that β4 integrin, a major CD151 partner, not only acts as an adhesive receptor for laminins but also as an intracellular signaling platform promoting cell proliferation and invasive growth upon interaction with Met, the tyrosine kinase receptor for hepatocyte growth factor (HGF). Here we show that RNAi-mediated silencing of CD151 expression in cancer cells impairs HGF-driven proliferation, anchorage-independent growth, protection from anoikis, and tumor progression in xenograft models in vivo. Mechanistically, we found that CD151 is crucially implicated in the formation of signaling complexes between Met and β4 integrin, a known amplifier of HGF-induced tumor cell growth and survival. CD151 depletion hampered HGF-induced phosphorylation of β4 integrin and the ensuing Grb2-Gab1 association, a signaling pathway leading to MAPK stimulation and cell growth. Accordingly, CD151 knockdown reduced HGF-triggered activation of MAPK but not AKT signaling cascade. These results indicate that CD151 controls Met-dependent neoplastic growth by enhancing receptor signaling through β4 integrin-mediated pathways, independent of cell-substrate adhesion.

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

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

Activation of HER family members in gastric carcinoma cells mediates resistance to MET inhibition

Background

Gastric cancer 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. Thus, MET is considered a good candidate for targeted therapeutic intervention in this type of tumor, and MET inhibitors recently entered clinical trials. 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. Perspective studies are thus mandatory to identify the molecular mechanisms that could cause resistance to these therapies.

Results

Our in vitro and in vivo results demonstrate that, in MET-addicted gastric cancer cells, the activation of HER (Human Epidermal Receptor) family members induces resistance to MET silencing or inhibition by PHA-665752 (a selective kinase inhibitor). We provide molecular evidences highlighting the role of EGFR, HER3, and downstream signaling pathways common to MET and HER family in resistance to MET inhibitors. Moreover, we show that an in vitro generated gastric cancer cell line resistant to MET-inhibition displays overexpression of HER family members, whose activation contributes to maintenance of resistance.

Conclusions

Our findings predict that gastric cancer tumors bearing constitutive activation of HER family members are poorly responsive to MET inhibition, even if this receptor is constitutively active. Moreover, the appearance of these alterations might also be responsible for the onset of resistance in initially responsive tumors.

Patients' Understanding of a CYP2D6 Tamoxifen Genotyping Study

Background: Pharmacogenomics is an emerging area for breast cancer research. Little is known about how well patients understand pharmacogenomics or the rationale for research in this area. The objective of this study was to analyze patient understanding of a clinical trial involving CYP2D6 genotyping to guide tamoxifen (T) therapy for breast cancer.Methods: We conducted a survey of understanding of pharmacogenomics and the purposes of a clinical trial among patients (pts) eligible for LCCC0801, a prospective Phase 2 study of CYP2D6 genotype-guided therapy for pts on tamoxifen for breast cancer. In this trial, we evaluated baseline endoxifen (E) levels and the impact of increased T dose to 40 mg/day among pts with any dysfunctional CYP2D6 alleles. The primary endpoint of change in E levels is not yet reported. All trial participants and those who declined participation were eligible for this survey. The research nurse administered 11 written questions at time of consent related to the purpose of this study and the nature of pharmacogenomic research. Pts had unlimited time to complete the survey written in a 5 point scale (strongly agree, agree, not sure, disagree, strongly disagree). For pts declining to enroll in the parent study, we offered an identical companion survey to which they could separately give consent.Results: Of 118 pts in the parent study, 117 completed the survey. Following informed consent, all respondents expressed confidence that they understood the purpose of the trial, 75% strongly agreed that they understood the purpose of the study. 98% of participants understood that this was a study of how different people respond to T, but 42% also incorrectly felt that this was a study of how different types of breast cancer respond to T, and 30% incorrectly felt that this study evaluated genetic risk for developing breast cancer. Though the consent form clearly stated that there may be no direct benefit to participants and that the purpose of the study was to help future pts, 68% reported that they would benefit directly, and only 22% felt the study was designed only to help future pts. When asked if the study involved genetics, 14% of pts disagreed, or were unsure. 45% of participants were uncomfortable or unsure with “having your doctor determine your T dose from the results of a genetic test.” Among a small sample of pts who declined trial participation but consented to the survey (13/30 decliners, 43%), compared to trial participants, fewer reported strong confidence in understanding the purpose of the trial (38% vs. 75%, p=0.0034), and a greater percentage identified an inaccurate purpose of the trial (69% vs. 42%, p = 0.043).Conclusions: After informed consent, a high percentage of participants in a pharmacogenomic clinical trial are able to correctly identify the primary purpose of the research, but a substantial minority hold false views about what the trial is designed to investigate. The majority of participants believe that they will directly benefit from trial participation, and few may understand that the primary purpose of the study is to improve care for future patients. Opportunities exist for improved understanding and communication of pharmacogenomic research and further evaluation of this area is needed.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 6082.

MicroRNAs impair MET-mediated invasive growth

MicroRNAs (miRNA) are a recently identified class of noncoding, endogenous, small RNAs that regulate gene expression, mainly at the translational level. These molecules play critical roles in several biological processes, such as cell proliferation and differentiation, development, and aging. It is also known that miRNAs play a role in human cancers where they can act either as oncogenes, down-regulating tumor suppressor genes, or as onco-suppressors, targeting molecules critically involved in promotion of tumor growth. One of such molecules is the tyrosine kinase receptor for hepatocyte growth factor, encoded by the MET oncogene. The MET receptor promotes a complex biological program named "invasive growth" that results from stimulation of cell motility, invasion, and protection from apoptosis. This oncogene is deregulated in many human tumors, where its most frequent alteration is overexpression. In this work, we have identified three miRNAs (miR-34b, miR-34c, and miR-199a*) that negatively regulate MET expression. Inhibition of these endogenous miRNAs, by use of antagomiRs, resulted in increased expression of MET protein, whereas their exogenous expression in cancer cells blocked MET-induced signal transduction and the execution of the invasive growth program, both in cells expressing normal levels of MET and in cancer cells overexpressing a constitutively active MET. Moreover, we show that these same miRNAs play a role in regulating the MET-induced migratory ability of melanoma-derived primary cells. In conclusion, we have identified miRNAs that behave as oncosuppressors by negatively targeting MET and might thus provide an additional option to inhibit this oncogene in tumors displaying its deregulation.