Abstract 3255: Probing and overcoming KRASG12C inhibitor resistance by combination with a pan-KRAS SOS1 inhibitor

Abstract The recent accelerated approval of the KRASG12C mutant-selective inhibitor sotorasib (AMG 510) for the treatment of 2nd line KRASG12C mutation-positive NSCLC patients marks the first approved targeted therapy for tumors with any KRAS mutation. While KRASG12C inhibitors deliver clinical benefit, most patients who achieved an objective response ultimately progressed. Recent insights into clinical KRASG12C inhibitor resistance identified reactivation of the RAS/MAPK pathway as a common putative driver mechanism of resistance. Multiple ongoing trials seek to augment responses to KRASG12C inhibitors through rational combination strategies, including the pan-KRAS SOS1 inhibitor BI 1701963. Here we use different preclinical experimental approaches to interrogate KRASG12C inhibitor resistance mechanisms with the aim to identify strategies to overcome resistance. To predict on-target resistance, Ba/F3 cells were transduced with KRASG12C, ENU-mutagenized and chronically exposed to KRASG12C inhibitors. Resistant clones were screened for secondary KRAS mutations, highlighting that KRAS G12C/Y96D and Y96S cis mutations did confer resistance to KRASG12C inhibition but could be overcome by MEK inhibitor combination with a SOS1 inhibitor. As second strategy a high-complexity single site variant library of KRASG12C encompassing all possible secondary KRAS mutations was employed to establish Ba/F3 transgenic cell pools. The response of this KRASG12C Ba/F3 clone library harboring a comprehensive set of secondary mutations was tested following treatment with KRASG12C inhibitors alone and in combination with a pan-KRAS SOS1 inhibitor. In parallel, acquired KRASG12C inhibitor resistance was generated in solid cancer cells following long-term MRTX849 treatment. Clones were characterized and their response to KRASG12C inhibition and combination therapy was analyzed. Both in the Ba/F3 cell pool as well as in KRASG12C inhibitor resistant clones combining SOS1 inhibition to KRASG12C inhibition proved to be beneficial. Finally, bringing these findings in vivo, SW837(CRC) tumor-bearing mice were long-term treated with adagrasib until tumors relapsed after initial regression and resistant tumors were randomized for second line treatments. In this KRASG12C inhibitor resistant context, treatment with adagrasib plus cetuximab resulted in tumor stasis and adagrasib plus SOS1i resulted in tumor regression. While more work is currently being undertaken to map the resistance mechanisms in both our in vitro and in vivo settings, all results highlight the benefit of combining a SOS1 inhibitor with a KRASG12C inhibitor to prevent and/or overcome acquired resistance. The pan-KRAS SOS1 inhibitor BI 1701963 is the first direct RAS signaling modifier in phase I clinical trials both as a monotherapy as well as in combination with KRASG12C inhibitors, MEK inhibitors and liposomal irinotecan. Citation Format: Marco H. Hofmann, Sabine Jurado, Daniel Gerlach, Takamasa Koga, Francesca Trapani, Michael Gmachl, Donat Alpar, Simone Lieb, Astrid Jeschko, Tetsuya Mitsudomi, Norbert Kraut, Mark P. Petronczki. Probing and overcoming KRASG12C inhibitor resistance by combination with a pan-KRAS SOS1 inhibitor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3255.