Peptide and Small Molecules Rescue the Functional Activity and Agonist Potency of Dysfunctional Human Melanocortin-4 Receptor Polymorphisms^,

Abstract

The melanocortin pathway, specifically the melanocortin-4 receptor and the cognate endogenous agonist and antagonist ligands, have been strongly implicated in the regulation of energy homeostasis and satiety. Genetic studies of morbidly obese human patients and normal weight control patients have resulted in the discovery of over 70 human melanocortin-4 receptor (MC4R) polymorphisms observed as both heterozygous and homozygous forms. A number of laboratories have been studying these hMC4R polymorphisms attempting to understand the molecular mechanism(s) that might explain the obese human phenotype. Herein, we have studied 13 polymorphic hMC4Rs that have been identified to possess statistically significant decreased endogenous agonist potency with synthetic peptides and small molecules attempting to identify ligands that can pharmacologically rescue the hMC4R polymorphic agonist response. The ligands examined in this study include NDP-MSH, MTII, Ac-His-DPhe-Arg-Trp-NH2 (JRH887-9), Ac-Anc-DPhe-Arg-Trp-NH2 (amino-2-naphtylcarboxylic acid, Anc, JRH420-12), Ac-His-(pI)DPhe-Arg-Trp-NH2 (JRH322-18), chimeric AGRP-melanocortin based ligands (Tyr-c[Cys-His-DPhe-Arg-Trp-Asn-Ala-Phe-Cys]-Tyr-NH2, AMW3-130 and Ac-mini-(His-DPhe-Arg-Trp)-hAGRP-NH2, AMW3-106), and the small molecules JB25 and THIQ. The hMC4R polymorphisms included in this study are S58C, N97D, I102S, L106P, S127L, T150I, R165Q, R165W, L250Q, G252S, C271Y, Y287Stop, and I301T. These studies resulted in the NDP-MSH, MTII, AMW3-130, THIQ, and AMW3-106 ligands possessing nanomolar to subnanomolar agonist potency at the hMC4R polymorphisms examined in this study. Thus, these ligands could generically rescue the potency and stimulatory response of the abnormally functioning hMC4Rs studied and may provide tools to further clarify the molecular mechanism(s) involving these receptor modifications.

Novel pharmacological MC4R agonists can efficiently activate mutated MC4R from obese patient with impaired endogenous agonist response

“…In a recent study (Xiang et al 2007), distinct relative potencies versus a-MSH were observed for synthetic agonists depending on the mutated receptor as compared with wild-type hMC4R. In agreement with that work, differences in IRC-022493 and IRC-022511 potency depended on the mutation type, although in this study, the potency ratio of IRC-022493 or IRC-022511 versus a-MSH was unchanged in mutated hMC4R as compared to wild-type hMC4R.…”

“…hMC4R and the ligands. Except for Ser127Leu, they are positioned closer to the cytoplasmic side of the lipid bilayer and are likely to be involved in ligand-induced conformational changes important for G-protein-induced signal transduction events (Xiang et al 2007). Ser127Leu is located in the third transmembrane domain and was described to be an important residue for interacting with the endogenous melanocortin conserved His-Phe-Arg-Trp residues.…”

“…Ser127Leu is located in the third transmembrane domain and was described to be an important residue for interacting with the endogenous melanocortin conserved His-Phe-Arg-Trp residues. Ser127 residue might be important for receptor local hydrogen bonding interactions that might shift the hMC4R from the inactive to the active conformation state on ligand binding (Xiang et al 2007).…”

“…due to missense or frameshift mutations), intracellular retention, altered basal activity, and altered a-MSH stimulation. Synthetic ligands, from classical NDP-MSH peptides to the multiple tetrapeptides and small molecule MC4R agonists, have been tested in vitro with distinct improvement of hMC4R functional activity depending on both agonist potency and nature of the mutation (Ujjainwalla & Sebhat 2007, Xiang et al 2007. Determining which of the hMC4R mutations might be pharmacologically rescued by newly developed MC4R agonists is a promising approach to identify potential patients who may benefit the most from such drug candidates.…”

Tackling obesity: new therapeutic agents for assisted weight loss

“…128 Numerous MC4-R agonists are being developed as potential targets for obesity therapy. [129][130][131] Other experimental drugs Several other medications are at different stages of investigation for their ability to induce weight loss and include: tesofensine (sympathomimietic), SIRT 1, peptide analog of growth hormone fragnment hGH 177-191, somatostatin, Axokine, Neuropeptide Y Receptor antagonists, pancreatic lipase inhibitor (cetilistat), cholecystokinin, beta3 adrenergic receptors agonists, and combination of anti-obesity drugs, in addition to multiple experimental drugs in early phase of development. 132 …”