Radiotracers for Addicts

Well, actually the radiotracers that are being developed at the U.S. Department of Energy’s Brookhaven National Laboratory will be for the scientists, to study how the central nervous system is influenced by addictive drugs:

“Addiction is a brain disease that is devastating for families and society,” said Fowler. [Chemist Joanna Fowler is the Director of the Center for Translational Neuroimaging at Brookhaven –ed.] “Chemistry — through the development of radiotracers that can monitor the distribution and kinetics of drugs and receptors in the brain — is at the core of understanding the addictive process and finding new ways to help people overcome it.”
In PET studies, radiotracers (compounds labeled with a radioactive form of certain chemical elements such as carbon or fluorine) are injected into a research subject’s bloodstream. A PET scanner picks up the radioactive signal from the tracer and continuously tracks its concentration and movement through the body. The data can be used to reconstruct three-dimensional images that reveal where the compound goes in the body/brain and how long it stays, for example.
The Brookhaven group, led by Fowler, has developed radiotracers to track the movement of various addictive drugs including cocaine, nicotine, and methamphetamine, and also to measure the levels of certain “chemical messengers,” or neurotransmitters, and their receptors in the brain. PET studies using these radiotracers have revealed, for example, that all addictive drugs elevate levels of a neurotransmitter called dopamine, a chemical that helps us experience feelings of pleasure, reward, and motivation — and also plays a role in physical movement. Through the process of addiction, these studies show, the brain’s ability to respond to pleasure signals becomes depleted as receptors for dopamine are lost. The research has also indicated that initial differences in people’s dopamine systems may help explain why some people find drugs pleasurable and become addicted while others do not.
One of the challenges for the researchers has been developing extremely rapid methods for synthesizing the radiotracer compounds. The radioactive elements (isotopes) most commonly used, carbon-11 (¹¹C) and fluorine-18 (¹⁸F), have very short half-lives (20 and 110 minutes, respectively). The half-life is the time it takes for half of the radioactive atoms in the sample to decay to a non-radioactive form. Since the PET scanner depends on the radioactive signal to detect the substance in the body, the compounds must be made and injected quickly to generate useful data.
“We are currently developing new ways to label complex molecules with carbon-11 and fluorine-18 to gain a better understanding of how different drugs of abuse disrupt brain function and how we may be able to treat addiction,” said Fowler. “This is an area that benefits enormously from creative synthetic chemistry. It is also an area that desperately needs new talent to develop the scientific tools needed to solve this major public health problem.”

FYI, Dr. Fowler knows what she is talking about: she is the inventor of 18F-fluorodeoxyglucose (FDG) radiotracer of brain glucose metabolism for PET scans, a chemical widely used today in clinical practice.
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