Blockade of the dopamine (DA) transporter (DAT) is central to the effects of cocaine, and the DAT has been a focus of discovery research on cocaine-abuse medications. JHW007, an analogue of benztropine, binds to the DAT but is less effective than cocaine in producing psychomotor stimulant and subjective effects, and has been shown to antagonize these effects of cocaine in mice (Desai et al., J. Neurosci. 2005). We tested the hypothesis that the antagonism of cocaine by JHW 007 is mediated by a reduction in DA transmission. We compared the interactions of cocaine with JHW 007 or WIN 35,428 (a cocaine-like DAT inhibitor) on extracellular DA levels, measured by brain microdialysis in the shell of the nucleus accumbens of Swiss-Webster mice. All drugs dose dependently increased DA levels, with JHW 007 having a slower onset and lower effectiveness than cocaine or WIN 35428. A 4-hr pretreatment with JHW 007 (3–10 mg/kg i.p.) attenuated the elevation of DA levels produced by cocaine (10, 20, and 40 mg/kg). WIN 35428 (0.3, 1.0 mg/kg) administered with cocaine produced effects on DA levels that were not different from the addition of the effects of each drug alone. The present data suggest that antagonism of the behavioral effects of cocaine by JHW 007 results from a reduced cocaine-stimulated DA transmission. Results with WIN 35428 suggest that not all DAT blockers can reduce the neurochemical effects of cocaine, and further support consideration of JHW007 as a lead compound in the search for medications to treat cocaine abuse.
Chronic psychostimulant use causes long-lasting changes to neural and cognitive function that persist after long periods of abstinence. As cocaine users transition from drug use to abstinence, a parallel transition from hyperactivity to hypoactivity has been found in orbitofrontal-striatal glucose metabolism and striatal D
Abstract Although aminergic GPCRs are the target for ~25% of approved drugs, developing subtype selective drugs is a major challenge due to the high sequence conservation at their orthosteric binding site. Bitopic ligands are covalently joined orthosteric and allosteric pharmacophores with the potential to boost receptor selectivity and improve current medications by reducing off-target side effects. However, the lack of structural information on their binding mode impedes rational design. Here we determine the cryo-EM structure of the hD 3 R:Gα O βγ complex bound to the D 3 R selective bitopic agonist FOB02-04A. Structural, functional and computational analyses provide insights into its binding mode and point to a new TM2-ECL1-TM1 region, which requires the N-terminal ordering of TM1, as a major determinant of subtype selectivity in aminergic GPCRs. This region is underexploited in drug development, expands the established secondary binding pocket in aminergic GPCRs and could potentially be used to design novel and subtype selective drugs.
Determining the structural elements that define substrates and inhibitors at the monoamine transporters is critical to elucidating the mechanisms underlying these disparate functions. In this study, we addressed this question directly by generating a series of N-substituted 3,4-methylenedioxyamphetamine analogs that differ only in the number of methyl substituents on the terminal amine group. Starting with 3,4-methylenedioxy-N-methylamphetamine, 3,4-methylenedioxy-N,N-dimethylamphetamine (MDDMA) and 3,4-methylenedioxy-N,N,N-trimethylamphetamine (MDTMA) were prepared. We evaluated the functional activities of the compounds at all three monoamine transporters in native brain tissue and cells expressing the transporters. In addition, we used ligand docking to generate models of the respective protein-ligand complexes, which allowed us to relate the experimental findings to available structural information. Our results suggest that the 3,4-methylenedioxyamphetamine analogs bind at the monoamine transporter orthosteric binding site by adopting one of two mutually exclusive binding modes. 3,4-methylenedioxyamphetamine and 3,4-methylenedioxy-N-methylamphetamine adopt a high-affinity binding mode consistent with a transportable substrate, whereas MDDMA and MDTMA adopt a low-affinity binding mode consistent with an inhibitor, in which the ligand orientation is inverted. Importantly, MDDMA can alternate between both binding modes, whereas MDTMA exclusively binds to the low-affinity mode. Our experimental results are consistent with the idea that the initial orientation of bound ligands is critical for subsequent interactions that lead to transporter conformational changes and substrate translocation.
Modafinil has been used off‐label to treat psychostimulant use disorders (PSUD). However, its effectiveness in clinical trials seems limited to a subpopulation of subjects without concurrent alcohol or poly‐drug use. Since the main pharmacological target of cocaine is the dopamine transporter (DAT), recent efforts to develop more globally effective pharmacotherapies for PSUD have focused on two new DAT inhibitors and structural analogs of modafinil, JJC8‐088 and JJC8‐091, as promising lead compounds. In this study, the behavioral effects of these compounds were tested in rat models of cocaine self‐administration and reinstatement to drug seeking. Neurochemical correlates to those behaviors were assessed in microdialysis and fast‐scan cyclic voltammetry (FSCV) procedures aimed to measure extracellular dopamine levels and potential changes in dopamine dynamics in the nucleus accumbens shell (NAS). Our results show that JJC8‐088 (3, 10, 30 mg/kg, i.p.) dose‐dependently decreased the number of cocaine infusions under a fixed ratio schedule of self‐administration, while JJC8‐091 (10, 30, 56 mg/kg) failed to significantly alter cocaine self‐administration. In contrast, JJC8‐088 failed, while JJC8‐091 effectively decreased the break‐point for cocaine self‐administration under a progressive ratio schedule of behavior. JJC8‐088 maintained self‐administration behavior in both drug‐naïve and cocaine trained rats, while JJC8‐091 did not. Moreover, only priming injections of JJC8‐088 dose‐dependently reinstated drug‐seeking behavior in rats following previous cocaine extinction. Importantly, in the same rats, JJC8‐091 pretreatment blocked cocaine‐induced reinstatement of drug seeking behavior. The neurochemical assessment of JJC8‐088 and JJC8‐091 effects showed that both drugs dose‐dependently increased extracellular DA concentrations in dialysates from the NAS. However, JJC8‐088 was more potent and more efficacious in increasing DA levels compared to JJC8‐091. Indeed, the maximal changes in DA levels elicited by JJC8‐088 resemble those obtained with cocaine, in contrast to JJC8‐091. The FSCV studies showed that both JJC8‐088 and JJC8‐091 dose dependently reduced the rate of DA clearance, with JJC8‐088 producing effects greater in magnitude at lower doses than JJC8‐091. Finally, like cocaine, cumulative doses of JJC8‐088 produced a dose‐dependent increase in DA Max , while JJC8‐091 was ineffective at all doses tested. Collectively, these data show that despite sharing significant structural similarity, JJC8‐088 was cocaine‐like, while JJC8‐091 was not. Indeed, in contrast with JJC8‐088, JJC8‐091 did not elicit significant reinforcing actions and reduced or blunted the reinforcing effects of cocaine. Taken together, our data support further development of JJC8‐091, as a potential pharmacotherapy for the treatment of PSUD. Support or Funding Information Support for this research was provided by the Medication Development Program, National Institute on Drug Abuse ‐ Intramural Research Program, NIH/DHHS This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .
Prescription opioids, such as oxycodone, are highly effective analgesics for clinical pain management, but approximately 25% of patients who are prescribed opioids misuse them, and 5%-10% develop an opioid use disorder (OUD). Effective therapies for the prevention and treatment of opioid abuse and addiction need to be developed. The present study evaluated the effects of the highly selective dopamine D3 receptor antagonist VK4-116 ([R]-N-[4-(4-[3-chloro-5-ethyl-2-methoxyphenyl]piperazin-1-yl)-3-hydroxybutyl]-1H-indole-2-carboxamide) on oxycodone addictive-like behaviors. We used a model of extended access to oxycodone self-administration and tested the effects of VK4-116 on the escalation of oxycodone self-administration and withdrawal-induced hyperalgesia and irritability-like behavior in male and female rats. Pretreatment with VK4-116 (5-25 mg/kg, i.p.) dose-dependently decreased the escalation of oxycodone self-administration and reduced withdrawal-induced hyperalgesia and irritability-like behavior in opioid-dependent rats. These findings demonstrate a key role for D3 receptors in both the motivation to take opioids and negative emotional states that are associated with opioid withdrawal and suggest that D3 receptor antagonism may be a viable therapeutic approach for the treatment of OUD.
