Discovery of Prototype Peptidomimetic Agonists at the Human Melanocortin Receptors MC1R and MC4R

Abstract

[Nle4, DPhe7]-alpha-MSH (NDP-MSH), a highly potent analogue of alpha-melanocyte-stimulating hormone (alpha-MSH), possesses nanomolar efficacies at all the melanocortin receptor subtypes except the MC2R. Evaluation of the melanocortin "message" sequence of [Nle4, DPhe7]-alpha-MSH was performed on the human melanocortin receptor subtypes designated hMC1, hMC3R, hMC4R, and hMC5R. Tetrapeptides and tripeptides were stereochemically modified to explore topochemical preferences at these receptors and to identify lead peptides possessing agonist activity and subtype selectivity. Four peptides were discovered to only bind to the hMC1 and hMC4 receptor subtypes. The tetrapeptide Ac-His-DPhe-Arg-Trp-NH2 (1) possessed 0.6 microM binding affinity at the hMC1R, 1.2 microM binding affinity at the hMC4R, and agonist activity at both receptors. The tripeptides Ac-DPhe-Arg-Trp-NH2 (6) and Ac-DPhe-Arg-DTrp-NH2 (7) possessed 2.0 and 9.1 microM binding affinities, respectively, only at the hMC4R, and both compounds effected agonist activity. The tetrapeptide Ac-His-Phe-Arg-DTrp-NH2 (4) possessed 6.3 microM affinity and full agonist activity at the hMC1R, while only binding 7% at the hMC3R, 36% at the hMC4R, and 11% at the hMC5R at a maximal concentration of 10 microM. These data demonstrate that the His-Phe-Arg-Trp message sequence of the melanocortin peptides does not bind and stimulate each melanocortin receptor in a similar fashion, as previously hypothesized. Additionally, this study identified the simplest structural agonists for the hMC1R and hMC4R receptors reported to date.

Solution structures of the melanocyte‐stimulating hormones by two‐dimensional NMR spectroscopy and dynamical simulated‐annealing calculations

“…The tetrapeptide His-DPhe-Arg-Trp only bound and exhibited an agonist activity to both human MC1R and human MC4R. Stereochemical and deletion studies have shown that His6 residue of A-MSH is important for activity not on the human MC4R but on the skin melanocortin receptor [41]. This result suggests that His6 of A-MSH may not be critical for human MC4R binding.…”

Third Transmembrane Domain of the Adrenocorticotropic Receptor Is Critical for Ligand Selectivity and Potency

“…␣-MSH shares the first 13 amino acids with ACTH, and they share the core sequence His 6 -Phe 7 -Arg 8 -Trp 9 . This region was identified as important for ligand binding and activities at hMC1R, hMC2R, hMC3R, hMC4R, and hMC5R (27)(28)(29)(30)(31)(32)(33)(34). Our previous results indicate that [Nle 4 ]ACTH(1-39) (with norleucine substituted for methionine at position 4) is equipotent to ACTH(1-39) in ligand binding and signaling (35).…”

Synthesis and Pharmacology of α/β3-Peptides Based on the Melanocortin Agonist Ac-His-dPhe-Arg-Trp-NH2 Sequence

“…2−4 The conserved tetrapeptide sequence has been determined to be important for the ligand binding/molecular recognition and stimulation of melanocortin receptors (MCRs). 5,6 The MCRs are G protein-coupled receptors (GPCRs) that activate the cyclic adenosine monophosphate (cAMP) signal transduction pathway and generate a cascade of intracellular events, which result in physiological responses. Five melanocortin receptors (MC1−5R) have been cloned and characterized.…”