Friday, April 23, 2010
A Shot for Cigarette Addiction?
NIDA’s Nora Volkow on addiction vaccines.
Nora Volkow, director of the National Institute on Drug Abuse (NIDA), predicted in a telephone interview on Friday that a vaccine for cigarettes could be available in as little as three years, if two large ongoing Phase 3 trials—the last major FDA hurdle—prove as successful as earlier studies.
NicVax (Nicotine Conjugate Vaccine) from Nabi Biopharmaceuticals, with a boost from a $40 million up-front cash infusion from GlaxoSmithKline Biologicals SA, is poised to become the first of a new kind of science-based addiction treatment—an avenue of approach that brings with it great promise, and a significant number of problems.
I asked Dr. Volkow if the NicVax studies had shown evidence that the effects could be overcome with greater levels of smoking. This is a hurdle that has plagued early research on a promising cocaine vaccine, as reported in the Archives of General Psychiatry (See my post "Cocaine Vaccine Hits Snag"). In the cocaine studies, researchers found that users could overcome the blunting effects of cocaine antibodies by ingesting as much as ten times their normal level of cocaine—clearly a dangerous outcome that could enhance the possibility of lethal overdose. (See discussions at Neurotopia and DrugMonkey).
“I am very sensitive to that issue,” Volkow said during a conference call from NIDA's Eighth Annual Blending Conference in Albuquerque, NM, where she was a featured speaker. “But the data we have give no evidence that smokers increase their cigarettes to overcome the antibodies. It was that piece of the data that led me to approve funding.”
In fact, said Volkow, “craving decreased after these vaccinations, so we would not necessarily expect smokers to try to overcome the effects. We’ve also seen a dramatic decrease in cocaine administration in animal models.” The matter of defeating a vaccine by overindulging remains a theoretical rather than an established risk, Volkow believes.
Vaccines may operate somewhat differently that we think, she explained, by helping to extinguish the conditioned responses to craving cues as well. “We did not expect to see [anti-craving effects],” she said. “Craving is a product of memory, associated stimuli, the anticipation of a pleasant response. With cigarettes, if you feel nothing, the brain mechanism of conditioning that drives craving starts to weaken.”
The vaccine itself “is not totally stopping all of the drug from getting into the brain. But it affects the pharmacological properties, so users don’t get the expected outcome. Nobody knows exactly how this might accelerate the extinction process—we haven’t done the studies. It’s going to be intriguing to have a product that has the capacity to make extinction much more universal.”
Volkow admitted that “we need to get a wider response,” since a significant number of smokers and cocaine users do not form antibodies from the vaccines. In addition, “we need longer-lasting responses so we don’t have to re-vaccinate.” The cocaine vaccine under study is in Phase 2 trials, and it will be several years before more definitive results are in.
The Blending Conference Volkow was attending was titled “Blending Addiction Science and Practice: Evidence-Based Treatment and Prevention in Diverse Populations and Settings.” Despite her emphasis on science-based treatments, Volkow stated firmly that social intervention and psychological treatment can be equally important, and characterized the supposed line between physical addiction and psychological addiction as an “obsolete distinction.” It is important to remember, she said, that “psychosocial interventions make biological changes in the brain” as well.
“People are desperate, and vaccines will be very helpful to those who develop antibodies. People want these magic bullets, but we don’t yet know how these vaccines will effect the therapeutic landscape.”
Graphics Credit: http://www.attcnetwork.org/