Carbonic Anhydrase Inhibition Sensitizes Group 3 Medulloblastoma to Radiotherapy

Group 3 (G3) medulloblastoma constitutes the most aggressive molecular subgroup, and nearly all patients present with metastases upon recurrence. Treatment for newly diagnosed medulloblastoma relies on a combination of maximal safe surgical resection, followed by chemotherapy and ionizing radiation, and no therapies have been shown to confer a survival benefit at the time of recurrence. Given the limited therapeutic options available for patients with medulloblastoma, especially at recurrence, and the incomplete understanding of the molecular mechanisms underlying resistance to treatment, we sought to uncover actionable targets and biomarkers that could help refine patient selection and treatment of newly diagnosed medulloblastoma to reduce the risk of recurrence. In clinically relevant mouse models of G3 medulloblastoma, CT-guided fractionated radiotherapy extended overall survival and induced the clonal selection of radioresistant subpopulations of tumor cells that drove medulloblastoma recurrence. Comparison of recurrent tumors with treatment-naïve newly diagnosed tumors revealed a gene expression signature that was found to be a biomarker of radioresistance and poor prognosis. This prognostic gene signature was shown to be subgroup specific in a large patient cohort. Recurrent tumors had elevated expression of carbonic anhydrase 4, and genetic and pharmacologic modulation of carbonic anhydrase 4 could promote or reduce resistance to radiotherapy. These data suggest that the FDA-approved carbonic anhydrase inhibitor acetazolamide may be a useful radiosensitizer to improve the efficacy of the treatment of newly diagnosed G3 medulloblastoma that could reduce the risk of tumor recurrence and improve survival in pediatric patients. Significance: G3 medulloblastoma features a prognostic subgroup-specific gene expression signature and can be targeted with a carbonic anhydrase inhibitor to enhance radiosensitivity, reducing the risk of recurrence and improving survival.