Mutant-selective KRAS^G12C inhibitors, such as MRTX849 (adagrasib) and AMG 510 (sotorasib), have demonstrated efficacy in KRAS^G12C-mutant cancers, including non–small cell lung cancer (NSCLC). However, mechanisms underlying clinical acquired resistance to KRAS^G12C inhibitors remain undetermined. To begin to define the mechanistic spectrum of acquired resistance, we describe a patient with KRAS^G12C NSCLC who developed polyclonal acquired resistance to MRTX849 with the emergence of 10 heterogeneous resistance alterations in serial cell-free DNA spanning four genes (KRAS, NRAS, BRAF, MAP2K1), all of which converge to reactivate RAS–MAPK signaling. Notably, a novel KRAS^Y96D mutation affecting the switch-II pocket, to which MRTX849 and other inactive-state inhibitors bind, was identified that interferes with key protein–drug interactions and confers resistance to these inhibitors in engineered and patient-derived KRAS^G12C cancer models. Interestingly, a novel, functionally distinct tricomplex KRAS^G12C active-state inhibitor RM-018 retained the ability to bind and inhibit KRAS^G12C/Y96D and could overcome resistance.

In one of the first reports of clinical acquired resistance to KRAS^G12C inhibitors, our data suggest polyclonal RAS–MAPK reactivation as a central resistance mechanism. We also identify a novel KRAS switch-II pocket mutation that impairs binding and drives resistance to inactive-state inhibitors but is surmountable by a functionally distinct KRAS^G12C inhibitor.

See related commentary by Pinnelli and Trusolino, p. 1874.

This article is highlighted in the In This Issue feature, p. 1861