RT Journal Article SR Electronic T1 Initial pharmacological characterization of a major hydroxy metabolite of PF-5190457: inverse agonist activity of PF-6870961 at the ghrelin receptor JF Journal of Pharmacology and Experimental Therapeutics JO J Pharmacol Exp Ther FD American Society for Pharmacology and Experimental Therapeutics SP JPET-AR-2022-001393 DO 10.1124/jpet.122.001393 A1 Sara L. Deschaine A1 Morten A. Hedegaard A1 Claire L. Pince A1 Mehdi Farokhnia A1 Jacob E Moose A1 Ingrid A Stock A1 Sravani Adusumalli A1 Fatemeh Akhlaghi A1 James L. Hougland A1 Agnieszka Sulima A1 Kenner C. Rice A1 George F. Koob A1 Leandro Vendruscolo A1 Birgitte Holst A1 Lorenzo Leggio YR 2023 UL http://jpet.aspetjournals.org/content/early/2023/01/11/jpet.122.001393.abstract AB Preclinical and clinical studies have identified the ghrelin receptor (growth hormone secretagogue receptor 1a; GHSR1a) as a potential target for treating alcohol use disorder. A recent Phase 1a clinical trial of a GHSR1a antagonist/inverse agonist, PF-5190457, in individuals with heavy alcohol drinking, identified a previously undetected major hydroxy metabolite of PF-5190457, namely PF-6870961. Here, we further characterized PF-6870961 by screening for off-target interactions in a high throughput screen and determined its in vitro pharmacodynamic profile at GHSR1a through binding and concentration-response assays. Moreover, we determined whether the metabolite demonstrated an in vivo effect by assessing effects on food intake in male and female rats. We found that PF-6870961 had no off-target interactions and demonstrated both binding affinity and inverse agonist activity at GHSR1a. In comparison to its parent compound, PF-5190457, the metabolite PF-6870961 had lower binding affinity and potency at inhibiting GHSR1a-induced inositol phosphate accumulation. However, PF-6870961 had increased inhibitory potency at GHSR1a-induced β-arrestin recruitment relative to its parent compound. Intraperitoneal injection of PF-6870961 suppressed food intake under conditions of both food restriction and with ad libitum access to food in male and female rats, demonstrating in vivo activity. The effects of PF-6870961 on food intake were abolished in male and female rats knock-out for GHSR, thus demonstrating that its effects on food intake are in fact mediated by the GHSR receptor. Our findings indicate that the newly discovered major hydroxy metabolite of PF-5190457 may contribute to the overall activity of PF-5190457 by demonstrating inhibitory activity at GHSR1a. Significance Statement Antagonists or inverse agonists of the growth hormone secretagogue receptor (GHSR1a) have demonstrated substantial potential as therapeutics for alcohol use disorder. We here expand understanding of the pharmacology of one such GHSR1a inverse agonist, PF-5190457, by studying the safety and pharmacodynamics of its major hydroxy metabolite, PF-6870961. Our data demonstrate biased inverse agonism of PF-6870961 at GHSR1a and provides new structure-activity relationship insight into GHSR1a inverse agonism.