Development of Melanocortin 4 Receptor Agonists by Exploiting Animal-Derived Macrocyclic, Disulfide-Rich Peptide Scaffolds

G protein-coupled receptors are among the most widely studied classes of drug targets. A major challenge in this field is to develop ligands that will selectively modulate a single receptor subtype to overcome the disadvantages of undesired off target effects caused by lack of target and thus signaling specificity. In the current study, we explored ligand design for the melanocortin 4 receptor (MC4R) since it is an attractive target for developing antiobesity drugs. Endogenously, the receptor is activated by peptide ligands, i.e., three melanocyte-stimulating hormones (alpha-MSH, beta-MSH, and.-MSH) and by adrenocorticotropic hormone. Therefore, we utilized a peptide drug design approach, utilizing molecular grafting of pharmacophore peptide sequence motifs onto a stable nature-derived peptide scaffold. Specifically, protegrin-4-like-peptide1 (Pr4LP1) and arenicin-1-like-peptide-1 (Ar3LP1) fully activated MC4R in a functional cAMP assay with potencies of 3.7 and 1.0 nM, respectively. In a nanoluciferase complementation assay with less signal amplification, the designed peptides fully recruited miniGs with subnanomolar and nanomolar potencies. Interestingly, these novel peptide MC4R ligands recruited beta-arrestin-2 with similar to 2-fold greater efficacies and similar to 20-fold increased potencies as compared to the endogenous alpha-MSH. The peptides were inactive at related MC1R and MC3R in a cAMP accumulation assay. These findings highlight the applicability of animal-derived disulfide-rich scaffolds to design pathway and subtype selective MC4R pharmacological probes. In the future, this approach could be exploited to develop functionally selective ligands that could offer safer and more effective obesity drugs.

Automated summary

In this study, peptide ligands for MC4R were designed using a peptide drug design approach. The designed peptides fully activated MC4R and recruited beta-arrestin-2 with higher efficacies and potencies than the endogenous alpha-MSH. These findings suggest the potential of these novel peptide ligands in developing safer and more effective antiobesity drugs.