06 January 2011

Vaccine protects mice from cocaine's effects

Injection might one day help humans who are addicted to drugs, researcher suggests.


Injection might one day help humans who are addicted to drugs, researcher suggests

New animal research suggests that cocaine addiction might be treatable with a vaccine that has been engineered from pieces of the common cold virus in combination with a cocaine-like substance that mimics cocaine's molecular composition.

In mice, the vaccine appears to provoke an effective and long-lasting antibody immune response, attacking cocaine molecules and keeping them from reaching the brain where they would normally trigger the drug's classic hyperactive response.

The study, funded by the US National Institute on Drug Abuse, is published in the 4 January online edition of Molecular Therapy.

Vaccine would be offered to cocaine addicts

If successful in people, the vaccine would be the first of its kind and could offer cocaine addicts - and perhaps even nicotine, heroin and opiate addicts as well - a simple way to kick their habit, according to study author Dr Ronald G. Crystal, chairman and professor of genetic medicine at Weill Cornell Medical College in New York City, and his colleagues.

To date, however, the vaccine has not been tested in humans and is not approved for therapeutic use by the US Food and Drug Administration.

Crystal nonetheless expressed enthusiasm for the vaccine's potential.

"Our very dramatic data shows that we can protect mice against the effects of cocaine, and we think this approach could be very promising in fighting addiction in humans," he said in a Weill Cornell news release.

The study

As a first step, the study authors fashioned the vaccine around an infectious agent: namely, specific parts of the adenovirus (a common cold virus) that pose no risk in terms of causing sickness. This ensured that the vaccine would elicit an immune response.

Then the team attached the cold virus agent to a chemical that is structurally similar to cocaine.

The result: When injected into mice, the vaccine prompted their immune system to generate a strong antibody response to cocaine, something the immune system normally doesn't do effectively. In test tubes these antibodies stopped cocaine in its tracks, and when the vaccine was injected into mice before cocaine exposure, the animals displayed much less hyperactivity when given cocaine (even in large, repeated doses) than no vaccinated mice.

The vaccine effect was found to last for a minimum of 13 weeks, all the while effectively arming the mice with an immunity to cocaine's effects when consumed in amounts equivalent to those humans might ingest.

Other attempts

"While other attempts at producing immunity against cocaine have been tried, this is the first that will likely not require multiple, expensive infusions, and that can move quickly into human trials," Crystal stated.

Crystal suggested that if human testing proves successful, the vaccine would be most appropriate for patients already addicted to cocaine.

"The vaccine may help them kick the habit because if they use cocaine, an immune response will destroy the drug before it reaches the brain's pleasure centre," he explained.

Great need for a better vaccine

As someone who himself has been working on a cocaine vaccine for the better part of two decades, Dr Thomas Kosten, from Baylor College of Medicine in Houston, expressed support for Crystal's work, noting that "there is a great need for a better vaccine." But he cautioned that the development process is rife with obstacles.

"First of all, the immune response is considerably less robust in people than it is in animals," said Kosten, who also serves as director of the Veterans Health Administration Quality Enhancement Research Initiative Centre for Substance Abuse, also in Houston. "Secondly, for people to get close to the animal response we have to give them a lot more vaccinations than we have to give the animals," he explained.

"And people have a whole lot more genetic diversity than these mice do," he added. "And that ends up producing pretty important differences in response in people, so that about 25 to 30% of the people who you vaccinate with these vaccines don't produce much antibody response at all."

Kosten also stressed that no vaccine should be thought of as a magic bullet.

"The data we have suggests that it takes people about two years of abstinence to change their lifestyle and get over all the behavioural aspects of addiction," he noted. "And because the duration of the vaccine's effectiveness is only two to three months, we will need to offer repeated vaccinations for two years. But certainly people with severe addictions are going to need central nervous system interventions and behavioural interventions to address the multiple number of brain abnormalities that are induced with this drug over time.

Withdrawal itself lasts about two weeks at the most. But normalising many of the harmful brain changes can take six months or so, and some changes simply do not improve with abstinence alone. So a vaccine alone will not be enough."(HealthDay News/ January 2011)

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