Abstract 837: IDH mutations disable the tumor suppressive activity of GSX2 to promote gliomagenesis.

Abstract Isocitrate dehydrogenase (IDH) mutations arise early in glioma development and are associated with a defined neurodevelopmental cancer cell hierarchy. However, how mutant IDH contributes to this hierarchy and whether this interaction promotes gliomagenesis remain unclear. Progress in addressing these questions has been hindered by technical limitations. Patient-derived models rarely capture the biology of tumor initiation, as surgical specimens are obtained only after these phases of cancer evolution have passed. Moreover, the lack of faithful preclinical models of mutant IDH has constrained mechanistic investigation. To overcome these challenges, we developed a genetic mouse model of mutant IDH-driven gliomagenesis and IDH-wildtype companion models to enable direct testing of causal genotype-phenotype relationships involving the Idh1-R132H oncogene. We leveraged these models to survey IDH-mutant glioma initiation by performing time-resolved, joint single-cell RNA and ATAC sequencing analysis of engineered neural cells. Mutant IDH activates neural progenitor cells (NPCs) and drives NPC lineage switching. These actions expand oligodendrocyte precursor cells, the predominant cell-of-origin for these tumors, at the expense of interneurons, a lineage incompatible with mutant IDH-induced transformation. We further find that lineage switching is mediated by promoter hypermethylation and silencing of Gsx2, a homeobox gene required for neurogenesis. Critically, Gsx2 ablation recapitulates NPC fate reprogramming by mutant IDH while restoring Gsx2 expression in IDH-mutant neurosphere lines impairs their self-renewal and tumorigenic potential. Our work uncovers the molecular mechanisms by which mutant IDH reprograms neural lineage specification to promote cancer initiation, providing a new model of neural cell fate control by IDH oncogenes and insights into the developmental origins of glioma. Citation Format: Yi Xiao, Diana D. Shi, Lei Guo, Ethan Neumann, Michael M. Levitt, Pranita Kaphle, Tracey Shipman, Haocheng Li, Feng Cai, Denise M. Ramirez, Lauren G. Zacharias, Zhenkang Chen, Mathew Lin, Vinesh T. Puliyappadamba, Tao Chen, Milan R. Savani, Salvador Peña, Janaka Wansapura, Thomas P. Mathews, Prashant Mishra, Yoon Jung Kim, Prithvi Raj, Timothy E. Richardson, Jian Xu, Stephen C. Mack, Gilbert J. Rahme, Bradley E. Bernstein, Ralph J. DeBerardinis, Itay Tirosh, Mario L. Suvà, Lin Xu, Kalil G. Abdullah, Samuel K. McBrayer. IDH mutations disable the tumor suppressive activity of GSX2 to promote gliomagenesis 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 837.