The fate of bacterial cocaine esterase (CocE): an in vivo study of CocE-mediated cocaine hydrolysis, CocE pharmacokinetics, and CocE elimination

PEGylation but Not Fc-Fusion Improves in Vivo Residence Time of a Thermostable Mutant of Bacterial Cocaine Esterase

It is very popular to fuse a protein drug or drug candidate to the Fc domain of immunoglobulin G (IgG) in order to prolong the in vivo half-life. In this study, we have designed, prepared, and tested an Fc-fused thermostable cocaine esterase (CocE) mutant (known as E196-301, with the T172R/G173Q/L196C/I301C substitutions on CocE) expressed in E. coli. As expected, Fc-fusion does not affect the in vitro enzyme activity and thermal stability of the enzyme and that Fc-E196-301 can favorably bind FcRn with K_d = 386 ± 35 nM. However, Fc-fusion does not prolong the in vivo half-life of E196-301 at all; Fc-E196-301 and E196-301 have essentially the same PK profile (t_1/2 = 0.4 ± 0.1 h) in rats. This is the first time demonstrating that Fc-fusion does not prolong in vivo half-life of a protein. This finding is consistent with the mechanistic understanding that E196-301 and Fc-E196-301 are all degraded primarily through rapid proteolysis in the body. The Fc fusion cannot protect E196-301 from the proteolysis in the body. Nevertheless, it has been demonstrated that PEGylation can effectively protect E196-301, as the PEGylated E196-301, i.e., PEG-E196-301, has a significantly prolonged in vivo half-life. It has also been demonstrated that both E196-301 and PEG-E196-301 have dose-dependent in vivo half-lives (e.g., 19.9 ± 6.4 h for the elimination t_1/2 of 30 mg/kg PEG-E196-301), as the endogenous proteolytic enzymes responsible for proteolysis of E196-301 (PEGylated or not) are nearly saturated by the high plasma concentration produced by a high dose of E196-301 or PEG-E196-301.

A thermostable bacterial cocaine esterase rapidly eliminates cocaine from brain in nonhuman primates

A long-acting, thermostable bacterial cocaine esterase (CocE) has been identified that rapidly degrades cocaine with a K(M) of 1.33+0.085 μM. In vivo evaluation of CocE has shown protection against convulsant and lethal effects of cocaine in rodents, confirming the therapeutic potential of CocE against cocaine overdose. However, the current study is the first to evaluate the effects of CocE on cocaine brain levels. Positron emission tomogrpahy neuroimaging of [(11)C]cocaine was used to evaluate the time course of cocaine elimination from brain in the presence and absence of CocE in nonhuman primates. Systemic administration of CocE eliminated cocaine from the rhesus-monkey brain approximately three times faster than control conditions via peripheral actions through attenuating the input function from blood plasma. The efficiency of this process is sufficient to alleviate or prevent adverse central nervous system effects induced by cocaine. Although the present study used tracer doses of cocaine to access brain clearance, these findings further support the development of CocE for the treatment of acute cocaine toxicity.

Bacterial cocaine esterase: a protein-based therapy for cocaine overdose and addiction

Cocaine is highly addictive and there are no pharmacotherapeutic drugs available to treat acute cocaine toxicity or chronic abuse. Antagonizing an inhibitor such as cocaine using a small molecule has proven difficult. The alternative approach is to modify cocaine's pharmacokinetic properties by sequestering or hydrolyzing it in serum and limiting access to its sites of action. We took advantage of a bacterial esterase (CocE) that has evolved to hydrolyze cocaine and have developed it as a therapeutic that rapidly and specifically clears cocaine from the subject. Native enzyme was unstable at 37°C, thus limiting CocE's potential. Innovative computational methods based on the protein's structure helped elucidate its mechanism of destabilization. Novel protein engineering methodologies were applied to substantially improve its stability in vitro and in vivo. These improvements rendered CocE as a powerful and efficacious therapeutic to treat cocaine intoxication and lead the way towards developing a therapy for addiction.

Repeated administration of a mutant cocaine esterase: effects on plasma cocaine levels, cocaine-induced cardiovascular activity, and immune responses in rhesus monkeys

Previous studies have demonstrated the capacity of a long-acting mutant form of a naturally occurring bacterial double mutant cocaine esterase (DM CocE) to antagonize the reinforcing, discriminative, convulsant, and lethal effects of cocaine in rodents and reverse the increases in mean arterial pressure (MAP) and heart rate (HR) produced by cocaine in rhesus monkeys. This study was aimed at characterizing the immunologic responses to repeated dosing with DM CocE and determining whether the development of anti-CocE antibodies altered the capacity of DM CocE to reduce plasma cocaine levels and ameliorate the cardiovascular effects of cocaine in rhesus monkeys. Under control conditions, intravenous administration of cocaine (3 mg/kg) resulted in a rapid increase in the plasma concentration of cocaine (n = 2) and long-lasting increases in MAP and HR (n = 3). Administration of DM CocE (0.32 mg/kg i.v.) 10 min after cocaine resulted in a rapid hydrolysis of cocaine with plasma levels below detection limits within 5 to 8 min. Elevations in MAP and HR were significantly reduced within 25 and 50 min of DM CocE administration, respectively. Although slight (10-fold) increases in anti-CocE antibodies were observed after the fourth administration of DM CocE, these antibodies did not alter the capacity of DM CocE to reduce plasma cocaine levels or ameliorate cocaine's cardiovascular effects. Anti-CocE titers were transient and generally dissipated within 8 weeks. Together, these results suggest that highly efficient cocaine esterases, such as DM CocE, may provide a novel and effective therapeutic for the treatment of acute cocaine intoxication in humans.

The ability of bacterial cocaine esterase to hydrolyze cocaine metabolites and their simultaneous quantification using high-performance liquid chromatography-tandem mass spectrometry

Cocaine toxicity is a widespread problem in the United States, responsible for more than 500,000 emergency department visits a year. There is currently no U.S. Food and Drug Administration-approved pharmacotherapy to directly treat cocaine toxicity. To this end, we have developed a mutant bacterial cocaine esterase (DM-CocE), which has been previously shown to rapidly hydrolyze cocaine into inert metabolites, preventing and reversing toxicity with limited immunogenic potential. Herein we describe the ability of DM-CocE to hydrolyze the active cocaine metabolites norcocaine and cocaethylene and its inability to hydrolyze benzoylecgonine. DM-CocE hydrolyzes norcocaine and cocaethylene with 58 and 45% of its catalytic efficiency for cocaine in vitro as measured by a spectrophotometric assay. We have developed a mass spectrometry method to simultaneously detect cocaine, benzoylecgonine, norcocaine, and ecgonine methyl ester to quantify the effect of DM-CocE on normal cocaine metabolism in vivo. DM-CocE administered to rats 10 min after a convulsant dose of cocaine alters the normal metabolism of cocaine, rapidly decreasing circulating levels of cocaine and norcocaine while increasing ecgonine methyl ester formation. Benzoylecgonine was not hydrolyzed in vivo, but circulating concentrations were reduced, suggesting that DM-CocE may bind and sequester this metabolite. These findings suggest that DM-CocE may reduce cocaine toxicity by eliminating active and toxic metabolites along with the parent cocaine molecule.