title: Pharmacological characterization of a highly selective and potent partial agonist of the MT₂ melatonin receptor.
abstract: OBJECTIVE
  The MT₂ melatonin receptor is a potential target for treating circadian rhythm sleep disorders. This study aims to characterize the recently identified MT₂ melatonin receptor agonist.
  
  
  METHODS
  The pharmacological properties of the MT₂ melatonin receptor-selective agonist as exemplified by compound 1 [N-(2-[7-benzyl-1,6-dihydro-2H-indeno(5,4-b)furan-8-yl]ethyl)acetamide] were evaluated by use of cell-free binding and cell-based functional assays.
  
  
  RESULTS
  Competition binding assays using 2-[(125)I]iodomelatonin revealed rapid, reversible, and high-affinity binding of compound 1 to human, mouse, and rat MT₂ melatonin receptors. cAMP, ERK1/2, and PathHunter β-arrestin recruitment assays revealed partial agonist activities. However, compound 1 induced a more intense internalization of human MT₂ melatonin receptor than melatonin. Based on studies using structurally related analogs of compound 1, we further demonstrated that the extent of internalization is independent of the intrinsic efficacy of agonists.
  
  
  CONCLUSIONS
  These findings provide novel insights into the relationship between intrinsic agonist efficacy and agonist-induced internalization and demonstrate that compound 1 could serve as a pharmacological tool for future studies to elucidate the detailed molecular mechanism of MT₂ receptor internalization.
authors: Biomolecular Research Laboratories, Pharmaceutical Research Division, Takeda Pharmaceutical Company Ltd., Fujisawa, Japan.
authors: Taku
authors: T
authors: Sakurai
authors: Tatsuki
authors: T
authors: Koike
authors: Masaharu
authors: M
authors: Nakayama
mesh_terms: D000081:Acetamides / Q000378:metabolism*; D000818:Animals; D019390:Arrestins / Q000378:metabolism; D001667:Binding, Competitive; D016466:CHO Cells; D003412:Cricetulus; D000242:Cyclic AMP / Q000378:metabolism; D006801:Humans; D008550:Melatonin / Q000031:analogs & derivatives / Q000378:metabolism*; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D051381:Rats; D044123:Receptor, Melatonin, MT2 / Q000819:agonists* / Q000378:metabolism*; D000071557:beta-Arrestins
chemical_list: D000081:Acetamides; D019390:Arrestins; D044123:Receptor, Melatonin, MT2; D000071557:beta-Arrestins; D000242:Cyclic AMP; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D008550:Melatonin