Abstract PR-16: Evaluating direct KRASQ61H inhibition in pancreatic cancer models

Abstract KRASQ61 mutations are associated with the worst prognosis among the various KRAS mutational subtypes of pancreatic ductal adenocarcinoma (PDAC). RMC-7977 is a RAS (ON) multi-selective noncovalent inhibitor with broad spectrum activity against oncogenic RAS mutants and wild-type RAS. The related investigational agent RMC-6236 is currently undergoing clinical trials. Binary complexes of CypA: RMC-7977 bind equipotently to multiple KRAS mutational subtypes however RMC-7977 is less potent at inhibiting growth in KRASQ61H-mutant cell lines. In contrast, RM-047 is a preclinical RAS (ON) Q61H-selective inhibitor tool compound. We evaluated direct KRASQ61H inhibition using both RMC-7977 and RM-047 in cell culture models. We found that in KRASQ61H-rescued RASless mouse embryonic fibroblasts (MEFs), RM-047 inhibited ERK activity and suppressed growth more potently than RMC-7977. Conversely, in a panel of KRASQ61H-mutant PDAC cell lines, RM-047 was less potent than RMC-7977 in two out of three KRASQ61H-mutant PDAC cell lines. Furthermore, we discovered that ERK activity rapidly rebounded with treatment in KRASQ61H-mutant PDAC cell lines, whereas ERK activity remained suppressed in KRASQ61H-rescued RASless MEFS lacking WT RAS alleles. Our analysis of DepMap data indicated that among the KRAS mutational subtypes frequently found in pancreatic cancer, KRASQ61H is the least dependent on KRAS for survival. This suggests that in a KRASQ61H-mutant PDAC setting, additional factors such as WT RAS expression may mediate growth. From our KRAS drug-anchored CRISPR loss-of-function screens, we found that the loss of EGFR sensitized cells to KRAS inhibition, particularly in a KRASQ61H-dependent context. Therefore, we combined erlotinib, an FDA-approved EGFR inhibitor, with either RM-047 or RMC-7977, and found that the addition of erlotinib prevented ERK rebound activity and synergized with RM-047 or RMC-7977 to reduce growth in KRASQ61H-mutant PDAC cell lines. These data provide insights into mechanisms by which KRASQ61H-mutant PDAC may be less dependent on KRAS for survival and further support the clinical evaluation of combined EGFR and RAS (ON) inhibition as a potential therapeutic strategy in the treatment of PDAC patients harboring KRASQ61H mutations. Citation Format: Szu-Aun Long, Amber M Amparo, Haley Todd, Grace Goodhart, Syed A Ahmad, Andrew M Waters. Evaluating direct KRAS inhibition in pancreatic cancer models abstract. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84 (17 Suppl₂): Abstract nr PR-16.