Uptake2 transporters: Novel sex-dependent molecular targets to treat stimulant use disorder

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Medications to treat substance use disorders (SUD) exist for many drugs of abuse, but not for psychostimulants, such as amphetamine (AMPH), and methamphetamine. They are also lacking for increasingly used synthetic drugs designed to mimic the actions of known psychostimulants. Both known and new psychoactive substances continue to pose a major and increasing public health threat. To develop effective treatments, the mechanisms by which these stimulants produce their abuse-related effects need to be better understood. Many stimulants interact with the dopamine (DA) transporter (DAT), which is thought to mediate their abuse-related effects. However, strategies targeting DAT have yielded little to no benefit in the treatment of psychostimulant addiction, raising the possibility that these stimulants have significant actions elsewhere to modulate dopaminergic neurotransmission. Consistent with this, a rapidly growing literature supports a prominent role for organic cation transporter 3 (OCT3) in regulating dopaminergic neurotransmission. Our preliminary data support this idea, showing that decynium-22 (D22), an inhibitor of OCT3, inhibits DA release in vivo in male OCT3 wild-type (WT) mice, an effect lost in constitutive OCT3 knockout (KO) mice. Furthermore, in vitro studies showed that AMPH-induced substrate efflux could be inhibited by D22 in a manner independent of cocaine-sensitive transporters. These finding were paralleled by a loss of conditioned place preference (CPP) for AMPH in male mice, and an attenuation in female OCT3 KO, with D22 preventing CPP in both WT sexes. Preliminary data in male mice show that the dose-response curve for self-administration of AMPH is dramatically downward and rightward shifted in male OCT3 KO mice relative to their WT counterpart. In light of these findings, we have established and validated OCT3 floxed mice so as to examine the role of OCT3 in the absence of any developmental compensation that may occur in germline KOs. Harnessing the power of these mice, new data show that tamoxifen inducible or viral KO of OCT3 robustly attenuates AMPH- evoked DA release and CPP. Proposed studies will interrogate OCT3’s role in the ability of AMPH to impact behavior and DA efflux by testing the novel and potentially transformative hypothesis that AMPH driven DA release is not mediated solely by DAT but by reverse transport via OCT3 as well. Thus, DAT-OCT3 redundancy may explain why DAT-based therapeutics have been unsuccessful in treating AMPH use disorders. We will use a combination of pharmacology, novel and established transgenic mouse models (DA neuron-specific vs glia- specific), and brain-region specific viral knockdown, to determine the role of OCT3 in AMPH-induced behavioral effects (locomotion, rearing, stereotypy, sensitization, CPP, self-administration) (Aim 1), and AMPH-induced DA efflux and clearance in vivo (Aim 2). In Aim 3 we will determine how tamoxifen inducible KO or viral KO of OCT3 impacts key elements in DA signaling and how OCT3 adapts to chronic AMPH self-administration. These studies will fill fundamental knowledge gaps about the importance of OCT3 in abuse-related effects of AMPH, and its congeners, which will help identify novel molecular targets for medications to treat AMPH addiction.