Title

UND scientists develop a smart cocaine mimic to identify where cocaine lurks and hooks users

Document Type

News Article

Publication Date

11-3-2014

Campus Unit

School of Medicine & Health Sciences

Abstract

GRAND FORKS, N.D.—Cocaine grips users by targeting neurons in the brain that use the neurotransmitter dopamine to control the brain's reward and pleasure pathways. Cocaine binds to the dopamine transmitter known as DAT and acts like a cork to bottle up the ability of DAT to control how much dopamine flows across the bridges—the synapses—between neurons. It's the uncontrolled flow or hyperstimulation from dopamine that leads to euphoria, craving and eventual addiction.

Unlike heroin use, which can be treated with replacement drugs like methadone, there are no effective drugs that can be used to bind to DAT and block cocaine from making itself at home.

Scientists have long sought to find just where in neurons cocaine snaps and locks itself in place like a 3-D jigsaw puzzle piece. Detecting where cocaine connects with DAT would enable scientists to experiment with potential molecules to crowd out cocaine and develop potential replacement drugs to treat cocaine addiction.

Now, a research team, led by biomedical scientists in the Department of Basic Sciences at the University of North Dakota School of Medicine and Health Sciences, reports they have discovered the binding site of a cocaine-like molecule at its target the dopamine transporter, DAT.

Chester Fritz Distinguished Professor of Biochemistry and Molecular Biology Roxanne A. Vaughan, Ph.D., and Associate Professor Keith Henry, Ph.D., set out to identify the direct contacts between cocaine and DAT. They enlisted the expertise of medicinal chemist Amy Newman, Ph.D., chief of the Molecular Targets and Medications Discovery Branch at the National Institute on Drug Abuse, radiochemist John Lever, Ph.D., at the University of Missouri, and molecular biologist James Foster, Ph.D., at UND. They developed and characterized a special radioactive cocaine analog—RTI 82. After RTI 82 binds to DAT, ultraviolet light is used to activate the drug causing it to irreversibly attach to the transporter, essentially handcuffing the molecule to DAT.

"Our research provides a critical first step in understanding the molecular components necessary for the addictive effects of cocaine," Henry said.

Postdoctoral fellows Pramod Akula Bala and Babita Sharma from Henry's lab employed high-performance computing resources at the UND Computational Research Center to perform the billions of calculations necessary to run sophisticated computational molecular modeling strategies. They were able to predict a single point of attachment out of more than 600 possible sites on DAT and to determine a three-dimensional pose for cocaine and how it interacts with surrounding regions of the binding pocket. Graduate student Rejwi Dahal in Vaughan's group then chemically chopped the irreversibly labeled transporter into small pieces and then using the radioactive signature of the cocaine-like molecule biochemically validated the computational prediction. Foster and Danielle Krout, a graduate student in Henry's lab, provided additional verification of these results by employing further genetic and chemical analyses.

"The success of this study hinged upon a team of talented scientists that were able to bring together a unique and powerful set of synergistic tools and approaches to address a fundamental question in addiction research," Henry said. "Now that the foundation has been laid, we look ahead to understanding why atypical dopamine transporter blockers do not exhibit addictive properties."

The editors of the Journal of Biological Chemistry deemed that the scientists' discovery and the research paper detailing their work deserved prominence as the cover article in the journal's October 24 issue. The cover art for the article was designed by Drs. Henry and Vaughan and by Victoria Swift, a graphic designer at the UND SMHS. The article will also be highlighted in the November issue of ASBMB Today, the online newsletter of the American Society for Biochemistry and Molecular Biology.

Funding for the research was supported, in whole or in part, by grants from the following institutes of the National Institutes of Health:

  • National Institute on Drug Abuse - Research Project Grant
  • National Institute on Drug Abuse - Intramural Research Program
  • National Center for Research Resources
    • IDeA (Institutional Development Award) Network of Biomedical Research Excellence Program and
    • Center of Biomedical Research Excellence Program

Funding was also provided through ND EPSCoR—the North Dakota Experimental Program to Stimulate Competitive Research.

The research paper titled "Computational and Biochemical Docking of the Irreversible Cocaine Analog RTI 82 Directly Demonstrates Ligand Positioning in the Dopamine Transporter Central Substrate-binding Site" is available online at http://www.jbc.org/content/289/43/29712#xref-fn-1-1.

On the Cover: Cocaine addiction places a tremendous burden on our society, and efforts to provide effective therapeutic intervention require molecular insight into the interaction of cocaine with its primary target, the dopamine transporter. The new study by Dahal et al., pages 29712–29727, provides direct identification of the binding site of cocaine analogs on the transporter, which is a critical first step to uncovering the mechanisms by which cocaine induces its effects.

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