N-Methyl Amine-substituted Fluoxetine Derivatives: New Dopamine Transporter Inhibitors

Transport of dopamine (DA) by the dopamine transporter from the synaptic cleft into the presynaptic terminals plays a key role in terminating dopaminergic neurotransmission. The binding of psychostimulants to their recognition sites on the DA transporter leads to an inhibition of DA transport and a subsequent rising of the dopamine contents in the synaptic cleft is ascribed to a mode of psychostimulation. Discovery of dopamine transporter inhibitors would be useful with regard to substituting for cocaine and minimizing its abuse. Recently, a number of fluoxetine analogues were synthesized, especially focusing on the substitution of N-methyl amine group through modifying the structure of the fluoxetine, N-methyl-3-[p-trifluoromethylphenoxy]-3-phenylpropylamine, widely used as an antidepressant. Among them, the pharmacological properties of FD-2, (R)-N-ethanol-3-(4-trifluorophenoxy)-3-phenyl propaneamine and FD-4, N-(R)-3-trifluorophenoxy-3-phenylpropane-imidazole with a higher affinity for the DA transporter were characterized in terms of dopamine transporter inhibition expecting for useful cocaine substitutes. Effects of the compounds on [H3]dopamine uptake, [I125]RTI-55 binding, and DA transporter-associated currents were examined with the ligand binding assays and voltage clamping technique in human embryonic kidney (HEK)-293 cells where the recombinant human DA transporter (hDAT) was stably expressed. Our results showed that (i) fluoxetine was potent in inhibiting both the uptake of [H3]DA (IC50 = 0.21 ± 0.032 mM, n = 3) and the [I125]RTI-55 binding (IC50 = 0.23 ± 0.012 mM, n = 10); (ii) N-methyl amine substituted fluoxetine analogues, FD-2 and FD-4 were equally or more potent than fluoxetine itself in terms of inhibition of [H3]DA uptake (IC50 FD-2: 0.077 ± 0.0032 mM (n = 3); FD-4: 0.26 ± 0.13 mM (n = 3), inhibition of [I125]RTI-55 binding, and reduction in DA transporter-associated currents, suggesting that these analogues could be a new class of dopamine transporter inhibitors.