HUMAN BUTYRYLCHOLINESTERASE MUTANTS FOR COCAINE DETOXIFICATION

Cocaine is one of the most reinforcing drugs of abuse and has caused serious medical and social problems. There is no FDA-approved medication specific for cocaine. It is of a high priority to develop an effective therapeutic treatment for cocaine abuse. Human butyrylcholinesterase (BChE) has been recognized as a promising candidate of enzyme therapy to metabolize cocaine into biologically inactive metabolites and prevent it from reaching central nervous system (CNS). However, the catalytic activity of wide-type human BChE against cocaine is not sufficiently high for treatment of cocaine abuse. Dr. Zhan’s lab has successfully designed and discovered a series of high-activity mutants of human BChE specific for cocaine metabolism. This dissertation is mainly focused to address the possible concerns in further development of promising human BChE mutants for cocaine detoxification, including whether the administration of this exogenous enzyme will affect the cholinergic system, whether it can efficiently hydrolyze cocaine’s toxic metabolites, and whether the commonly used therapeutic agents will significantly affect the catalytic activity of the BChE mutants against cocaine when they are co-administered. According to the results obtained, all of the examined BChE mutants have a considerably improved catalytic efficiency against (-)-cocaine, without significantly improving the catalytic efficiency against any of the other examined substrates, including neurotransmitter acetylcholine. Two representative mutants (including E12-7) also have a considerably improved catalytic activity against cocaethylene (formed from combined use of cocaine and alcohol) compared to wild-type BChE, and E12-7 can rapidly metabolize cocaethylene, in addition to cocaine, in rats. Further evaluation of possible drug-drug interactions between E12-7 and some other commonly used therapeutic agents revealed that all of the examined agents, except some tricyclic antidepressants, do not significantly inhibit E12-7. In addition, an effort to discover new mutants with further improved activity against cocaine led to the discovery of a new BChE mutant, denoted as E20-7, according to both the in vitro and in vivo assays. The encouraging outcomes of the present investigation suggest that it is possible to develop a more effective enzyme therapy for cocaine abuse treatment using one of the most promising BChE mutants, such as E12-7 or E20-7