Abstract A016: GAP mimetics display synergy with K-Ras Switch-II inhibition

Abstract Tricomplex inhibitors (TCIs) represent a new class of direct Ras inhibitors that engage the active, GTP-loaded Ras(on) state through recruitment of Cyclophilin A. Daraxonrasib (RMC-6236) is a pan-Ras TCI which has been recently reported to restore intrinsic GTPase activity of G12-mutant Ras isoforms. Structural analysis of a pan-Ras TCI bound to K-Ras(GDP–AlF3) reveals a transition-state arrangement of Tyr32 and Gln61 that closely mirrors endogenous GTPase–GAP complexes. This includes a closed Switch-I conformation engaging the cis-GTPase machinery in a manner analogous to non-arginine-finger GAPs such as RanGAP. These observations position pan-Ras TCIs as pharmacologic GAP mimetics. The engagement of K-Ras(GTP) by first generation Switch-II pocket K-Ras inhibitors, including the approved GDP-state selective K-Ras G12C inhibitor adagrasib (MRTX-849), is kinetically constrained by slow endogenous hydrolysis of the mutant GTPase. The GTPase-promoting activity of daraxonrasib therefore suggests synergy with adagrasib and other Switch-II pocket inhibitors by enriching the more sensitive GDP-state. We demonstrate that daraxonrasib sensitizes K-Ras(GTP) G12C to covalent adagrasib labeling in both recombinant protein and cellular context. In K-Ras G12C and G12D mutant cell lines, combinations of daraxonrasib with adagrasib or HRS-4642 (MRTX-1133 analog) yield accelerated K-Ras engagement, rapid p-ERK suppression, and significant Loewe synergy scores in viability assays. These findings establish GAP mimetics as rational and potent combination partners for SW-II inhibitors. The synergistic combination has potential to deepen and prolong pathway suppression while enabling dose reductions that may mitigate on-target toxicity and resistance. Citation Format: Patrick Pfaff, Kevan Shokat. GAP mimetics display synergy with K-Ras Switch-II inhibition [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: RAS Oncogenesis and Therapeutics; 2026 Mar 5-8; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(5_Suppl_1):Abstract nr A016.