Nishiyama Keiji, Hirai Keisuke
CNS Drug Discovery Unit, Pharmaceutical Research Division, Takeda Pharmaceutical Company Ltd., 26-1, Muraoka-Higashi 2-chome, Fujisawa, Kanagawa 251-8555, Japan.
CNS Drug Discovery Unit, Pharmaceutical Research Division, Takeda Pharmaceutical Company Ltd., 26-1, Muraoka-Higashi 2-chome, Fujisawa, Kanagawa 251-8555, Japan.
Eur J Pharmacol. 2015 Jun 15;757:42-52. doi: 10.1016/j.ejphar.2015.03.009. Epub 2015 Mar 20.
Melatonin MT1 and MT2 receptors are Gi protein-coupled receptors and promising therapeutic targets for a number of diseases. A proportion of G protein-coupled receptor agonists and antagonists have been classified according to their duration of action, which influences their pharmacological efficacy. However, the duration of action of melatonin agonists remains unclear. In this study, we investigated the duration of action of melatonin agonists (melatonin, 2-iodomelatonin, ramelteon, and the ramelteon metabolite M-II) at the melatonin MT1 receptor, which is more resistant to agonist-induced desensitization than the melatonin MT2 receptor. In Chinese hamster ovary cells stably expressing the human melatonin MT1 receptor, significant differences in the duration of action were observed after 2-h pretreatment with agonists followed by washout. In contrast to melatonin and M-II, the agonist activities of ramelteon and 2-iodomelatonin were persistent (i.e. inhibition of forskolin-stimulated cAMP formation and increase in ERK 1/2 phosphorylation) even after repeated washouts. Similar activities were observed for INS-1 cells endogenously expressing the rat MT1 receptor. Further, we examined potential factors linked to the duration of action. Residual activities of melatonin agonists after washout strongly correlated with their dissociation rates from the human melatonin MT1 receptor, but not their lipophilicity or extent of desensitization. These data suggest that the in vitro duration of action significantly differs between melatonin agonists and might dictate dissociation kinetics. Characterization of these in vitro properties may facilitate further in vivo study of the duration of action.
褪黑素MT1和MT2受体是与Gi蛋白偶联的受体，是多种疾病有前景的治疗靶点。一部分G蛋白偶联受体激动剂和拮抗剂已根据其作用持续时间进行了分类，这会影响它们的药理功效。然而，褪黑素激动剂的作用持续时间仍不清楚。在本研究中，我们研究了褪黑素激动剂（褪黑素、2-碘褪黑素、雷美替胺及其代谢产物M-II）在褪黑素MT1受体上的作用持续时间，该受体比褪黑素MT2受体对激动剂诱导的脱敏更具抗性。在用激动剂预处理2小时后冲洗，在中国仓鼠卵巢细胞中稳定表达人褪黑素MT1受体时，观察到作用持续时间有显著差异。与褪黑素和M-II不同，即使反复冲洗后，雷美替胺和2-碘褪黑素的激动剂活性仍然持续存在（即抑制福斯高林刺激的cAMP形成和增加ERK 1/2磷酸化）。在内源性表达大鼠MT1受体的INS-1细胞中也观察到类似的活性。此外，我们研究了与作用持续时间相关的潜在因素。冲洗后褪黑素激动剂的残留活性与其从人褪黑素MT1受体的解离速率密切相关，但与其亲脂性或脱敏程度无关。这些数据表明，褪黑素激动剂的体外作用持续时间存在显著差异，可能决定解离动力学。对这些体外特性的表征可能有助于进一步研究其体内作用持续时间。
