Glioblastoma remains a lethal brain tumor in adults with limited therapeutic options. TIC10/ONC201, a first-in-class imipridone we discovered, achieved meaningful therapeutic effects in phase I/II trials in patients with diffuse gliomas (DG's) harboring H3K27M mutations, and currently the drug is in randomized phase III testing (ACTION trial; NCT05580562). ONC201 targets mitochondrial protease ClpP to disrupt oxidative phosphorylation and trigger the integrated stress response (ISR), TRAIL/DR5, and tumor cell death. While ONC201 and its analog ONC206 are undergoing clinical trials as single agents, there is limited information on their interactions with stand-of-care therapy. We show that ONC201 and ONC206 synergize with temozolomide (TMZ) and Radiotherapy (RT). ONC201 enhances TMZ- or RT-induced apoptosis, ISR and cytotoxicity. ClpP-silencing suppresses ONC201-induced cytotoxicity but not TMZ. Both ONC201 and ONC206 reduce expression of TMZ-resistance mediator MGMT observed in H3K27M-mutated DG cells following treatment with imipridones+TMZ. Cytokine profiling indicates distinct effects of ONC201 relative to TMZ treatment. These results suggest mechanisms underlying ONC201's anti-tumoral activity are distinct from those associated with TMZ or RT with potential for synergy between these three treatments. Triple ONC201+RT+TMZ (IRT) therapy prolonged median survival to 123 days with tail on survival curve (3-of-7 mice alive beyond 200-days) in orthotopic U251 GBM 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 231-days, the only surviving mice were in IRT group. Our results support investigation of ONC201/ONC206 in combination with RT/TMZ (IRT) in GBM or H3K27M mutated DG therapy.
Keywords: IDH; MGMT; ONC201; ONC206; glioblastoma multiforme; radiotherapy; temozolomide.