Tamoxifen Directly Interacts with the Dopamine Transporter

Area of Science:

• Neuroscience
• Pharmacology
• Molecular Biology

Background:

• Tamoxifen, a selective estrogen receptor modulator, is known to increase extracellular dopamine and offer neuroprotection.
• Its precise mechanisms regulating dopamine transporter (DAT) function remain incompletely understood.

Purpose of the Study:

• To investigate tamoxifen's effects on dopamine transporter (DAT)-mediated dopamine uptake, efflux, and binding.
• To elucidate the molecular interactions between tamoxifen and the DAT.

Main Methods:

• In vitro assays measuring dopamine uptake and efflux in rat striatal synaptosomes.
• Radioligand binding studies using [3H]WIN 35,428 to assess DAT binding.
• Biotinylation and cysteine accessibility assays to determine DAT conformation and surface expression.
• Studies with mutant DAT constructs (D476A, I159A) to identify interaction sites.
• In vivo locomotor activity tests in rats.

Main Results:

• Tamoxifen dose-dependently inhibited dopamine uptake and amphetamine-stimulated dopamine efflux.
• Tamoxifen weakly reduced [3H]WIN 35,428 binding, suggesting interaction with the DAT substrate site.
• Evidence indicated tamoxifen stabilizes an outward-facing DAT conformation, similar to cocaine.
• Mutant DAT studies suggested a direct interaction with a secondary binding site.
• Tamoxifen attenuated amphetamine-induced hyperactivity without affecting baseline locomotor activity.

Conclusions:

• Tamoxifen acts as a complex regulator of the dopamine transporter (DAT).
• Its cocaine-like inhibition of DAT function and attenuation of amphetamine effects are significant.
• Tamoxifen's structure is a promising scaffold for developing therapeutics for psychostimulant abuse.