RAS-GTP Inhibition Overcomes Acquired Resistance to KRASG12C Inhibitors Mediated by Oncogenic and Wildtype RAS Activation in Non-Small Cell Lung Cancer

Small molecule KRASG12C(OFF) inhibitors that bind to the inactive GDP-bound state of KRAS have demonstrated efficacy in patients with KRASG12C mutant tumors, yet responses tend to be transient due to emergence of on-treatment resistance. Recently, RAS(ON) G12C-selective inhibitors, which bind to the active GTP-bound state of RAS, were described, and elironrasib is undergoing evaluation in multiple clinical trials. Here, we generated resistant cell lines and patient-derived xenograft models to KRASG12C(OFF) and RAS(ON) G12C-selective inhibitors and interrogated resistance mechanisms using a multi-omics strategy consisting of phosphoproteomics, whole exome sequencing, and RNA-sequencing combined with functional testing using small molecule and CRISPR screens and RAS(ON) inhibitors being evaluated in clinical trials. Two models reactivated RAS signaling, either via KRASG12C gene amplification or NRASG13R mutation, and were vulnerable to dual inhibition by RAS(ON) G12C-selective and RAS(ON) multi-selective inhibitors, RMC-4998 and RMC-7977. Two models, which lacked any discernable genomic alteration, acquired resistance associated with increased receptor tyrosine kinase activity and downstream persistent RAS activity and were sensitive to RAS-GTP inhibition by RMC-7977. Finally, one model displayed epithelial-mesenchymal transition, loss of RAS dependance, and acquired reliance on cell cycle kinases and proteins associated with DNA damage response. This work highlights KRASG12C-selective inhibitor resistant states that parallel and complement clinical findings and demonstrate that a large subset could be overcome with a RAS(ON) multi-selective inhibitor as a standalone agent or in combination with other therapies.