Abstract 5688: IND-enabling characterization of ONC206 as the next bitopic antagonist for oncology (2020)

Abstract ONC201 is the first clinical bitopic antagonist of dopamine receptor D2 (DRD2), that is well tolerated and induces durable tumor regressions in H3 K27M-mutant glioma patients. ONC206, a derivative of ONC201 that shares the imipridone core structure, is also a bitopic DRD2 antagonist that exhibits enhanced non-competitive effects, high specificity, nanomolar potency, and disruption of DRD2 homodimers. ONC206 exhibited a Ki of ~320nM for DRD2 with complete specificity across human GPCRs and complete DRD2 antagonism. Schild analyses of ONC206 in cAMP and β-Arrestin recruitment assays revealed hallmarks of non-competitive DRD2 antagonism, unlike antipsychotics but similar to ONC201. Shotgun mutagenesis across DRD2 identified 7 residues critical for ONC206-mediated antagonism at orthosteric and allosteric sites. Six residues were critical for ONC201 and ONC206, however the impact varied between the two compounds and one allosteric residue was exclusive to ONC206 located at the region that mediates the DRD2 homodimer interface. Gene expression profiling revealed ONC206 and ONC201 (upon 200nM treatment, 72 h) induce distinct signatures in U87 glioblastoma cells, further supporting distinct functional effects. Cell lines resistant to ONC201 and ONC206 are being generated to profile acquired-resistance mechanisms. Broad nanomolar efficacy of ONC206 (GI50 &amp;lt;78-889nM, 72h) was observed in &amp;gt;1,000 GDSC cancer cell lines with the highest sensitivity in cell lines exhibiting a DRD2+/DRD5- RNA expression signature. ONC206 reduced the viability of normal human fibroblasts at higher doses (GI50 &amp;gt; 5µM), suggesting a wide therapeutic window. Antitumor efficacy without body weight loss was observed with 50 mg/kg weekly oral ONC206 in a dopamine-secreting HuCCT1 cholangiocarcinoma subcutaneous xenograft model. Oral ONC206 at 50mg/kg exhibited a ~12 µM plasma Cmax and ~6 hours terminal half-life in Sprague-Dawley rats. Additionally, 5-10 fold higher ONC206 concentrations were observed in adrenal gland, bile duct, brain and bone marrow relative to plasma. Nanomolar concentrations were also observed in the CSF above DRD2 antagonism thresholds, unlike ONC201. GLP toxicology studies with weekly oral ONC206 in Sprague-Dawley rats and beagle dogs revealed no dose-limiting toxicities. Mild and reversible body weight changes were observed at the highest evaluated dose in both species. The no observed adverse effect level was ≥ 16.7 mg/kg in dogs and ≥ 50 mg/kg in rats that exceed efficacious doses. A 50 mg starting dose of ONC206 was selected for the first-in-human clinical trial in biomarker-enriched adult recurrent CNS tumors. In summary, ONC206 is poised for clinical introduction as the next imipridone bitopic DRD2 antagonist for oncology that exhibits differentiated target engagement, signaling, and biodistribution profiles. Citation Format: Varun Vijay Prabhu, Sara Morrow, Caroline A. Cuoco, Abed R. Kawakibi, Jinkyu Jung, Neel Madhukar, Matthew J. Garnett, Ultan McDermott, Cyril H. Benes, Robert Wechsler-Reya, Lakshmi Anantharaman, Neil Charter, Joseph B. Rucker, Benjamin J. Doranz, Joel Basken, Olivier Elemento, R. Benjamin Free, David R. Sibley, Martin Stogniew, Wolfgang Oster, Mark R. Gilbert, Sharon DeMorrow. IND-enabling characterization of ONC206 as the next bitopic antagonist for oncology [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5688.