Published June 25, 2012
Could one shot cure a hard drug addiction? Researchers have developed not one, but two cocaine vaccines that show promise in blocking the highly addictive drug before it reaches the brain.
The vaccines have been successful in monkeys and mice injected with cocaine.
The vaccines were both developed by teams led by Ronald Crystal, a researcher at Weill Cornell Medical College in New York. They could be the first of a new line of anti-addiction treatments that use our own bodies to fight off addiction.
"Cocaine addiction is a major social problem. It s causes changes to behavior, it's expensive and it's illegal," Crystal told LiveScience. "It's very difficult to stop. If we could successfully develop a cocaine vaccine it would really be a very positive social advance."
The vaccines are still in the labs and not yet available for humans, but could be within a few years, Crystal said. They use antibodies — proteins of the immune system that attach to potentially dangerous molecules, tagging them for take-down by white blood cells — against a cocaine-like molecule to clear the body of the drug. [Trippy Tales: The History of 8 Hallucinogens]
The first so-called "active" vaccine uses harmless viral proteins to introduce the body's immune system to a cocaine-like molecule. The body's immune system sees the virus-molecule combination as a threat and produces anti-cocaine antibodies.
The latest work on this vaccine was presented June 12 at the Society of Nuclear Medicine's annual meeting in Miami Beach by study researcher Shankar Vallabhajosula, also of Weil Cornell Medical College.
Since imaging techniques can't detect cocaine in the brain, the researchers injected monkeys with an imaging molecule (which can be detected when it binds to receptors in the brain). The molecule they chose binds to the same receptor proteins in the brain as cocaine does. The thinking goes that if the vaccine blocks cocaine from reaching the brain there would be a stronger signal from the imaging molecule on the receptors; if it doesn't block it, then the cocaine and this molecule would both take up spots on the receptors and there would be a weaker signal from the molecule on the positron emission tomography (PET) scans.
In the monkeys with the cocaine vaccine, the imaging molecule lit up the brain like fireworks. This means little to none of the cocaine administered made it into their brains, so most of the receptors were open to bind to the imaging molecule. Unvaccinated monkeys gave a much dimmer signal in the brain. [10 Things You Didn't Know About the Brain]
These effects were seen in the monkeys up to four months after their vaccination.
The second vaccine, detailed June 18 in the journal Human Gene Therapy, uses a different virus to inject genetic material into liver cells. These liver cells start expressing the proteins encoded in that genetic material, which happens to contain the blueprint for an antibody against cocaine.
In the mice that received this gene therapy vaccine, the researchers saw that the body used this antibody the same way as it does in the first vaccine — to latch onto cocaine in the blood, and tag it to be taken out by the body's white blood cells.
In the new journal article, the researchers explain that when they gave mice this so-called "passive" vaccine, the mice produced plenty of the antibody against cocaine, and they no longer get "high" when given the drug. The vaccinated mice acted calmly instead of crazily running around their cages, an effect that lasted at least 17 weeks.
Stopping drug use
In either case, the antibodies created by these vaccines seem to work quickly enough to seek out cocaine as it enters the system, and stop it before it crosses into the brain. This is important because cocaine's addictive properties and physiological effects are created in the brain.
"If the vaccine works, then it would block the cocaine from reaching the brain and they wouldn't feel anything," Crystal said. Though there is a worry that drug addicts would try to "out-compete" their antibodies against the drug by taking it in much larger amounts, it remains to be seen if this work-around could defeat the vaccine.
The researchers are still working to test the toxicity of these injections in animals, before they can move on to human testing. They are hoping to start trials of the active vaccine in humans within a year, Crystal said.
"This is an interesting carrier for these vaccines," Thomas Kosten, a researcher from Baylor College of Medicine who wasn't involved in the study, told LiveScience in an email. He mentioned that a similar vaccine developed against nicotine had some issues: "The human studies were disappointing. I hope Crystal has more success as they move to human studies."
Kosten has worked on another cocaine vaccine, currently in human trials. His approach uses a protein complex from the cholera bacteria to activate the immune system, but requires multiple injections to work. Crystal's approaches would hopefully require only a single injection.
If any of these approaches work, the researchers could repeat the procedure to develop vaccines against heroin, nicotine and other addictions. "We could hook heroin to it [this harmless virus], or meth," Crystal said. "We've shown that it works for cocaine, and we think that it could work for a whole variety of drugs."