RAS(ON) multi-selective inhibitors stimulate the hydrolysis of RAS-GTP to RAS-GDP and drive synergistic combination benefit with KRAS(OFF) inhibitors in G12 mutant tumors

KRAS mutations are among the most common oncogenic drivers across human cancers. Although RAS was long considered undruggable, recent advances have led to multiple classes of direct RAS inhibitors. KRAS(OFF) inhibitors preferentially target the inactive GDP-bound state whereas RAS(ON) tri-complex inhibitors selectively engage the active, GTP-bound form. In addition to suppressing RAS signaling by disrupting interactions with downstream effectors via steric occlusion, the RAS(ON) multi-selective inhibitor daraxonrasib (RMC-6236) and the preclinical tool compound RMC-7977 also activate RAS(ON) GTPase activity and promote the conversion of RAS(ON) to RAS(OFF). By stimulating formation of the inactive, GDP-bound state the RAS(ON) inhibitor enables potent target engagement by a KRAS(OFF) inhibitor and synergistic inhibition of oncogenic KRAS G12 mutant signaling. The inhibitory activity of the combination of daraxonrasib or RMC-7977 with representative mutant-selective KRAS(OFF) and pan-KRAS(OFF) inhibitors was evaluated in a series of KRAS G12 mutant cancer cell lines. In addition, real-time RAS-RAF complex disruption assays were used to monitor the kinetics of target engagement. As predicted, the RAS(ON) multi-selective inhibitors accelerated the rate of RAS-RAF disruption for KRAS(OFF) inhibitors. Consistent with this, a synergistic increase in potency of inhibition of KRAS signaling and cell viability was observed with the combinations. Synergy was dependent on the ability of the RAS(ON) inhibitors to convert RAS(ON) to RAS(OFF) and was abolished with the use of RAS(ON) inhibitors that do not stimulate GTP hydrolysis or the introduction of mutations in RAS that block GTP hydrolysis. In vivo , the combination of daraxonrasib and KRAS(OFF) inhibitors at well-tolerated doses drove deep and durable RAS pathway suppression and tumor regressions in various KRAS G12 mutant xenograft models, including models with reduced sensitivity to either single agent, e.g., those with mutant KRAS amplification. Overall, these preclinical findings provide a mechanistic rationale for, and experimental evidence in support of, the clinical evaluation of the combination of a RAS(ON) multi-selective inhibitor that stimulates the GTPase activity of oncogenic KRAS mutants with a KRAS(OFF) inhibitor as a potential therapeutic strategy to maximize RAS inhibition and enhance antitumor activity in RAS-addicted cancers.