Abstract B007: Allosteric ClpP agonist ONC206 alters mitochondrial metabolism and stress response to elicit apoptosis in meningioma

Abstract Introduction: 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 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 anticancer agents, and downstream pharmacodynamics including mitochondrial function with ONC206 treatment in models of human meningioma. Methods: ClpP was expressed in E coli and purified by His-tag affinity for biochemical assays. Meningioma (IOMM-Lee, HKBMM, BEN-MEN-1) cell lines were commercially sourced. Cell viability (CellTiter-Glo, CyQuant) and apoptosis (Caspase Glo, annexin V) assays, Seahorse analysis, and multiomics were conducted in meningioma cells treated with vehicle/ONC206. In vivo efficacy was evaluated in the Ben-Men-1-fluc orthotopic meningioma model in female C. B-17 SCID mice. Results: Cocrystallization 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 increased resolved pore size and decreased complex height. ONC206 exhibits nanomolar potency in cell-free human ClpP casein/peptide degradation assays. Accordingly, meningioma cell lines 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. 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 anticancer efficacy with ONC206 in vitro. Proteomics indicated inhibition of mitochondrial metabolism by ONC206, while metabolomics revealed elevated α-ketoglutaric acid, glutamine, and citric acid. Consistent with epigenetic regulation by metabolites, ATACseq revealed ONC206 altered chromatin accessibility while RNAseq demonstrated upregulated stress response and apoptosis. Western blot analysis confirmed ONC206 upregulates the integrated stress response (ATF4/CHOP), elevates H3K27 trimethylation, and downregulates mitochondrial proteins (ClpX, TSFM). 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. Antitumor efficacy was observed with oral ONC206 but not sunitinib in vivo. Conclusion: Our results indicate that ClpP agonism is directly involved in mediating the anticancer effects of potent novel agent ONC206 in meningioma. Citation Format: Andrew K. Lee, Cristina Maranto, Scott Foster, Varun V. Prabhu, Joshua E. Allen. Allosteric ClpP agonist ONC206 alters mitochondrial metabolism and stress response to elicit apoptosis in meningioma abstract. In: Proceedings of the AACR Special Conference in Cancer Research: Brain Cancer; 2026 Mar 23-25; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2026;86 (6Suppl): Abstract nr B007.