An experimental vaccine that could help treat millions of methamphetamine addicts is showing promising results, according to scientists at The Scripps Research Institute in La Jolla, California.
In a research study on laboratory rats, scientists say 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 drug to target methamphetamine addiction.
“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 Michael A. Taffe, an associate professor in Scripp’s addiction science group and senior author of the study.
Methamphetamine has become one of the most commonly abused drugs in the world. In the U.S. there are more than 400,000 estimated users. Meth has characteristics, both physiological and psychological, that make it more addictive than other drugs. In California and other states, meth accounts for more drug abuse treatment admissions than any other drug.
Researchers have been trying to develop vaccines that evoke antibody responses against drug molecules, just as traditional vaccines evoke antibody responses against viruses or bacteria. In theory, the anti-drug antibodies would grab hold of drug molecules and keep them from getting into the brain, thus 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 earlier meth vaccines have been tested on animals but with mixed results. Scientists say the structure of the methamphetamine molecule is what makes it so difficult to target. Often unnoticed in the immune system, it tends to linger once it gets in the nervous system.
“The simple structure and long half-life of this drug make it a particularly difficult vaccine target,” said Kim Janda, Professor of Chemistry and member of the Skaggs Institute for Chemical Biology.
To overcome that problem, Janda and his team developed six potential meth vaccines. In each, the main ingredient was a derivative of a meth molecule that would normally be too small to evoke an antibody response. But when linked to a larger molecule, three of the vaccines evoked a strong antibody response to meth.
One vaccine, designated MH6, worked best at blocking two typical effects of methamphetamine —an increase in physical activity and a loss of the ability to regulate body temperature. Additional studies found that MH6 provoked an antibody response, in which vaccinated rats kept more of the drug in the bloodstream and out of the nervous system, compared to control rats.
“These are encouraging results that we’d like to follow up with further animal tests, and, we hope, with clinical tests in humans someday,” said Research Associate Michelle L. Miller, lead author of the study. “I think that this vaccine has all the right features to allow it to move forward in development.”
Antibody-based therapies are commonly used to treat cancer and chronic immunological conditions. But they are often expensive and the effects of a dose last for a few weeks at most. Both Janda and Taffe believe that with further refinement, a meth vaccine could sustain an anti-meth antibody response for a much longer period, offering an addict protection for months per dose, rather than weeks.
“Extending the duration of protection is the next big scientific challenge in this field,” said Taffe.
The results of the study, funded in part by a National Institute on Drug Abuse grant, were published in Biological Psychiatry, a journal of psychiatric neuroscience and therapeutics.