The Design of an Antagonist that Improves Cardiac Function through Ligand-Directed Signaling.

The signaling pathway of a peptide that impacts cardiovascular physiology may be targeted to influence cardiac function. Through previous studies, we discovered that human RFRP-1 (RFamide-related peptide-1; MPHSFANLPLRF-NH ) decreases cardiac contractility. The structure and activity of RFRP-1 are conserved across phylogeny, suggesting it plays a role in physiology. We determined RFRP-1 structure-activity relationship (SAR) in cardiomyocytes and demonstrated that it acts through RFRP-1R, a G protein-coupled receptor (GPCR). Based on RFRP-1 SAR data, we designed LPLAF-NH and found that it acts as a RFRP-1R antagonist in cardiomyocytes and in animals. The alanyl-substituted analog diminished the effects of the full-length peptide and active core, but not at equimolar concentrations; the antagonist was less effective. In order to design a better antagonist, we turned to molecular docking software to investigate ligand-receptor binding. As a result, we designed an antagonist with increased receptor interactions that improved cardiac function in human cardiomyocytes and consistent with ligand-directed RFRP-1R signaling.