KRAS G12C: Kinetic and Redox Characterization of Covalent Inhibition

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ABSTRACT Inhibition of oncogenic KRAS is a highly pursued goal in drug discovery efforts, as RAS mutations are found in ~25% of human cancers. One key oncogenic KRAS mutation (KRASG12C) contains a reactive cysteine at a hotspot location, is the fourth most prevalent mutation in KRAS-driven tumors and is found at particularly high frequency (40% of RAS mutations, 13% overall) in non-small cell lung cancer (NSCLC). Excitement has accelerated rapidly around the discovery and application of covalent, Cys12-specific inhibitors of KRASG12C in recent years as these compounds have shown efficacy in advanced clinical trials, with Sotorasib (AMG510, LUMAKRAS™) recently receiving FDA approval for treatment of locally advanced or metastatic NSCLC. However, the kinetic mechanisms underlying the activity of this class of inhibitors remain poorly understood impeding rational drug design efforts. To address this gap in knowledge, we developed a new fluorescence- based approach to kinetically characterize the reactions of the proteins with these acrylamide-based inhibitors. Intriguingly, we find that the two clinical compounds, AMG510 (Amgen) and MRTX849/Adagrasib (Mirati Therapeutics) possess distinctly different kinetic properties, which we propose to investigate in further detail here. Recognizing the oxidative environment promoted by oncogenic KRAS signaling and tumorigenesis, we also evaluated the redox sensitivity and oxidative status in cells and found that Cys12 of KRASG12C is prone to oxidation. Moreover, oxidation at this site prevents inhibitor attachment, suggesting that redox modification of KRASG12C may constitute a mechanism of resistance to AMG510 and other covalent inhibitors. Other unanswered questions remain in the field, including the propensity of the protein-drug adducts to undergo chemical reversibility of the Michael addition reactions through which they bind, and how this could be affected by altered acrylamide “warheads”. Aim 1 proposes structural and kinetic studies combined with computational modeling and molecular dynamics simulations to elucidate the differential mechanisms of KRASG12C inhibitor engagement, inactivation and reversal. As development of treatment resistance remains a significant hurdle for targeted inhibition strategies, Aims 2 and 3 propose to investigate the linkage between the redox sensitivity of KRASG12C and inhibitor efficacy by measuring functional, signaling-relevant outputs for recombinant proteins and biological samples (lung cancer cell lines and patient-derived organoids). For Aim 2, lung cancer cells under variably oxidizing conditions, with and without inhibitor present, will be assessed for KRASG12C modifications and downstream signaling outputs; use of HyPer-DAAO genetic constructs with targeting to the plasma membrane will allow spatiotemporal and dosage control over hydrogen peroxide production within cells, near KRASG12C. In Aim 3, the relationship between tumor redox properties and inhibitor efficacy will be investigated using fresh NSCLC tumor specimens carrying KRASG12C mutations. Cumulatively, the results will provide improved under- standing of the drugs and will serve as a platform for characterizing and developing future direct KRAS inhibitors.