Biological evaluation of cyclized cystine knot peptides targeting human melanocortin receptors

Abstract

Because of their multiplicity and ubiquity in mammalian systems as central modulators of signaling, GPCRs have held a special interest in drug design. Specifically, ligands targeting the homeostatic class of GPCRs known as melanocortin receptors (MCRs) have the potential to remedy the symptoms of obesity, diabetes, and pain. Adenylate cyclase assays were performed on HEK 293 cells expressing hMC1R, hMC3R, hMC4R, and hMC5R to assess a class of 39 multiple‐disulfide, cyclized MSH analogues featuring strategic N‐methylation and based on the protein topology of conotoxins found in the venoms of marine cone snails. Because of their potency and selectivity, conotoxins offer a promising avenue for drug design; furthermore, the combined cyclic backbone and cystine knot motifs of the MSH conotoxin analogues afforded specific conformational constraining in addition to enhanced proteolytic stability and bioavailability. Several antagonists of hMC4R and agonists of hMC5R were identified from the library with EC50 values in the low micromolar range; these results provide important starting points for further optimization. This research was supported by the PHS (DK17420), NIH (DA06248), and HHMI (52003749).