Characterisation of human melatonin mt(1) and MT(2) receptors by CRE-luciferase reporter assay.

A cyclic AMP response element (CRE)-luciferase reporter gene assay was used to characterise the functional responses of human melatonin mt(1) and human melatonin MT(2) receptors, stably expressed in the human embryonic kidney cell line HEK293, to a series of six naphthalenic analogues of melatonin. By comparison to the observed melatonin-mediated inhibition of stimulated luciferase levels the naphthalenic series was identified as comprising agonists, partial agonists and one antagonist of melatonin mt(1) and melatonin MT(2) receptor function. Three of the agonist/partial agonist members of this series were also identified as displaying a functional selectivity for the melatonin MT(2) receptor. Competitive displacement of 2-[125I]iodomelatonin binding to the ovine pars tuberalis melatonin ML(1) receptor demonstrated a close correlation to the observed functional luciferase responses of the human melatonin mt(1) receptor. We conclude that the CRE-luciferase reporter gene assay provides an effective functional screening method for the pharmacological characterisation of human melatonin receptor subtypes.