Targeting KRAS Mutant Cancers with a Covalent G12C-Specific Inhibitor.

KRASG12C was recently identified to be potentially druggable by allele-specific covalent targeting of Cys-12 in vicinity to an inducible allosteric switch II pocket (S-IIP). Success of this approach requires active cycling of KRASG12C between its active-GTP and inactive-GDP conformations as accessibility of the S-IIP is restricted only to the GDP-bound state. This strategy proved feasible for inhibiting mutant KRAS in vitro; however, it is uncertain whether this approach would translate to in vivo. Here, we describe structure-based design and identification of ARS-1620, a covalent compound with high potency and selectivity for KRASG12C. ARS-1620 achieves rapid and sustained in vivo target occupancy to induce tumor regression. We use ARS-1620 to dissect oncogenic KRAS dependency and demonstrate that monolayer culture formats significantly underestimate KRAS dependency in vivo. This study provides in vivo evidence that mutant KRAS can be selectively targeted and reveals ARS-1620 as representing a new generation of KRASG12C-specific inhibitors with promising therapeutic potential.

Selective Inhibition of Oncogenic KRAS Output with Small Molecules Targeting the Inactive State.

UNLABELLED: KRAS gain-of-function mutations occur in approximately 30% of all human cancers. Despite more than 30 years of KRAS-focused research and development efforts, no targeted therapy has been discovered for cancers with KRAS mutations. Here, we describe ARS-853, a selective, covalent inhibitor of KRAS(G12C) that inhibits mutant KRAS-driven signaling by binding to the GDP-bound oncoprotein and preventing activation. Based on the rates of engagement and inhibition observed for ARS-853, along with a mutant-specific mass spectrometry-based assay for assessing KRAS activation status, we show that the nucleotide state of KRAS(G12C) is in a state of dynamic flux that can be modulated by upstream signaling factors. These studies provide convincing evidence that the KRAS(G12C) mutation generates a "hyperexcitable" rather than a "statically active" state and that targeting the inactive, GDP-bound form is a promising approach for generating novel anti-RAS therapeutics. SIGNIFICANCE: A cell-active, mutant-specific, covalent inhibitor of KRAS(G12C) is described that targets the GDP-bound, inactive state and prevents subsequent activation. Using this novel compound, we demonstrate that KRAS(G12C) oncoprotein rapidly cycles bound nucleotide and responds to upstream signaling inputs to maintain a highly active state.