Abstract A053: Targeting Acquired Resistance to KRASG12D Inhibitors: designing rationale synergistic treatments

Abstract KRASG12D (G12D) is one of the most prevalent and therapeutically challenging oncogenic mutations across pancreatic, colorectal, and lung cancers. The recent development of MRTX1133, a selective, non-covalent G12D inhibitor, represents a major therapeutic breakthrough. Although clinical data are not yet mature, emerging preclinical studies suggest that, as seen with KRASG12C (G12C) inhibitors, activation of alternate signaling pathways can promote tumor survival. Despite the therapeutic promise of G12D inhibitors, the mechanisms of acquired resistance, remain poorly understood. We have generated pancreatic and colorectal acquired resistant models to G12D inhibitors by drug escalation of MRTX1133. Our results show that although the IC50 for parental AsPC-1 and GP2d cells is 0.2nM and 0.1nM, respectively but drug resistant AsPC-1M-R and GP2dM-R cells can grow normally at 10 µM. To determine the underlying mechanisms of acquired drug resistance to MRTX1133, the resistant cells were subject to RNAseq. Processed reads were aligned with STAR and gene changes were normalized with DeSeq. Subsequent characterization of the resistant cells using differential gene expression and GSEA reveled the deep transcriptomic reorganization in our pancreatic model (AsPC-1M-R) points out the relevance of phenotypic transformation with overexpression of CD24 and the EMT signature. In contrast, colorectal MRTX133 resistant model (GP2dM-R) highlights the relevance and need to activate oxidative stress related genes to escape drug inhibition. RNAseq results were used to perform a complex bioinformatic analysis with iLINCS to describe potential therapeutic vulnerabilities specific to the drug-resistant cells. The targets obtained were then collapsed to determine the most significant gene targets to synergize with G12D inhibition. Both proteasome and mTOR inhibitors were identified to synergize with MRTX1133 in AsPC-1M-R cells, whereas in GP2dM-R cells BRD inhibitors and mTOR inhibitors are the top candidates to inhibit drug resistant cells. Interestingly, co-treatment of MRTX133 with MG-132 or bortezomib- potent proteasome inhibitors- or dactolisib -dual PI3K and mTOR inhibitor- increased cleaved PARP levels. We previously evaluated and confirmed the maintenance of proliferation and survival pathways via multiple RTKs, with the ERBB3-PI3K axis being particularly prominent. Thus, drug resistant models were sensitive to dual MRTX1133 and patritumab deruxtecan inhibition. These results confirm that to achieve durable responses clinically, these mechanisms need to be efficiently shut down. More importantly, these drug combinations were also effective in sensitive and de novo MRTX1133 resistant patient-derived organoids. Our findings emphasize the necessity to design combinatorial treatments to prevent and delay the acquisition of drug resistance in KRAS-driven cancers. Citation Format: Ines Pulido, Ali Rahnama, Frida Pantoja, Tiffani Curry, Malek Massad, Ian Papautsky, Agustin Lahoz, Julian Carretero, Takeshi Shimamura. Targeting Acquired Resistance to KRASG12D Inhibitors: designing rationale synergistic treatments [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2025 Oct 22-26; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2025;24(10 Suppl):Abstract nr A053.