Peptide and small molecules rescue the functional activity and agonist potency of dysfunctional human melanocortin-4 receptor polymorphisms.

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.