Abstract LBA005: Detection of KRAS amplification on extrachromosomal DNA (ecDNA) upon acquired resistance to KRASG12C inhibitors

Abstract

Abstract The recent discovery and clinical validation of KRAS inhibitors (KRASi) has ushered in a new therapeutic approach to directly address the previously undruggable mutant KRAS-driven cancers. Unfortunately, as with other oncogene-directed therapies, acquired resistance to KRASi has been observed that is partially attributed to secondary mutations in KRAS and/or mutations or fusions in other mitogen-activated protein kinase (MAPK) signaling genes. Emerging evidence suggests that amplification of oncogenes on acentric extrachromosomal DNA (ecDNA) might constitute an important mechanism of rapid resistance to receptor tyrosine kinase (RTK) and MAPK targeting therapies. Therefore, we investigated whether resistance to KRASi monotherapy is mediated through an ecDNA mechanism. We previously noted focal gene amplification of KRAS and MET in recurrent tumors isolated from patients treated with the selective KRASG12C inhibitor, adagrasib. Analysis of next-generation sequencing (NGS) data from a patient tumor revealed evidence of circular DNA structures encompassing the KRAS locus. Consistent with this finding, interphase FISH analysis indicated the presence of KRAS amplifications on ecDNA in this adagrasib-treated patient tumor. To further interrogate this biology, we examined a genetically modified CT26 murine tumor model harboring KRASG12C alteration. Analogous to the clinical observations, both adagrasib as well as the recently approved KRASi sotorasib, induced transient tumor regressions that subsequently resumed growth following several weeks of continuous therapy. Strikingly, whole-genome sequencing data from isolated recurrent tumors revealed focal amplification of KRASG12C and metaphase FISH confirmed high levels of KRASG12C on ecDNA as compared to vehicle-treated samples. Further mechanistic studies are underway. Collectively, these observations implicate ecDNA as an important mediator of resistance to KRASi monotherapy and reinforce the critical need for novel therapeutic strategies to address ecDNA oncogene amplification-driven cancers. Citation Format: Ryan J Hansen, Steven Horton, Julie Wiese, BellJohn Bibay, E.Lorena Mora-Blanco, Nam-Phuong Nguyen, Lars D Engstrom, David M Briere, Andres Calinisan, Peter Olson, Mark M Awad, Andrew J Aguirre, Jason Christiansen, Christian Hassig, Shailaja Kasibhatla. Detection of KRAS amplification on extrachromosomal DNA (ecDNA) upon acquired resistance to KRASG12C inhibitors [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr LBA005.