Discovery of agonists for orphan GPR52 using a ligand-based pharmacophore model and virtual screening

Abstract ID 130118 Poster Board 294 GPR52 is an orphan G protein-coupled receptor (GPCR) that is a promising target for neuropsychiatric disorders including schizophrenia and substance abuse disorders. GPR52 is a constitutively active receptor that couples to Gs/olf G proteins to stimulate adenylyl cyclase and increase intracellular cAMP. As with most understudied GPCRs, there is a paucity of structural diversity among known GPR52 ligands. To expand the chemical space of GPR52 ligands, we utilized a proprietary ligand based-pharmacophore model and virtual screening method to identify new potential compounds for GPR52. Greater than 500k synthesis-ready compounds were screened in silico for their structural similarity to the GPR52 agonist c17. This screening provided a compound priority list of 400 predicted GPR52 ligands. These priority compounds were obtained and subsequently screened at 10 μM using a Glosensor cAMP assay in HEK293 cells expressing human GPR52. The primary screen showed 21 hit compounds activated GPR52 cAMP signaling at > 40% of the maximal response to the positive control agonist 4-(3-(3-fluoro-5-(trifluoromethyl) benzyl)-5-methyl-1H-1,2,4-triazol-1-yl)-2-methylbenzamide (FTBMT). Subsequent re-testing confirmed activities, and the five most active compounds were evaluated in concentration responses to determine potency (EC₅₀) and efficacy (Emax). All five compounds exhibited low micromolar potency (ranging from 1.6 to 4.0 μM) and were partial agonists when compared to FTBMT. Two promising validated compounds included 2-B3 (N-(5-{[3-(trifluoromethyl)phenyl]methyl}-1,3-thiazol-2-yl)cyclopropanecarboxamide) and 5-E1 (ethyl 2-benzyl-4-methyl-1,3-thiazole-5-carboxylate). Compound 2-B3 showed lower partial agonist activity (Emax = 39 ± 2%) with a potency (pEC₅₀) of 5.80 ± 0.07 [1.6 μM]. Compound 5-E1 showed moderate partial agonist activity (Emax = 71 ± 2%) and potency (pEC₅₀) of 5.47 ± 0.02 [3.4 μM]. 2-B3 was docked into the previously solved GPR52 crystal structure (PBD 6LI0) using AMDock program. 2-B3 docked into a similar binding site as the agonist c17, with potential hydrogen bonding at the ECL2 amino acid D188. Structural derivatives of agonist 2-B3 are being actively screened to define structure activity relationships important for GPR52 potency and efficacy. Taken together, this virtual screening with pharmacological validation provides a viable method for the discovery of ligands for orphan GPCRs. Compounds 2-B3 and 5-E1 are promising GPR52 agonist ligands amenable to further chemical optimization to expand ligand diversity for GPR52. This work was supported in part by grant# T32DA007287 from the National Institutes of Health and the UTMB Center for Addiction Sciences and Therapeutics.