Abstract B083: Secondary KRAS mutations lead to acquired resistance to KRASG12D inhibitor in colorectal cancer

Abstract

KRAS is the most frequently mutated oncogene, with high prevalence in tumor types with a significant unmet clinical need, such as colorectal cancer (CRC). Activating mutations in the KRAS gene leading to amino acid exchange at position 12 from Glycine to Asparagine, G12D, occur in approximately 12.5% of CRC. The approval of mutant specific KRASG12C inhibitors MRTX849 and AMG510 by the FDA raised the question if KRAS targeted therapy approaches could provide benefit to cancer patients with other mutant alleles.  Several KRASG12D inhibitors have recently been described and MRTX1133, a selective KRASG12D inhibitor from Mirati Therapeutics, has now entered clinical trial, recruiting patients with advanced solid tumors harboring a KRAS G12D mutation. Alongside the great hopes placed in KRAS targeting therapy, resistance is likely to occur, as it was observed in patients relapsing in response to KRASG12C inhibitors.  We aimed to use this pre-clinical study to predict and understand potential resistance mechanisms that may arise during targeted treatment against KRASG12D in the CRC setting. To this aim, the colorectal cancer cell line GP2d was continuously treated with MRTX1133 to generate resistance and individual outgrowing clones were subsequently profiled in a series of assays to identify potential mechanism(s). These assays included analysis of gene expression changes, mutation calling, as well as qPCR and protein-based assays. Interestingly, we identified two individual secondary on-target mutations in the KRAS gene, which could affect binding of MRTX1133 to the pocket in KRAS. These findings were confirmed in an orthogonal assay, by screening for resistance in Ba/F3 cells transduced with the corresponding KRAS double mutant. Combination assays were then performed in parental and resistant cells to study whether additional vertical or alternative pathway inhibition could address the resistance. Collectively our pre-clinical study identified secondary KRAS mutations in the compound binding pocket as a mechanism of resistance to KRAS G12D inhibition by MRTX1133 in colorectal cancer cells.

Citation Format: Simone Lieb, Sabine Jurado, Sergej Nowoshilow, Krzysztof M. Zak, Marco H. Hofmann. Secondary KRAS mutations lead to acquired resistance to KRASG12D inhibitor in colorectal cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr B083.