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Vaccine for Methamphetamine Addiction Shows Promise in Early Tests
Blocking meth ‘high’ could help addicts committed to recovery (Nov. 1)
Scientists at The Scripps Research Institute (TSRI) in La Jolla, California, have conducted successful tests of an experimental methamphetamine (“meth”) vaccine in rats. Vaccinated animals that received the drug were largely protected from typical signs of meth intoxication. If the vaccine proves effective in humans, it could become the first specific treatment for meth addiction, which is estimated to affect 25 million people worldwide.
The findings were published in the current issue of Biological Psychiatry.
“This is an early-stage study, but its results are comparable to those for other drug vaccines that have then gone to clinical trials,” said senior author Dr. Michael A. Taffe.
In recent years, scientists at TSRI and other institutions have worked on developing vaccines against addictive drugs. These vaccines evoke antibody responses against drug molecules, just as traditional vaccines evoke antibody responses against viruses or bacteria. Anti-drug antibodies are meant to “grab” drug molecules and keep them from getting into the brain — thereby preventing the drug from giving the user a “high” and removing the incentive for taking the drug.
Vaccines against nicotine and cocaine are already in clinical trials. Some meth vaccines have been tested in animals, but generally with unpromising results. The methamphetamine molecule is structurally simple, making it relatively unnoticeable to the immune system. Meth and its main metabolite, ordinary amphetamine, also tend to linger once they get into the nervous system, so that even a little drug goes a long way. The simple structure and long half-life of methamphetamine make it a particularly difficult vaccine target, according to the TSRI researchers.
Two years ago, Taffe’s laboratory tested three vaccines in rats and found one, designated MH6, that worked best at blocking two typical effects of meth — an increase in physical activity and a loss of the usual ability to regulate body temperature.
In the new study, researchers investigated the MH6 vaccine in more depth. They again found that the vaccine prevented the rise in body temperature and the burst of hyperactivity that otherwise occur after meth exposure. Underlying these promising effects on behavioral measures was a notable antibody response, which in vaccinated rats kept more of the drug in the bloodstream and out of the nervous system, compared with control rats.A separate group of researchers has reported promising animal test results for an antibody-based treatment. In this approach, the anti-meth antibodies are grown in cultured cells using standard biotechnology methods and are then injected into the animal in a concentrated dose, preventing a meth high. Antibody-based therapies are commonly used to treat cancer and chronic immunological conditions, but they can be expensive, costing thousands of dollars per dose, and the effects of a dose last for only a few weeks at most. A meth treatment would have to be much more cost-effective to be widely useful, as addicts frequently have little money and no health insurance and receive their treatments from government health services.
In principle, an active vaccine would be cheap to make and administer and would confer protection for months per dose, rather than weeks with conventional monoclonal antibody therapy. In practice, active meth vaccine candidates don’t last that long; for example, the MH6 candidate in the current study was given in four doses over 12 weeks. But Taffe believes that with further adjustment, an active meth vaccine could sustain an anti-meth antibody response for a much longer period.
Source: Scripps Research Institute, November 1, 2012.