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.

Personalized therapeutic strategies in HER2-driven gastric cancer.

BACKGROUND: Trastuzumab is the only approved targeted therapy in patients with HER2-amplified metastatic gastric cancer (GC). Regrettably, in clinical practice, only a fraction of them achieves long-term benefit from trastuzumab-based upfront strategy. To advance precision oncology, we investigated the therapeutic efficacy of different HER2-targeted strategies, in HER2 "hyper"-amplified (≥ 8 copies) tumors. METHODS: We undertook a prospective evaluation of HER2 targeting with monoclonal antibodies, tyrosine kinase inhibitors and antibody-drug conjugates, in a selected subgroup of HER2 "hyper"-amplified gastric patient-derived xenografts (PDXs), through the design of ad hoc preclinical trials. RESULTS: Despite the high level of HER2 amplification, trastuzumab elicited a partial response only in 2 out of 8 PDX models. The dual-HER2 blockade with trastuzumab plus either pertuzumab or lapatinib led to complete and durable responses in 5 (62.5%) out of 8 models, including one tumor bearing a concomitant HER2 mutation. In a resistant PDX harboring KRAS amplification, the novel antibody-drug conjugate trastuzumab deruxtecan (but not trastuzumab emtansine) overcame KRAS-mediated resistance. We also identified a HGF-mediated non-cell-autonomous mechanism of secondary resistance to anti-HER2 drugs, responsive to MET co-targeting. CONCLUSION: These preclinical randomized trials clearly indicate that in HER2-driven gastric tumors, a boosted HER2 therapeutic blockade is required for optimal efficacy, leading to complete and durable responses in most of the cases. Our results suggest that a selected subpopulation of HER2-"hyper"-amplified GC patients could strongly benefit from this strategy. Despite the negative results of clinical trials, the dual blockade should be reconsidered for patients with clearly HER2-addicted cancers.

MicroRNA/gene profiling unveils early molecular changes and nuclear factor erythroid related factor 2 (NRF2) activation in a rat model recapitulating human hepatocellular carcinoma (HCC).

UNLABELLED: Studies on gene and/or microRNA (miRNA) dysregulation in the early stages of hepatocarcinogenesis are hampered by the difficulty of diagnosing early lesions in humans. Experimental models recapitulating human hepatocellular carcinoma (HCC) are then used to perform this analysis. We performed miRNA and gene expression profiling to characterize the molecular events involved in the multistep process of hepatocarcinogenesis in the resistant-hepatocyte rat model. A high percentage of dysregulated miRNAs/genes in HCC were similarly altered in early preneoplastic lesions positive for the stem/progenitor cell marker cytokeratin-19, indicating that several HCC-associated alterations occur from the very beginning of the carcinogenic process. Our analysis also identified miRNA/gene-target networks aberrantly activated at the initial stage of hepatocarcinogenesis. Activation of the nuclear factor erythroid related factor 2 (NRF2) pathway and up-regulation of the miR-200 family were among the most prominent changes. The relevance of these alterations in the development of HCC was confirmed by the observation that NRF2 silencing impaired while miR-200a overexpression promoted HCC cell proliferation in vitro. Moreover, T3-induced in vivo inhibition of the NRF2 pathway accompanied the regression of cytokeratin-19-positive nodules, suggesting that activation of this transcription factor contributes to the onset and progression of preneoplastic lesions towards malignancy. The finding that 78% of genes and 57% of dysregulated miRNAs in rat HCC have been previously associated with human HCC as well underlines the translational value of our results. CONCLUSION: This study indicates that most of the molecular changes found in HCC occur in the very early stages of hepatocarcinogenesis. Among these, the NRF2 pathway plays a relevant role and may represent a new therapeutic target.

Human ASH-1 promotes neuroendocrine differentiation in androgen deprivation conditions and interferes with androgen responsiveness in prostate cancer cells.

BACKGROUND: Neuroendocrine differentiation in prostate cancer is a dynamic process associated to the onset of hormone-refractory disease in vivo. The molecular mechanisms underlying this process are poorly recognized. Our study aimed at testing in vitro the role of hASH-1, a transcription factor implicated in neuroendocrine differentiation, in the onset of neuroendocrine phenotype in prostate cancer cells. METHODS: Androgen sensitive LNCAP, androgen insensitive PC-3, and three immortalized prostate cancer cell lines were cultured in standard and androgen deprivation conditions. Expression of hASH-1 was modulated by either specific lentiviral transduction or shRNA interference. Inhibitors of WNT-11, a WNT family member associated to the development of neuroendocrine differentiation in prostate cancer, were also used. Cell viability was measured using the MTS method. Neuroendocrine phenotype was assessed by morphology, immunohistochemistry and real time PCR for several neuroendocrine markers. RESULTS: hASH-1 was up-modulated by androgen deprivation in LNCaP cells and in androgen-sensitive immortalized prostate cancer cells, and associated with the onset of a neuroendocrine phenotype. Silencing of hASH-1 prevented neuroendocrine differentiation, as did also the selective interference with the WNT-11 pathway. Moreover, hASH-1 over-expression in LNCaP cells was sufficient to promote neuroendocrine differentiation and increased cell viability at basal and androgen-deprived growth conditions. CONCLUSION: In summary, the present data support previous evidence that the acquisition of a neuroendocrine phenotype is linked to androgen responsiveness profiles and suggest a pivotal role of hASH-1 transcription factor, whose activity might be explored as a potential therapeutic target in prostate cancer, with special reference to hormone refractory disease.

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.

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.

Diverse MicroRNAs-mRNA networks regulate the priming phase of mouse liver regeneration and of direct hyperplasia.

OBJECTIVES: Adult hepatocytes are quiescent cells that can be induced to proliferate in response to a reduction in liver mass (liver regeneration) or by agents endowed with mitogenic potency (primary hyperplasia). The latter condition is characterized by a more rapid entry of hepatocytes into the cell cycle, but the mechanisms responsible for the accelerated entry into the S phase are unknown. MATERIALS AND METHODS: Next generation sequencing and Illumina microarray were used to profile microRNA and mRNA expression in CD-1 mice livers 1, 3 and 6 h after 2/3 partial hepatectomy (PH) or a single dose of TCPOBOP, a ligand of the constitutive androstane receptor (CAR). Ingenuity pathway and DAVID analyses were performed to identify deregulated pathways. MultiMiR analysis was used to construct microRNA-mRNA networks. RESULTS: Following PH or TCPOBOP we identified 810 and 527 genes, and 102 and 10 miRNAs, respectively, differentially expressed. Only 20 genes and 8 microRNAs were shared by the two conditions. Many miRNAs targeting negative regulators of cell cycle were downregulated early after PH, concomitantly with increased expression of their target genes. On the contrary, negative regulators were not modified after TCPOBOP, but Ccnd1 targeting miRNAs, such as miR-106b-5p, were downregulated. CONCLUSIONS: While miRNAs targeting negative regulators of the cell cycle are downregulated after PH, TCPOBOP caused downregulation of miRNAs targeting genes required for cell cycle entry. The enhanced Ccnd1 expression may explain the more rapid entry into the S phase of mouse hepatocytes following TCPOBOP.

Cancer-Associated Fibroblasts Promote Aggressive Gastric Cancer Phenotypes via Heat Shock Factor 1-Mediated Secretion of Extracellular Vesicles.

Gastric cancer is the third most lethal cancer worldwide, and evaluation of the genomic status of gastric cancer cells has not translated into effective prognostic or therapeutic strategies. We therefore hypothesize that outcomes may depend on the tumor microenvironment (TME), in particular, cancer-associated fibroblasts (CAF). However, very little is known about the role of CAFs in gastric cancer. To address this, we mapped the transcriptional landscape of human gastric cancer stroma by microdissection and RNA sequencing of CAFs from patients with gastric cancer. A stromal gene signature was associated with poor disease outcome, and the transcription factor heat shock factor 1 (HSF1) regulated the signature. HSF1 upregulated inhibin subunit beta A and thrombospondin 2, which were secreted in CAF-derived extracellular vesicles to the TME to promote cancer. Together, our work provides the first transcriptional map of human gastric cancer stroma and highlights HSF1 and its transcriptional targets as potential diagnostic and therapeutic targets in the genomically stable tumor microenvironment. SIGNIFICANCE: This study shows how HSF1 regulates a stromal transcriptional program associated with aggressive gastric cancer and identifies multiple proteins within this program as candidates for therapeutic intervention. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/81/7/1639/F1.large.jpg.

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.

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.

Potential role of two novel agonists of thyroid hormone receptor-ß on liver regeneration.

OBJECTIVES: Although the hepatomitogenic activity of triiodothyronine (T3) is well established, the wide range of harmful effects exerted by this hormone precludes its use in liver regenerative therapy. Selective agonists of the beta isoform of thyroid hormone receptor (TRß) do not exhibit T3-induced cardiotoxicity and show a good safety profile in patients with NASH. The aim of this study was to investigate whether two novel TRß agonists, the prodrug TG68 and the active compound IS25 could stimulate hepatocyte proliferation without T3/TRα-dependent side effects. METHODS: Rats were treated with three different doses (12.5, 25 and 50 µg/100 g body weight) for one week. Hepatocyte proliferation, liver injury and serum biochemical parameters were measured by immunohistochemistry, qRT-PCR and Western blot. RESULTS: Both drugs increased hepatocyte proliferation as assessed by bromodeoxyuridine incorporation (from 14% to 28% vs 5% of controls) and mitotic activity. Enhanced proliferation occurred in the absence of significant signs of liver injury as shown by lack of increased serum transaminase levels or of apoptosis. No cardiac or renal hypertrophy typically associated with treatment with T3 was observed. Importantly, no proliferation of pancreatic acinar cells, such as that seen after administration of T3 or the TRß agonist GC1 was detected following either TG68 or IS25, demonstrating the hepato-specificity of these novel TRß agonists. CONCLUSIONS: The present study shows that TG68 and IS25 induce massive hepatocyte proliferation without overt toxicity. Hence, these agents may have a significant clinical application for regenerative therapies in liver transplantation or other surgical settings.

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.

Molecular cancer therapy: can our expectation be MET?

Altered regulation of tyrosine kinase receptors (RTKs) is frequent in solid tumours and it is often associated with the acquisition of an aggressive phenotype. Thus, therapies targeting these receptors have been proposed as molecular approaches to treat human cancers. The MET proto-oncogene, encoding the tyrosine kinase receptor for hepatocyte growth factor (HGF), controls genetic programmes leading to cell growth, invasion and protection from apoptosis. Germ-line mutations of MET in patients affected by hereditary papillary renal carcinomas (HPRC) have provided strong genetic evidences for its role in human malignancies; moreover, constitutive activation of this receptor, as a consequence of different mechanisms such as over-expression, autocrine stimulation or point mutations, is frequent in sporadic cancers. Several strategies to block the activation of MET are under development, such as the use of tyrosine kinase inhibitors or monoclonal antibodies and some of these compounds have already been used in clinical trials. In this review, we will discuss the molecular mechanisms underlying MET involvement in tumourigenesis and present pre-clinical and clinical data obtained with compounds aimed at targeting MET in the frame of cancer therapy.

miR-205 mediates adaptive resistance to MET inhibition via ERRFI1 targeting and raised EGFR signaling.

The onset of secondary resistance represents a major limitation to long-term efficacy of target therapies in cancer patients. Thus, the identification of mechanisms mediating secondary resistance is the key to the rational design of therapeutic strategies for resistant patients. MiRNA profiling combined with RNA-Seq in MET-addicted cancer cell lines led us to identify the miR-205/ERRFI1 (ERBB receptor feedback inhibitor-1) axis as a novel mediator of resistance to MET tyrosine kinase inhibitors (TKIs). In cells resistant to MET-TKIs, epigenetically induced miR-205 expression determined the downregulation of ERRFI1 which, in turn, caused EGFR activation, sustaining resistance to MET-TKIs. Anti-miR-205 transduction reverted crizotinib resistance in vivo, while miR-205 over-expression rendered wt cells refractory to TKI treatment. Importantly, in the absence of EGFR genetic alterations, miR-205/ERRFI1-driven EGFR activation rendered MET-TKI-resistant cells sensitive to combined MET/EGFR inhibition. As a proof of concept of the clinical relevance of this new mechanism of adaptive resistance, we report that a patient with a MET-amplified lung adenocarcinoma displayed deregulation of the miR-205/ERRFI1 axis in concomitance with onset of clinical resistance to anti-MET therapy.

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.

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.

RRM1 modulates mitotane activity in adrenal cancer cells interfering with its metabolization.

The anti-proliferative activity of mitotane (o,p'DDD) in adrenocortical cancer is mediated by its metabolites o,p'DDE and o,p'DDA. We previously demonstrated a functional link between ribonucleotide reductase M1(RRM1) expression and o,p'DDD activity, but the mechanism is unknown. In this study we assessed the impact of RRM1 on the bioavailability and cytotoxic activity of o,p'DDD, o,p'DDE and o,p'DDA in SW13 and H295R cells. In H295R cells, mitotane and its metabolites showed a similar cytotoxicity and RRM1 expression was not influenced by any drug. In SW13 cells, o,p'DDA only showed a cytotoxic activity and did not modify RRM1 expression, whereas the lack of sensitivity to o,p'DDE was associated to RRM1 gene up-modulation, as already demonstrated for o,p'DDD. RRM1 silencing in SW13 cells increased the intracellular transformation of mitotane into o,p'DDE and o,p'DDA. These data demonstrate that RRM1 gene interferes with mitotane metabolism in adrenocortical cancer cells, as a possible mechanisms of drug resistance.

Resistance to targeted therapies: a role for microRNAs?

The discovery of oncogene addiction dramatically changed the therapeutic approach for cancer treatment, and many drugs targeting specific molecular alterations are now in clinics. Despite the big success of these new compounds, the main limit to their efficacy is represented by resistance to therapy. The alteration of the activity or of the expression of many proteins has already been linked to the onset of resistance, but recent evidence indicates a role of microRNAs (miRNAs) as well. In this context, the idea of exploiting miRNAs as predictors of response or resistance to cancer therapy represents an intriguing possibility. The purpose of this review is to address the relationship between miRNAs and targeted therapies response and resistance.

MiR-1 downregulation cooperates with MACC1 in promoting MET overexpression in human colon cancer.

PURPOSE: MET, the tyrosine kinase receptor for hepatocyte growth factor, is frequently overexpressed in colon cancers with high metastatic tendency. We aimed to evaluate the role of its negative regulators, miR-1 and miR-199a*, and its transcriptional activator, the metastasis-associated in colon cancer 1 (MACC1), in controlling MET expression in human colon cancer samples. EXPERIMENTAL DESIGN: The expression of MET, miR-1, miR-199a*, and MACC1 was evaluated by real-time PCR in 52 matched pairs of colorectal cancers and nontumoral surrounding tissues. The biological role of miR-1 in controlling MET expression and biological activity was assessed in colon cancer cells either by its forced expression or by AntagomiR-mediated inhibition. RESULTS: MiR-1 was downregulated in 84.6% of the tumors and its decrease significantly correlated with MET overexpression, particularly in metastatic tumors. We found that concurrent MACC1 upregulation and miR-1 downregulation are required to elicit the highest increase of MET expression. Consistent with a suppressive role of miR-1, its forced in vitro expression in colon cancer cells reduced MET levels and impaired MET-induced invasive growth. Finally, we identified a feedback loop between miR-1 and MET, resulting in their mutual regulation. CONCLUSIONS: This study identifies an oncosuppressive role of miR-1 in colorectal cancer in which it acts by controlling MET expression through a feedback loop. Concomitant downregulation of miR-1 and increase of MACC1 can thus contribute to MET overexpression and to the metastatic behavior of colon cancer cells.

HIF-1α stabilization by mitochondrial ROS promotes Met-dependent invasive growth and vasculogenic mimicry in melanoma cells.

The "angiogenic switch" during tumor progression is increasingly recognized as a milestone event in tumorigenesis, although the surprising prometastatic effect of antiangiogenic therapies has recently shaken the scientific community. Tumor hypoxia has been singled out as a possible responsible factor in this prometastatic effect, although the molecular pathways are completely unknown. We report herein that human melanoma cells respond to hypoxia through a deregulation of the mitochondrial release of reactive oxygen species (ROS) by the electron transfer chain complex III. These ROS are mandatory to stabilize hypoxia-inducible factor-1α (HIF-1α), the master transcriptional regulator of the hypoxic response. We found that melanoma cells sense hypoxia-enhancing expression/activation of the Met proto-oncogene, which drives a motogenic escape program. Silencing analyses revealed a definite hierarchy of this process, in which mitochondrial ROS drive HIF-1α stabilization, which in turn activates the Met proto-oncogene. This pathway elicits a clear metastatic program of melanoma cells, enhancing spreading on extracellular matrix, motility, and invasion of 3D matrices, as well as growth of metastatic colonies and the ability to form capillary-like structures by vasculogenic mimicry. Both pharmacological and genetic interference with mitochondrial ROS delivery or Met expression block the hypoxia-driven metastatic program. Hence, we propose that hypoxia-driven ROS act as a primary driving force to elicit an invasive program exploited by aggressive melanoma cells to escape from a hypoxic hostile environment.