Abstract 1877: Acquired resistance to Tri-complex inhibitors in colorectal cancer.

Abstract KRAS is the most frequently mutated oncogene, with high prevalence in indications with significant unmet clinical needs, such as lung, pancreatic and colorectal cancer. The most frequent alterations result in an amino acid exchange at position 12 from Glycine to Aspartic Acid (G12D), Valine (G12V) or Cysteine (G12C). The approval of mutant specific KRAS G12C inhibitors by the FDA opened a new field of treatment options for patients with KRAS G12C mutation and additional KRAS targeted therapy approaches are currently being clinically tested in the hope to provide benefit to cancer patients with cancers harboring other KRAS mutant alleles. These therapies include pan-RAS, pan-KRAS and allele selective inhibitors as well as degraders. For patients with advanced solid tumors harboring a KRAS G12D mutation, several selective inhibitors have entered clinical trials (MRTX1133, RMC-9805, QTX3034/46, LY3962673...) and RMC-6236, a pan-RAS inhibitor from Revolution Medicines, has recently shown promising early clinical data. However, alongside the great hopes placed in (K)RAS targeting therapy, resistance is likely to occur, as it was already observed in patients relapsing in response to KRAS G12C inhibitors. We aimed to use this pre-clinical study to predict and understand potential resistance mechanisms that may arise during targeted treatment against (K)RAS in the CRC setting. To this aim, the colorectal cancer cell line GP2d, expressing KRAS G12D, was continuously treated with a pan-RAS inhibitor to generate resistance. Once the resistance was confirmed, individual outgrowing clones were subsequently profiled in a series of assays to identify potential mechanism(s) and cross-tested with other inhibitors. Interestingly, cells were cross resistant to both pan-RAS (RMC-6236) and KRAS G12D (RMC-9805) inhibitors from Revolution Medicine, highlighting a common mechanism of action, while remaining sensitive to other KRAS G12D inhibitors. These findings were then confirmed in an orthogonal assay. Collectively our in vitro preclinical study identified a resistance mechanism to Tri-complex inhibitors in colorectal cancer cells. This resistance can still be addressed by other KRAS G12D inhibitors, opening options for patients harboring this characteristic post RMC-therapy. Future investigations may focus on characterizing tumors from patients who relapse on RMC-6236 and RMC-9805 to validate these findings clinically. Citation Format: Sabine Jurado, Simone Lieb, Marco H. Hofmann, Mark Pearson, Phillipp Schmalhorst, Krzysztof Zak. Acquired resistance to Tri-complex inhibitors in colorectal cancer abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 1877.