DNAR-03. ONC201 synergizes with concurrent temozolomide-radiotherapy against newly diagnosed glioblastomas

Abstract BACKGROUND Glioblastoma, the most common form of adult primary brain cancer, remains a lethal disease with therapeutic options limited by the blood-brain barrier (BBB). ONC201 (also known as TIC10) is a first-in-class, BBB penetrant imipridone that showed promise in phase I/II glioma trials as monotherapy. The drug targets key oncogenic pathways, including ERK/AKT, integrated stress response (ISR), TRAIL/DR5, and ClpP-dependent mitochondrial stress. OBJECTIVE Here, we investigated the efficacy of ONC201 in combination with temozolomide and radiation to explore the potential as a therapeutic strategy for newly diagnosed glioblastoma. METHODS pre-clinical laboratory investigation. RESULTS ONC201 synergized with the cytotoxic effects of temozolomide (TMZ) and Radiotherapy (RT) in vitro. Specifically, ONC201 enhances TMZ- or RT-induced apoptosis and integrated stress response (ISR). Consistent with the specific interaction between ClpP and ONC201, the cytotoxic effect of ONC201 was abolished upon ClpP silencing. In contrast, silencing of ClpP did not affect the cytotoxic effects of RT or TMZ. These results suggest that the mechanisms underlying ONC201’s anti-tumoral activity are distinct from those associated with TMZ or RT, with potential for synergy between these agents. Supporting this hypothesis, cytokine profiling and RNAseq experiments demonstrate that ONC201 and TMZ induced distinct responses. Additionally, ONC201 reduced Methyl-guanine methyl transferase (MGMT) expression. Further supporting the synergy between ONC201 and TMZ/RT, ONC201+RT+TMZ therapy prolonged median survival to 123 days with tail on survival curve (3-of-7 mice alive beyond 200-days) in orthotopic U251 glioblastoma model versus ONC201 (44-days; p = 0.000197), RT (63-days; p = 0.0012), TMZ (78-days; p = 0.0354), ONC201+RT (55-days; p = 0.0004), ONC201+TMZ (80-days; p = 0.0041) and RT+TMZ (103-days; p > 0.05). By day 231, the only surviving mice were in the ONC201+RT+TMZ group. CONCLUSION These results support the consideration of incorporating ONC201 into the current standard of care for newly diagnosed glioblastomas.