NDARC Technical Report No. 168 (2003)
EXECUTIVE SUMMARY
Cocaine dependence is a highly treatment-refractory condition. Cocaine is a potent and efficient drug that acts rapidly on the brain’s reward pathways to deliver the cocaine high. To-date there have been no pharmacological treatments recognised as more effective than placebo in initiating and maintaining abstinence in cocaine dependent patients (Shearer & Gowing, 2004) while the success of psychosocial interventions has been modest (Simpson et al., 2002). This is in contrast to heroin, nicotine and alcohol dependence where a range of effective pharmacological treatment modalities exist. This unmet treatment need has prompted a search for novel approaches such as vaccines. Cocaine vaccines are designed to stimulate antibodies that target cocaine molecules in the bloodstream and thereby reduce the amount of cocaine reaching the brain. They differ from other pharmacological approaches that have targeted neurotransmitter sites within the brain. The potential advantages of an effective cocaine vaccine include assured compliance, fewer side effects than CNS-acting drugs and an effective therapy where none has previously existed.
The harnessing of the body’s natural immune system to protect against illness and disease represented an historic advance in modern medicine. Recent developments in biotechnology have extended vaccines from their traditional protective role to therapeutic uses in diseases including HIV/AIDS, cancer, allergies and the prevention of organ transplant rejection. Addiction vaccines extend the use of this technology to a complex disorder with physiological, psychological and behavioural aspects. There are three main approaches to cocaine vaccination: (1) active immunisation seeks to stimulate the immune system to produce cocaine antibodies that recognise and bind to cocaine molecules or the active metabolites with resultant cocaine-antibody complexes that are too large to cross the blood brain barrier; (2) passive immunisation does not seek to elicit an immune response but rather directly loads in monoclonal antibodies that have been produced in the laboratory; and (3) passive immunisation with catalytic antibodies that seek to increase the rate of cocaine metabolism rendering cocaine inactive before it can reach the brain. The effectiveness and duration of these approaches vary - most are unlikely to be permanent. Potential therapeutic applications of vaccines include the management of overdose, detoxification and as a pharmacological supplement to relapse prevention.
Pre-clinical studies have shown that cocaine vaccines block the effects of cocaine in animal models reducing cocaine self-administration and protecting against lethal doses (Bunce et al., 2003). This review has identified four potential candidate vaccines for cocaine disorders. One of these has progressed to phase II trials in humans with three still in pre-clinical development. Human trials of one vaccine, TA-CD, have found that it was well tolerated and provoked an immune response to cocaine that peaked at about 3 months (Kosten et al., 2002). However, there are technical, economic and ethical challenges for the development of immunotherapy for cocaine. Technical barriers include underlying behavioural pathology, craving, drug substitution and inadequate duration of effective antibody levels. There may also be risks of overdose should users attempt to override vaccines with high doses of cocaine. Vaccines are associated in the public mind with prevention or protection and responses to a ‘vice’ vaccine have been alarmist and cynical. However, the effects of the therapeutic vaccines under investigation have been temporary and do not offer long-term protection from cocaine effects. Rather, they offer the potential to provide cocaine users with a valuable and rare therapeutic window or respite to engage with psychosocial therapy and make the lifestyle and personal changes central to relapse prevention.
The cost associated with the production of cocaine vaccines is considerable and several vaccine candidates have failed due to difficulties in achieving commercial scale production. The burden of disease in Australia associated with cocaine-related disorders may not be sufficient to justify the substantial investment required to conduct large scale original research studies into cocaine vaccines. Research into vaccines targeted towards other drugs of dependence such as nicotine may be more viable in the Australian context. It will be many years before a clinically useful cocaine vaccine becomes available. Earlier availability through clinical trials or special access may occur although this may be limited by substantial manufacturing costs. Vaccines are unlikely to completely block cocaine effects or act as stand-alone treatments, but they may be a valuable additional therapeutic pathway in conjunction with psychosocial and pharmacological approaches.
Citation: Shearer, J. and Mattick, R.P. (2003) Feasibility, rationale and prospects for therapeutic cocaine vaccines, Sydney: National Drug and Alcohol Research Centre.