The RAS gene family encodes the small GTPase proteins NRAS, HRAS, and KRAS, which play an essential role in cellular growth and proliferation. KRAS is one of the most frequently mutated oncogenes in human cancer, with KRAS p.G12D, p.G12V, and p.G12C constituting the major mutational subtypes across lung, colon, and pancreatic cancers. Despite more than three decades of research, indirect approaches targeting KRAS mutant cancers have largely failed to show clinical benefit, and direct approaches have been stymied by the apparently ‘undruggable’ nature of KRAS. Cysteine-12 of KRASG12C has recently emerged as a unique vulnerability in KRAS-mutant cancers, and a small number of cysteine-reactive inhibitory tool molecules have been disclosed. We here report independent efforts to identify cysteine-reactive molecules capable of selectively inhibiting KRASG12C. Through iterative screening and structural biology efforts, we identified a novel Cys12-reactive inhibitor scaffold that derived its potency from occupancy of a previously unknown cryptic pocket induced by side-chain motion of the His95 residue of KRAS. Employing a scaffold-hopping approach, we leveraged knowledge of this cryptic pocket to design a series of N-aryl quinazolin-2(1H)-one-based inhibitors that demonstrated significantly enhanced potency relative to prior tool compounds. Extensive optimization of these leads led to the identification of a highly potent, selective, and well-tolerated inhibitor of KRASG12C, which was nominated for clinical development as AMG 510. In preclinical tumor models, AMG 510 rapidly and irreversibly binds to KRASG12C, providing durable suppression of the mitogen-activated protein kinase (MAPK) signaling pathway. Dosed orally (once daily) as a single agent, AMG 510 is capable of inducing tumor regression in mouse models of KRASG12C cancer. AMG 510 is, to the best of our knowledge, the first direct KRASG12C therapeutic to reach human clinical testing and is currently in a Phase I clinical trial evaluating safety, tolerability, PK, and efficacy in subjects with solid tumors bearing the KRAS p.G12C mutation (NCT03600883).

Citation Format: Brian A. Lanman, Jian Jeffrey Chen, Longbin Liu, Patricia Lopez, Alexander J. Pickrell, Anthony B. Reed, Hui-Ling Wang, Pragathi Achanta, Jude Canon, Daniel A. Erlanson, Raymond V. Fucini, Joon Won Jeong, Christopher Mohr, Anne Y. Saiki, Victor J. Cee, J. Russell Lipford, Karen Rex, Laurie P. Volak. Discovery of AMG 510, a first-in-human covalent inhibitor of KRASG12C for the treatment of solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4455.