TMET-13. DNA DAMAGE SIGNALING ACTIVATES GTP SYNTHESIS TO PROMOTE GLIOBLASTOMA TREATMENT RESISTANCE

Abstract

Abstract Glioblastoma (GBM) is the most common type of invasive brain tumor in adults and is uniformly fatal due to inherent resistance to radiation therapy (RT) and chemotherapy. Our group and others have found that metabolites can regulate DNA repair and therapy resistance in brain tumors, but little is known about how DNA damage regulates metabolic pathway activity in cancer. Here we show that following treatment with RT, GBMs increase rates of de novo guanylate synthesis in vitro and in orthotopic patient-derived xenograft models via signaling through the DNA repair protein DNA-PK. To determine if disrupting this regulation can augment GBM treatment efficacy, we combined an FDA-approved inhibitor of purine synthesis (mycophenolate mofetil, MMF) with chemoradiation in a variety of mouse models of GBM. Critically, targeting GTP synthesis improved the efficacy of both RT alone and chemoradiation in multiple patient-derived and syngeneic intracranial models. Our translational studies have shown that mycophenolic acid, the active metabolite of MMF, penetrates the blood-brain barrier at concentrations sufficient to inhibit GTP synthesis in GBMs of human patients. The phase 1 arms of our study, which are ongoing, are testing the safety and efficacy of combining MMF with standard of care chemoradiation for patients with primary and recurrent GBM.