Discovery of ASP6918, a KRAS G12C inhibitor: Synthesis and structure-activity relationships of 1-{2,7-diazaspiro[3.5]non-2-yl}prop-2-en-1-one derivatives as covalent inhibitors with good potency and oral activity for the treatment of solid tumors.

Although KRAS protein had been classified as an undruggable target, inhibitors of KRAS G12C mutant protein were recently reported to show clinical efficacy in solid tumors. In our previous report, we identified 1-{2,7-diazaspiro[3.5]non-2-yl}prop-2-en-1-one derivative (1) as a KRAS G12C inhibitor that covalently binds to Cys12 of KRAS G12C protein. Compound 1 exhibited potent cellular pERK inhibition and cell growth inhibition against a KRAS G12C mutation-positive cell line and showed an antitumor effect on subcutaneous administration in an NCI-H1373 (KRAS G12C mutation-positive cell line) xenograft mouse model in a dose-dependent manner. In this report, we further optimized the substituents on the quinazoline scaffold based on the structure-based drug design from the co-crystal structure analysis of compound 1 and KRAS G12C to enhance in vitro activity. As a result, ASP6918 was found to exhibit extremely potent in vitro activity and induce dose-dependent tumor regression in an NCI-H1373 xenograft mouse model after oral administration.

Discovery and biological evaluation of 1-{2,7-diazaspiro[3.5]nonan-2-yl}prop-2-en-1-one derivatives as covalent inhibitors of KRAS G12C with favorable metabolic stability and anti-tumor activity.

RAS protein plays a key role in cellular proliferation and differentiation. RAS gene mutation is a known driver of oncogenic alternation in human cancer. RAS inhibition is an effective therapeutic treatment for solid tumors, but RAS protein has been classified as an undruggable target. Recent reports have demonstrated that a covalent binder to KRAS protein at a mutated cysteine residue (G12C) is effective for the treatment of solid tumors. Here, we report a series of 1-{2,7-diazaspiro[3.5]nonan-2-yl}prop-2-en-1-one derivatives as potent covalent inhibitors against KRAS G12C identified throughout structural optimization of an acryloyl amine moiety to improve in vitro inhibitory activity. From an X-ray complex structural analysis, the 1-{2,7-diazaspiro[3.5]nonan-2-yl}prop-2-en-1-one moiety binds in the switch-II pocket of KRAS G12C. Further optimization of the lead compound (5c) led to the successful identification of 1-[7-[6-chloro-8-fluoro-7-(5-methyl-1H-indazol-4-yl)-2-[(1-methylpiperidin-4-yl)amino]quinazolin-4-yl]-2,7-diazaspiro[3.5]nonan-2-yl]prop-2-en-1-one (7b), a potent compound with high metabolic stabilities in human and mouse liver microsomes. Compound 7b showed a dose-dependent antitumor effect on subcutaneous administration in an NCI-H1373 xenograft mouse model.