S32212, a novel serotonin type 2C receptor inverse agonist/α2-adrenoceptor antagonist and potential antidepressant: I. A mechanistic characterization.

Although most antidepressants suppress serotonin (5-HT) and/or noradrenaline reuptake, blockade of 5-HT2C receptors and alpha(2)-adrenoceptors likewise enhances monoaminergic transmission. These sites are targeted by the urea derivative N-[4-methoxy-3-(4-methylpiperazin-1-yl)phenyl]-1,2-dihydro-3H-benzo[e]indole-3-carboxamide (S32212). S32212 was devoidof affinity for monoamine reuptake sites, yet displayed pronounced affinity (pK(i), 8.2) for constitutively active human 5-HT2CINI (h5-HT2CINI) receptors, behaving as an inverse agonist in reducing basal G alpha(q) activation, [H-3]inositol-phosphate production, and the spontaneous association of h5-HT2CINI Renilla luciferase receptors with beta-arrestin2-yellow fluorescent protein. Furthermore, upon 18-h pretreatment, S32212 enhanced the plasma membrane expression of h5-HT2CINI receptors as visualized by confocal microscopy and quantified by enzyme-linked immunosorbent assay. Its actions were prevented by the neutral antagonist 6-chloro-5-methyl-N-[6-(2-methylpyridin-3-yloxy)pyridin-3-yl]indoline-1-carboxamide (SB242,084), which also impeded the induction by long-term exposure to S32212 of otherwise absent Ca2+ mobilization in mouse cortical neurones. In vivo, S32212 blunted the inhibitory influence of the 5-HT2C agonist 2-(3-chlorobenzyloxy)-6-(1-piperazinyl)pyrazine (CP809,101) on ventrotegmental dopaminergic neurones. S32212 also blocked 5-HT-induced G alpha(q) and phospholipase C activation at the h5-HT2A and, less potently, h5-HT2B receptors and suppressed the discriminative stimulus properties of the 5-HT2A agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane in rats. S32212 manifested marked affinity for human alpha(2A)-(pK(i) 7.2), alpha(2B)- (pK(i) 8.2), and alpha(2C) -(pK(i) 7.4) adrenoceptors, at which it abolished noradrenaline-induced recruitment of G alpha(i3), G alpha(o), adenylyl cyclase, and extracellular-regulated kinase1/2. Moreover, S32212 dose-dependently abolished the discriminative stimulus effects of the alpha(2)-adrenoceptor agonist (S)-spiro[(1-oxa-2-amino-3-azacyclopent-2-ene)-4,2'-(1',2',3',4'-tetrahydronaphthalene)] (S18616). Finally, S32212 displayed negligible affinity for alpha(1A)-adrenoceptors, histamine H-1 receptors, and muscarinic M-1 receptors. In conclusion, S32212 behaves as an inverse agonist at h5-HT2C receptors and as an antagonist at human alpha(2)-adrenoceptors (and h5-HT2A receptors). Its promising profile in preclinical models potentially relevant to the treatment of depression is described in J Pharmacol Exp Ther 340:765-780, 2012.