Pharmacological characterization of the aminorex analogs 4-MAR, 4,4'-DMAR, and 3,4-DMAR

4,4'-Dimethylaminorex (4,4'-DMAR) is a novel psychoactive substance (NPS) that appeared on the illicit drug market in addition to the psychostimulant 4-methylaminorex (4-MAR). Both substances are methylated derivatives of aminorex, an amphetamine-like anorectic used in the 1960ies and withdrawn from the marked due to severe cardiovascular toxicity. The aim of the present study was to characterize the in vitro pharmacological profiles of 4-MAR, 4,4'-DMAR, and 3,4-dimethylaminorex (3,4-DMAR, direx). We assessed norepinephrine (NE), dopamine (DA), and serotonin (5-HT) transporter inhibition potencies and monoamine release in transporter-transfected human embryonic kidney (HEK) 293 cells. We also assessed monoamine receptor and transporter binding affinities. 4,4'-DMAR potently inhibited all monoamine transporters (IC₅₀<1 μM) with greater potency than 3,4-methlyenedioxymethamphetaime (MDMA) and displayed a higher serotonergic over dopaminergic preference, relatively similar to MDMA (DA transporter / 5-HT transporter inhibition ratio of 0.4 and 0.08 for 4,4'-DMAR and MDMA, respectively). In contrast, 4-MAR preferentially inhibited the NE and DA transporter, exhibiting a pharmacological profile more similar to amphetamine. Both 4-MAR and 4,4'-DMAR were also substrate releasers at the DAT. 3,4-DMAR only weakly inhibited the NE transporter and showed no relevant activity at the DA and 5-HT transporter. Binding affinities of all three aminorex derivatives at various monoamine receptors were negligible (K_i values >2 μM). The in vitro pharmacological profiles indicate that 4,4'-DMAR has comparable psychoactive properties and serotonergic toxicity to MDMA and may be more potent. 4-MAR is a psychostimulant similar to amphetamine or methamphetamine. 3,4-DMAR likely has only weak psychostimulant properties.