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Aim: Melatonin (MT) is a neurohormone produced and secreted primarily by the pineal gland in a circadian manner, and mainly acts through 2 receptor subtypes: MT1 and MT2 in humans. The diversity in their tissue distribution is in favor of different functions for each receptor subtype. Selective modulators are therefore required to determine the physiological roles of these melatonin receptor subtypes and their implications in pathological processes. Methods: A homogenous MT1/MT2 receptor binding assay was established for high-throughput screening of new ligands at the hMT1 and/or hMT2 receptors. The functional properties (agonists or antagonists) were assessed by a conventional guanosine-5′[γ-35S] triphosphate (GTP-γS) assay. Results: Three hMT1 receptor-selective small molecule antagonists and 1 hMT2 receptor-selective small molecule antagonist with novel structural features were identified following a high-throughput screening campaign of 48 240 synthetic and natural compounds. Conclusion: The findings may assist in the expansion of chemical probes to these 2 receptor subtypes. [ABSTRACT FROM AUTHOR]

Aim: To find new antagonists on human melanin-concentrating hormone recep-tor-1 (MCHR-1) through high-throughput screening (HTS) of a diverse compound library. Methods: MCHR-1, [3H]SNAP7941, and FlashBlue G-protein-coupled receptor beads were used to measure the receptor-binding activities of various compounds based on scintillation proximity assay (SPA) technology. The guanosine 5′ (γ-[35S]thio) triphosphate ([35S]GTPγS) binding assay was subsequently applied to functionally characterize the “hits” identified by the HTS campaign. Results: Of the 48 240 compounds screened with the SPA method, 12 hits were confirmed to possess MCHR-1 binding activities, 8 were functionally studied subsequently with the [35S]GTPγS binding assay, and only 1 compound (NC127816) displayed moderate human MCHR-1 binding affinity ( Ki=115.7 nmol/L) and relatively potent antagonism ( KB=23.8 nmol/L). This compound shares a novel scaffold (1-ethoxy-2 H-2-aza-1-phospha-naphthalene 1-oxide) with 3 other analogs in the group. Conclusion: Considering the marked difference in molecular shape and electrostatic status between NC127816 and the structures reported elsewhere, we anticipate that its derivatives may represent a new class of potent MCHR-1 modulators. [ABSTRACT FROM AUTHOR]