Molecular and functional characterization of reversible-sunitinib-tolerance state in human renal cell carcinoma.

Therapy failure with the tyrosine kinase inhibitor (TKI) sunitinib remains a great challenge in metastatic renal cell carcinoma (mRCC). Growing evidence indicates that the tumour subpopulation can enter a transient, non-mutagenic drug-tolerant state to endure the treatment underlying the minimal residual disease and tumour relapse. Drug tolerance to sunitinib remains largely unexplored in RCC. Here, we show that sunitinib-tolerant 786-O/S and Caki-2/S cells are induced by prolonged drug treatment showing reduced drug sensitivity, enhanced clonogenicity, and DNA synthesis. Sunitinib-tolerance developed via dynamic processes, including (i) engagement of c-MET and AXL pathways, (ii) alteration of stress-induced p38 kinase and pro-survival BCL-2 signalling, (iii) extensive actin remodelling, which was correlated with activation of focal adhesion proteins. Remarkably, the acute drug response in both sensitive and sunitinib-tolerant cell lines led to dramatic fine-tuning of the actin-cytoskeleton and boosted cellular migration and invasion, indicating that the drug-response might depend on cell state transition rather than pre-existing mutations. The drug-tolerant state was transiently acquired, as the cells resumed initial drug sensitivity after >10 passages under drug withdrawal, reinforcing the concept of dynamic regulation and phenotypic heterogeneity. Our study described molecular events contributing to the reversible switch into sunitinib-tolerance, providing possible novel therapeutic opportunities in RCC.

Novel therapeutic strategies for rare mutations in non-small cell lung cancer.

Lung cancer is still the leading cause of cancer-related mortality. Over the past two decades, the management of non-small cell lung cancer (NSCLC) has undergone a significant revolution. Since the first identification of activating mutations in the epidermal growth factor receptor (EGFR) gene in 2004, several genetic aberrations, such as anaplastic lymphoma kinase rearrangements (ALK), neurotrophic tropomyosin receptor kinase (NTRK) and hepatocyte growth factor receptor (MET), have been found. With the development of gene sequencing technology, the development of targeted drugs for rare mutations, such as multikinase inhibitors, has provided new strategies for treating lung cancer patients with rare mutations. Patients who harbor this type of oncologic driver might acquire a greater survival benefit from the use of targeted therapy than from the use of chemotherapy and immunotherapy. To date, more new agents and regimens can achieve satisfactory results in patients with NSCLC. In this review, we focus on recent advances and highlight the new approval of molecular targeted therapy for NSCLC patients with rare oncologic drivers.

PAI-1 mediates acquired resistance to MET-targeted therapy in non-small cell lung cancer.

Mechanisms underlying primary and acquired resistance to MET tyrosine kinase inhibitors (TKIs) in managing non-small cell lung cancer remain unclear. In this study, we investigated the possible mechanisms acquired for crizotinib in MET-amplified lung carcinoma cell lines. Two MET-amplified lung cancer cell lines, EBC-1 and H1993, were established for acquired resistance to MET-TKI crizotinib and were functionally elucidated. Genomic and transcriptomic data were used to assess the factors contributing to the resistance mechanism, and the alterations hypothesized to confer resistance were validated. Multiple mechanisms underlie acquired resistance to crizotinib in MET-amplified lung cancer cell lines. In EBC-1-derived resistant cells, the overexpression of SERPINE1, the gene encoding plasminogen activator inhibitor-1 (PAI-1), mediated the drug resistance mechanism. Crizotinib resistance was addressed by combination therapy with a PAI-1 inhibitor and PAI-1 knockdown. Another mechanism of resistance in different subline cells of EBC-1 was evaluated as epithelial-to-mesenchymal transition with the upregulation of antiapoptotic proteins. In H1993-derived resistant cells, MEK inhibitors could be a potential therapeutic strategy for overcoming resistance with downstream mitogen-activated protein kinase pathway activation. In this study, we revealed the different mechanisms of acquired resistance to the MET inhibitor crizotinib with potential therapeutic application in patients with MET-amplified lung carcinoma.

Deficiency of the HGF/Met pathway leads to thyroid dysgenesis by impeding late thyroid expansion.

The mechanisms of bifurcation, a key step in thyroid development, are largely unknown. Here we find three zebrafish lines from a forward genetic screening with similar thyroid dysgenesis phenotypes and identify a stop-gain mutation in hgfa and two missense mutations in met by positional cloning from these zebrafish lines. The elongation of the thyroid primordium along the pharyngeal midline was dramatically disrupted in these zebrafish lines carrying a mutation in hgfa or met. Further studies show that MAPK inhibitor U0126 could mimic thyroid dysgenesis in zebrafish, and the phenotypes are rescued by overexpression of constitutively active MEK or Snail, downstream molecules of the HGF/Met pathway, in thyrocytes. Moreover, HGF promotes thyrocyte migration, which is probably mediated by downregulation of E-cadherin expression. The delayed bifurcation of the thyroid primordium is also observed in thyroid-specific Met knockout mice. Together, our findings reveal that HGF/Met is indispensable for the bifurcation of the thyroid primordium during thyroid development mediated by downregulation of E-cadherin in thyrocytes via MAPK-snail pathway.

Recording and classifying MET receptor mutations in cancers.

Tyrosine kinase inhibitors (TKI) directed against MET have been recently approved to treat advanced non-small cell lung cancer (NSCLC) harbouring activating MET mutations. This success is the consequence of a long characterization of MET mutations in cancers, which we propose to outline in this review. MET, a receptor tyrosine kinase (RTK), displays in a broad panel of cancers many deregulations liable to promote tumour progression. The first MET mutation was discovered in 1997, in hereditary papillary renal cancer (HPRC), providing the first direct link between MET mutations and cancer development. As in other RTKs, these mutations are located in the kinase domain, leading in most cases to ligand-independent MET activation. In 2014, novel MET mutations were identified in several advanced cancers, including lung cancers. These mutations alter splice sites of exon 14, causing in-frame exon 14 skipping and deletion of a regulatory domain. Because these mutations are not located in the kinase domain, they are original and their mode of action has yet to be fully elucidated. Less than five years after the discovery of such mutations, the efficacy of a MET TKI was evidenced in NSCLC patients displaying MET exon 14 skipping. Yet its use led to a resistance mechanism involving acquisition of novel and already characterized MET mutations. Furthermore, novel somatic MET mutations are constantly being discovered. The challenge is no longer to identify them but to characterize them in order to predict their transforming activity and their sensitivity or resistance to MET TKIs, in order to adapt treatment.

Clinical, pathologic, and genomic characteristics of two pediatric glioneuronal tumors with a CLIP2::MET fusion.

Integration of molecular data with histologic, radiologic, and clinical features is imperative for accurate diagnosis of pediatric central nervous system (CNS) tumors. Whole transcriptome RNA sequencing (RNAseq), a genome-wide and non-targeted approach, allows for the detection of novel or rare oncogenic fusion events that contribute to the tumorigenesis of a substantial portion of pediatric low- and high-grade glial and glioneuronal tumors. We present two cases of pediatric glioneuronal tumors occurring in the occipital region with a CLIP2::MET fusion detected by RNAseq. Chromosomal microarray studies revealed copy number alterations involving chromosomes 1, 7, and 22 in both tumors, with Case 2 having an interstitial deletion breakpoint in the CLIP2 gene. By methylation profiling, neither tumor had a match result, but both clustered with the low-grade glial/glioneuronal tumors in the UMAP. Histologically, in both instances, our cases displayed characteristics of a low-grade tumor, notably the absence of mitotic activity, low Ki-67 labeling index and the lack of necrosis and microvascular proliferation. Glial and neuronal markers were positive for both tumors. Clinically, both patients achieved clinical stability post-tumor resection and remain under regular surveillance imaging without adjuvant therapy at the last follow-up, 6 months and 3 years, respectively. This is the first case report demonstrating the presence of a CLIP2::MET fusion in two pediatric low-grade glioneuronal tumors (GNT). Conservative clinical management may be considered for patients with GNT and CLIP2:MET fusion in the context of histologically low-grade features.

Efficacy and safety of tepotinib in Asian patients with advanced NSCLC with MET exon 14 skipping enrolled in VISION.

BACKGROUND: Tepotinib, a MET inhibitor approved for the treatment of MET exon 14 (METex14) skipping NSCLC, demonstrated durable clinical activity in VISION (Cohort A + C; N = 313): objective response rate (ORR) 51.4% (95% CI: 45.8, 57.1); median duration of response (mDOR) 18.0 months (95% CI: 12.4, 46.4). We report outcomes in Asian patients from VISION (Cohort A + C) (cut-off: November 20, 2022). METHODS: Patients with advanced METex14 skipping NSCLC, detected by liquid or tissue biopsy, received tepotinib 500 mg (450 mg active moiety) once daily. PRIMARY ENDPOINT: objective response (RECIST 1.1) by independent review. Secondary endpoints included: DOR, progression-free survival (PFS), overall survival (OS), safety, and health-related quality of life (HRQoL). RESULTS: Across treatment lines in 106 Asian patients (39.6% female, 43.4% smoking history, 79.2% adenocarcinoma, 47.2% treatment-naive), ORR was 56.6% (95% CI: 46.6, 66.2), mDOR 18.5 months (10.4, ne), mPFS 13.8 months (10.8, 22.0), and mOS 25.5 months (19.3, 36.4). Consistent efficacy observed, regardless of baseline characteristics. HRQoL remained stable during treatment. Treatment-related adverse events (TRAEs) occurred in 95.3% of patients (39.6% Grade ≥3). Most common TRAEs: peripheral edema (62.3%), creatinine increase (38.7%). CONCLUSIONS: Tepotinib demonstrated robust and durable efficacy, with a manageable safety profile, in Asian patients with METex14 skipping NSCLC. CLINICAL TRIAL REGISTRATION: NCT02864992.

Exploring the association of POSTN+ cancer-associated fibroblasts with triple-negative breast cancer.

Triple-negative breast cancer (TNBC) is a subtype of breast cancer with a poor prognosis. Cancer-associated fibroblasts (CAFs) play a critical role in regulating TNBC tumor development. This study aimed to identify and characterize a specific subtype of CAFs associated with TNBC. Initially, using high-throughput bulk transcriptomic data in two cohorts, we identified three CAF-related subtypes (CS1, CS2, CS3) in TNBC samples. These three CAFs subtypes were closely linked to the tumor microenvironment. The CS1 subtype exhibited a relatively immune-rich microenvironment and a favourable prognosis, whereas the CS3 subtype displayed an immune-deprived tumor microenvironment and an unfavourable prognosis. Through WGCNA analysis, POSTN was identified as a key biomarker for CAFs associated with TNBC. Then, POSTN+CAFs was identified and characterized. Both POSTN and POSTN+CAFs showed significant positive correlations with stromal molecules HGF and MET at both the transcriptional and protein levels. Specifically co-localized with CAFs in the tumor stromal area, POSTN, produced by POSTN+CAFs, could modulate the HGF-MET axis, serving as a bypass activation pathway to regulate tumor cell proliferation in response to EGFR inhibitor and MET inhibitor. This study underscores the significance of POSTN and POSTN+CAFs as crucial targets for the diagnosis and treatment of TNBC.

Development of an Engineered Single-Domain Antibody for Targeting MET in Non-Small Cell Lung Cancer.

The Mesenchymal Epithelial Transition (MET) receptor tyrosine kinase is upregulated or mutated in 5% of non-small-cell lung cancer (NSCLC) patients and overexpressed in multiple other cancers. We sought to develop a novel single-domain camelid antibody with high affinity for MET that could be used to deliver conjugated payloads to MET expressing cancers. From a naïve camelid variable-heavy-heavy (VHH) domain phage display library, we identified a VHH clone termed 1E7 that displayed high affinity for human MET and was cross-reactive with MET across multiple species. When expressed as a bivalent human Fc fusion protein, 1E7-Fc was found to selectively bind to EBC-1 (MET amplified) and UW-Lung 21 (MET exon 14 mutated) cell lines by flow cytometry and immunofluorescence imaging. Next, we investigated the ability of [89Zr]Zr-1E7-Fc to detect MET expression in vivo by PET/CT imaging. [89Zr]Zr-1E7-Fc demonstrated rapid localization and high tumor uptake in both xenografts with a %ID/g of 6.4 and 5.8 for EBC-1 and UW-Lung 21 at 24 h, respectively. At the 24 h time point, clearance from secondary and nontarget tissues was also observed. Altogether, our data suggest that 1E7-Fc represents a platform technology that can be employed to potentially both image and treat MET-altered NSCLC.

MET alterations in advanced non-small cell lung cancer.

Precision medicine has helped identify several tumor molecular aberrations to be treated with targeted therapies. These therapies showed substantial improvement in efficacy without excessive toxicity in patients with specific oncogenic drivers with advanced cancers. In metastatic lung cancers, the implementation of broad platforms for molecular tumor sequencing has helped oncology providers identify oncogenic drivers linked with better outcomes when treated upfront with targeted therapies. Mesenchymal-epithelial transition factor (MET) alterations are present in up to 60% of non-small cell lung cancer and are associated with a poor prognosis. Capmatinib and tepotinib are currently the only two approved targeted therapies by the U.S. Food and Drug Administration (FDA) for patients with MET exon 14 skipping mutation. Several agents are being developed to tackle an unmet need in patients with MET alterations. Some of these agents are being used in combination with EGFR targeted therapy to mitigate resistance to EGFR inhibitor. These agents are poised to provide new hope for these patients.

p53 modulates kinase inhibitor resistance and lineage plasticity in NF1-related MPNSTs.

Malignant peripheral nerve sheath tumors (MPNSTs) are chemotherapy resistant sarcomas that are a leading cause of death in neurofibromatosis type 1 (NF1). Although NF1-related MPNSTs derive from neural crest cell origin, they also exhibit intratumoral heterogeneity. TP53 mutations are associated with significantly decreased survival in MPNSTs, however the mechanisms underlying TP53-mediated therapy responses are unclear in the context of NF1-deficiency. We evaluated the role of two commonly altered genes, MET and TP53, in kinome reprograming and cellular differentiation in preclinical MPNST mouse models. We previously showed that MET amplification occurs early in human MPNST progression and that Trp53 loss abrogated MET-addiction resulting in MET inhibitor resistance. Here we demonstrate a novel mechanism of therapy resistance whereby p53 alters MET stability, localization, and downstream signaling leading to kinome reprogramming and lineage plasticity. Trp53 loss also resulted in a shift from RAS/ERK to AKT signaling and enhanced sensitivity to MEK and mTOR inhibition. In response to MET, MEK and mTOR inhibition, we observed broad and heterogeneous activation of key differentiation genes in Trp53-deficient lines suggesting Trp53 loss also impacts lineage plasticity in MPNSTs. These results demonstrate the mechanisms by which p53 loss alters MET dependency and therapy resistance in MPNSTS through kinome reprogramming and phenotypic flexibility.

Multicenter evaluation of an automated, multiplex, RNA-based molecular assay for detection of ALK, ROS1, RET fusions and MET exon 14 skipping in NSCLC.

The current study assessed the performance of the fully automated RT-PCR-based Idylla™ GeneFusion Assay, which simultaneously covers the advanced non-small cell lung carcinoma (aNSCLC) actionable ALK, ROS1, RET, and MET exon 14 rearrangements, in a routine clinical setting involving 12 European clinical centers. The Idylla™ GeneFusion Assay detects fusions using fusion-specific as well as expression imbalance detection, the latter enabling detection of uncommon fusions not covered by fusion-specific assays. In total, 326 archival aNSCLC formalin-fixed paraffin-embedded (FFPE) samples were included of which 44% were resected specimen, 46% tissue biopsies, and 9% cytological specimen. With a total of 179 biomarker-positive cases (i.e., 85 ALK, 33 ROS1, 20 RET fusions and 41 MET exon 14 skipping), this is one of the largest fusion-positive datasets ever tested. The results of the Idylla™ GeneFusion Assay were compared with earlier results of routine reference technologies including fluorescence in situ hybridization, immunohistochemistry, reverse-transcription polymerase chain reaction, and next-generation sequencing, establishing a high sensitivity/specificity of 96.1%/99.6% for ALK, 96.7%/99.0% for ROS1, 100%/99.3% for RET fusion, and 92.5%/99.6% for MET exon 14 skipping, and a low failure rate (0.9%). The Idylla™ GeneFusion Assay was found to be a reliable, sensitive, and specific tool for routine detection of ALK, ROS1, RET fusions and MET exon 14 skipping. Given its short turnaround time of about 3 h, it is a time-efficient upfront screening tool in FFPE samples, supporting rapid clinical decision making. Moreover, expression-imbalance-based detection of potentially novel fusions may be easily verified with other routine technologies without delaying treatment initiation.

Prediction of MET Overexpression in Lung Adenocarcinoma from Hematoxylin and Eosin Images.

Mesenchymal epithelial transition (MET) protein overexpression is a targetable event in non-small cell lung cancer and is the subject of active drug development. Challenges in identifying patients for these therapies include lack of access to validated testing, such as standardized immunohistochemistry assessment, and consumption of valuable tissue for a single gene/protein assay. Development of prescreening algorithms using routinely available digitized hematoxylin and eosin (H&E)-stained slides to predict MET overexpression could promote testing for those who will benefit most. Recent literature reports a positive correlation between MET protein overexpression and RNA expression. In this work, a large database of matched H&E slides and RNA expression data were leveraged to train a weakly supervised model to predict MET RNA overexpression directly from H&E images. This model was evaluated on an independent holdout test set of 300 overexpressed and 289 normal patients, demonstrating a receiver operating characteristic area under curve of 0.70 (95th percentile interval: 0.66 to 0.74) with stable performance characteristics across different patient clinical variables and robust to synthetic noise on the test set. These results suggest that H&E-based predictive models could be useful to prioritize patients for confirmatory testing of MET protein or MET gene expression status.

TWIST1 is a critical downstream target of the HGF/MET pathway and is required for MET driven acquired resistance in oncogene driven lung cancer.

MET amplification/mutations are important targetable oncogenic drivers in NSCLC, however, acquired resistance is inevitable and the majority of patients with targetable MET alterations fail to respond to MET tyrosine kinase inhibitors (TKIs). Furthermore, MET amplification is among the most common mediators of TKI resistance. As such, novel therapies to target MET pathway and overcome MET TKI resistance are clearly needed. Here we show that the epithelial-mesenchymal transition (EMT) transcription factor, TWIST1 is a key downstream mediator of HGF/MET induced resistance through suppression of p27 and targeting TWIST1 can overcome resistance. We found that TWIST1 is overexpressed at the time of TKI resistance in multiple MET-dependent TKI acquired resistance PDX models. We have shown for the first time that MET directly stabilized the TWIST protein leading to TKI resistance and that TWIST1 was required for MET-driven lung tumorigenesis as well as could induce MET TKI resistance when overexpressed. TWIST1 mediated MET TKI resistance through suppression of p27 expression and genetic or pharmacologic inhibition of TWIST1 overcame TKI resistance in vitro and in vivo. Our findings suggest that targeting TWIST1 may be an effective therapeutic strategy to overcome resistance in MET-driven NSCLC as well as in other oncogene driven subtypes in which MET amplification is the resistance mechanism.

Activity of Tepotinib in Hepatocellular Carcinoma With High-Level MET Amplification: Preclinical and Clinical Evidence.

PURPOSE: MET amplification (METamp) has been reported in 1%-5% of patients with hepatocellular carcinoma (HCC) and may be sensitive to MET inhibition. Tepotinib, a selective MET inhibitor, has shown promising activity in HCC with MET overexpression. We investigated the preclinical and clinical activity of tepotinib in HCC with METamp (MET gene copy number [GCN] ≥5), including high-level METamp (MET GCN ≥10). METHODS: Preclinical antitumor activity of tepotinib 100 mg/kg (orally, days 1-5, every 7 days, 3-5 weeks; 3-12 replicates) was evaluated according to METamp status, as determined using the nCounter platform (NanoString), in 37 HCC patient-derived xenografts (PDXs) in immunodeficient mice. Clinical outcomes were evaluated in patients with METamp by fluorescence in situ hybridization who received tepotinib 500 mg (450 mg active moiety) in two phase Ib/II trials in HCC with MET overexpression. RESULTS: Across the PDX models, tepotinib induced complete or near-complete tumor regression in the only two models with high-level METamp. Median tumor volume reductions were 100% and 99.8% in models with MET GCN 47.1 and 44.0, respectively. Across the two clinical trials, 15/121 patients had METamp. Disease control was achieved by 11/15 patients with METamp (complete response [CR], n = 1; partial response [PR], n = 4; stable disease [SD], n = 6) and 4/4 with high-level METamp (CR, n = 1; PR, n = 2; SD, n = 1). All three patients with high-level METamp and objective response received treatment for >1 year, including one patient who received first-line tepotinib for >6 years. CONCLUSION: High-level METamp may be an oncogenic driver in HCC that is sensitive to MET inhibitors such as tepotinib.

Comparison of Tepotinib, Paclitaxel, or Ramucirumab Efficacy According to the Copy Number or Phosphorylation Status of the MET Gene: Doublet Treatment versus Single Agent Treatment.

Although conventional combination chemotherapies for advanced gastric cancer (GC) increase survival, such therapies are associated with major adverse effects; more effective and less toxic treatments are required. Combinations of different anti-cancer drugs, for example, paclitaxel plus ramucirumab, have recently been used as second-line treatments for advanced GC. This study evaluated how copy number variations of the MET gene, MET mutations, and MET gene and protein expression levels in human GC cells modulate the susceptibility of such cells to single-agent (tepotinib, ramucirumab, or paclitaxel) and doublet (tepotinib-plus-paclitaxel or ramucirumab-plus-paclitaxel treatment regimens. Compared with ramucirumab-plus-paclitaxel, tepotinib-plus-paclitaxel better inhibited the growth of GC cells with MET exon 14 skipping mutations and those lacking MET amplification but containing phosphorylated MET; such inhibition was dose-dependent and associated with cell death. Tepotinib-plus-paclitaxel and ramucirumab-plus-paclitaxel similarly inhibited the growth of GC cells lacking MET amplification or MET phosphorylation, again in a dose-dependent manner, but without induction of cell death. However, tepotinib alone or tepotinib-plus-ramucirumab was more effective against c-MET-positive GC cells (>30 copy number variations) than was ramucirumab or paclitaxel alone or ramucirumab-plus-paclitaxel. These in vitro findings suggest that compared with ramucirumab-plus-paclitaxel, tepotinib-plus-paclitaxel better inhibits the growth of c-MET-positive GC cells, cells lacking MET amplification but containing phosphorylated MET, and cells containing MET mutations. Clinical studies are required to confirm the therapeutic effects of these regimens.

Unraveling the Significance of MET Focal Amplification in Lung Cancer: Integrative NGS, FISH, and IHC Investigation.

MET amplification (METamp) represents a promising therapeutic target in non-small cell lung cancer, but no consensus has been established to identify METamp-dependent tumors that could potentially benefit from MET inhibitors. In this study, an analysis of MET amplification/overexpression status was performed in a retrospectively recruited cohort comprising 231 patients with non-small cell lung cancer from Shanghai Chest Hospital (SCH cohort) using 3 methods: fluorescence in situ hybridization (FISH), hybrid capture-based next-generation sequencing, and immunohistochemistry for c-MET and phospho-MET. The SCH cohort included 130 cases known to be METamp positive by FISH and 101 negative controls. The clinical relevance of these approaches in predicting the efficacy of MET inhibitors was evaluated. Additionally, next-generation sequencing data from another 2 cohorts including 22,010 lung cancer cases were utilized to examine the biological characteristics of different METamp subtypes. Of the 231 cases, 145 showed MET amplification/overexpression using at least 1 method, whereas only half of them could be identified by all 3 methods. METamp can occur as focal amplification or polysomy. Our study revealed that the inconsistency between next-generation sequencing and FISH primarily occurred in the polysomy subtype. Further investigations indicated that compared with polysomy, focal amplification correlated with fewer co-occurring driver mutations, higher protein expressions of c-MET and phospho-MET, and higher incidence in acquired resistance than in de novo setting. Moreover, patients with focal amplification presented a more robust response to MET inhibitors compared with those with polysomy. Notably, a strong correlation was observed between focal amplification and programmed cell death ligand-1 expression, indicating potential therapeutic implications with combined MET inhibitor and immunotherapy for patients with both alterations. Our findings provide insights into the molecular complexity and clinical relevance of METamp in lung cancer, highlighting the role of MET focal amplification as an oncogenic driver and its feasibility as a primary biomarker to further investigate the clinical activity of MET inhibitors in future studies.

Aberrant MET Receptor Tyrosine Kinase Signaling in Glioblastoma: Targeted Therapy and Future Directions.

Brain tumors represent a heterogeneous group of neoplasms characterized by a high degree of aggressiveness and a poor prognosis. Despite recent therapeutic advances, the treatment of brain tumors, including glioblastoma (GBM), an aggressive primary brain tumor associated with poor prognosis and resistance to therapy, remains a significant challenge. Receptor tyrosine kinases (RTKs) are critical during development and in adulthood. Dysregulation of RTKs through activating mutations and gene amplification contributes to many human cancers and provides attractive therapeutic targets for treatment. Under physiological conditions, the Met RTK, the hepatocyte growth factor/scatter factor (HGF/SF) receptor, promotes fundamental signaling cascades that modulate epithelial-to-mesenchymal transition (EMT) involved in tissue repair and embryogenesis. In cancer, increased Met activity promotes tumor growth and metastasis by providing signals for proliferation, survival, and migration/invasion. Recent clinical genomic studies have unveiled multiple mechanisms by which MET is genetically altered in GBM, including focal amplification, chromosomal rearrangements generating gene fusions, and a splicing variant mutation (exon 14 skipping, METex14del). Notably, MET overexpression contributes to chemotherapy resistance in GBM by promoting the survival of cancer stem-like cells. This is linked to distinctive Met-induced pathways, such as the upregulation of DNA repair mechanisms, which can protect tumor cells from the cytotoxic effects of chemotherapy. The development of MET-targeted therapies represents a major step forward in the treatment of brain tumours. Preclinical studies have shown that MET-targeted therapies (monoclonal antibodies or small molecule inhibitors) can suppress growth and invasion, enhancing the efficacy of conventional therapies. Early-phase clinical trials have demonstrated promising results with MET-targeted therapies in improving overall survival for patients with recurrent GBM. However, challenges remain, including the need for patient stratification, the optimization of treatment regimens, and the identification of mechanisms of resistance. This review aims to highlight the current understanding of mechanisms underlying MET dysregulation in GBM. In addition, it will focus on the ongoing preclinical and clinical assessment of therapies targeting MET dysregulation in GBM.

Gap junction beta-4 accelerates cell cycle progression and metastasis through MET-AKT activation in pancreatic cancer.

Despite continuing advances in the development of effective new therapies, including immunotherapies, the prognosis of pancreatic cancer remains extremely poor. Gap junction proteins have become attractive targets for potential cancer therapy. However, the role of gap junction beta-4 (GJB4) protein remains unexplored in pancreatic cancer. Through bioinformatic analyses we discovered pancreatic cancer tissues showed higher levels of GJB4 transcripts compared to normal pancreatic tissues and this had a negative effect on overall survival in patients that had pancreatic cancer. The high expression of nuclear GJB4 was identified as a negative prognostic factor in such patients. Knockdown of GJB4 in cultured pancreatic cancer cells resulted in G0/G1 arrest followed by decreased cell proliferation and suppression of metastatic potential. The overexpression of GJB4 accelerated cell proliferation, migration, and invasion in a SUIT-2 cell line, whereas MET inhibitor canceled the acceleration. GJB4 suppression with siRNA significantly inhibited tumor growth in a mouse xenograft model. Mechanistically, suppression of GJB4 inhibited MET-AKT activities. Such data suggest that targeting the GJB4-MET axis could represent a promising new therapeutic strategy for pancreatic cancer.

Functional Heterogeneity in MET Pathway Activation in PDX Models of Osimertinib-resistant EGFR-driven Lung Cancer.

MET pathway activation is one of the most common mechanisms of resistance to osimertinib in EGFR-mutant non-small cell lung cancer (NSCLC). We previously demonstrated spatial and temporal heterogeneity in MET pathway activation upon osimertinib resistance in EGFR-mutant NSCLC; however, the functional relevance of these findings is unclear. Here, we generated 19 patient-derived xenografts (PDX) from 9 patients with multi-region and temporal sampling of osimertinib-resistant tumor tissue from patients with EGFR-mutant NSCLC. MET pathway activation was a putative mechanism of osimertinib resistance in 66% (n = 6/9) patients from whom PDXs were generated. Significant spatial and temporal heterogeneity in MET pathway activation was evident. Osimertinib-resistant PDXs with MET amplification by FISH (defined as MET/CEP7 ratio ≥2.0 or mean MET ≥ 6.0 copies/cell) and high-level phospho-MET, but not c-MET expression, had better responses to osimertinib and savolitinib combination than to osimertinib alone. MET polysomy tumors by FISH from both PDXs and patients had evidence of subclonal phospho-MET expression. Select MET polysomy PDX tumors with phospho-MET expression responded better to osimertinib and savolitinib combination than MET polysomy PDX tumors without phospho-MET expression. Our results suggest osimertinib and savolitinib combination is most effective for osimertinib-resistant EGFR-mutant tumors with MET pathway activation as evidenced by phospho-MET. As subclonal MET amplification may be evident in MET polysomy tumor progression, MET polysomy warrants close clinical follow-up with phospho-MET IHC in parallel with FISH diagnostic. SIGNIFICANCE: Using a novel cohort of in vivo PDX models of MET pathway activation with acquired resistance to osimertinib in EGFR-mutant lung cancer, we demonstrate that phospho-MET may be a clinically relevant assay to guide treatment selection with osimertinib and savolitinib combination. In addition, our work shows that patients with MET polysomy tumors may have subclonal MET amplification and therefore require close follow up for the use of osimertinib and savolitinib combination.