Abstract 1285: In vitro characterization of sotorasib and other RAS ‘His95-groove' binders and investigation of resistance mechanisms
Authors: Saiki Anne Y. , Mohn Deanna , Li Yu , Osgood Tao , Rex Karen , Wang Hui-Ling , Archibeque Ivonne , Mohr Christopher , Achanta Pragathi , Stapper Andres Plata , Rapaport Aaron S. , Canon Jude , Cee Victor J. , Lanman Brian A. , Lipford J. Russell 
Published: July 2021

Abstract
Sotorasib (formerly known as AMG 510), the first-in-class KRASG12C inhibitor, has demonstrated promising clinical efficacy in KRAS p.G12C mutant cancers. Sotorasib binds to KRASG12C through a unique interaction with a surface groove created by side-chain rotation of histidine 95 (His95). Characterization of sotorasib and other His95-groove binders revealed enhanced potency and selectivity as compared to other KRASG12C inhibitor scaffolds, which bind in the P2 pocket via hydrogen bonding with His95. The novel binding mode of sotorasib also translated to similar biochemical and cellular potencies against both NRASG12C and HRASG12C, which encode leucine and glutamine at position 95, respectively. In contrast, other KRASG12C inhibitor scaffolds demonstrated a dramatic loss of potency against NRASG12C and HRASG12C, suggesting that the alternate residues impacted the binding of these molecules in the P2 pocket. To extend characterization of the cellular effects of RAS ‘His95-groove' binders, we analyzed the expression of major histocompatibility complex (MHC) class I proteins and other inflammatory markers in multiple human and murine KRAS p.G12C cell lines. These studies revealed a partial dependency on the cytosolic DNA-sensing (cGAS/STING) pathway for the effects observed with some markers. Finally, His95-groove binders were evaluated for potential mechanisms of resistance to this class of KRASG12C inhibitors. In the mouse syngeneic Lewis Lung Carcinoma (LL/2) cell line, which carries both KRAS p.G12C and NRAS p.Q61H mutations, intrinsic resistance to KRASG12C inhibition was observed, but combination treatment with the MEK inhibitor trametinib demonstrated synergistic improvement in the effects on viability. MIA PaCa-2 and NCI-H358 models of acquired resistance to KRASG12C inhibition were also developed through long-term exposure to high concentrations of sotorasib. Characterization of these resistant cell lines indicated a requirement for constant exposure to sotorasib and also showed that the resistance was not due to genetic alterations but involved either overexpression of KRAS or bypass signaling through alternative pathways. Taken together, these data demonstrate that His95-binders like sotorasib display superior potency and off-target selectivity, as well as unique activity against all versions of RASG12C. In addition, characterization of potential resistance mechanisms to sotorasib will inform combination strategies in the clinic.
Citation Format: Anne Y. Saiki, Deanna Mohn, Yu Li, Tao Osgood, Karen Rex, Hui-Ling Wang, Ivonne Archibeque, Christopher Mohr, Pragathi Achanta, Andres Plata Stapper, Aaron S. Rapaport, Jude Canon, Victor J. Cee, Brian A. Lanman, J. Russell Lipford. In vitro characterization of sotorasib and other RAS ‘His95-groove' binders and investigation of resistance mechanisms [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1285.