Demonstration of a common DPhe 7 to DNal(2’) 7 peptide ligand antagonist switch for the melanocortin-3 and melanocortin-4 receptors identifies systematic mischaracterization of the ph

ABSTRACT Melanocortin peptides containing a D-naphthylalanine residue in position 7 (DNal(2’) 7 ), reported as melanocortin-3 receptor (MC3R) subtype-specific agonists in two separate publications, were found to lack significant MC3R agonist activity. The cell lines used at the University of Arizona for pharmacological characterization of these peptides, consisting of HEK293 cells stably transfected with human melanocortin receptor subtypes MC1R, MC3R, MC4R, or MC5R, were then obtained and characterized by quantitative PCR. While the MC1R cell line correctly expressed only the hMCR1, the three other cell lines were mischaracterized with regard to receptor subtype expression. Demonstration that a D-naphthylalanine residue in position 7, irrespective of the melanocortin peptide template, results primarily in antagonism of the MC3R and MC4R, then allowed us to search the published literature for additional errors. The erroneously characterized DNal(2’) 7 -containing peptides date back to 2003; thus, our analysis suggests that systematic mischaracterization of the pharmacological properties of melanocortin peptides occurred.