Researchers at The Scripps Research Institute have developed a vaccine against heroin addiction, according to a Scripps press release.

With decades of scientists working on antibodies to prevent a drug from entering the brain, the quest for vaccines against drug addiction is nothing new. For heroin, however, the story is more complicated.

When ingested, the drug quickly metabolizes and breaks down into compounds called 6-acetylmorphine and morphine in the bloodstream, says Scripps.

To get around the problem, the researchers developed a "dynamic vaccine" that creates antibodies against heroin and its metabolites all at once, according to the study published today in the Proceedings of the National Academy of Sciences. When tested in rats, the vaccine caused the brain-permeating compounds in heroin that provoke a psychoactive response to be effectively and continuously sequestered in the bloodstream.

"The result is efficient blockade of heroin activity in treated rats, preventing various features of drugs of abuse," the team writes. "The dynamic vaccine shows the capability to significantly devalue the reinforcing and motivating properties of heroin, even in subjects with a history of dependence."

In one test, the Scripps press release says rats were trained to press a lever three times to receive a dose of heroin, and then went through what is called extinction training, in which the lever no longer produced the heroin infusion. Some were then vaccinated, while others weren't, and in the unvaccinated rats, a single infusion of heroin was enough to make them return to pressing the lever for more of the drug, mimicking human relapse behaviors. Rats that received the vaccine didn't resume their lever-pressing behavior.

In a second test, researchers gave escalating amounts of heroin to a group of rats, then forced them to abstain for 30 days before giving them the drug once again. The rats that received a placebo resumed taking escalating amounts of heroin, but the vaccinated rats didn't escalate.

Scripps' Kim Janda, one of the lead researchers on the study, notes that in other heroin vaccine trials, rats have doubled or tripled their intake of heroin to compensate for the diminished effect of the drug. But with this vaccine, Scripps adds, they cease their heroin intake altogether.

"Basically we were able to stop them from going through that cycle of taking more and more heroin," said the study's first author, Joel Schlosburg, in the press release. "And that was with the vaccine alone; ideally for human patients, the vaccine would be given with other treatments."

With that in mind, Scripps says that the vaccine does not block the effects of methadone, buprenorphine, or other opioid-receptor-targeting drugs that are commonly used to wean addicts off of heroin.

Janda says the vaccine is ready to move to human trials and is now seeking a partner in the pharmaceutical industry to conduct them.