Abstract 3857: Selective targeting of dopamine receptor dysregulation in high grade gliomas with imipridone ONC201
Authors: Prabhu Varun Vijay , Madhukar Neel , Kline C. Leah B. , Tarapore Rohinton , El-Deiry Wafik S. , Rucker Joseph , Doranz Benjamin , Doherty Faye , VanEngelenburg Alexander , Durrant Jessica , Benes Cyril , Deacon Sean , Charter Neil , Free R. Benjamin , Oster Wolfgang , Sibley David , Arrillaga Isabel , Elemento Olivier , Allen Joshua E. 
Published: August 2018

Abstract
D2-like dopamine receptors (DRD2/3/4) are G protein-coupled receptors (GPCRs) that are overexpressed in glioblastoma (GBM) and their antagonism induces tumor cell apoptosis. We describe the first selective DRD2/3 antagonist for neuro-oncology using computational, receptor pharmacology, biochemical and clinical studies. Consistent with an in-silico prediction and in contrast to antipsychotics that target several dopamine receptors and other GPCRs, β-arrestin recruitment and cAMP assays determined that ONC201 is a selective DRD2/3 antagonist. Schild analyses and radioligand competition assays revealed competitive and non-competitive DRD2 antagonism with a potency (2-3 µM) that is consistent with anticancer activity and driven by an unusually slow association rate. Proof-of-concept studies show that selective DRD2 inhibition induces superior anti-cancer efficacy relative to pan-targeting of the dopamine receptor family. In accordance with superior selectivity, ONC201 also exhibited a wider therapeutic window compared to antipsychotics. Shotgun mutagenesis across 350 amino acids of DRD2 identified 8 residues that are critical for ONC201-mediated DRD2 antagonism. Consistent with competitive inhibition, several mutated residues were within the orthosteric binding site. However, distal residues were identified that were not involved in DRD2 antagonism by antipsychotics and may explain the selectivity and non-competitive antagonism of ONC201. In vitro and in vivo studies have previously demonstrated single agent ONC201 efficacy in GBM models (Allen et al 2013). Analyses of The Cancer Genome Atlas and tissue microarrays revealed high DRD2 expression relative to other dopamine receptors, correlation with poor prognosis and high DRD2 expression in primary rather than secondary GBM. A linear correlation between DRD2 mRNA and ONC201 GI50 was observed among GBM cell lines in the NCI60 panel. Interestingly expression of DRD5, a D1-like dopamine receptor that counteracts DRD2 signaling, was significantly inversely correlated with ONC201 potency in the NCI60 dataset (P &lt;.05). Furthermore, a de novo missense DRD5 mutation was identified in cancer cells with acquired resistance to ONC201, and overexpression of the mutant construct could recapitulate resistance. ONC201 exhibited biological activity in a phase II recurrent GBM study, including tumor regressions (Arrillaga et al, 2017). Among the 15 available archival patient tumor specimens from the first cohort of this trial, all had DRD2 expression and 8 had low DRD5 expression that was associated with superior progression-free and overall survival, with 4/8 DRD5- and 0/7 DRD5+ patients alive after 15 months (P=0.012). Thus, ONC201 possesses unique receptor pharmacology as the first selective DRD2/3 antagonist for clinical neuro-oncology that has exhibited clinical activity in biomarker-defined recurrent high grade glioma patients.
Citation Format: Varun Vijay Prabhu, Neel Madhukar, C. Leah B. Kline, Rohinton Tarapore, Wafik S. El-Deiry, Joseph Rucker, Benjamin Doranz, Faye Doherty, Alexander VanEngelenburg, Jessica Durrant, Cyril Benes, Sean Deacon, Neil Charter, R. Benjamin Free, Wolfgang Oster, David Sibley, Isabel Arrillaga, Olivier Elemento, Joshua E. Allen. Selective targeting of dopamine receptor dysregulation in high grade gliomas with imipridone ONC201 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3857.