KRAS is one of the most frequently mutated genes in cancer with alterations occurring in > 14% of all tumors. Recent advances have led to the discovery and development of inhibitors that bind the inactive (GDP-bound) form of KRASG12C. The most advanced of these first-generation molecules demonstrated clinical response rates of 30-45% and approximately 6-month progression-free survival in lung cancer patients. While significant, a majority of patients failed to achieve a clinical response and acquired resistance can be rapid. One hypothesis to explain tumor resistance is the failure of existing inhibitors to recognize the activated (GTP-bound) form of KRASG12C that can be upregulated in response to these first-generation inhibitors. Here we report the discovery of a series of novel inhibitors that effectively inhibit both the GTP- and GDP-bound forms of KRASG12C. These “dual-acting” inhibitors bind in the switch II pocket of both GTP-bound and GDP-bound KRASG12C and rapidly form a covalent bond with cysteine 12. This results in significantly increased inhibition of RAF1 and PI3Kα effector interactions (IC50 < 5 nM at 2 hrs.) in comparison to inactive state inhibitors. Dual targeting of both GTP- and GDP-bound KRASG12C results in potent cellular activity in models that are both sensitive (NCI-H358 and MIA PaCa-2) and resistant (NCI-H2122) to adagrasib and sotorasib. In contrast to adagrasib and sotorasib which are less effective in the NCI-H2122 cell line model, dual-acting inhibitors of GTP- and GDP-bound KRASG12C elicit rapid inhibition of pERK in < 1 hour with sustained inhibition of MAPK signaling through 48 hours. To model resistance to first generation inhibitors, an A59G mutation was introduced into KRASG12C, abrogating GTPase activity. This decreases the activity of both adagrasib and sotorasib in tumor cell viability assays by more than an order of magnitude whereas dual-acting inhibitors of GTP- and GDP-bound KRASG12C are equally effective in the G12C/A59G and parental G12C cell lines. Evaluation of dual-acting inhibitors of KRASG12C in vivo demonstrated rapid and > 90% KRASG12C target occupancy, resulting in regression of MIA PaCa-2 tumors. Dual-acting inhibitors of both the active and inactive states of KRASG12C may provide the potential for broader and more durable responses in the clinic.
Citation Format: Philamer Calses, Sam Clark, Jacob Corpuz, Susan Fong, Phil Gerkin, Mohammad Hekmatnejad, Evan McMahon, Megan Murray, Truc Nguyen, Tony Phan, Allison Roberts, Phillip Schwartz, Mikayla Shanafelt, Hiroko Tanaka, Jennifer Tomczyk, John Widen, Monika Williams, John Eksterowicz, Daniel Erlanson, Marie Evangelista, Johannes Hermann, Richard M. Neve, Snahel Patel, Kevin R. Webster. Discovery of novel dual-acting KRASG12C inhibitors that target both the active and inactive forms of the protein [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 3601.