Development of a Human Hydrolase to Treat Cocaine Abuse and Overdose: Rat Models

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DESCRIPTION (provided by applicant): A novel concept for treatment of cocaine abuse envisages radically accelerated metabolism of cocaine as a means of reducing drug-seeking behavior. We propose a study of "metabolic therapy" for cocaine overdose and two critical stages of cocaine addiction: steady-state maintenance of drug self-administration, and drug-primed relapse or reinstatement of drug-seeking behavior after a period of abstinence. Our therapeutic agent is a human plasma cholinesterase converted by structure-driven mutagenesis into a cocaine hydrolase (CocH) that metabolizes cocaine with exceptional speed and is far more stable than bacterial cocaine esterase. Injections of this protein hastened drug elimination 100-fold or more, prevented toxicity from a lethal dose of cocaine given up to 12 hr later, and rescued rats from overdose even after convulsive seizures commenced. In preliminary trials this hydrolase prevented reinstatement of cocaine-seeking behavior in rats that had previously self-administered the drug. These findings indicate that long-term delivery of CocH might aid in dealing with cocaine abuse and its associated toxicity. The research plan addresses this prospect with three aims. FIRST are studies to extend the surprising finding that toxicity from cocaine overdose abates in seconds after CocH injection. Extensive pharmacokinetics and mechanistic studies of dopamine transients in the neostriatum of cocaine-challenged rats will test the hypothesis that recovery from seizures reflects the creation of steep cocaine diffusion gradients between brain and plasma. SECOND are tests of CocH on the motivation for cocaine self-administration in rats working under a progressive ratio schedule for several doses of drug. Rats will also be pretreated with CocH to further investigate its ability to block cocaine-primed reinstatement of cocaine-seeking behavior. THIRD are studies on CocH gene transfer. Preliminary results with a first-generation adenoviral gene transfer vector showed that high-level transduction of cocaine hydrolase in liver blocked the induction of delta-FosB in neostriatum, a molecular signal of cocaine addiction. We now plan to test advanced helper-dependent adenoviral vectors that should sustain expression for months in the periphery and the brain. Along with viral vectors we will also examine the delivery of hydrolase by modified stem cells. Our Research Plan is based on the premise that one or more of these gene-transfer approaches will suppress drug-seeking behavior in addicted rats and also reduce the propensity for relapse. This hypothesis, if substantiated, might later be extended to human patients. Previous attempts to block such behavior, which involves activation of dopaminergic reward circuitry, have used dopamine receptor antagonists. In contrast to the many side effects of those agents, we expect our proposed treatment to lack adverse effects at doses that suppress drug seeking. Our results should increase understanding of the biology of abuse and test the concept that cocaine abuse might be effectively treated by methods that prevent drug access to targets in the brain. Program Narrative: Recent advances in protein engineering have led to a human enzyme that destroys cocaine rapidly enough to prevent it from reaching the heart or brain. Our preliminary results show that this enzyme rescues rats from lethal seizures after drug overdose and also prevent formerly addicted rats from relapsing when they get access to cocaine. This application will investigate whether direct treatment or gene therapy with this enzyme can reduce drug-seeking behavior in rats as a model for cocaine addiction in humans.