New selective ligands of human cloned melatonin MT1 and MT2 receptors

Abstract

Melatonin has a key role in the circadian rhythm relay to periphery organs. Melatonin exerts its multiple roles mainly through two seven transmembrane domain, G-coupled receptors, namely MT1 or MT2 receptors. A pharmacological characterization of these human cloned melatonin hMT1 and hMT2 receptors stably expressed in HEK-293 or CHO cells is presented using a 2-[125I]-iodo-melatonin binding assay and a [35S]-GTPgammaS functional assay. Both reference compounds and new chemically diverse ligands were evaluated. Binding affinities at each receptor were found to be comparable on either HEK-293 or CHO cell membranes. Novel non-selective or selective hMT1 and hMT2 ligands are described. The [35S]-GTPgammaS functional assay was used to define the functional activity of these compounds which included partial, full agonist and/or antagonist activity. None of the compounds acted as an inverse agonist. We report new types of selective antagonists, such as S 25567 and S 26131 for MT1 and S 24601 for MT2. These studies brought other new molecular tools such as the selective MT1 agonist, S 24268, as well as the non-selective antagonist, S 22153. Finally, we also discovered S 25150, the most potent melatonin receptor agonist, so far reported in the literature.

Convergence of Melatonin and Serotonin (5-HT) Signaling at MT2/5-HT2C Receptor Heteromers

“…Some agonistic activity is seen at micromolar concentrations. In contrast, 4-PPDOT and luzindole, two reported antagonists of MT 2 on the G i /cAMP pathway (7,25), showed pathway-biased properties on MT 2 /5-HT 2C heteromers as they behaved as full antagonists on the G i /cAMP pathway (K i ϭ 0.04 Ϯ 0.01 nM and K i ϭ 7.73 Ϯ 4.98 nM, respectively) but as a partial (4-PPDOT) or full (luzindole) agonist on the G q /PLC pathway (EC 50 ϭ 2.5 Ϯ 1.7 nM and EC 50 ϭ 223 Ϯ 97 nM, respectively) (Fig. 6, A and C, and Table 1).…”

“…We next studied the effect of agomelatine, the antidepressant with agonistic activity at MT 2 receptors and neutral antagonistic properties at 5-HT 2C receptors (7,8). In cells expressing MT 2 in the absence or presence of 5-HT 2C receptors, agomelatine behaved as an agonist of the G i /cAMP pathway (EC 50 ϭ 0.29 Ϯ 0.16 nM and EC 50 ϭ 0.89 Ϯ 0.35 nM, respectively) ( Fig.…”

“…Their putative existence is of particular interest inasmuch as the clinically proven antidepressant ago-melatine, the first to possess a non-monoaminergic component of action, behaves as an agonist at G i -coupled MT 1 and MT 2 receptors but as a neutral antagonist at G q/11 -coupled 5-HT 2C receptors (7,8). Intriguingly, although the affinity of agomelatine is substantially lower at 5-HT 2C versus MT 1 and MT 2 in vitro, this apparent difference is much less pronounced in vivo, suggesting that it may exert its actions "synergistically" via these sites.…”

Molecular evidence that melatonin is enzymatically oxidized in a different manner than tryptophan: investigations with both indoleamine 2,3-dioxygenase and myeloperoxidase

“…Grohmann et al [17]). Our laboratory group has been involved for several years in understanding the mechanisms of action of melatonin at the molecular level, including the enzymology of its biosynthesis [18][19][20][21] and its interaction with melatonin receptors [22][23][24][25]. In order to explore further the catabolism of melatonin, which to date is based on only a few reports, we expressed recombinant human IndoDO in bacteria, leading to expression of a protein tagged with a hexahistidine moiety [12].…”

Mechanisms Contributing to the Phase-Dependent Regulation of Neurogenesis by the Novel Antidepressant, Agomelatine, in the Adult Rat Hippocampus

“…Agomelatine is a novel antidepressant possessing melatonergic receptor agonist (MT1 and MT2) (Audinot et al, 2003) and 5-HT 2C receptor antagonist properties (Millan et al, 2003), which displays robust antidepressant and anxiolytic-like actions in preclinical models (Papp et al, 2003;Millan et al, 2005) and alleviates various symptoms of major depression in humans (Loo et al, 2002;Kennedy and Emsley, 2006;Olié and Kasper, 2007;Dubocovich, 2006). Interestingly, both under basal and stressful conditions, agomelatine enhances hippocampal neurogenesis in rats (Maccari S, unpublished data;Banasr et al, 2006), with a distinctive profile in that it (1) selectively increases cell proliferation and neurogenesis in the ventral hippocampus (VH), a region connected with limbic structures, such as the amygdala, the prefrontal cortex and the nucleus accumbens, and strongly implicated in the response to stress (Bannerman et al, 2004), and (2) enhances the survival of newly generated cells throughout the entire hippocampus.…”