TMET-26. Allosteric ClpP agonist ONC206 alters mitochondrial metabolism and stress response to elicit apoptosis in meningioma

Abstract Malignant meningioma is an aggressive central nervous system cancer with limited established systemic therapies. Imipridone ONC206, a derivative of dordaviprone (ONC201) with nanomolar potency, is an allosteric caseinolytic protease P (ClpP) agonist and dopamine receptor D2/3 (DRD2/3) antagonist, that is being evaluated in clinical trials that include central nervous system tumors. We characterized ClpP binding, in vitro efficacy, comparison to other relevant anti-cancer agents, downstream pharmacodynamics including mitochondrial function with ONC206 treatment in models of human meningioma. Co-crystallization with ClpP that assembles as a tetradecameric complex revealed an allosteric ligand interaction with distinctions in the ONC206-ClpP resolved crystal structure relative to the dordaviprone-bound or apo complex, including an increase in the resolved pore size and decreased complex height. ONC206 exhibits nanomolar potency in cell-free human ClpP casein/peptide degradation assays. Accordingly, meningioma lines (IOMM-Lee, HKBMM, BEN-MEN-1) demonstrated nanomolar sensitivity to ONC206 in cell viability assays. ONC206 induced dose- and time-dependent apoptosis in HKBMM but not in IOMM-Lee as measured with Caspase-Glo and Annexin V assays. ONC206 also demonstrated superior potency in cell viability inhibition compared to sunitinib at equivalent concentrations. A 24/48-hour duration of exposure was sufficient to induce sustained anti-cancer efficacy with ONC206 in vitro. Western blot analysis showed ONC206 upregulates the integrated stress response (CHOP) and downregulates mitochondrial proteins (ClpX, TSFM), as expected from ClpP agonism. Accordingly, Seahorse analysis of mitochondrial function revealed ONC206 substantially impairs basal, maximal, and ATP-coupled mitochondrial respiration. CRISPR/Cas9-mediated knockout of ClpP abrogates ONC206 sensitivity in meningioma cells and ONC206 effects on mitochondrial respiratory capacity. Our results indicate that ClpP agonism is directly involved in mediating the anti-cancer effects of potent novel agent ONC206 in meningioma.