Abstract 441: Breaking the KRAS inhibitor induced resistance-wall: Targeting KRAS-SOS1 to disarm hypoxic survival.

Abstract Significant progress has been made in targeting KRAS, however, KRAS G12C inhibitors like sotorasib and adagrasib have shown only modest efficacy with ORR of 28-43% and PFS of around 6 months, highlighting unmet needs for overcoming the resistance compared to EGFR inhibitors like osimertinib with ORR of 77% and PFS of 18.9 months. Acquired resistance involves KRASG12C amplifications, activating KRAS/NRAS mutations, and bypass activation of RTK, PI3K-AKT, YAP/TAZ-TEAD or JAK-STAT3 pathway. KRAS inhibitors also disrupt ERK-driven negative feedback, causing ERK reactivation and adaptive resistance. To address these limitations, vertical inhibition across the RTK-RAS-MAPK axis has gained attention1). Here, to investigate mechanisms underlying acquired resistance and identify effective combination strategies, we established KRAS G12C inhibitor-resistant clones from NCI-H358 cells by performing ENU mutagenesis followed by single-cell selection, and then gradually exposing the selected clones to increasing concentrations of sotorasib and adagrasib for 6-9 months. In both sotorasib- and adagrasib-resistant clones, p-ERK was suppressed while elevation of p-AKT and YAP expression with enhanced nuclear localization was observed compared with parental cells. Surprisingly, SOS1 expression was significantly elevated over 3-fold in both sotorasib- and adagrasib-resistant clones without change in SOS2 levels, which is known to play a compensatory role, indicating that SOS1 co-inhibition is critical for overcoming KRAS inhibitor resistance. Our SOS1-panKRAS modulator, HM101207 exhibited strong synergy with KRAS G12C, RAS(ON) or MAPK pathway inhibitors in KRAS G12C-mutant NCI-H2122 and SNU-1411 cells. In NCI-H1373 and NCI-H2122 xenograft models, oral administration of HM101207 at 100 mg/kg produced a marked enhancement of antitumor activity when combined with adagrasib at low dose 20 mg/kg and high dose 100 mg/kg, or with RMC-6236 25 mg/kg. Notably, HM101207 restored tumor regression even after tumors relapsed under adagrasib or RMC-6236 monotherapy. To explore how SOS1 inhibitor modulates KRAS inhibitor-induced resistance, we performed RNA-seq on mouse xenograft tumors derived from KYSE-410 cell harboring the KRAS G12C mutation after HM101207 treatment. Differential expression analysis revealed that HM101207 significantly inhibited the expression of hallmark hypoxia genes including ALDOC, ENO2, HK2, MKNK2, PFKFB3, PGK1, SERPINE1, SLC2A1, VEGFA. Hypoxia is associated with the drug-tolerant persister state and eventually leads to drug-resistance. Therefore, HM101207 can overcome KRAS inhibitor resistance by strongly suppressing both MAPK and hypoxic pathways. As a combination therapy, it enables more durable pathway inhibition and enhanced antitumor efficacy. GLP toxicology studies are ongoing to support IND submission. Citation Format: Jooyun Byun, Heesun Moon, Jongmin Hong, Soye Jeon, Jaeyul Choi, Seung Hyun Jung, Yongjae Park, YoungGil Ahn, In Young Choi. Breaking the KRAS inhibitor induced resistance-wall: Targeting KRAS-SOS1 to disarm hypoxic survival [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 441.