Abstract

KRAS mutation occurs in nearly 30% of human cancers, yet the most prevalent and oncogenic KRAS mutation (G12D) still lacks inhibitors. Herein, we explored the formation of a salt-bridge between KRASs Asp12 residue and a series of potent inhibitors. Our ITC results show that these inhibitors bind to and inhibit both GDP-bound and GTP-bound KRAS G12D, and our crystallographic studies revealed the structural basis of inhibitor binding in the switch-II pocket, experimentally confirming the formation of a salt-bridge between the piperazine moiety of the inhibitors and the 12D residue of the mutant protein. Among KRAS family proteins and mutants, both ITC and enzymatic assays support the selectivity of the inhibitors for KRAS G12D, and the inhibitors disrupt the KRAS-CRAF interaction. We also observed inhibition of cancer cell proliferation and inhibition of MAPK signaling by a representative inhibitor (TH-Z835); however, since this was not fully dependent on KRAS mutation status, it is possible that our inhibitors may have off-target effects via non-KRAS small GTPases. Experiments with a mouse model of pancreatic cancer showed that TH-Z835 significantly reduced tumor volume and synergized with an anti-PD-1 antibody. Collectively, our study demonstrates proof-of-concept for a salt-bridge, induced-fit pocket strategy for KRAS G12D, which warrants future medicinal chemistry efforts for optimal efficacy and minimized off-target effects.