Cocaine Immunization Successfully Tested in Rats

TREATMENT February 1996

On December 14, the National Institute on Drug Abuse (NIDA) announced that researchers funded by NIDA had successfully tested a substance that acts to immunize rats from the effects of cocaine (John A. Bowersox, "New Strategy Would Neutralize Cocaine in the Bloodstream," NIDA Notes, September/October 1995, p. 1, "Research Finds Immunization Can Block the Effects of Cocaine," Substance Abuse Letter, January 2, 1996, p. 1).

Researchers, in a process called "active immunization," injected rats with cocaine linked to a large protein that causes the body to produce antibodies. These antibodies recognize and chemically hook on to cocaine molecules, preventing them from producing an effect. Over long periods of time, the cocaine drops off the protein and is processed by the body.

The researchers found that rats with the antibodies had 70 percent less cocaine in their brains than non-immunized rats when the two populations were administered equal amounts of cocaine. Immunized rats also showed substantially less physical effect from cocaine.

Researchers Kim Janda, PhD, Rocio Carrera, MA, and George Koob, PhD of The Scripps Research Institute said the immunization method has an advantage over other cocaine addiction treatment programs because antibodies remain in the blood for a long period of time. The vaccine also has the advantage of not affecting brain chemistry as other cocaine treatments do. The vaccine may also prove useful in treating cocaine overdoses.

Dr. Alan Leshner, director of the National Institute on Drug Abuse (NIDA), said that development of a cocaine treatment or prevention medication is "this country's most important need in the fight against drug abuse and addiction."

Researchers cautioned that there are a number of issues to be studied before human clinical trials could begin: how long the vaccine remains in the bloodstream, the effect of "booster" shots, and the possibility that cocaine addicts will take more cocaine to overcome the effects of the vaccine.

Dr. Charles Schuster, former director of NIDA (1986-92), who is now Director of the Clinical Program for Substance Abuse at Wayne State University, tested an active immunization process for heroin in monkeys in the 1970s at the University of Chicago. Immunized monkeys stopped self-administering heroin although they would self-administer other drugs. Further, when the dose of heroin was increased 16-fold, the antibody pool became saturated and the monkey began to self-administer heroin again.

An even more important problem with immunization, Schuster told NewsBriefs, is that people immunized to the effects of one drug may substitute another drug to produce the same effect. Producing immunizations for all drugs would be an impossible task.

"We can't look at this as a magic bullet to substance abuse," Schuster said. "It will help individuals stop using cocaine, but we will need other interventions to prevent them from switching to other stimulant drugs such as amphetamines."

[For more information about the cocaine vaccine, contact the NewsBriefs office.]