CDK12 regulates cellular metabolism to promote glioblastoma growth.

Glioblastoma IDH-wildtype is the most common and aggressive primary brain tumor in adults, with poor prognosis despite current therapies. To identify new therapeutic vulnerabilities, we investigated the role of CDK12, a transcription-associated cyclin-dependent kinase, in glioblastoma. Genetic or pharmacologic inactivation of CDK12 impaired tumor growth in patientderived xenograft (PDX) models and enhanced the efficacy of temozolomide. Metabolic profiling using extracellular flux analysis and stable isotope tracing with U-¹³C-glucose and U-¹³Cglutamine showed that CDK12 inhibition disrupted mitochondrial respiration, resulting in energy depletion and apoptotic cell death characterized by caspase activation and Noxa induction. Mechanistically, we identified a direct interaction between CDK12 and GSK3β. CDK12 inhibition activated GSK3β, leading to downregulation of PPARD, a transcriptional regulator of oxidative metabolism. This CDK12-GSK3β-PPARD axis was required for glioblastoma cell proliferation and metabolic homeostasis. In vivo, CDK12 inhibition significantly extended survival without overt toxicity and induced complete tumor regression in a subset of animals. Strikingly, combined CDK12 inhibition and temozolomide treatment led to complete tumor eradication in all animals tested. These findings establish CDK12 as a key regulator of glioblastoma metabolism and survival, and provide strong preclinical rationale for its therapeutic targeting in combination with standard-of-care treatments.