PHGDH Sustains Oncometabolite Production to Drive Resistance to Mutant IDH Inhibition in Glioma that can be Monitored by Metabolic Imaging

Mutations in isocitrate dehydrogenase (IDHm) define a distinct molecular class of gliomas. IDHm converts α-ketoglutarate (α-KG) to the oncometabolite D-2-hydroxyglutarate (D-2HG), which drives tumorigenesis. The IDHm inhibitor vorasidenib suppresses D-2HG production and prolongs progression-free survival in some, but not all, patients. Here, using patient-derived models, genetically engineered glioma cells, orthotopic xenografts, and patient tissue, we showed that phosphoglycerate dehydrogenase (PHGDH) mediates intrinsic resistance to vorasidenib by sustaining D-2HG production despite IDHm inhibition. Silencing PHGDH suppressed residual D-2HG synthesis and restored vorasidenib sensitivity in resistant models, whereas PHGDH overexpression restored D-2HG production and induced resistance in sensitive models. Importantly, restoration of intracellular D-2HG rescued growth despite continued vorasidenib treatment, demonstrating a causal role for residual D-2HG production in the resistant phenotype. Mechanistically, a permissive chromatin state characterized by increased H3K4me3, reduced H3K27me3, and enhanced ATF4 occupancy at the PHGDH promoter facilitated PHGDH upregulation in resistant models. Pharmacologic induction of this chromatin state induced PHGDH expression, restored D-2HG production, and conferred resistance to vorasidenib in sensitive models. Consistently, tumor tissue from patients with poor response to IDHm inhibitor treatment exhibited higher PHGDH expression, coupled with the ATF4-enriched permissive chromatin state observed in resistant models. Finally, deuterium metabolic imaging of D-2HG production from diethyl-[3,3′-2H]-α-KG provided an early, non-invasive readout of response and resistance to vorasidenib in vivo. Collectively, this study identifies a chromatin-regulated ATF4-PHGDH-D-2HG axis as a mechanism of intrinsic resistance to IDHm inhibition and establishes diethyl-[3,3′-2H]-α-KG as a metabolic imaging probe for interrogating treatment response in IDHm gliomas.