Synthesis and Biological Evaluation in Vitro of a Selective, High Potency Peptide Agonist of Human Melanin-concentrating Hormone Action at Human Melanin-concentrating Hormone Receptor 1

Abstract

Human melanin-concentrating hormone (hMCH) is a nonselective natural ligand for the human melanin-concentrating hormone receptors: hMCH-1R and hMCH-2R. Similarly, the smaller peptide encompassing the disulfide ring and 50 ‫؍‬ 47 nM) with more than 200-fold selectivity with respect to hMCH-2R. Apparently, these structural changes in positions 6 and 10 results in peptide conformations that allow for efficient interactions with hMCH-1R but are unfavorable for molecular recognition at hMCH-2R.In the last couple of years, melanin-concentrating hormone (MCH) 1 emerged as an important regulator of feeding behavior in rodents (1-7). Similarly to neuropeptide Y, this hormone stimulates appetite in rats when injected intracerebroventricularly, and this orexigenic effect is inhibited by anorectic peptides such as ␣-melanocyte stimulating hormone, glucagon-like peptide 1, and neurotensin (1-7). Additionally, in the hypothalamus of genetically obese (ob/ob) and fasting mice, the level of MCH messenger RNA is elevated, and the metabolic rate of mice lacking MCH is increased. MCH (see Structure 1 for human/rat MCH) also appears to be involved in other biological functions such as regulation of the hypothalamic-pituitarythyroid axis. In humans, this 19-amino acid cyclic peptide is found in the brain, in the lateral hypothalamus and the zona incerta, and acts through specific receptors (8 -12). At present, two receptors are known with which hMCH interacts: hMCH-1R and hMCH-2R (13-23). These receptors are members of the family of G-protein-coupled receptors and their activation leads to mobilization of intracellular calcium. Binding of hMCH to hMCH-1R results in reduction of forskolin-elevated cyclic AMP levels, but binding to hMCH-2R does not cause this effect. The physiological role of hMCH-2R is less well understood than the physiological role of hMCH-1R, but the presence of the MCH-2R messenger RNA in the brain regions implicated in the regulation of body weight suggests that this receptor might also be involved in the regulation of feeding behavior (19 -23).To understand and separate the physiological functions of the MCH receptors, selective agonists are required, because hMCH is a nonspecific natural ligand for both hMCH-1R and hMCH-2R. Similarly, the synthetic ligands reported in the literature do not distinguish between the receptors (13-23).Our previous structure-function studies on hMCH yielded a cyclic peptide consisting of the disulfide ring and Arg 6 of hMCH: the so-called "active core" of hMCH with the four residues, Arg 6 , Met 8 , Arg 11 , and Tyr 13 , critical for molecular recognition at hMCH-1R and hMCH-2R (24 -27). This compound, Ac-hMCH(6 -16)-NH 2 (Structure 2), was equipotent to the fulllength hMCH at both receptors. Moreover, at hMCH-1R, an analog of Ac-hMCH(6 -16)-NH 2 with D-Arg in position 6 was as potent as the parent compound, but, at hMCH-2R, this analog was a noticeably weaker agonist. The D-Arg 6 compound was the first described peptide agonist with enhanced hMCH-1R selectivity with respect to ...

Effects of intracerebroventricular and intra-accumbens melanin-concentrating hormone agonism on food intake and energy expenditure

“…The control and the MCH test conditions consisted in the injection of either the vehicle (0.9% saline) or the MCHR1 agonist [Compound A (36) kindly provided by Merck Research Laboratories, Rahway, NJ]. Compound A is a truncated analog of MCH whose biophysical properties have previously been described as being very close to the full-length MCH molecule (4,5). It has a clear effect on food intake (36), which is comparable to that of MCH (Guesdon, B and Richard, D, unpublished data) and therefore represents a useful tool to investigate the MCH system.…”

Peptide Ligands for the Melanin-Concentrating Hormone (MCH) Receptor 1

“…7), was even more potent at and selective for hMCH-1R (EC 50 = 47 nM, 6600-fold higher binding affinity for hMCH-1R than hMCH-2R). This hMCH-1R agonist was practically inactive at hMCH-2R at micromolar concentrations [47]. It has displayed the highest selectivity for hMCH-1R among the peptide hMCH-1R agonists reported in the literature.…”

“…4), was a noticeably weaker agonist at hMCH-2R than hMCH-1R, the Merck group developed a detailed structure-function study around position 6 of this compound [40,47]. A number of analogs of 10 with various amino acids incorporated in place of Arg 6 were evaluated to define a structure of the side chain in position 6 that was the most favorable to high peptide selectivity at hMCH-1R.…”

Expression of Receptors for Melanin-Concentrating Hormone (Mch) in Different Tissues and Cell Lines

“…The most important steps along these investigations were (i) the establishment of a reliable fish scale bioassay; [5] (ii) the discovery of mammalian MCH, its precursor and gene(s) as well as its multiple physiological effects (reviewed by Nahon [6] ); (iii) the chemical synthesis of a biologically active radiolabeled MCH analog [7][8][9] and the establishment of a MCH receptor binding assay; [10] (iv) the finding of a relatively broad distribution pattern of the MCH precursor in the human, ranging from the lateral hypothalamus, zona incerta and medulla oblongata to various peripheral organs such as spleen, thymus, brown fat, duodenum, adrenal gland, bone marrow, testis, and lymphatic gland; [11] (v) the discovery of the orexigenic activity of MCH, [12] confirmed by MCH gene knock-out animals that are hypophagic and lean [13] and by a MCH transgenic mouse model; [14] (vi) the physiological antagonism between MCH and a-MSH which is not confined to teleost melanophores [5] but also evident in the mammalian brain; [15][16][17] (vii) the characterization of MCH binding sites by photocrosslinking on melanoma cells, [18,19] by chemical crosslinking on keratinoytes, [20] and by early structureactivity studies; [5,10,[21][22][23] and (viii) the synthesis of novel MCH peptide or nonpeptide analogs with potent agonist [24,25] and antagonist [26][27][28] activity.…”