Scientists will also be able to study disorders that have been linked to the cannabinoid system, such as schizophrenia and Parkinson’s disease. For example, smoking marijuana appears to precipitate symptoms of schizophrenia. Furthermore, schizophrenics seem to have higher levels of cannabinoids in their brains. But animal studies of these diseases have produced conflicting results, says Andrea Giuffrida, a neuroscientist at the University of Texas Health Science Center in San Antonio. The new imaging method, he says, “will be useful to understand exactly what’s going on.”
The same is true for Parkinson’s disease. Some scientists speculate that cannabinoids play a protective role in the brain, slowing the rate of disease. But knowing exactly what happens to patients as the disease progresses is crucial, says Giuffrida.
The new tracer could also aid in drug development. Marijuana is already used to help cancer and AIDS patients with chronic pain or nausea. But many of these patients would prefer a version of the drug that comes without the mood-altering high. “[The tracer] may help us design the next generation of cannabinoid-based medicines – for example, chemicals that boost the activity of brain marijuana-like compounds without directly activating cannabinoid receptors,” says Daniele Piomelli, director of the Center for Drug Discovery at the University of California, Irvine.
Paris-based drug maker Sanofi-Aventis has already developed an anti-obesity drug that blocks cannabinoid receptors. The drug, which is expected to gain Food and Drug Administration approval within the next few months, will be the first cannabinoid blocker in use. Such PET tracers could help drug designers by giving them a direct way to measure how well an experimental compound binds to its target.
The new tracer will also help scientists learn more about marijuana addiction, and possibly treat it more effectively, says Henry Wagner, director of the division of radiation health sciences at Johns Hopkins University (who was not involved in the research). With the new tracer, neuroscientists could determine if smoking marijuana increases the number of cannabinoid receptors in the brain, which could lead to a craving for more of the drug.
Horti and colleagues have tested the tracer in rodents and baboons and confirmed that the compound accurately portrays the distribution of receptors, as shown by post-mortem studies. They’re now conducting safety studies, required by the FDA for using the compound in humans, which they estimate will be complete in three to six months.