A vaccine designed to help combat heroin addiction by virtually eliminating the drug’s psychoactive properties has shown promising results in preclinical trials, helping prevent addicted rats from escalating their habit.
One of the newest frontiers in addiction therapy is the promise of vaccines that put a person’s body on guard against psychoactive drugs. These kinds of treatments generally do not eliminate the desire for the drug, but block the drug’s pleasant effects for the user. There’s already some promising work being done in vaccines for other drugs like cocaine.
New research shows that a heroin vaccine in development has “the capability to significantly devalue the reinforcing and motivating properties of heroin, even in subjects with a history of dependence,” Scripps Research Institute scientists wrote in a paper published Monday in the Proceedings of the National Academy of Sciences.
Researchers designed the vaccine to provoke a subject’s immune system to produce antibodies against both the heroin molecule and the chemical products of the drug – particularly one breakdown product called 6-acetylmorphine -- that cross into the brain and are mostly responsible for a heroin user’s “high.”
"The vaccine effectively tracks the drug as it is metabolized, keeping the active breakdown products out of the brain, and that, I think, explains its success," co-author Kim Janda said in a statement Monday.
In previous research published in 2011, the team already established that the vaccine could take the edge off of heroin’s pain-relieving appeal. Now, the researchers have put the drug through more rigorous tests to see how it fares with laboratory models of addiction.
One experiment involved rats that had been recently trained to receive heroin by pressing a lever. The rats’ supply was then cut off – pressing the lever no longer got them their fix. Then, vaccinated and unvaccinated rates were given a dose of heroin. The unvaccinated rats returned to their heroin-seeking behavior, pressing the lever again; the vaccinated rats did not relapse.
Another experiment used rats that were seriously addicted to heroin, which were taking more and more of the drug -- eventually taking doses that would have killed unaddicted rats. The rodents were forced to go cold-turkey for 30 days, after which they were given access to the heroin-producing lever again for 12-hour stretches. Both the rats that were given a placebo shot and the actual vaccine resumed pressing the lever, but the rats that got the dummy vaccine began escalating their use right away. The vaccinated rats merely continued to consume the drug at the rates they’d taken it before the abstinence period.
"Basically we were able to stop them from going through that cycle of taking more and more heroin," coauthor Joel Schlosburg said in a statement. "And that was with the vaccine alone; ideally for human patients, the vaccine would be given with other treatments."
Sometimes, in experiments with other drug vaccines, medicated rats will take more and more of the drug in an attempt to overcome the shot’s ability to block the “high.” But this didn’t seem to be the case with the heroin vaccine, which is a promising result. The vaccine also does not block other drugs used in heroin treatment, like methadone, meaning that the shot could be used in addition to current therapies.
The researchers are currently looking for a drug company to sponsor clinical trials in humans.
“Although it may not be a ‘magic bullet’ against all aspects of drug addiction, the dynamic nature of our heroin vaccine represents a promising and innovative adjunct therapy in the treatment of heroin addiction,” the authors wrote.
SOURCE: Schlosburg et al. “Dynamic vaccine blocks relapse to compulsive intake of heroin.” Proceedings of the National Academy of Sciences published online 6 May 2013.