Identification of a novel selective inverse agonist probe and analogs for the Retinoic acid receptor-related Orphan Receptor Alpha (RORα)

Several nuclear receptors (NRs) are still characterized as orphan receptors because endogenous ligands have not yet been identified for these proteins. Evidence is growing suggesting the retinoic acid receptor-related orphan receptors (RORs) bind to and are modulated by oxysterols. Recently we discovered that the synthetic liver X receptor (LXRα) agonist T0901317 (ML125) was a potent inverse agonist of RORα and RORγ. Structure activity relationship (SAR) studies quickly revealed a strategy to remove the LXRα activity from the T0901317 chemical scaffold which lead to ML124 (PubChem CID 44237404). ML124 represented the first synthetic RORα/RORγ dual inverse agonist devoid of LXRα activity. While there appears to be clear non-overlapping roles for RORα and RORγ, chemical probes that are isoform selective are needed to dissect this biology. Here, we describe the identification of a selective RORα synthetic ligand, ML176 (SR3335; PubChem CID 2360837). ML176 directly binds to RORα, but not other RORs, and functions as a selective inverse agonist of RORα in cell-based assays. Furthermore, ML176 suppresses the expression of endogenous RORα target genes in HepG2 cells that are involved in hepatic gluconeogenesis including glucose-6-phosphatase () and phosphoenolpyruvate carboxykinase (). Given the excellent pharmacokinetics (PK) of the parent compound ML125 in animals as well as humans, it was not too surprising that PK studies revealed that ML176 has reasonable exposure following an intraperitoneal (i.p.) injection into mice. We assessed the ability of ML176 to suppress gluconeogenesis using a diet-induced obesity (DIO) mouse model where the mice were treated with 15 mg/kg , i.p. for 6 days followed by a pyruvate tolerance test. ML176-treated mice displayed lower plasma glucose levels following the pyruvate challenge consistent with suppression of hepatic gluconeogenesis. Thus, we have identified the first synthetic RORα selective inverse agonist, and this compound can be utilized as a chemical tool to probe the function of this receptor both and . Additionally, our data suggests that RORα inverse agonists may hold utility for suppression of elevated hepatic glucose production in type 2 diabetics.