👤 Robert Speth

The melanocortin receptors are a class of centrally and peripherally expressed G protein-coupled receptors, of which the MC3R and MC4R subtypes are implicated in the regulation of appetite and energy homeostasis and can serve as potential therapeutic targets for disorders such as obesity and cachexia. An unbiased high-throughput mixture-based library screen was implemented to identify novel ligands with an emphasis on the identification of nanomolar-potent agonists of the mouse melanocortin-3 receptor. This screen yielded the discovery of an N-branched tricyclic guanidine scaffold (TPI2408) that contained three nanomolar potent mMC3R agonists and additional compounds that possessed antagonism for the mMC4R. The antagonist character of this scaffold library at the mMC4R was confirmed by a follow-up positional scanning antagonist screen. Additionally, molecular dynamics simulations herein provide mechanistic insight into the polypharmacological characteristics of melanocortin receptors. The disclosed materials have the potential to serve as important tools and SAR scaffolds in the study of melanocortin receptor function. Show less

The melanocortin receptors (MCRs) are important for numerous biological pathways, including feeding behavior and energy homeostasis. In addition to endogenous peptide agonists, this receptor family has two naturally occurring endogenous antagonists, agouti and agouti-related protein (AGRP). At the melanocortin-4 receptor (MC4R), the AGRP ligand functions as an endogenous inverse agonist in the absence of agonist and as a competitive antagonist in the presence of agonist. At the melanocortin-3 receptor (MC3R), AGRP functions solely as a competitive antagonist in the presence of agonist. The molecular interactions that differentiate AGRP's inverse agonist activity at the MC4R have remained elusive until the findings reported herein. Upon the basis of homology molecular modeling approaches, we previously postulated a unique interaction between the D189 position of the hMC4R and Asn114 of AGRP. To further test this hypothesis, six D189 mutant hMC4Rs (D189A, D189E, D189N, D189Q, D189S, and D189K) were generated and pharmacologically characterized resulting in the discovery of differences in inverse agonist activity of AGRP and an 11 macrocyclic compound library. These data support the hypothesized interaction between the hMC4R D189 position and Asn114 residue of AGRP and define critical ligand-receptor molecular interactions responsible for the inverse agonist activity of AGRP at the hMC4R. Show less

While the melanocortin receptors (MCRs) are known to be involved in numerous biological pathways, the potential roles of the MC5R have not been clearly elucidated in humans. Agouti-related protein (AgRP), an MC3R/MC4R antagonist and MC4R inverse agonist, contains an exposed β-hairpin loop composed of six residues (Arg-Phe-Phe-Asn-Ala-Phe) that is imperative for binding and function. Within this active loop of AgRP, four human missense polymorphisms were deposited into the NIH Variation Viewer database. These polymorphisms, Arg111Cys, Arg111His, Phe112Tyr, and Ala115Val (AgRP full-length numbering), were incorporated into the peptide macrocycles c[Pro Show less