Vaccines for Addictions
Therapies that block the high of addictive drugs are finally making their way from the lab into reality.
Britney, Lindsay, and even Miss USA–they’ve all made headlines in recent months for their forays in and out of rehab. Could vaccines that help prevent relapse provide the boost they need to quit their habits for good? While progress developing such vaccines has been slow–they were first conceived of more than 30 years ago–results from clinical trials of two vaccines, one for nicotine and one for cocaine, are expected within months, suggesting that this novel treatment may finally be on its way.
“I think these vaccines will be effective in helping people who want to quit stay quit,” says Thomas Kosten, director of the division of alcohol and addictive disorders at Baylor College of Medicine, in Houston.
Vaccines for addictive drugs work just like those for the flu: they trigger the immune system to produce antibodies that bind to the foreign substance and inactivate it. Molecules of cocaine, methamphetamine, nicotine, and other drugs are too small to spark an antibody response on their own, so scientists attach drug-like molecules to larger proteins that trigger formation of antibodies when injected into the blood. When a person takes a drug that he or she has been vaccinated against, antibodies bind to it and reduce the amount of drug that reaches the brain.
An addict who has been vaccinated might still fall off the wagon, but he or she wouldn’t get the rush of that next snort of cocaine or meth. Addiction experts say that thwarting the high should help prevent the person from spiraling back into regular use, allowing him or her to return to therapy or a treatment program much more quickly. “It could be comforting to know that even when you have dark moments and slip, you have the opportunity to get back on track,” says Michael Owens, a psychopharmacologist at the University of Arkansas for Medical Sciences, in Little Rock.
Long-awaited nicotine vaccines are likely to be the first available on doctors’ shelves. In initial clinical trials of smokers who were administered an experimental vaccine, a third of those given the highest dose quit, even though they were not asked to, versus 9 percent of those given placebos. A larger study of 200 patients has just concluded, with results expected in April.
Progress developing vaccines for cocaine, methamphetamine, and PCP has been considerably slower, a holdup that scientists say is largely due to lack of funding. “The cocaine vaccine has been almost entirely supported by NIDA [the National Institute of Drug Abuse],” says Kosten, rather than by the pharmaceutical companies that usually sponsor drug trials. Kosten and collaborators are now analyzing results from a clinical trial of a cocaine vaccine. Initial findings suggest that those who produced the biggest antibody response also reported the biggest change in their subjective response to cocaine, and they used less of the drug–a sign that the vaccine is working. But scientists don’t yet know the vaccine’s impact on the true test of success: a reduction in relapse rate.
Next-generation immunotherapies already in development could address some of the problems of earlier vaccines. For example, not everyone makes enough antibodies against drug vaccines to effectively block the high, and a determined addict could probably overcome the vaccine by taking large amounts of the drug. So some scientists are creating antibodies in the lab and then selecting only the most potent to be directly injected into the patient, a strategy known as passive vaccination.
Owens is creating such vaccines for PCP and methamphetamine. Rather than triggering antibody production in the person being vaccinated, antibodies are made in an animal and then converted into a form that can be injected into humans. Owens has started a biotech company, Intervexion Therapeutics, to commercialize his vaccines, and he aims to start tests for a PCP vaccine within the next year, with tests of a methamphetamine vaccine a year after that.
The passive-vaccination approach is costly–making and refining these vaccines is an expensive process–but it offers other advantages. Owens’s methamphetamine vaccine, for example, can also bind to other types of amphetamines and ecstasy, potentially giving patients a three-in-one anti-addiction punch. It could also be used to treat overdose by mopping up excess drugs in the system, says Frank Vocci, director of the pharmacotherapies division at the National Institute of Drug Abuse. Still, he cautions, such vaccines are probably several years away. They may not arrive soon enough for Britney, but perhaps the next wave of pop princesses and beauty queens will benefit.
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