Kinetic characterization of an efficient cocaine hydrolase against toxic metabolites of cocaine.

In the presence of alcohol, cocaine metabolism produces a number of metabolites, including three toxic ones (cocaethylene, norcocaine, and norcocaethylene) which are all more toxic than cocaine itself, with the toxicity in the order of cocaine < cocaethylene < norcocaine < norcocaethylene. In this study, we performed kinetic analysis on our previously reported cocaine hydrolase (E30-6) for its catalytic activities accelerating the hydrolysis of the three toxic metabolites in comparison with cocaine. Based on the obtained kinetic data, the in vitro catalytic efficiencies of the enzyme against these substrates are in the order of cocaine > cocaethylene > norcocaine > norcocaethylene. It has been demonstrated that E30-6 can efficiently accelerate the hydrolysis of not only cocaine itself, but also all three toxic metabolites in vitro and in vivo. E30-6 is the most efficient enzyme for each of these toxic substrates (cocaine, cocaethylene, norcocaine, and norcocaethylene) among all the reported enzymes as far as we know at this point. These findings suggest that E30-6 is capable of efficiently treating cocaine toxicity even when alcohol and cocaine are used concurrently.

Development of a Highly Efficient Long-Acting Cocaine Hydrolase Entity to Accelerate Cocaine Metabolism.

It is particularly challenging to develop a truly effective pharmacotherapy for cocaine use disorder (CUD) treatment. Accelerating cocaine metabolism via hydrolysis at cocaine benzoyl ester using an efficient cocaine hydrolase (CocH) is known as a promising pharmacotherapeutic approach to CUD treatment. Preclinical and clinical studies on our first CocH (CocH1), in its human serum albumin-fused form known as TV-1380, have demonstrated the promise of a general concept of CocH-based pharmacotherapy for CUD treatment. However, the biological half-life of TV-1380 (t1/2 = 8 h in rats, associated with t1/2 = 43-77 h in humans) is not long enough for practical treatment of cocaine dependence, which requires enzyme injection for no more than once weekly. Through protein fusion of a human butyrylcholinesterase mutant (denoted as CocH5) with a mutant (denoted as Fc(M6)) of Fc from human IgG1, we have designed, prepared, and tested a new fusion protein (denoted as CocH5-Fc(M6)) for its pharmacokinetic profile and in vivo catalytic activity against (-)-cocaine. CocH5-Fc(M6) represents the currently most efficient long-acting cocaine hydrolase with both the highest catalytic activity against (-)-cocaine and the longest elimination half-life (t1/2 = 229 ± 5 h) in rats. As a result, even at a single modest dose of 3 mg/kg, CocH5-Fc(M6) can significantly and effectively accelerate the metabolism of cocaine in rats for at least 60 days. In addition, ∼70 nM CocH5-Fc(M6) in plasma was able to completely block the toxicity and physiological effects induced by intraperitoneal injection of a lethal dose of cocaine (60 mg/kg).

Cocaine hydrolase blocks cocaine-induced dopamine transporter trafficking to the plasma membrane.

Cocaine blocks dopamine uptake via dopamine transporter (DAT) on plasma membrane of neuron cells and, as a result, produces the high and induces DAT trafficking to plasma membrane which contributes to the drug seeking or craving. In this study, we first examined the dose dependence of cocaine-induced DAT trafficking and hyperactivity in rats, demonstrating that cocaine at an intraperitoneal dose of 10 mg/kg or higher led to redistribution of most DAT to the plasma membrane while inducing significant hyperactivity in rats. However, administration of 5-mg/kg cocaine (ip) did not significantly induce DAT trafficking or hyperactivity in rats. So the threshold (intraperitoneal) dose of cocaine that can significantly induce DAT trafficking or hyperactivity should be between 5 and 10 mg/kg. These data suggest that when a cocaine dose is high enough to induce significant hyperactivity, it can also significantly induce DAT trafficking to the plasma membrane. Further, the threshold brain cocaine concentration required to induce significant hyperactivity and DAT trafficking was estimated to be ~2.0 ± 0.8 µg/g. Particularly, for treatment of cocaine abuse, previous studies demonstrated that an exogenous cocaine-metabolizing enzyme, for example, CocH3-Fc(M3), can effectively block cocaine-induced hyperactivity. However, it was unknown whether an enzyme could also effectively block cocaine-induced DAT trafficking to the plasma membrane. This study demonstrates, for the first time, that the enzyme is also capable of effectively blocking cocaine from reaching the brain even with a lethal dose of 60-mg/kg cocaine (ip) and, thus, powerfully preventing cocaine-induced physiological effects such as the hyperactivity and DAT trafficking.

Recovery of dopaminergic system after cocaine exposure and impact of a long-acting cocaine hydrolase.

Dysregulation of dopamine transporters (DAT) within the dopaminergic system is an important biomarker of cocaine exposure. Depending on cocaine amount in-taken, one-time exposure in rats could lead to most (>95% of total) of DAT translocating to plasma membrane of the dopaminergic neurons compared to normal DAT distribution (~5.7% on the plasma membrane). Without further cocaine exposure, the time course of striatal DAT distribution, in terms of intracellular and plasma membrane fractions of DAT, represents a recovery process of the dopaminergic system. In this study, we demonstrated that after an acute cocaine exposure of 20 mg/kg (i.p.), the initial recovery process from days 1 to 15 in rats was relatively faster (from >95% on day 1 to ~35.4% on day 15). However, complete recovery of the striatal DAT distribution may take about 60 days. In another situation, with repeated cocaine exposures for once every other day for a total of 17 doses of 20 mg/kg cocaine (i.p.) from days 0 to 32, the complete recovery of striatal DAT distribution may take an even longer time (about 90 days), which represents a consequence of chronic cocaine use. Further, we demonstrated that a highly efficient Fc-fused cocaine hydrolase, CocH5-Fc(M6), effectively blocked cocaine-induced hyperactivity and DAT trafficking with repeated cocaine exposures by maintaining a plasma CocH5-Fc(M6) concentration ≥58.7 ± 2.9 nM in rats. The cocaine hydrolase protected dopaminergic system and helped the cocaine-altered DAT distribution to recover by preventing the dopaminergic system from further damage by cocaine.

Gender differences in cocaine-induced hyperactivity and dopamine transporter trafficking to the plasma membrane.

As well known, cocaine induces stimulant effects and dopamine transporter (DAT) trafficking to the plasma membrane of dopaminergic neurons. In the present study, we examined cocaine-induced hyperactivity along with cocaine-induced DAT trafficking and the recovery rate of the dopaminergic system in female rats in comparison with male rats, demonstrating interesting gender differences. Female rats are initially more sensitive to cocaine than male rats in terms of both the DAT trafficking and hyperactivity induced by cocaine. Particularly, intraperitoneal (i.p.) administration of 5 mg/kg cocaine induced significant hyperactivity and DAT trafficking in female rats but not in male rats. After repeated cocaine exposures (i.e., i.p. administration of 20 mg/kg cocaine every other day from Day 0 to Day 32), cocaine-induced hyperactivity in female rats gradually became a clear pattern of two phases, with the first phase of the hyperactivity lasting for only a few minutes and the second phase lasting for over an hour beginning at ~30 min, which is clearly different from that of male rats. It has also been demonstrated that the striatal DAT distribution of female rats may recover faster than that of male rats after multiple cocaine exposures. Nevertheless, despite the remarkable gender differences, our recently developed long-acting cocaine hydrolase, known as CocH5-Fc(M6), can similarly and effectively block cocaine-induced DAT trafficking and hyperactivity in both male and female rats.

In vitro and in vivo stability of a highly efficient long-acting cocaine hydrolase.

It is recognized as a promising therapeutic strategy for cocaine use disorder to develop an efficient enzyme which can rapidly convert cocaine to physiologically inactive metabolites. We have designed and discovered a series of highly efficient cocaine hydrolases, including CocH5-Fc(M6) which is the currently known as the most efficient cocaine hydrolase with both the highest catalytic activity against (-)-cocaine and the longest biological half-life in rats. In the present study, we characterized the time courses of protein appearance, pH, structural integrity, and catalytic activity against cocaine in vitro and in vivo of a CocH5-Fc(M6) bulk drug substance produced in a bioreactor for its in vitro and in vivo stability after long-time storage under various temperatures (- 80, - 20, 4, 25, or 37 °C). Specifically, all the tested properties of the CocH5-Fc(M6) protein did not significantly change after the protein was stored at any of four temperatures including - 80, - 20, 4, and 25 °C for ~ 18 months. In comparison, at 37 °C, the protein was less stable, with a half-life of ~ 82 days for cocaine hydrolysis activity. Additionally, the in vivo studies further confirmed the linear elimination PK profile of CocH5-Fc(M6) with an elimination half-life of ~ 9 days. All the in vitro and in vivo data on the efficacy and stability of CocH5-Fc(M6) have consistently demonstrated that CocH5-Fc(M6) has the desired in vitro and in vivo stability as a promising therapeutic candidate for treatment of cocaine use disorder.

Catalytic activities of a highly efficient cocaine hydrolase for hydrolysis of biologically active cocaine metabolites norcocaine and benzoylecgonine.

Cocaine is a widely abused, hepatotoxic drug without an FDA-approved pharmacotherapy specific for cocaine addiction or overdose. It is recognized as a promising therapeutic strategy to accelerate cocaine metabolism which can convert cocaine to pharmacologically inactive metabolite(s) using an efficient cocaine-metabolizing enzyme. Our previous studies have successfully designed and discovered a highly efficient cocaine hydrolase, denoted as CocH5-Fc(M6), capable of rapidly hydrolyzing cocaine at the benzoyl ester moiety. In the present study, we determined the kinetic parameters of CocH5-Fc(M6) against norcocaine (kcat = 9,210 min-1, KM = 20.9 µM, and kcat/KM = 1.87 × 105 min-1 M-1) and benzoylecgonine (kcat = 158 min-1, KM = 286 µM, and kcat/KM = 5.5 × 105 min-1 M-1) for the first time. Further in vivo studies have demonstrated that CocH5-Fc(M6) can effectively accelerate clearance of not only cocaine, but also norcocaine (known as a cocaine metabolite which is more toxic than cocaine itself) and benzoylecgonine (known as an unfavorable long-lasting metabolite with some long-term toxicity concerns) in rats. Due to the desired high catalytic activity against norcocaine, CocH5-Fc(M6) is capable of quickly detoxifying both cocaine and its more toxic metabolite norcocaine after intraperitoneally administering lethal dose of 60 or 180 mg/kg cocaine. In addition, the ability of CocH5-Fc(M6) to accelerate clearance of benzoylecgonine should also be valuable for the use of CocH5-Fc(M6) in treatment of cocaine use disorder.

Effects of alcohol on metabolism and toxicity of cocaine in rats.

As most cocaine users drink alcohol, it is interesting to understand how a non-lethal dose of alcohol affects the metabolism and toxicity of cocaine. In this study, we examined the correlation between dose-dependent toxicity and the metabolism/pharmacokinetic (PK) profile of cocaine with or without alcohol (ethanol, 1 g/kg) co-administration in rats. The cocaine toxicity in rats with or without alcohol co-administration is characterized by not only the commonly used LD50, but also the average times for the appearance of convulsion and death as well as total toxicity level (TTL) in the blood. All these data have consistently demonstrated that co-administration of alcohol increased cocaine toxicity, and that the alcohol-enhanced toxicity of cocaine is mainly attributed to the observed two additional metabolites (cocaethylene and norcocaethylene - products of chemical reactions of cocaine with alcohol catalyzed by metabolic enzymes carboxylesterase-1 and liver microsomal cytochrome P450 3A4) that are more toxic than cocaine itself. So, evaluation of the substance TTL should account for the blood levels of not only cocaine itself, but also its all toxic metabolites. In addition, for rats died of a lethal dose of cocaine (60 or 100 mg/kg) combined with 1 g/kg alcohol, we also determined the TTL at the time of death, demonstrating that death would occur once the TTL reached a threshold (~16 µM).

Effects of Cebranopadol on Cocaine-induced Hyperactivity and Cocaine Pharmacokinetics in Rats.

Cebranopadol is known as a highly potent analgesic. Recent studies also demonstrated that administration of cebranopadol significantly decreased cocaine self-administration and significantly reduced cue-induced cocaine-seeking behaviors in rats. However, it was unclear whether these interesting behavioral observations are related to any potential effects of cebranopadol on cocaine pharmacokinetics or cocaine-induced hyperactivity. In principle, a promising therapeutic candidate for cocaine dependence treatment may alter the cocaine pharmacokinetics and/or attenuate cocaine-induced reward and hyperactivity and, thus, decrease cocaine self-administration and reduce cue-induced cocaine-seeking behaviors. In this study, we examined possible effects of cebranopadol on cocaine pharmacokinetics and cocaine-induced hyperactivity for the first time. According to our animal data in rats, cebranopadol did not significantly alter the pharmacokinetics of cocaine. According to our more extensive locomotor activity testing data, cebranopadol itself also dose-dependently induced hyperactivity in rats at doses higher than 50 µg/kg. Cebranopadol at a low dose of 25 µg/kg (p.o.) did not induce significant hyperactivity itself, but significantly potentiated cocaine-induced hyperactivity on Days 4 to 7 after the repeated daily dosing of the drug.

In vivo characterization of toxicity of norcocaethylene and norcocaine identified as the most toxic cocaine metabolites in male mice.

BACKGROUND: Majority of cocaine users also consume alcohol, and concurrent use of cocaine and alcohol produces cocaethylene, norcocaine, norcocaethylene, and other non-toxic metabolites. It is essential to know their relative toxicity for development of a truly effective therapeutics for cocaine toxicity treatment. METHODS: Drug (norcocaethylene or norcocaine)-induced acute toxicity was characterized by the occurrence (and the timing) of prostration, seizure, and death after intraperitoneal administration of the drug (n = 15) using the same strain (Swiss Webster) of male mice reported in previous study by Hearn et al. to determine LD50 of cocaine and cocaethylene. In addition, drug (cocaine, cocaethylene, norcocaine, or norcocaethylene)-induced hyperactivity was determined by locomotor activity testing (n = 8). RESULTS: According to the animal data, norcocaethylene (LD50=∼39.4 mg/kg) and norcocaine (LD50=∼49.7 mg/kg) are the most toxic metabolites, but they do not induce significant hyperactivity. In addition, the relative toxicity of drugs correlates with the time to the occurrence of prostration/seizure/death after the drug administration. CONCLUSIONS: The relative toxicity of these toxic drugs can be ranked in this order: norcocaethylene > norcocaine > cocaethylene > cocaine. The data suggest that norcocaethylene, norcocaine, and cocaethylene are all significant contributors to acute toxicity of cocaine in concurrent use of cocaine and alcohol. Hence, future therapeutic development for cocaine toxicity treatment must account for detoxification of these more toxic metabolites. In addition, the relative toxicity of different drugs correlates with the average time to the occurrence of death, seizure, or prostration after the drug administration with a same dose close to their LD50 values.

Reengineering of Albumin-Fused Cocaine Hydrolase CocH1 (TV-1380) to Prolong Its Biological Half-Life.

Therapeutic treatment of cocaine toxicity or addiction is a grand medical challenge. As a promising therapeutic strategy for treatment of cocaine toxicity and addiction to develop a highly efficient cocaine hydrolase (CocH) capable of accelerating cocaine metabolism to produce physiologically/biologically inactive metabolites, our previously designed A199S/S287G/A328W/Y332G mutant of human butyrylcholinesterase (BChE), known as cocaine hydrolase-1 (CocH1), possesses the desirably high catalytic activity against cocaine. The C-terminus of CocH1, truncated after amino acid #529, was fused to human serum albumin (HSA) to extend the biological half-life. The C-terminal HSA-fused CocH1 (CocH1-HSA), known as Albu-CocH1, Albu-CocH, AlbuBChE, Albu-BChE, or TV-1380 in literature, has shown favorable preclinical and clinical profiles. However, the actual therapeutic value of TV-1380 for cocaine addiction treatment is still limited by the short half-life. In this study, we designed and tested a new type of HSA-fused CocH1 proteins, i.e., N-terminal HSA-fused CocH1, with or without a linker between the HSA and CocH1 domains. It has been demonstrated that the catalytic activity of these new fusion proteins against cocaine is similar to that of TV-1380. However, HSA-CocH1 (without a linker) has a significantly longer biological half-life (t1/2 = 14 ± 2 h) compared to the corresponding C-terminal HSA-fused CocH1, i.e., CocH1-HSA (TV-1380 with t1/2 = 5-8 h), in rats. Further, the N-terminal HSA-fused CocH1 proteins with a linker have further prolonged biological half-lives: t1/2 = 17 ± 2 h for both HSA-EAAAK-CocH1 and HSA-PAPAP-CocH1, and t1/2 = 18 ± 3 h for HSA-(PAPAP)2-CocH1. These N-terminal HSA-fused CocH1 proteins may serve as more promising protein drug candidates for cocaine addiction treatment.