Revisiting the Tamoxifen Scaffold to Create Therapeutics to TreatAmphetamine Abuse

[摘要] Amphetamine (AMPH) and its congeners are the second most widely abused drugs globally and their continued overuse comes with a high economic, health and social cost. Yet after decades of research, an effective treatment for AMPH abuse and addiction remains elusive. To tackle this unmet need, we have taken a step back to re-examine and further elucidate the mediators of AMPH reinforcement in hopes of finding novel targets for drug development. The reinforcing properties of AMPH are believed to stem from its reversal of the dopamine transporter (DAT), which greatly increases extracellular dopamine levels in the brain. Protein kinase C (PKC) is a major mediator of DAT localization and activity, and PKC activation facilitates AMPH-stimulated dopamine release. Inhibiting PKC attenuates the neurochemical and behavioral effects of AMPH. Therefore PKC inhibitors could be an appropriate pharmacological treatment for AMPH abuse and addiction. In pursuit of a blood-brain barrier permeant PKC inhibitor, we identified tamoxifen, a drug commonly used to prevent the recurrence of breast cancer, as a promising candidate. In fact, tamoxifen stands as the only validated CNS-permeant PKC inhibitor to date. Tamoxifen does act on other molecular targets, including the estrogen receptor (ER), and its promiscuity makes it an unattractive contender for AMPH abuse treatment. Nonetheless, tamoxifen has been the object of many structure-activity relationship studies and we have used the information from these investigations to make a new generation of selective CNS permeant PKC inhibitors based on the tamoxifen scaffold.I evaluated the actions of these tamoxifen analogues at PKC and ER, in hopes of finding compounds with increased selectivity for PKC inhibition and reduced ER affinity compared to tamoxifen. This led me to our lead compound, 6c, which asymmetrically modulates DAT functioning in in vitro rat models. Specifically, 6c more potently blocks dopamine efflux compared to uptake. I demonstrated that 6c does not elicit these effects on dopamine transport by altering DAT levels or binding near the dopamine substrate site. Significantly, as predicted, 6c crosses the blood-brain barrier and potently inhibits striatal PKC activity in vivo. I also illustrate that 6c has a direct effect on PKC and can disrupt PKC conformational changes without having effects on PKC translocation. Peripheral administration of the compound leads to significant decreases in AMPH-induced dopamine release, hyperlocomotion and reinforcement in vivo, predicting therapeutic effectiveness of 6c. Finally, I demonstrate that the in vivo effects of 6c are not due to its action on other closely related kinases that regulate DAT function. Together, the results from my thesis work highlight the potential of repurposing the tamoxifen scaffold to create new CNS-permeant PKC inhibitors and provide a foundation for developing therapeutics to treat AMPH addiction.

[发布机构] University of Michigan

[效力级别] Science (General)

[关键词] Amphetamine Abuse Treatment;Science (General);Science;Pharmacology