The KRASG12C mutation is found in 11% of non-small cell lung cancers, 4% of colorectal cancers, and 2% of pancreatic cancers in the U.S., and drives these cancers by shifting the cellular equilibrium of KRAS towards the GTP-bound, active state, KRASG12C(ON). The resulting increased levels of KRASG12C(ON) in turn increase signaling output to initiate and support the oncogenic state. In recent years, a class of KRASG12C(OFF) inhibitors has transformed the treatment landscape for patients with cancers bearing KRASG12C. These inhibitors work via sequestration of the GDP-bound, inactive state, KRASG12C(OFF), starving cancer cells of their oncogenic driver, KRASG12C(ON). Recent reports on the nature of resistance to KRASG12C(OFF) inhibitors suggest this class of drugs can be overcome through reactivation of KRASG12C to the ON form. Direct inhibition of KRASG12C(ON) with a first in class, potent, orally bioavailable, selective, tri-complex inhibitor RMC-6291, represents a more robust approach and presents the possibility that RMC-6291 will be a ‘best-in-class’ inhibitor of tumors harboring KRASG12C.

RMC-6291 is a potent covalent inhibitor of KRASG12C(ON) that forms a tri-complex within tumor cells between KRASG12C(ON) and cyclophilin A (CypA), a highly abundant immunophilin. The assembled tri-complex prevents KRASG12C(ON) from signaling via steric blockade of RAS effector binding. In cells, kinetic analyses demonstrate near-immediate disruption of RAS effector binding and extinction of KRASG12C(ON) signaling.

Oral administration of RMC-6291 produces deep and durable suppression of RAS pathway activity in KRASG12C tumor models and drives profound tumor regressions in vivo at well-tolerated doses. In a mouse clinical trial consisting of multiple patient- and cell line-derived xenograft models of KRASG12C NSCLC, RMC-6291 outperformed adagrasib, a KRASG12C(OFF) inhibitor, by increasing the number of responses, the depth of tumor regressions, and the durability of responses.

Combination treatment with RMC-6291 and SHP2 or SOS1 inhibitors was well tolerated in preclinical models and further increased anti-tumor activity, likely by preventing reactivation of wild-type RAS proteins that cooperate with KRASG12C to fuel cancer growth. RMC-6291 also combined well with immune checkpoint inhibitors, sensitizing KRASG12C-bearing cancer models to anti-tumor immunity.

RMC-6291 is a next-generation, mutant-selective inhibitor of KRASG12C(ON) that overcomes limitations of first-generation KRASG12C(OFF) inhibitors in preclinical models by directly targeting the active form of this important oncogenic driver.

Citation Format: Robert J. Nichols, Y.C. Yang, Jim Cregg, Chris J. Schulze, Zhican Wang, Richa Dua, Jingjing Jiang, Lindsay S. Garrenton, Nicole Nasholm, Alun Bermingham, John E. Knox, Kyle Seamon, Michael Longhi, Kang-Jye Chou, Shaoling Li, David P. Wildes, Mallika Singh, Elena S. Koltun, Adrian L. Gill, Jacqueline A.M. Smith. RMC-6291, a next-generation tri-complex KRASG12C(ON) inhibitor, outperforms KRASG12C(OFF) inhibitors in preclinical models of KRASG12C cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3595.