Antidepressant-like activity of VN2222, a serotonin reuptake inhibitor with high affinity at 5-HT 1A receptors

Abstract

It has been suggested that drugs combining serotonin (5-hydroxytryptamine, 5-HT) transporter blockade and 5-HT 1A autoreceptor antagonism could be a novel strategy for a shorter onset of action and higher therapeutic efficacy of antidepressants. The present study was aimed at characterizing the pharmacology of 1-(3-benzo[b]tiophenyl)-3-[4-(2-methoxyphenyl)-1-piperazinyl]-1-propanol (VN2222) a new synthetic compound with high affinity at both the 5-HT transporter and 5-HT 1A receptors and devoid of high affinity at other receptors studied, with the only exception of α 1-adrenoceptors. In keeping with the binding affinity at the 5-HT transporter, VN2222 inhibited 5-HT uptake in vitro both in rat cortical synaptosomes and in mesencephalic cultures and also in vivo when administered locally into the rat ventral hippocampus. After systemic administration, VN2222 exhibited an inverted U-shape effect so the inhibition of [ 3H]5-HT uptake ex vivo and the increase in 5-HT extracellular levels in microdialysis experiments was observed at low doses of 0.01–0.1 mg/kg whereas higher doses were ineffective. In studies related to 5-HT 1A receptor function, 0.01–0.1 μM VN2222 produced a partial inhibition of forskolin-stimulated cAMP formation behaving as a weak agonist of 5-HT 1A receptors. In body temperature studies, 5 mg/kg VN2222 produced a mild hypothermic effect in mice, suggesting a weak agonist activity at presynaptic 5-HT 1A receptors; much lower doses (0.01–0.5 mg/kg) partially antagonized the hypothermia induced by 8-hydroxy-2-(di- n-propylamino)tetralin (8-OH-DPAT) possibly through 5-HT transporter blockade. In the learned helplessness test in rats, an animal model for antidepressants, 1–5 mg/kg VN2222 reduced significantly the number of escape failures. Consequently, VN2222 is a new compound with a dual effect on the serotonergic system, as 5-HT uptake blocker and 5-HT 1A receptor partial agonist, and with a remarkable activity in an animal model of depression with high predictive validity.