Cysteine-reactive allosteric inhibitors irreversibly bind a pocket on the KRASG12C-mutant protein.

  • Major finding: Cysteine-reactive allosteric inhibitors irreversibly bind a pocket on the KRASG12C-mutant protein.

  • Mechanism: Inhibitor binding increases the preference of KRASG12C for GDP and impairs binding to RAS effectors.

  • Impact: The identification of an allosteric regulatory site on KRAS may guide design of allele-specific inhibitors.

Activating mutations in KRAS are among the most frequent genetic events in human cancer and are predictive of poor response to many cytotoxic and targeted therapies. KRASG12C is one of the most prevalent oncogenic KRAS alleles and is the most common KRAS mutation in non–small cell lung cancer. Ostrem and colleagues devised a small molecule screening strategy to identify selective inhibitors of the G12C mutant protein that exploited the unique ability of cysteine to react with disulphide-containing molecules. Binding of the hit compounds, which did not interact with wild-type KRAS, was not affected by GDP but was impaired by GTP, suggesting that the compounds preferentially bind an allosteric site in the inactive form of KRAS. Indeed, a crystal structure of the G12C mutant protein in complex with a derivative of one of the identified compounds showed that the compound did not bind in the nucleotide pocket but bound a previously uncharacterized adjacent pocket. The authors then synthesized carbon-based electrophile, acrylamide, and vinyl sulphonamide analogues that potently and irreversibly bound the G12C mutant protein. These compounds, which disrupted the conformation of the switch-I and switch-II regions that mediate interactions with nucleotides and effector proteins, shifted the native nucleotide preference of the G12C mutant protein from GTP to GDP and decreased binding to the RAS effector proteins BRAF and CRAF in KRASG12C-mutant lung cancer cell lines. Moreover, treatment with one such compound specifically decreased the viability of KRASG12C-mutant lung cancer cell lines but had little effect on KRAS-mutant cell lines with non-G12C mutations. These findings suggest that compounds that exploit specific features of mutant KRAS proteins may selectively block oncogenic KRAS signaling and provide a structural and biochemical framework for further development of allele-specific KRAS inhibitors.

Ostrem JM, Peters U, Sos ML, Wells JA, Shokat KM. K-Ras(G12C) inhibitors allosterically control GTP affinity and effector interactions. Nature 2013;503:548–51.

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