IDH1 inhibition potentiates gemcitabine efficacy in pancreatic ductal adenocarcinoma

Background: Pancreatic ductal adenocarcinoma (PDAC) is the most aggressive cancers, with a 5-year survival rate of approximately 13%. Gemcitabine remains standard first-line chemotherapy, over 80% of patients develop resistance, limiting its clinical benefit. Wild-type isocitrate dehydrogenase 1 (wt-IDH1) is highly expressed in PDAC, catalyzing the conversion of isocitrate to alpha-ketoglutarate and NADPH to support mitochondrial metabolism. Ivosidenib (AG-120) is an FDA-approved oral allosteric inhibitor originally developed for mutant IDH1, but it also effectively inhibits wt-IDH1 under nutrient-deprived and low-magnesium conditions typical of PDAC. This inhibition reduces NADPH, increases chemotherapy-induced reactive oxygen species (ROS), and markedly impairs the survival of resistant cells, providing a mechanistic rationale for combining AG-120 with gemcitabine to overcome chemoresistance. Methods: The synergistic effect of AG-120 and gemcitabine was evaluated in gemcitabine-resistant PDAC cell lines (MIA PaCa-2 and BxPC-3) using the PicoGreen dsDNA assay. Optimal drug doses were applied in functional assays, including wound healing, migration/invasion, and colony formation, to evaluate effects on cell growth and motility. Mechanistically, wt-IDH1 inhibition reduces NADPH and impairs mitochondrial metabolism, intracellular ROS levels were measured following treatment to evaluate oxidative stress. Mitochondrial function was further examined using Seahorse assays. Transcriptomic profiling via RNA sequencing, combined with qRT-PCR and Western blot validation, was performed to identify key pathways driving the synergistic response. The efficacy of the combination therapy was further confirmed in vivo using a PDAC xenograft model. Results: The combination of AG-120 and gemcitabine exhibited synergistic anticancer effects on cell proliferation, migration, invasion, and colony formation in gemcitabine-resistant PDAC cell lines. Transcriptomic analysis of genes downregulated by IDH1 inhibition revealed significant enrichment of OXPHOS pathways (enrich score = 2.32, P <0.01), supported by Seahorse assays showing suppression of mitochondrial OXPHOS. Mechanistically, gemcitabine-resistant cells exhibited a marked upregulation of the magnesium influx transporter TRPM7, an essential regulator of magnesium homeostasis in mammalian cells, suggesting increased sensitivity and dependency on magnesium. These findings suggest that low-magnesium conditions enhance the responsiveness of resistant PDAC cells to wt-IDH1 inhibition, contributing to the observed synergistic anticancer effect of the combination therapy. Conclusion: This study provides mechanistic insight into how AG-120 overcomes gemcitabine resistance in PDAC cells by targeting wt-IDH1 and modulating the OXPHOS pathway, highlighting a potential therapeutic strategy to improve treatment outcomes.