The Melanocortin System: Structure Activity Relationships of Alpha-N-Methylated MT-II Analogues and Mutation Studies of Human Melanocortin Receptor Subtypes 1 and 4
AuthorDedek, Matthew Milan
Keywordsstructure activity relationship
melanocortin 1 receptor
melanocortin 4 receptor
AdvisorHruby, Victor J.
Committee ChairHruby, Victor J.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractThe melanocortin system regulates various physiological processes including feeding behavior, sexual function, skin pigmentation and photoprotection via five G-protein coupled receptors and several endogenous ligands. There is a need for selective and potent ligands to the human melanocortin receptors (hMCRs) that can chemically resolve these various functions. This thesis presents three studies aimed at refining the understanding of the structural differences between binding pockets of the hMCR subtypes. In the first study α-N-methylated analogues of the non-selective agonist, MT-II, are evaluated for their in vitro function. This study produced the most potent hMC1R selective agonist to date. The following two studies examine the effects of mutations on the biological activity of melanocortin receptor subtypes 1 and 4. Much of the mutation study data is preliminary and requires a demonstration of reproducibility.
Degree ProgramMedical Pharmacology
Degree GrantorUniversity of Arizona
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Synthesis of Novel Amino Acids and Use of Peptides & Peptidomimetics Containing Unnatural Amino Acids for the Development of Selective Melanocortin Peptide Antagonists and for the Study of Melanocortin Receptor SignalingHruby, Victor J; Qu, Hongchang; Mash, Eugene A.; Pyun, Jeffrey; Walker, F. Ann (The University of Arizona., 2007)Unnatural amino acids are indispensible tools, not only for the elucidation of molecular mechanisms during the study of the complicated biological system, but also for the development of novel peptide and protein drugs with better efficacy and lower toxicity. Beta-substituted gamma,delta-unsaturated amino acids have been shown to be an important type of novel amino acid because of the terminal double bond which can be converted to many other functionalities. The methodology for the synthesis of syn-beta-substituted gamma,delta-unsaturated amino acids has been developed. However, there is no satisfactory general method for the synthesis of anti-beta-substituted gamma,delta-unsaturated amino acids. Therefore, a general methodology was developed by using the Eschenmoser-Claisen rearrangement for the synthesis of both racemic and optically active anti-beta-substituted gamma,delta-unsaturated amino acids. This rearrangement is highly diastereoselective and good asymmetric induction was obtained with a relatively small C2-symmetric chiral auxiliary (2R,5R)-dimethylpyrrolidine. In an effort to design peptide antagonists that are selective for human melanocortin 4 receptor, highly constrained trans and cis 4-guanidinium proline derivatives were synthesized and incorporated in various melanotropin analogues designed to mimic the endogenous hMC1,4R selective antagonist hASIP (Agouti Signaling Protein) central loop. Biological assays show that some of these analogues are highly selective for hMC1R and/or hMC4R with partial agonist or antagonist activities due to a new beta-turn structure induced by the presence of the constrained amino acids. According to molecular modeling studies, the lowest energy conformations of these selective analogues resemble the NMR solution structure of the hASIP central loop. Therefore, a new template was developed for the rational design of novel selective melanotropin analogues that may have therapeutic potential. To further understand the molecular mechanisms of hMC4R signaling upon agonist activation, an hMC4R selective nonpeptide agonist THIQ and its fluorescent dye labeled derivatives were needed to compare to peptide agonist MTII with regard to receptor phosphorylation, internalization, etc. An improved synthetic method was developed for the efficient synthesis of THIQ. A method for the synthesis of TRITC labeled THIQ derivatives was also developed.
Developing Melanocortin 3 Selective Ligands through C-Terminal Modification of Melanocortin PeptidesHruby, Victor J.; Nyberg, Joel Benjamin; Ghosh, Indraneel; Jewett, John; Mash, Eugene; Brown, Michael; Hruby, Victor J. (The University of Arizona., 2013)The melanocortin 3 and 4 receptors share 58% overall amino acid identity and 76% similarity. This high level of similarity between the MC3R and the MC4R underscores the difficulties associated with developing MC3R selective ligands, and as a consequence little is known of the physiological functions of the melanocortin 3 receptor. Previous research showing the differences between endogenous non-selective ligands and melanocortin 3 receptor selective ligands are mainly within the C-terminus of the melanocortin peptide. These findings have been exploited in this research using known melanocortin 3 and 4 selective ligands modified at their respective C-termini to develop some very promising melancortin 3 selective antagonists and agonists, analog 5 ([CO(CH₂)₂CO-DNal(2')-Arg-Trp-Lys]-Gly-Lys-Pro-Val-NH₂) and analog 20 ((H-DNal(2')-c[Asp-Pr6-DPhe-Arg-Trp-Lys]-Ala-Gly-Pro-Val-NH₂) respectively. Additional studies using molecular modeling have produced further insights into the structural basis for selectivity. Finally, we have been developing a new scaffold for the melanocortin receptor using cyclic dipeptide derivatives.
Design and synthesis of novel melanocortin receptor ligandsHruby, Victor J.; Stankova, Magdalena (The University of Arizona., 2004)Melanocortin receptors (MC1R-MC5R) belong to the G-protein coupled receptor superfamily. The interactions of peptide hormones (ACTH, alpha-, beta- and gamma-MSH) with the melanocortin receptors regulate multiple physiological functions in the human body. Pharmacological studies of the melanocortin receptors have revealed very broad biological effects including pigmentation, steroidogenesis, energy homeostasis, thermoregulation, anti-inflammation, nerve regeneration, sexual behavior, feeding behavior and memory, and others. Due to the lack of selectivity of the endogenous ligands (except ACTH) the exact biological roles of the melanocortin receptor subtypes have not been fully elucidated. The objectives of our research are the design and synthesis of new, selective and potent ligands for the melanocortin receptor subtypes to help elucidate their biological functions. Since the three-dimensional structures of the melanocortin receptors and their endogenous ligands are unknown, receptor structure-based design has not been applied. We have chosen a "classical" ligand-based design with the primary structure of an endogenous ligand, gamma-MSH, as a starting point. Our design strategy is to gain high selectivity and potency by fixing the spatial structure of this very flexible peptide ligand in hopes that we can induce the bioactive conformation. We have examined two strategies to constrain the peptide backbone. The first approach is based on global constraint of the peptides by cyclization. A group of 36 cyclic peptides has been synthesized using thioether bond formation as a cyclization step. Macrocyclic peptide ligands varied from 15- to 30-membered rings. The truncated sequence of gamma-MSH has been applied in the cyclic series. In the second strategy we have introduced a local constraint into the peptide backbone similar to a reverse turn structure. We have made a very radical change in ligand conformation by peptide complexation with a transition metal in different positions of the sequence. In this approach we have conserved all amino acid residues of gamma-MSH. All novel modified peptides have been synthesized by solid phase methodology. Preliminary biological studies indicate that we have identified very selective and potent ligands.