Effects of the new psychoactive substances diclofensine, diphenidine, and methoxphenidine on monoaminergic systems

Diclofensine, diphenidine, and methoxphenidine are new psychoactive substances (NPSs) that recently appeared on the illicit drug market. Pharmacological profiling of such newly emerged drugs is crucial for a better understanding of their psychotropic effects and toxicity. We therefore investigated the potential of these NPSs to inhibit the norepinephrine, dopamine, and serotonin transporters in human embryonic kidney cells stably transfected with the respective transporters. In addition, we determined monoamine transporter and receptor affinities for the substances. Diclofensine potently bound to the monoamine transporters in the submicromolar range and had similar inhibition potential for all three transporters in the range of 2.5-4.8μM. Moreover, diclofensine bound to adrenergic, dopamine, serotonin, and trace amine-associated receptors. Diphenidine was an equipotent inhibitor of the norepinephrine and dopamine transporters in the low micromolar range and a very weak inhibitor of the serotonin transporter. Besides binding to transporters, diphenidine bound to adrenergic α_1A and α_2A receptors and serotonin 5-hydroxytryptamine 1A (5-HT_1A) and 5-HT_2A receptors in the range of 4-11μM. Methoxphenidine bound to all transporters, but considerable inhibition (IC₅₀ < 10μM) was observed only for the norepinephrine transporter. Moreover, methoxphenidine bound to adrenergic α_2A and serotonin 5-HT_2A and 5-HT_2C receptors in the range of 2.5-8.2μM. None of the test drugs mediated substrate-type efflux of monoamines. These data demonstrate that the monoamine transporter inhibition and receptor interactions most likely mediate the psychoactive effects of diclofensine and possibly play a contributory role for diphenidine and methoxphenidine.