Sensitivity and Resistance of MET Exon 14 Mutations in Lung Cancer to Eight MET Tyrosine Kinase Inhibitors In Vitro

MET-dependent solid tumours - molecular diagnosis and targeted therapy

Attempts to develop MET-targeted therapies have historically focused on MET-expressing cancers, with limited success. Thus, MET expression in the absence of a genomic marker of MET dependence is a poor predictor of benefit from MET-targeted therapy. However, owing to the development of more sensitive methods of detecting genomic alterations, high-level MET amplification and activating MET mutations or fusions are all now known to be drivers of oncogenesis. MET mutations include those affecting the kinase or extracellular domains and those that result in exon 14 skipping. The activity of MET tyrosine kinase inhibitors varies by MET alteration category. The likelihood of benefit from MET-targeted therapies increases with increasing levels of MET amplification, although no consensus exists on the optimal diagnostic cut-off point for MET copy number gains identified using fluorescence in situ hybridization and, in particular, next-generation sequencing. Several agents targeting exon 14 skipping alterations are currently in clinical development, with promising data available from early-phase trials. By contrast, the therapeutic implications of MET fusions remain underexplored. Here we summarize and evaluate the utility of various diagnostic techniques and the roles of different classes of MET-targeted therapies in cancers with MET amplification, mutation and fusion, and MET overexpression.

Progress on treatment of MET signaling pathway in non-small cell lung cancer

MET activation includes gene mutation, amplification, and protein overexpression. Clinical evidence suggests that MET activation is both a primary oncogenic driver in lung cancer, and a secondary driver after acquired resistance to EGFR tyrosine kinase inhibitors (TKIs). Several small molecule TKIs have already shown to be effective in the MET pathway. However, the activation form and the diagnostic criteria of MET oncogene are still controversial, especially in patients resistant to EGFR TKIs or ALK TKIs. With the development of new MET inhibitors, a quantity of emerging trials has focused on the mechanism of acquired resistance to MET TKIs and therapeutic strategies after resistance.

Targeting the HGF/MET Axis in Cancer Therapy: Challenges in Resistance and Opportunities for Improvement

Among hundreds of thousands of signal receptors contributing to oncogenic activation, tumorigenesis, and metastasis, the hepatocyte growth factor (HGF) receptor - also called tyrosine kinase MET - is a promising target in cancer therapy as its axis is involved in several different cancer types. It is also associated with poor outcomes and is involved in the development of therapeutic resistance. Several HGF/MET-neutralizing antibodies and MET kinase-specific small molecule inhibitors have been developed, resulting in some context-dependent progress in multiple cancer treatments. Nevertheless, the concomitant therapeutic resistance largely inhibits the translation of such targeted drug candidates into clinical application. Until now, numerous studies have been performed to understand the molecular, cellular, and upstream mechanisms that regulate HGF/MET-targeted drug resistance, further explore novel strategies to reduce the occurrence of resistance, and improve therapeutic efficacy after resistance. Intriguingly, emerging evidence has revealed that, in addition to its conventional function as an oncogene, the HGF/MET axis stands at the crossroads of tumor autophagy, immunity, and microenvironment. Based on current progress, this review summarizes the current challenges and simultaneously proposes future opportunities for HGF/MET targeting for therapeutic cancer interventions.

Management of Non-small Cell Lung Cancer Patients with MET Exon 14 Skipping Mutations

OPINION STATEMENT

The MET exon 14 skipping mutation is found in approximately 3% of lung adenocarcinomas and slightly more than 2% of lung squamous cell carcinomas. In recent years, more and more evidence has shown that MET inhibitors have achieved good anti-tumor effect in patients with MET exon 14 skipping mutation, suggesting that MET exon 14 skipping mutation may be a new target for NSCLC patients. Patients with positive MET exon 14 skipping mutation are recommended to be administered MET inhibitors, and crizotinib is recommended by the NCCN guideline. Due to the presence of gene amplification, second site mutation, bypass activation, and pathological type transformation, one of the inevitable problems of targeted therapy is drug resistance. If type I MET inhibitors (crizotinib, capmatinib, tepotinib, savolitinib) drug resistance is developed, type II MET inhibitors (cabozantinib, glesatinib, merestinib) can be considered.

New Targets in Lung Cancer (Excluding EGFR, ALK, ROS1)

PURPOSE OF REVIEW

Over the last two decades, the identification of targetable oncogene drivers has revolutionized the therapeutic landscape of non-small cell lung cancer (NSCLC). The extraordinary progresses made in molecular biology prompted the identification of several rare molecularly defined subgroups. In this review, we will focus on the novel and emerging actionable oncogenic drivers in NSCLC.

RECENT FINDINGS

Recently, novel oncogene drivers emerged as promising therapeutic targets besides the well-established EGFR mutations, and ALK/ROS1 rearrangements, considerably expanding the list of potential exploitable genetic aberrations. However, the therapeutic algorithm in these patients is far less defined. The identification of uncommon oncogene drivers is reshaping the diagnostic and therapeutic approach to NSCLC. The introduction of novel highly selective inhibitors is expanding the use of targeted therapies to rare and ultra-rare subsets of patients, further increasing the therapeutic armamentarium of advanced NSCLC.

Molecular Mechanisms of Acquired Resistance to MET Tyrosine Kinase Inhibitors in Patients with MET Exon 14-Mutant NSCLC

PURPOSE

Molecular mechanisms of acquired resistance to MET tyrosine kinase inhibitors (TKI) are poorly understood. We aimed to characterize the genomic mechanisms of resistance to type I and type II MET TKIs and their impact on sequential MET TKI therapy outcomes in patients with metastatic MET exon 14-mutant NSCLC.

EXPERIMENTAL DESIGN

Genomic alterations occurring at the time of progression on MET TKIs were studied using plasma and tissue next-generation sequencing (NGS).

RESULTS

A total of 20 patients had tissue or plasma available for analysis at the time of acquired resistance to a MET TKI. Genomic alterations known or suspected to be mechanisms of resistance were detected in 15 patients (75%). On-target acquired mechanisms of resistance, including single and polyclonal MET kinase domain mutations in codons H1094, G1163, L1195, D1228, Y1230, and high levels of amplification of the MET exon 14-mutant allele, were observed in 7 patients (35%). A number of off-target mechanisms of resistance were detected in 9 patients (45%), including KRAS mutations and amplifications in KRAS, EGFR, HER3, and BRAF; one case displayed both on- and off-target mechanisms of resistance. In 2 patients with on-target resistant mutations, switching between type I and type II MET TKIs resulted in second partial responses.

CONCLUSIONS

On-target secondary mutations and activation of bypass signaling drive resistance to MET TKIs. A deeper understanding of these molecular mechanisms can support the development of sequential or combinatorial therapeutic strategies to overcome resistance.