DIPG-12. ASSESSING THE EFFICACY OF BAY2402234 IN COMBINATION WITH ONC201 IN IMMUNE-COMPETENT MURINE MODELS OF DIFFUSE MIDLINE GLIOMA

BACKGROUND Radiation therapy remains the sole standard-of-care treatment for Diffuse Midline Glioma (DMG), an aggressive and lethal brain tumor. Despite numerous clinical trials, median overall survival has not improved. Therefore, precise preclinical modeling is essential to guide clinical trials toward positive patient outcomes. ONC201, a ClpP antagonist, has demonstrated efficacy in treating DMG (NCT05580562, NCT05476939). However, efficacy is short-term and acquired resistance necessitates combination therapies. Therefore, we assessed the efficacy of BAY2402234, a potent and selective Dihydroorotate Dehydrogenase (DHODH) inhibitor, in combination with ONC201 in a murine model of DMG. METHODS Forty 6-week-old C57/B6 mice underwent pontine orthotopic injection with isogenic DMG cells via stereotactic surgery. The cell line used, 24B-7, has a mutational profile (PDGFRA+p53+H3.3K27M) and growth morphology representative of pontine DMGs. In our previous work, untreated mice injected with these cells had a median survival of 58 days. Upon confirmation of tumor growth using IVIS, mice were assigned to treatment groups based on BLI signal, and treatment was initiated. When mice showed signs of tumor burden or >20% weight loss they were euthanized. At euthanasia, the brain was collected, sectioned sagittally, and divided between fixation and freezing. These samples will evaluate tumor growth, morphology, and characterization compared between treatment groups by both immunohistochemistry and western blot. RESULTS As expected, ONC201 treated mice demonstrated an increase in median survival compared to the untreated group. While well-tolerated, neither BAY2402234 nor the combination of BAY2402234 and ONC201 exhibited a statistically significant increase in median survival after statistical correction. (Vehicle: 55 days, ONC201: 62 days, p=0.0026; BAY2402234: 58.5 days, p=0.0403; Combination: 57 days, p=0.1491). Ongoing efforts include target validation and tumor analysis through western blot and immunohistochemistry. ONC201 treatment will be evaluated by investigating ATF4, DR5, and CHOP. BAY2402234 treatment will be evaluated by investigating phosphor-gH2AX and gH2AX. CONCLUSIONS Pending tumor analysis.