1. INTRODUCTION  -MSH and ACTH are two classical hormones derived from proopiomelanocortin (POMC) precursor protein. They have been studied for many years for their biological activities at the pigmentary melanocortin 1 receptor (MC1R) and at the adrenal receptor (MC2R), respectively. Recently, three additional melanocortin receptors have been cloned and stably transfected in cell lines: the melanocortin 3 receptor (MC3R -- found primarily in the brain); the melanocortin 4 receptor (MC4R -- found primarily in the brain); and the melanocortin 5 receptor (MC5R -- found throughout the body). The endogenous ligands for these receptors are unknown but likely candidates include POMC peptides such as  -MSH,  -MSH,  - MSH and modified versions of these peptides.

2. POSSIBLE BIOLOGICAL ACTIVITIES ASSOCIATED WITH NEW MCRs FEEDING BEHAVIOR -- Obesity, Anorexia ERECTILE FUNCTION CARDIOVASCULAR FUNCTION -- Blood Pressure and Heart Rate KIDNEY FUNCTION -- Natriuresis THERMOREGULATION LEARNING OTHERS

3. GOALS OF RESEARCH To develop peptides and peptidomimetic derivatives and analogues of POMC peptides that have high affinity and selectivity for melanocortin 3, 4 and 5 receptors and that are stable to enzymatic breakdown in vitro and in vivo. Both AGONISTS and ANTAGONISTS are needed.

4. METHODS Computer assisted design based on conformational and topographical considerations. Solid phase synthesis including cyclic (backbone - backbone, side chain - side chain, and backbone - side chain) and acyclic analogues. Biological assays including binding affinity determination and second messenger measurements using cloned receptors, and in vitro and in vivo bioassays. Conformational analysis, X-ray crystallography, NMR, and other biophysical methods for selected analogues.

5. IMPORTANT STRUCTURES

6. FROG SKIN BIOASSAY FOR CYCLIC “SOMATOSTATIN-RELATED” ANALOGUES

7. AFFINITIES OF CYCLIC “SOMATOSTATIN- RELATED” ANALOGUES

8. ANTAGONIST ACTIVITIES OF CYCLIC LACTAM ANALOGUES

9. BINDING AFFINITIES OF CYCLIC MELANOTROPIN PEPTIDES

10. CONCLUSIONS I Effective ligands for the MC1R based on Somatostatin have been successfully designed, synthesized and bio- assayed. All the synthesized peptides are being tested at the MC3-5 receptors. It was demonstrated that one class of compounds can be converted into another class via rational design based on our understanding of conformationally and topographically constrained ligands and their receptor interactions. New applications of these compounds and of this novel concept for designing effective bioactive compounds are being applied to other areas.

11. CONCLUSIONS II CYCLIC LACTAM ANALOGUES of MT-II substituted in positions 6, 7 and 9 with various modified, constrained aromatic residues can lead to potent antagonists. SELECTIVITY for MC4R vs MC3R and MC5R most readily obtained. POTENCY and SELECTIVITY of cyclic Somatostatin-derived melanotropin analogues at MCRs are highly dependent on ring conformation. MC3, MC4 and MC5 receptors have different structure-activity relationships with melanotropins.

12. SUMMARY OF CURRENT STATUS OF SELECTIVE AGONIST AND ANTAGONIST LIGANDS FOR MC3-5Rs MC3R –Have Both Agonists and Antagonists –Selectivity Good vs MC5R (>300) Modest vs MC4R (10-50) MC4R –Have Both Agonists and Antagonists –Selectivity Good vs MC3R (>100) Excellent vs MC5R (>500) MC5R –Have Agonists and Recently Discovered Antagonists –Selectivity A Few Equil. vs MC3R A Few Equil. vs MC4R