MET exon 14 skipping in NSCLC — capmatinib, tepotinib, and what skipping really means

Most oncogenic kinase events in lung cancer are point mutations or fusions that rewire the kinase domain itself. MET exon 14 skipping is a stranger kind of oncogene: the kinase domain is unchanged, but a regulatory cassette that normally tags MET for destruction gets spliced out of the mRNA. The receptor that hits the membrane lasts longer than it should, and that extra half-life is enough to drive a real cancer. Capmatinib and tepotinib both exploit that single biological fact — and the clinical results have been convincing enough that METex14 is now a standard biomarker in NSCLC molecular panels.

The Y1003 trick

MET is a receptor tyrosine kinase for hepatocyte growth factor (HGF). After HGF binding, MET autophosphorylates, signals through PI3K, MAPK, and STAT, and is then turned off by the same mechanism that turns off most RTKs: ubiquitination and degradation. The ubiquitin handle is a single tyrosine in the juxtamembrane domain at position 1003. When Y1003 is phosphorylated, the E3 ligase CBL binds, ubiquitinates MET, and routes it to the lysosome. Steady-state MET levels are kept low because activated receptor is constantly being recycled out.

Exon 14 of the MET gene encodes the juxtamembrane region that contains Y1003. Splice-site mutations — point mutations or deletions at the splice donor, the splice acceptor, or the surrounding intronic region — cause exon 14 to be skipped during pre-mRNA processing. The resulting protein lacks Y1003, cannot be efficiently ubiquitinated by CBL, and is therefore not degraded after activation. The kinase domain is fully wild-type. The oncogenic signal is just the same kinase, present at higher steady-state levels and active for longer.

Why this is good for medicinal chemistry

Because the kinase domain is wild-type, ATP-competitive MET inhibitors developed before METex14 was recognized as a biomarker still work on it. The pocket has the same shape, the same gatekeeper, the same hinge contacts. METex14 is not a structural problem at the protein level — it is a mRNA problem. The drug just has to bind MET well; the oncogenicity of the variant takes care of itself.

Two ATP-competitive MET inhibitors have FDA approval in this setting:

• Capmatinib (Tabrecta, Novartis) — Type Ib MET inhibitor, FDA approved May 2020 for advanced NSCLC with a MET exon 14 skipping mutation, based on the GEOMETRY mono-1 trial. Final results showed a 68% objective response rate in treatment-naive patients (n=28) and 41% in previously treated patients (n=69). Capmatinib is highly selective for MET over related kinases — the off-target profile is comparatively clean.
• Tepotinib (Tepmetko, Merck KGaA) — Type Ib MET inhibitor, FDA approved February 2021 for the same indication, based on the VISION trial. Objective response rate was 51.4% with median duration of response of 18.0 months and median progression-free survival of 11.2 months. Tepotinib has good CNS penetration, which matters because MET-driven NSCLC has a high rate of brain metastases.

Both are once-daily oral agents. Peripheral edema is the on-target class effect for MET inhibitors — not life threatening, but enough of an issue that supportive care and dose reductions are routine. Crizotinib (originally developed for ALK) also has MET activity and has been used off-label in this setting, but it is multikinase and is no longer the standard of care once capmatinib or tepotinib is available.

Resistance: what to expect

Resistance to capmatinib and tepotinib has begun to be characterized in the clinic and falls into recognizable patterns. On-target secondary mutations in the MET kinase domain — particularly D1228 substitutions (D1228N, D1228H, D1228V) and Y1230 substitutions (Y1230H, Y1230C, Y1230S) — disrupt the Type Ib binding mode of both drugs. These are the MET equivalents of EGFR T790M gatekeeper-style mutations: cleanly on-target, predictably located near the drug-binding face. Bypass-track activation through HER3, EGFR, or KRAS amplification is also seen, and combination strategies with EGFR inhibitors are in clinical testing.

The next-generation MET inhibitor most likely to address D1228/Y1230 resistance is elzovantinib (TPX-0022), a Type II MET inhibitor designed to bind the kinase in the DFG-out conformation that the Type Ib resistance mutations do not disrupt. Elzovantinib is in early-phase trials and may eventually serve a similar second-line role to osimertinib in the EGFR setting.

Try the docking yourself

The canonical MET kinase domain structure for the Type Ib binding mode is 3R7O — MET kinase with a Type Ib inhibitor. Because METex14 leaves the kinase domain unchanged, docking against the wild-type kinase is the right starting point for any METex14 program. Open Studio and pick MET from the target catalog to dock your own ligands against the same structure. Liganx also exposes D1228N and Y1230H from the mutation chips, so you can see how a Type Ib chemotype loses contacts against the resistance mutants and where a Type II scaffold has room to make new contacts.

Liganx is molecular docking online: free, browser-based, and set up for exactly this kind of resistance question. If you want to try molecular docking on MET without a local install, that is the fastest path.

Primary sources

• Wolf J, Seto T, Han JY, et al. Capmatinib in MET Exon 14-Mutated or MET-Amplified Non-Small-Cell Lung Cancer. NEJM 383, 944–957 (2020). doi:10.1056/NEJMoa2002787
• Paik PK, Felip E, Veillon R, et al. Tepotinib in Non-Small-Cell Lung Cancer with MET Exon 14 Skipping Mutations. NEJM 383, 931–943 (2020). doi:10.1056/NEJMoa2004407
• Kong-Beltran M, Seshagiri S, Zha J, et al. Somatic mutations lead to an oncogenic deletion of Met in lung cancer. Cancer Research 66, 283–289 (2006). doi:10.1158/0008-5472.CAN-05-2749
• Recondo G, Bahcall M, Spurr LF, et al. Molecular Mechanisms of Acquired Resistance to MET Tyrosine Kinase Inhibitors in Patients with MET Exon 14-Mutant NSCLC. Clinical Cancer Research 26, 2615–2625 (2020). doi:10.1158/1078-0432.CCR-19-3608