Journal
BIOLOGICAL PSYCHIATRY
Volume 72, Issue 5, Pages 405-413Publisher
ELSEVIER SCIENCE INC
DOI: 10.1016/j.biopsych.2012.03.022
Keywords
Abuse liability; addiction; cocaine; dopamine transporter; methamphetamine; microdialysis
Categories
Funding
- National Institute on Drug Abuse Intramural Research Program
- Lundbeck Foundation
- Danish Council for Independent Research Sapere Aude programme
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Background: (+/-)-Modafinil has piqued interest as a treatment for attention-deficit/hyperactivity disorder and stimulant dependence. The R-enantiomer of modafinil might have unique pharmacological properties that should be further investigated. Methods: (+/-)-Modafinil and its R-(-)- and S-(+)-enantiomers were synthesized and tested for inhibition of [H-3] dopamine (DA) uptake and [H-3]WIN 35428 binding in human dopamine transporter (DAT) wild-type and mutants with altered conformational equilibria. Data were compared with cocaine and the atypical DA uptake inhibitor, JHW 007. R- and S-modafinil were also evaluated in microdialysis studies in the mouse nucleus accumbens shell and in a cocaine discrimination procedure. Results: (+/-)-, R-, and S-modafinil bind to the DAT and inhibit DA uptake less potently than cocaine, with R-modafinil having approximately threefold higher affinity than its S-enantiomer. Molecular docking studies revealed subtle differences in binding modes for the enantiomers. R-modafinil was significantly less potent in the DAT Y156F mutant compared with wild-type DAT, whereas S-modafinil was affected less. Studies with the Y335A DAT mutant showed that the R- and S-enantiomers tolerated the inward-facing conformation better than cocaine, which was further supported by [2-(trimethylammonium)ethyl]-methanethiosulfonate reactivity on the DAT E2C I159C. Microdialysis studies demonstrated that both R- and S-modafinil produced increases in extracellular DA concentrations in the nucleus accumbens shell less efficaciously than cocaine and with a longer duration of action. Both enantiomers fully substituted in mice trained to discriminate cocaine from saline. Conclusions: R-modafinil displays an in vitro profile different from cocaine. Future trials with R-modafinil as a substitute therapy with the potential benefit of cognitive enhancement for psychostimulant addiction are warranted.
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