10092-CB-3 Resistance Mechanisms and Target Identification sssin Mutant IDH Inhibitor Therapy

Abstract Background IDH1-mutant gliomas often undergo malignant transformation over time and progress into treatment-resistant, high-grade tumors. While mutant IDH1 inhibitors have shown some efficacy against lower-grade gliomas, their effects on high-grade gliomas remain limited. Under these circumstances, there is an urgent need to identify novel therapeutic targets from the perspective of synthetic lethality. Methods To identify genes exhibiting synthetic lethality with mutant IDH1 inhibitors, we performed a genome-wide CRISPR/Cas9 screen. Although treatment with the mutant IDH1 inhibitor alone effectively suppressed intracellular D-2-hydroxyglutarate production, it had minimal impact on cell proliferation. Therefore, we aimed to discover gene alterations that could elicit antitumor effects not achievable by monotherapy. Results The screening identified 176 gene candidates that demonstrated synthetic lethality with the mutant IDH1 inhibitor. Gene Ontology analysis revealed that many of these genes were associated with metabolic pathways. Among them, we focused on KMT5A, a gene involved in amino acid metabolism for which small-molecule inhibitors are already available. Knockdown of KMT5A using siRNA alone did not affect cell proliferation; however, its combination with the mutant IDH1 inhibitor significantly suppressed cell growth. Furthermore, the use of a KMT5A inhibitor in combination therapy led to a marked reduction in cell viability, G0/G1 cell cycle arrest, and induction of late apoptosis. These combinatorial effects were consistently observed across two different cell lines, suggesting potential broad applicability of the strategy. Conclusion This study successfully identified novel synthetic lethal targets that enhance the efficacy of mutant IDH1 inhibitors in IDH1-mutant gliomas. In particular, combination therapy with KMT5A inhibition emerged as a promising treatment strategy. Ongoing investigations aim to elucidate the underlying molecular mechanisms, including epigenomic alterations. These findings may contribute to the development of precision medicine approaches to overcome resistance to mutant IDH1 inhibitors.