Clinical Acquired Resistance to KRAS Inhibition through a Novel KRAS Switch-II Pocket Mutation and Polyclonal Alterations Converging on RAS-MAPK Reactivation.

Mutant-selective KRAS inhibitors, such as MRTX849 (adagrasib) and AMG 510 (sotorasib), have demonstrated efficacy in -mutant cancers, including non-small cell lung cancer (NSCLC). However, mechanisms underlying clinical acquired resistance to KRAS inhibitors remain undetermined. To begin to define the mechanistic spectrum of acquired resistance, we describe a patient with NSCLC who developed polyclonal acquired resistance to MRTX849 with the emergence of 10 heterogeneous resistance alterations in serial cell-free DNA spanning four genes (), all of which converge to reactivate RAS-MAPK signaling. Notably, a novel 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 cancer models. Interestingly, a novel, functionally distinct tricomplex KRAS active-state inhibitor RM-018 retained the ability to bind and inhibit KRAS and could overcome resistance. SIGNIFICANCE: In one of the first reports of clinical acquired resistance to KRAS 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 inhibitor...