An fMRI-study on the Effects of 3'-Aminomethylnicotine-P. Aeruginosa r-Exoprotein a Conjugate Vaccine (NicVAX®) and Placebo on Central Nervous System Activation and Behaviour Following a Nicotine Challenge

Rationale: To develop a more effective treatment for nicotine addiction is a public health priority. In order to do so a better understanding is needed of the mechanisms 1) underlying nicotine addiction and 2) the way treatments alter the way nicotine transiently and permanently alters multiple cognitive and executive functions. Most effects of nicotine on the Central Nervous System (CNS) are directly mediated by nicotine molecules. Treatment with 3'aminomethylnicotine P. aeruginosa r-Exoprotein A Conjugate Vaccine (NicVAX™) stimulates the production of nicotine specific antibodies. These antibodies bind the small nicotine molecules, preventing them to cross the Blood Brain Barrier (BBB) and thus preventing CNS stimulation. A nicotine challenge given after vaccination will show no or diminished direct effects of nicotine on CNS stimulation. The blocking effects of the nicotine specific antibodies will be evaluated on several cognitive tasks and on reactivity to smoking-related cues.

Objective: Main aim; to show that NicVAX attenuates nicotine induced CNS effects on brain activation and cognitive performance relative to placebo. The secondary aim is to evaluate how these changes in CNS stimulation alter subjective measures and the addictive properties of nicotine.

Study design: within-subject cross-over double-blind placebo controlled study. Study population: 48 current smokers, male, age 25-40, at least smoking 10 cigarettes /day the last year, in general good health. Additional criteria; 1) No contra-indications for MRI 2) No history of cognitive deficits or brain trauma 3) No use of psychoactive medication 4) No contra-indications for nicotine gum.

Intervention (if applicable): The group will be randomized in two sub-populations. 1) 28 volunteers will receive five injections of 3'aminomethylnicotine P. aeruginosa r-Exoprotein A Conjugate Vaccine (NicVAX™), 2) 20 smokers will receive five injections placebo. On test days both groups will be given a nicotine challenge; a chewing gum either containing nicotine (2mg) or a placebo.

Main study parameters/endpoints: correlation between nicotine specific antibody and 1) the BOLD response during resting state, during the smoking-cue reactivity paradigm and during task performance; in regions of interest associated with the specific tasks; 2) the number of correct response and the reaction time; 3) correlation between nicotine specific antibody and subjective signs of nicotine addiction, measured with several questionnaires.