Abstract 2749: Defining structure activity relationships for GPCR engagement and anti-cancer efficacy of imipridone small molecules
Authors: Prabhu Varun V. , Kawakibi Abed Rahman , Madhukar Neel S. , Anantharaman Lakshmi , Deacon Sean , Charter Neil S. , Garnett Mathew J. , McDermott Ultan , Benes Cyril H. , Oster Wolfgang , Elemento Olivier , Stogniew Martin , Allen Joshua E. 
Published: August 2019

Abstract
G protein-coupled receptors (GPCRs) represent the most widely exploited superfamily of drug targets for FDA-approved therapies for many diseases, however, these receptors are underexploited for oncology. ONC201 is a selective antagonist of GPCRs dopamine receptor D2 (DRD2) and DRD3 that has been shown to induce tumor regressions with a benign safety profile in high grade glioma patients. ONC201 (benzyl-2-methylbenzyl-imipridone) is the founding member of the imipridone class of small molecules that share a unique tri-heterocyclic core chemical structure. Imipridones share several chemical and biological properties that are desirable drug-like characteristics: oral administration, wide therapeutic window, chemical stability and blood brain barrier penetrance. In this study, we profiled a series of imipridones for GPCR engagement and anti-cancer efficacy. Several imipridones were screened against a large panel of human GPCRs using a β-arrestin recruitment assay. The imipridones tested resulted in GPCR agonist/antagonist activity (threshold set at &gt;20% activity) that was heterogenous, but exclusive among Class A GPCRs that represent the largest class. Minor chemical modifications to the ONC201 chemical structure caused large shifts in agonist versus antagonist activity and selectivity for GPCRs. Specifically, switching the ONC201 imipridone core from an angular to a linear isomer resulted in loss of DRD2 antagonist activity and impaired inhibition of cancer cell viability, indicating the imipridone core structure is critical for GPCR engagement and anti-cancer effects. The addition of electron withdrawing groups (e.g. di- or tri-halogen substitution) to the methyl benzyl ring improved potency for GPCR engagement and anti-cancer effects, but not for the benzyl ring. Loss of the benzyl ring impaired anti-cancer effects. Among all of the GPCR hits identified, maximal variance in imipridone GPCR engagement was identified for DRD2/DRD3 antagonism and GPR132 agonism that were prioritized considering their known biological relevance in oncology. ONC206 (benzyl-2,4-difluoromethylbenzyl-imipridone) emerged as the most selective and potent antagonist for D2-like dopamine receptors that are overexpressed and critical for survival in several cancers. ONC212 (benzyl-4-trifluoromethylbenzyl-imipridone) was the most selective and potent agonist for tumor suppressor GPR132. Both compounds were tested in the GDSC panel of &gt;1000 cancer cell lines and demonstrated broad spectrum nanomolar inhibition of cancer cell viability and a wide therapeutic window. GPCR target expression correlated with anti-cancer efficacy in the GDSC panel for both compounds, providing potential biomarkers of response. Thus, chemical derivatization of ONC201 has generated a class of novel GPCR-targeting agents with promising preclinical efficacy and safety profiles in oncology.
Citation Format: Varun V. Prabhu, Abed Rahman Kawakibi, Neel S. Madhukar, Lakshmi Anantharaman, Sean Deacon, Neil S. Charter, Mathew J. Garnett, Ultan McDermott, Cyril H. Benes, Wolfgang Oster, Olivier Elemento, Martin Stogniew, Joshua E. Allen. Defining structure activity relationships for GPCR engagement and anti-cancer efficacy of imipridone small molecules [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2749.