Conformational study on cyclic melanocortin ligands and new insight into their binding mode at the MC4 receptor

Development of Macrocyclic Peptidomimetics Containing Constrained α,α-Dialkylated Amino Acids with Potent and Selective Activity at Human Melanocortin Receptors

We report the development of macrocyclic melanocortin derivatives of MT-II and SHU-9119, achieved by modifying the cycle dimension and incorporating constrained amino acids in ring-closing. This study culminated in the discovery of novel agonists/antagonists with an unprecedented activity profile by adding pieces to the puzzle of the melanocortin receptor selectivity. Finally, the resulting 19- and 20-membered rings represent a suitable frame for the design of further therapeutic ligands as selective modulators of the melanocortin system.

From Peptides to Peptidomimetics: A Strategy Based on the Structural Features of Cyclopropane

Peptidomimetics, non-natural mimicries of bioactive peptides, comprise an important class of drug molecules. The essence of the peptidomimetic design is to mimic the key conformation assumed by the bioactive peptides upon binding to their targets. Regulation of the conformation of peptidomimetics is important not only to enhance target binding affinity and selectivity, but also to confer cell-membrane permeability for targeting protein-protein interactions in cells. The rational design of peptidomimetics with suitable three-dimensional structures is challenging, however, due to the inherent flexibility of peptides and their dynamic conformational changes upon binding to the target biomolecules. In this Minireview, a three-dimensional structural diversity-oriented strategy based on the characteristic structural features of cyclopropane to address this challenging issue in peptidomimetic chemistry is described.

DOTA-Derivatives of Octreotide Dicarba-Analogs with High Affinity for Somatostatin sst2,5 Receptors

In vivo somatostatin receptor scintigraphy is a valuable method for the visualization of human endocrine tumors and their metastases. In fact, peptide ligands of somatostatin receptors (sst's) conjugated with chelating agents are in clinical use. We have recently developed octreotide dicarba-analogs, which show interesting binding profiles at sst's. In this context, it was mandatory to explore the possibility that our analogs could maintain their activity also upon conjugation with DOTA. In this paper, we report and discuss the synthesis, binding affinity and conformational preferences of three DOTA-conjugated dicarba-analogs of octreotide. Interestingly, two conjugated analogs exhibited nanomolar affinities on sst₂ and sst₅ somatostatin receptor subtypes.

Cyclopropane-Based Peptidomimetics Mimicking Wide-Ranging Secondary Structures of Peptides: Conformational Analysis and Their Use in Rational Ligand Optimization

Detailed conformational analyses of our previously reported cyclopropane-based peptidomimetics and conformational analysis-driven ligand optimization are described. Computational calculations and X-ray crystallography showed that the characteristic features of cyclopropane function effectively to constrain the molecular conformation in a three-dimensionally diverse manner. Subsequent principal component analysis revealed that the diversity covers the broad chemical space filled by peptide secondary structures in terms of both main-chain and side-chain conformations. Based on these analyses, a lead stereoisomer targeting melanocortin receptors was identified, and its potency and subtype selectivity were improved by further derivatization. The presented strategy is effective not only for designing non-peptidic ligands from a peptide ligand but also for the rational optimization of these ligands based on the plausible target-binding conformation without requiring the three- dimensional structural information of the target and its peptide ligands.

Discovery of Novel Potent and Selective Agonists at the Melanocortin-3 Receptor

The melanocortin receptors 3 and 4 control energy homeostasis, food-intake behavior, and correlated pathophysiological conditions. The melanocortin-4 receptor (MC4R) has been broadly investigated. In contrast, the knowledge related to physiological roles of the melanocortin-3 receptor (MC3R) is lacking because of the limited number of known MC3R selective ligands. Here, we report the design, synthesis, biological activity, conformational analysis, and docking with receptors of two potent and selective agonists at the human MC3 receptor.

Azepinone-Containing Tetrapeptide Analogues of Melanotropin Lead to Selective hMC4R Agonists and hMC5R Antagonist

To address the need for highly potent, metabolically stable, and selective agonists, antagonists, and inverse agonists at the melanocortin receptor subtypes, conformationally constrained indolo- and benzazepinone residues were inserted into the α-MSH pharmacophore, His(6)-Phe(7)-Arg(8)-Trp(9)-domain. Replacement of His(6) by an aminoindoloazepinone (Aia) or aminobenzazepinone (Aba) moiety led to hMC4R and hMC5R selective agonist and antagonist ligands, respectively (tetrapeptides 1 to 3 and 4, respectively). In peptides 1 to 3 and depending on the para-substituent of the d-Phe residue in position 2, the activity goes from allosteric partial agonism (1, R = H) to allosteric full agonism (2, R = F) and finally allosteric partial agonism (3, R = Br).

The role of common and rare MC4R variants and FTO polymorphisms in extreme form of obesity

Melanocortin 4 receptor (MC4R) is an important regulator of food intake and number of studies report genetic variations influencing the risk of obesity. Here we explored the role of common genetic variation from MC4R locus comparing with SNPs from gene FTO locus, as well as the frequency and functionality of rare MC4R mutations in cohort of 380 severely obese individuals (BMI > 39 kg/m(2)) and 380 lean subjects from the Genome Database of Latvian Population (LGDB). We found correlation for two SNPs--rs11642015 and rs62048402 in the fat mass and obesity-associated protein (FTO) with obesity but no association was detected for rs17782313 located in the MC4R locus in these severely obese individuals. We sequenced the whole gene MC4R coding region in all study subjects and found five previously known heterozygous non-synonymous substitutions V103I, I121T, S127L, V166I and I251L. Expression in mammalian cells showed that the S127L, V166I and double V103I/S127L mutant receptors had significantly decreased quantity at the cell surface compared to the wild type MC4R. We carried out detailed functional analysis of V166I that demonstrated that, despite low abundance in plasma membrane, the V166I variant has lower EC50 value upon αMSH activation than the wild type receptor, while the level of AGRP inhibition was decreased, implying that V166I cause hyperactive satiety signalling. Overall, this study suggest that S127L may be the most frequent functional MC4R mutation leading to the severe obesity in general population and provides new insight into the functionality of population based variants of the MC4R.