Janda and his team therefore designed the heroin vaccine to elicit antibodies against not only heroin, but also 6-acetylmorphine and morphine. "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," Janda said.
Initial tests, reported in 2011, showed the vaccine could block some of the acute effects of heroin, such as obstructing pain. In the new study, the Koob laboratory put the vaccine through more rigorous tests.
"We gave the vaccine to rats that had already been exposed to heroin, a situation obviously relevant to a human clinical situation," said postdoctoral research associate Joel Schlosburg, who was first author of the study.
In one test, rats trained to press a lever three times to get an infusion of heroin later went through sessions of "extinction training," in which lever presses no longer produced infusions. Among rats that had not received the heroin vaccine, a single infusion of heroin could immediately reinstate a rat's drug-seeking lever-pressing behaviorjust as human users relapse to drug-seeking after re-exposure to heroin. However, rats that had been vaccinated failed to resume their heroin-seeking lever-presses.
In an even more challenging test, rats that had become severely addicted to heroin and were taking it compulsively in escalating amountsamounts that would have been lethal to drug-nave ratswere forced to abstain for 30 days before being given renewed access. In rats that had received a dummy vaccine, intake resumed and they re-escalated, taking the drug compulsively. But in the heroin-vaccinated rats, intake failed to escalate and compulsive drug taking did not redevelop.
"Basically we were able to stop them from going through that cycle of taking more and more heroin," said Schlosburg. "And that was with the
|Contact: Mika Ono|
Scripps Research Institute