Abstract LB187: KRAS-MAPK signaling adaptation underlies acquired resistance to wild-type IDH1 inhibition in pancreatic ductal adenocarcinoma

Abstract Background: Wild-type isocitrate dehydrogenase 1 (IDH1), a cytosolic NADP+-dependent enzyme is upregulated in pancreatic ductal adenocarcinoma (PDAC), where it supports redox balance and metabolic homeostasis. Pharmacologic inhibition of IDH1 induces metabolic stress, suppresses cell growth, and sensitizes PDAC models to chemotherapy; however, therapeutic durability is limited by acquired resistance. PDAC is characterized by near-universal KRAS activation, and oncogenic KRAS signaling is known to adapt to metabolic perturbations to sustain tumor fitness. Whether chronic disruption of IDH1-dependent metabolism promotes adaptive engagement of KRAS signaling pathways remains unknown. Here, we developed models of acquired resistance to wild-type IDH1 inhibition and investigated molecular features associated with the resistant state. Methods: Acquired resistance models were established in PDAC cell lines (MIA PaCa-2, PANC-1, KPC) through continuous exposure to a novel wild-type IDH1 inhibitor under physiologic glucose conditions. Resistance was defined by sustained proliferation at approximately fourfold the parental IC50. KRAS pathway activation was assessed by immunoblotting and active RAS pull-down assays. Functional dependence on KRAS-MAPK signaling in both acutely treated and IDH1 inhibitor-resistant cells was assessed using the pan-RAS inhibitor RMC-6236 and the MEK inhibitor trametinib, alone or in combination with IDH1 inhibition. Results: PDAC cells chronically maintained under IDH1 inhibition remained viable even at inhibitor doses 4-10 times higher than those required to suppress parental cells in 96-hour assays, consistent with acquired resistance. Resistant cells demonstrated increased KRAS pathway activity, including enhanced MAPK signaling and elevated levels of GTP-bound RAS relative to parental controls. Pharmacologic inhibition of RAS signaling with RMC-6236 or MEK inhibition with trametinib significantly decreased viability in resistant cells and in parental cells acutely treated with wild-type IDH1 inhibition. Combination treatment resulted in greater viability suppression than single-agent therapy, indicating KRAS-MAPK dependence in both acute IDH1 inhibition and acquired resistance. The molecular mechanisms driving KRAS pathway upregulation in the setting of chronic IDH1 inhibition and resistance remain under active investigation. Conclusions: Acquired resistance to wild-type IDH1 inhibition in PDAC is associated with adaptive upregulation of KRAS-MAPK signaling and sustained reliance on oncogenic signaling to maintain viability. Pharmacologic targeting of KRAS signaling vulnerabilities suppresses viability in IDH1 inhibitor-resistant models, supporting signaling adaptation as a key mechanism of resistance to metabolic therapy. Ongoing studies aim to define the molecular basis of KRAS pathway engagement in this context to inform rational combination therapies. Citation Format: Sami O. Abul-Khoudoud, Mehrdad Zarei, Priyashree Sunita, Goutam Dey, Semmer Ali, Faith Nakazzi, Hallie J. Graor, Jordan M. Winter. KRAS-MAPK signaling adaptation underlies acquired resistance to wild-type IDH1 inhibition in pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(8_Suppl):Abstract nr LB187.