Design and synthesis of melatonin receptors agonists and antagonists

Differences in Binding Sites of Two Melatonin Receptors Help to Explain Their Selectivity to Some Melatonin Analogs: A Molecular Modeling Study

Numerous diseases have been linked to the malfunction of G-protein coupled receptors (GPCRs). Their adequate treatment requires rational design of new high-affinity and high-selectivity drugs targeting these receptors. In this work, we report three-dimensional models of the human MT(1) and MT(2) melatonin receptors, members of the GPCR family. The models are based on the X-ray structure of bovine rhodopsin. The computational approach employs an original procedure for optimization of receptor-ligand structures. It includes rotation of one of the transmembrane alpha-helices around its axis with simultaneous assessment of quality of the resulting complexes according to a number of criteria we have developed for this purpose. The optimal geometry of the receptor-ligand binding is selected based on the analysis of complementarity of hydrophobic/hydrophilic properties between the ligand and its protein environment in the binding site. The elaborated "optimized" models are employed to explore the details of protein-ligand interactions for melatonin and a number of its analogs with known affinity to MT(1) and MT(2) receptors. The models permit rationalization of experimental data, including those that were not used in model building. The perspectives opened by the constructed models and by the optimization procedure in the design of new drugs are discussed.

Melatonin receptors in humans: biological role and clinical relevance

In addition to its antioxidative effects melatonin acts through specific nuclear and plasma membrane receptors. To date, two G-protein coupled melatonin membrane receptors, MT(1) and MT(2), have been cloned in mammals, while the newly purified MT(3) protein belongs to the family of quinone reductases. Screening studies have shown that various tissues of rodents express MT(1) and/or MT(2) melatonin receptors. In humans, melatonin receptors were also detected in several organs, including brain and retina, cardiovascular system, liver and gallbladder, intestine, kidney, immune cells, adipocytes, prostate and breast epithelial cells, ovary/granulosa cells, myometrium, and skin. This review summarizes the data published so far about MT(1) and MT(2) receptors in human tissues and human cells. Established and putative functions of melatonin after receptor activation as well as the clinical relevance of these findings will be discussed.

Synthesis of N1-phenethyl substituted indole derivatives as new melatoninergic agonists and antagonists

The potency of new indolic N1-phenethyl substituted melatoninergic ligands with and without methyl groups in the alpha and beta position of the alkanamidoethyl side chain was examined using the pigment aggregation response in a clonal line of Xenopus laevis melanophores. The non 5-OMe substituted compounds, 8a--e, are all weak antagonists while introduction of the 5-OMe group, 9a--e, increases both agonist and antagonist activity except for 9c (R=C3H7), which is only an agonist and 9e (R=c-C4H7), which is only an antagonist. Introduction of an alpha-methyl group into the 5-OMe derivatives, 14a-e, reduces the agonist potency while introduction of a beta-methyl group has only a small effect on either the agonist or antagonist potency. Double beta-methyl substitution of the 5-OMe derivatives, 20a--e, generally increases the agonist potential (20c, R=C3H7 is the most potent agonist of the compounds described) and decreases the antagonist potency, except for 20a (R=CH3), which is the most potent antagonist of this series of compounds.