LAUSR

ONC201 is the first bitopic dopamine receptor D2 (DRD2) antagonist and allosteric mitochondrial protease ClpP agonist. Downstream of target engagement, ONC201 activates the integrated stress response pathway resulting in selective tumor cell death. ONC201 is well tolerated and induces durable tumor regressions in H3 K27M-mutant glioma patients. ONC206, a derivative of ONC201 currently in Phase I trials for adult and pediatric brain tumors, is also a bitopic DRD2 antagonist and ClpP agonist with nanomolar potency. We further evaluated in vitro efficacy and mechanism of action specific to ClpP for ONC206 and investigated acquired resistance to ONC201 and ONC206. FITC-casein and peptide degradation assays confirmed that ONC206 acts as an agonist of human ClpP with enhanced potency relative to ONC201. Broad efficacy in the nanomolar range for ONC206 (GI50 <78-889nM, 72h) was observed in 1,088 Genomics of Drug Sensitivity in Cancer (GDSC) cancer cell lines with increased sensitivity in cell lines exhibiting high ClpP mRNA expression. Among solid tumors, nervous system-related cell lines were particularly sensitive. Gene Expression Profiling Interactive Analysis (GEPIA) database analysis showed ClpP mRNA was overexpressed in glioblastoma cells relative to normal cells. GDSC observations were confirmed in glioblastoma (GBM) (T98G, A172, U87MG), H3.3 K27M mutant diffuse intrinsic pontine glioma (DIPG) (SF8628, SF7761) and astrocytoma (H4, U118MG) cell lines. ONC206 was more potent than ONC201 in cell viability assays for all glioma lines tested. SF8628 cells with a CRISPR-mediated ClpP knockout were shown to demonstrate resistance to both ONC201 and ONC206. Polyclonal resistant cell lines were generated through prolonged passaging in increasing concentrations of ONC201 or ONC206 (SF8628 and T98G cells). Cells with acquired resistance to ONC201 (ONC201Res) or ONC206 (ONC206Res) showed cross resistance to both imipridones. Time-stability of resistance was confirmed by removing drug for 2 to 4 weeks and retesting. RNAseq analysis revealed upregulation of the integrated stress response with imipridone treatment in T98G parental cells but not resistant clones. Whole genome sequencing revealed ClpP mutations in both ONC201Res and ONC206Res cells. Our results confirm the role of ClpP in the mechanism of action of ONC201 and ONC206 in tumor cells. Citation Format: Andrew Lee, Cristina Maranto, Scott Foster, Sara Morrow, Joshua E. Allen, Randall Lanier, Phiroze Sethna, Varun V. Prabhu. Role of ClpP in the anti-cancer effects of imipridone ONC201 and ONC206. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4914.