Dual Probes for the Dopamine Transporter and σ1 Receptors:  Novel Piperazinyl Alkyl-bis(4‘-fluorophenyl)amine Analogues as Potential Cocaine-Abuse Therapeutic Agents

Both dopamine uptake inhibitors and σ1 receptor antagonists have been implicated as potential pharmacotherapeutics for the treatment of cocaine abuse. While the dopamine uptake inhibitors may share with cocaine neurochemical mechanisms underlying reinforcing properties, σ1 antagonists have been shown to attenuate some behavioral actions and toxic side effects associated with cocaine overdose. Rimcazole, a σ1 receptor antagonist that binds to the DAT (K i = 224 nM), is not behaviorally cocaine-like and attenuates some of the behavioral actions of cocaine. To determine the roles of both DAT and σ1 receptors in the behavioral actions of rimcazole, a series of analogues was synthesized. Initial studies identified two analogues (1 and 4) that showed high to moderate affinities for both DAT and σ1 receptors and failed to show cocaine-like discriminative stimulus (DS) effects. A second series of bis(4‘-fluorophenyl)amine analogues have now been prepared in which the most potent DAT compound, 19 (K i = 8.5 nM), was selective over serotonin transporter (SERT/DAT = 94), norepinephrine transporter (NET/DAT = 63), and σ1 receptor binding (σ1/DAT = 44). In addition, two other analogues 10 and 17 showed superior selectivity for DAT over SERT (170- and 140-fold, respectively) and DAT over NET (219- and 190-fold, respectively) but were essentially equipotent at DAT and σ1 receptors (10; K i = 77 and 124 nM, respectively, 17; K i = 28 and 13 nM, respectively). CoMFA studies at both DAT and σ1 receptors were performed to examine structural requirements for optimal binding at these two targets as well as to assess differences between them. Behavioral evaluation of analogues with varying affinities for both DAT and σ1 receptors may provide a novel approach toward designing medications for cocaine abuse.