A PET Exploration of the Mechanism of Action of Dopamine Beta-hydroxylase Inhibition in Cocaine Addicts

"Dopamine beta-hydroxylase (DHB) inhibition represents a promising approach to treating cocaine dependence. DBH is the enzyme responsible for hydroxylation of dopamine into noradrenaline. Its inhibition suppresses noradrenaline secretion. In animal studies, the efficacy of DBH inhibition in psychostimulants use could be linked to a reduced dopaminergic response, possibly in association with post synaptic dopaminergic receptor hypersensitivity. In humans, the clinical efficacy of DBH inhibition, in particular following disulfiram administration, is in the process of being established. However, its particular mode of action remains unclear: some publications suggest an increased aversive reaction to cocaine, whereas others report decreased positive effects. To date, the impact of DBH inhibition on dopaminergic response to psychostimulants has yet to be studied in humans.

This study represents a randomized, double blind placebo-controlled trial. Thirty cocaine dependant patients will be included in this study during their hospitalization for withdrawal. After the inclusion visit, they will be randomized to receive disulfiram 250 mg/day or placebo over the 15 days of their hospitalization. Main outcome criteria will be evaluated during two TEP imaging sessions with 11Craclopride, before and after stimulation by methylphenidate, 8 to 15 days after randomization. The main outcome criterion will be the variations in linkage rates of 11Craclopride in the nucleus accumbens between baseline TEP measurement and TEP measurement following administration of 20 mg of methylphenidate.

The primary objective of this trial is to show that in abstinent cocaine patients, DBH inhibition by disulfiram induces reduced dopaminergic response following methylphenidate administration. The secondary objectives of this trial are:

1. to show that methylphenidate stimulation induces less craving and more aversive responses in the disulfiram vs placebo condition;
2. to show that DBH inhibition by disulfiram elevates D2 dopaminergic receptor availability (in the absence of methylphenidate stimulation);
3. to show that the availability of D2 dopaminergic receptors (in the absence of methylphenidate stimulation) is linked to DBH activity;
4. to confirm that in abstinent cocaine patients, disulfiram reduces DBH activity vs placebo;
5. to confirm that subjects with weak DBH activity have more aversive reactions to cocaine.

Currently, disulfiram is the only drug on the market that inhibits DBH. Another more specific DBH inhibitor is currently under development. It is possible that other inhibitors could soon be developed by the pharmaceutical industry in the area of psychoactive drug addiction or other psychiatric or somatic disorders. The development of this new therapeutic approach requires a better understanding of its action mechanism.

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