Computational redesign of human butyrylcholinesterase for anticocaine medication

New insights into butyrylcholinesterase: Pharmaceutical applications, selective inhibitors and multitarget-directed ligands

Butyrylcholinesterase (BChE), also known as pseudocholinesterase and serum cholinesterase, is an isoenzyme of acetylcholinesterase (AChE). It mediates the degradation of acetylcholine, especially under pathological conditions. Proverbial pharmacological applications of BChE, its mutants and modulators consist of combating Alzheimer's disease (AD), influencing multiple sclerosis (MS), addressing cocaine addiction, detoxifying organophosphorus poisoning and reflecting the progression or prognosis of some diseases. Of interest, recent reports have shed light on the relationship between BChE and lipid metabolism. It has also been proved that BChE is going to increase abnormally as a compensator for AChE in the middle and late stages of AD, and BChE inhibitors can alleviate cognitive disorders and positively influence some pathological features in AD model animals, foreboding favorable prospects and potential applications. Herein, the selective BChE inhibitors and BChE-related multitarget-directed ligands published in the last three years were briefly summarized, along with the currently known pharmacological applications of BChE, aiming to grasp the latest research directions. Thereinto, some emerging strategies for designing BChE inhibitors are intriguing, and the modulators based on target combination of histone deacetylase and BChE against AD is unprecedented. Furthermore, the involvement of BChE in the hydrolysis of ghrelin, the inhibition of low-density lipoprotein (LDL) uptake, and the down-regulation of LDL receptor (LDLR) expression suggests its potential to influence lipid metabolism disorders. This compelling prospect likely stimulates further exploration in this promising research direction.

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.

Long-lasting blocking of interoceptive effects of cocaine by a highly efficient cocaine hydrolase in rats

Cocaine dependence is a serious world-wide public health problem without an FDA-approved pharmacotherapy. We recently designed and discovered a highly efficient long-acting cocaine hydrolase CocH5-Fc(M6). The present study examined the effectiveness and duration of CocH5-Fc(M6) in blocking interoceptive effects of cocaine by performing cocaine discrimination tests in rats, demonstrating that the duration of CocH5-Fc(M6) in blocking cocaine discrimination was dependent on cocaine dose and CocH5-Fc(M6) plasma concentration. Particularly, a dose of 3 mg/kg CocH5-Fc(M6) effectively attenuated discriminative stimulus effects of 10 mg/kg cocaine, cumulative doses of 10 and 32 mg/kg cocaine, and cumulative doses of 10, 32 and 56 mg/kg cocaine by ≥ 20% for 41, 19, and 10 days, and completely blocked the discriminative stimulus effects for 30, 13, and 5 days with corresponding threshold plasma CocH5-Fc(M6) concentrations of 15.9, 72.2, and 221 nM, respectively, under which blood cocaine concentration was negligible. Additionally, based on the data obtained, cocaine discrimination model is more sensitive than the locomotor activity to reveal cocaine effects and that CocH5-Fc(M6) itself has no long-term toxicity regarding behavioral activities such as lever pressing and food consumption in rats, further demonstrating that CocH5-Fc(M6) has the desired properties as a promising therapeutic candidate for prevenance of cocaine dependence.

Human Butyrylcholinesterase Mutants for (-)-Cocaine Hydrolysis: A Correlation Relationship between Catalytic Efficiency and Total Hydrogen Bonding Energy with an Oxyanion Hole

A combined computational and experimental study has been carried out to explore and test a quantitative correlation relationship between the relative catalytic efficiency (RCE) of human butyrylcholinesrase (BChE) mutant-catalyzed hydrolysis of substrate (-)-cocaine and the total hydrogen bonding energy (tHBE) of the carbonyl oxygen of the substrate with the oxyanion hole of the enzyme in the modeled transition-state structure (TS1), demonstrating a satisfactory linear correlation relationship between ln(RCE) and tHBE. The satisfactory correlation relationship has led us to computationally predict and experimentally confirm new human BChE mutants that have a further improved catalytic activity against (-)-cocaine, including the most active one (the A199S/F227S/S287G/A328W/Y332G mutant) with a 2790-fold improved catalytic efficiency (kcat/KM = 2.5 × 109 min-1 M-1) compared to the wild-type human BChE. Compared to the reference mutant (the A199S/S287G/A328W/Y332G mutant) tested in the reported clinical development of an enzyme therapy for cocaine dependence treatment, this new mutant (with a newly predicted additional F227S mutation) has an improved catalytic efficiency against (-)-cocaine by ∼2.6-fold. The good agreement between the computational and experimental ln(RCE) values suggests that the obtained correlation relationship is robust for computational prediction. A similar correlation relationship could also be explored in studying BChE or other serine hydrolases/esterases with an oxyanion hole stabilizing the carbonyl oxygen in the rate-determining reaction step of the enzymatic hydrolysis of other substrates.

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 (k_cat = 9,210 min^-1, K_M = 20.9 μM, and k_cat/K_M = 1.87 × 10⁵ min^-1 M^-1) and benzoylecgonine (k_cat = 158 min^-1, K_M = 286 μM, and k_cat/K_M = 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.

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.

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 (t_1/2 = 8 h in rats, associated with t_1/2 = 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 (t_1/2 = 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.

Pharmacokinetic Approach to Combat the Synthetic Cannabinoid PB-22

Synthetic cannabinoids are part of a group of drugs called new psychoactive substances. Most of these cannabinoids are unregulated, and there are no therapeutic treatments for their addictive properties or reversing a potential overdose. Vaccination and catalytic antibodies strategies were investigated to assess their ability to blunt the psychoactive properties of the cannabinoid PB-22. To complement these antibody concentric investigations, we also disclose the discovery of the enzymatic degradation of this cannabinoid. Serum factors including albumin and carboxylesterase were found to catalyze the hydrolysis of PB-22. Affinity, kinetics, animal behavior, and biodistribution studies were utilized to evaluate the efficiency of these pharmacokinetic approaches. Our findings suggest simple antibody binding as the most efficacious means for altering PB-22's effect on the brain. Catalytic approaches only translated to esterases being capable of PB-22's degradation with a catalytic antibody approach providing no proclivity for PB-22's hydrolysis. Pharmacokinetic approaches provide a powerful strategy for treating substance abuse disorders and overdose for drugs where no therapeutic is available.

A Genetically Modified Skin Graft for Treating Alcohol Use Disorder and/or Polysubstance Abuse With Cocaine

Alcohol use disorder (AUD) is one of the foremost public health problems. Alcohol is also frequently co-abused with cocaine. There is a huge unmet need for the treatment of AUD and/or cocaine co-abuse. We have developed and used a skin stem cell-based gene delivery platform and found that production of the glucagon-like peptide-1 (GLP1) from the grafted genetically modified skin reduced development and reinstatement of alcohol-induced drug-taking and seeking, voluntary oral alcohol consumption and alcohol-induced increase in dopamine (DA) levels in the nucleus accumbens (NAc). Moreover, we have developed a novel co-grafting procedure for both modified human butyrylcholinesterase (hBChE)- and GLP1-expressing cells. Skin grafts-derived hBChE and GLP1 reduced acquisition of drug-taking and toxicity induced by concurrent alcohol and cocaine injections. These results imply that gene delivery through skin transplants may add a new option to treat drug abuse and co-abuse.

A Comprehensive Review of Cholinesterase Modeling and Simulation

The present article reviews published efforts to study acetylcholinesterase and butyrylcholinesterase structure and function using computer-based modeling and simulation techniques. Structures and models of both enzymes from various organisms, including rays, mice, and humans, are discussed to highlight key structural similarities in the active site gorges of the two enzymes, such as flexibility, binding site location, and function, as well as differences, such as gorge volume and binding site residue composition. Catalytic studies are also described, with an emphasis on the mechanism of acetylcholine hydrolysis by each enzyme and novel mutants that increase catalytic efficiency. The inhibitory activities of myriad compounds have been computationally assessed, primarily through Monte Carlo-based docking calculations and molecular dynamics simulations. Pharmaceutical compounds examined herein include FDA-approved therapeutics and their derivatives, as well as several other prescription drug derivatives. Cholinesterase interactions with both narcotics and organophosphate compounds are discussed, with the latter focusing primarily on molecular recognition studies of potential therapeutic value and on improving our understanding of the reactivation of cholinesterases that are bound to toxins. This review also explores the inhibitory properties of several other organic and biological moieties, as well as advancements in virtual screening methodologies with respect to these enzymes.

Reducing alcohol and/or cocaine-induced reward and toxicity via an epidermal stem cell-based gene delivery platform

Alcohol use disorder (AUD) is one of the foremost public health problems. Alcohol is also frequently co-abused with cocaine. There is a huge unmet need for the treatment of AUD and/or cocaine co-abuse. We recently demonstrated that skin grafts generated from mouse epidermal stem cells that had been engineered by CRISPR-mediated genome editing could be transplanted onto mice as a gene delivery platform. Here, we show that expression of the glucagon-like peptide-1 (GLP1) gene delivered by epidermal stem cells attenuated development and reinstatement of alcohol-induced drug-taking and seeking as well as voluntary oral alcohol consumption. GLP1 derived from the skin grafts decreased alcohol-induced increase in dopamine levels in the nucleus accumbens. In exploring the potential of this platform in reducing concurrent use of drugs, we developed a novel co-grafting procedure for both modified human butyrylcholinesterase (hBChE)- and GLP1-expressing cells. Epidermal stem cell-derived hBChE and GLP1 reduced acquisition of drug-taking and toxicity induced by alcohol and cocaine co-administration. These results imply that cutaneous gene delivery through skin transplants may add a new option to treat drug abuse and co-abuse.

Structure and therapeutic uses of butyrylcholinesterase: Application in detoxification, Alzheimer's disease, and fat metabolism

Structural information of butyrylcholinesterase (BChE) and its variants associated with several diseases are discussed here. Pure human BChE has been proved safe and effective in treating organophosphorus (OPs) poisoning and has completed Phase 1 and 2 pharmacokinetic (PK) and safety studies. The introduction of specific mutations into native BChE to endow it a self-reactivating property has gained much progress in producing effective OPs hydrolases. The hydrolysis ability of native BChE on cocaine has been confirmed but was blocked to clinical application due to poor PK properties. Several BChE mutants with elevated cocaine hydrolysis activity were published, some of which have shown safety and efficiency in treating cocaine addiction of human. The increased level of BChE in progressed Alzheimer's disease patients made it a promising target to elevate acetylcholine level and attenuate cognitive status. A variety of selective BChE inhibitors with high inhibitory activity published in recent years are reviewed here. BChE could influence the weight and insulin secretion and resistance of BChE knockout (KO) mice through hydrolyzing ghrelin. The BChE-ghrelin pathway could also regulate aggressive behaviors of BChE-KO mice.

A plant-derived cocaine hydrolase prevents cocaine overdose lethality and attenuates cocaine-induced drug seeking behavior

Cocaine use disorders include short-term and acute pathologies (e.g. overdose) and long-term and chronic disorders (e.g. intractable addiction and post-abstinence relapse). There is currently no available treatment that can effectively reduce morbidity and mortality associated with cocaine overdose or that can effectively prevent relapse in recovering addicts. One recently developed approach to treat these problems is the use of enzymes that rapidly break down the active cocaine molecule into inactive metabolites. In particular, rational design and site-directed mutagenesis transformed human serum recombinant butyrylcholinesterase (BChE) into a highly efficient cocaine hydrolase with drastically improved catalytic efficiency toward (-)-cocaine. A current drawback preventing the clinical application of this promising enzyme-based therapy is the lack of a cost-effective production strategy that is also flexible enough to rapidly scale-up in response to continuous improvements in enzyme design. Plant-based expression systems provide a unique solution as this platform is designed for fast scalability, low cost and the advantage of performing eukaryotic protein modifications such as glycosylation. A Plant-derived form of the Cocaine Super Hydrolase (A199S/F227A/S287G/A328W/Y332G) we designate PCocSH protects mice from cocaine overdose, counters the lethal effects of acute cocaine overdose, and prevents reinstatement of extinguished drug-seeking behavior in mice that underwent place conditioning with cocaine. These results demonstrate that the novel PCocSH enzyme may well serve as an effective therapeutic for cocaine use disorders in a clinical setting.

Clinical potential of a rationally engineered enzyme for treatment of cocaine dependence: Long-lasting blocking of the psychostimulant, discriminative stimulus, and reinforcing effects of cocaine

It is a grand challenge to develop a truly effective treatment of substance use disorder (SUD), particularly for cocaine and other drugs without an FDA-approved treatment available, because a truly effective therapy must effectively block the drug's physiological and reinforcing effects during the entire period of treatment in order to achieve the long-time abstinence required by the FDA. Whether a biologic, such as monoclonal antibody, vaccine, or therapeutic enzyme, can be truly effective for SUD treatment or not has been the subject of extensive debate. The main debate question is whether a biologic, particularly an exogenous enzyme, can effectively block the drug's reinforcing effect. In this report, we demonstrate that a modest dose of a recently redesigned long-acting cocaine hydrolase, CocH3-Fc(M6), can be used to effectively block the psychostimulant, discriminative stimulus, and reinforcing effects of cocaine for a sufficiently long period of time. For example, a dose of 3 mg/kg CocH3-Fc(M6) completely blocked the discriminative stimulus and reinforcing effects for 24/25 days and continued to significantly attenuate/decrease the cocaine effects for at least 29 days in rats. All the animal data consistently suggest that the long-acting cocaine hydrolase is a truly promising candidate of enzyme therapy for treatment of cocaine use disorder.

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.

Structure-Based Design and Discovery of a Long-Acting Cocaine Hydrolase Mutant with Improved Binding Affinity to Neonatal Fc Receptor for Treatment of Cocaine Abuse

Despite decades of efforts to develop a pharmacotherapy for cocaine abuse treatment, there is still no FDA-approved treatment of diseases associated with this commonly abused drug. Our previously designed highly efficient cocaine hydrolases (CocHs) and the corresponding Fc-fusion proteins (e.g., CocH3-Fc) are recognized as potentially promising therapeutic enzyme candidates for cocaine abuse treatment, but all with limited biological half-lives. In order to prolong the biological half-life and, thus, decrease the required frequency of the enzyme administration for cocaine abuse treatment, we have modeled the Fc-fusion CocH binding with neonatal Fc receptor (FcRn) in the present study. This approach led to the design and testing of CocH3-Fc(M6), a CocH3-Fc mutant with nearly 100-fold increased binding affinity: from K_d = ~ 4 μM to K_d = 43 nM. As a result, CocH3-Fc(M6) indeed revealed a markedly prolonged biological half-life (t_1/2 = 206 ± 7 h or ~ 9 days) in rats, longer than other known Fc-fusion protein drugs such as abatacept and alefacept (for other therapeutic purposes) in the same species (rats). It has been demonstrated that a single dose of 3 mg/kg CocH3-Fc(M6) effectively blocked 20 mg/kg cocaine-induced hyperactivity on day 18 after CocH3-Fc(M6) administration. This is the first attempt to rationally design long-acting Fc-fusion enzyme mutant based on combined computational modeling and experimental measurement of the Fc-fusion CocH binding with FcRn. The similar structure-based design strategy may be used to prolong the biological half-lives of other Fc-fusion protein drugs.

Catalytic activities of cocaine hydrolases against the most toxic cocaine metabolite norcocaethylene

A majority of cocaine users also consume alcohol. The concurrent use of cocaine and alcohol produces the pharmacologically active metabolites cocaethylene and norcocaethylene, in addition to norcocaine. Both cocaethylene and norcocaethylene are more toxic than cocaine itself. Hence, a truly valuable cocaine-metabolizing enzyme for cocaine abuse/overdose treatment should be effective for the hydrolysis of not only cocaine, but also its metabolites norcocaine, cocaethylene, and norcocaethylene. However, there has been no report on enzymes capable of hydrolyzing norcocaethylene (the most toxic metabolite of cocaine). The catalytic efficiency parameters (kcat and KM) of human butyrylcholinesterase (BChE) and two mutants (known as cocaine hydrolases E14-3 and E12-7) against norcocaethylene have been characterized in the present study for the first time, and they are compared with those against cocaine. According to the obtained kinetic data, wild-type human BChE showed a similar catalytic efficiency against norcocaethylene (kcat = 9.5 min-1, KM = 11.7 μM, and kcat/KM = 8.12 × 105 M-1 min-1) to that against (-)-cocaine (kcat = 4.1 min-1, KM = 4.5 μM, and kcat/KM = 9.1 × 105 M-1 min-1). E14-3 and E12-7 showed an improved catalytic activity against norcocaethylene compared to wild-type BChE. E12-7 showed a 39-fold improved catalytic efficiency against norcocaethylene (kcat = 210 min-1, KM = 6.6 μM, and kcat/KM = 3.18 × 107 M-1 min-1). It has been demonstrated that E12-7 as an exogenous enzyme can efficiently metabolize norcocaethylene in rats.

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 (t_1/2 = 14 ± 2 h) compared to the corresponding C-terminal HSA-fused CocH1, i.e., CocH1-HSA (TV-1380 with t_1/2 = 5-8 h), in rats. Further, the N-terminal HSA-fused CocH1 proteins with a linker have further prolonged biological half-lives: t_1/2 = 17 ± 2 h for both HSA-EAAAK-CocH1 and HSA-PAPAP-CocH1, and t_1/2 = 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.

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.

Evaluation of the cholinesterase activity of a potential therapeutic cocaine esterase for cocaine overdose

BACKGROUND

Cocaine is a commonly abused drug and there is no approved medication specifically to treat its addiction or overdose. Bacterial cocaine esterase (CocE)-derived RBP-8000 is currently under clinical development for cocaine overdose treatment. It is proven to be effective for human use to accelerate cocaine metabolism into physiologically inactive products. Besides cocaine, RBP-8000 may hydrolyze the neurotransmitter acetylcholine (ACh), however, no study has reported its cholinesterase activity. The present study aims to examine RBP-8000's cholinesterase activity and substrate selectivity to address the potential concern that this enzyme therapy might produce cholinergic side-effects.

METHODS

Both computational modeling and experimental kinetic analysis were carried out to characterize the potential cholinesterase activity of RBP-8000. Substrates interacting with RBP-8000 were modeled for their enzyme-substrate binding complexes. In vitro enzymatic kinetic parameters were measured using Ellman's colorimetric assay and analyzed by Michaelis-Menten kinetics.

RESULTS

It is the first demonstration that RBP-8000 catalyzes the hydrolysis of acetylthiocholine (ATC). However, its catalytic efficiency (k_cat/K_M) against ATC is 1000-fold and 5000-fold lower than it against cocaine at 25 °C and 37 °C, respectively, suggesting RBP-8000 has the desired substrate selectivity for cocaine over ACh.

CONCLUSION

Given the fact that clinically relevant dose of RBP-8000 displays insignificant cholinesterase activity relative to endogenous cholinesterases in human, administration of RBP-8000 is unlikely to produce any significant cholinergic side-effects. This study provides supplemental evidences in support of further development of RBP-8000 towards a clinically used pharmacotherapy for cocaine overdose.

Engineering Dynamic Surface Peptide Networks on ButyrylcholinesteraseG117H for Enhanced Organophosphosphorus Anticholinesterase Catalysis

The single residue mutation of butyrylcholinesterase (BChE_G117H) hydrolyzes a number of organophosphosphorus (OP) anticholinesterases. Whereas other BChE active site/proximal mutations have been investigated, none are sufficiently active to be prophylactically useful. In a fundamentally different computer simulations driven strategy, we identified a surface peptide loop (residues 278-285) exhibiting dynamic motions during catalysis and modified it via residue insertions. We evaluated these loop mutants using computer simulations, substrate kinetics, resistance to inhibition, and enzyme reactivation assays using both the choline ester and OP substrates. A slight but significant increase in reactivation was noted with paraoxon with one of the mutants, and changes in K_M and catalytic efficiency were noted in others. Simulations suggested weaker interactions between OP versus choline substrates and the active site of all engineered versions of the enzyme. The results indicate that an improvement of OP anticholinesterase hydrolysis through surface loop engineering may be a more effective strategy in an enzyme with higher intrinsic OP compound hydrolase activity.

Dimerization of human butyrylcholinesterase expressed in bacterium for development of a thermally stable bioscavenger of organophosphorus compounds

Human butyrylcholinesterase (BChE) is a widely distributed plasma enzyme. For decades, numerous research efforts have been directed at engineering BChE as a bioscavenger of organophosphorus insecticides and chemical warfare nerve agents. However, it has been a grand challenge to cost-efficiently produce BChE in large-scale. Recently reported studies have successfully designed a truncated BChE mutant (with amino-acid substitutions on 47 residues that are far away from the catalytic site), denoted as BChE-M47 for convenience, which can be expressed in E. coli without loss of its catalytic activity. In this study, we aimed to dimerize the truncated BChE mutant protein expressed in a prokaryotic system (E. coli) in order to further improve its thermal stability by introducing a pair of cross-subunit disulfide bonds to the BChE-M47 structure. Specifically, the E377C/A516C mutations were designed and introduced to BChE-M47, and the obtained new protein entity, denoted as BChE-M48, with a pair of cross-subunit disulfide bonds indeed exists as a dimer with significantly improved thermostability and unaltered catalytic activity and reactivity compared to BChE-M47. These results provide a new strategy for optimizing protein stability for production in a cost-efficient prokaryotic system. Our enzyme, BChE-M48, has a half-life of almost one week at a 37°C, suggesting that it could be utilized as a highly stable bioscavenger of OP insecticides and chemical warfare nerve agents.

Development of a long-acting Fc-fused cocaine hydrolase with improved yield of protein expression

Human butyrylcholinesterase (BChE) is known as a safe and effective protein for detoxification of organophosphorus (OP) nerve agents. Its rationally designed mutants with considerably improved catalytic activity against cocaine, known as cocaine hydrolases (CocHs), are recognized as the most promising drug candidates for the treatment of cocaine abuse. However, it is a grand challenge to efficiently produce active recombinant BChE and CocHs with a sufficiently long biological half-life. In the present study, starting from a promising CocH, known as CocH3 (i.e. A199S/F227A/S287G/A328W/Y332G mutant of human BChE), which has a ~2000-fold improved catalytic activity against cocaine compared to wild-type BChE, we designed an N-terminal fusion protein, Fc(M3)-(PAPAP)₂-CocH3, which was constructed by fusing Fc of human IgG1 to the N-terminal of CocH3 and further optimized by inserting a linker between the two protein domains. Without lowering the enzyme activity, Fc(M3)-(PAPAP)₂-CocH3 expressed in Chinese hamster ovary (CHO) cells has not only a long biological half-life of 105 ± 7 h in rats, but also a high yield of protein expression. Particularly, Fc(M3)-(PAPAP)₂-CocH3 has a ~21-fold increased protein expression yield in CHO cells compared to CocH3 under the same experimental conditions. Given the observations that Fc(M3)-(PAPAP)₂-CocH3 has not only a high catalytic activity against cocaine and a long biological half-life, but also a high yield of protein expression, this new protein entity reported in this study would be a more promising candidate for therapeutic treatment of cocaine overdose and addiction.

Unexpected protonation state of Glu197 discovered from simulations of tacrine in butyrylcholinesterase

Butyrylcholinesterase (BChE) has been actively involved in drug discoveries from many fields for decades. In the crystal structure of the BChE-tacrine complex, there is an unanticipated formyl-proline molecule resolved very close to tacrine, raising an essential question on how reliable it is to apply the binding pose in a crystal structure to analyze related experimental observations, in which no formyl-proline is actually involved. In this study, by performing a series of 100 ns molecular dynamics simulations, we demonstrate that it is safe to employ the structural information from this crystal structure to analyze related experimental observations. Surprisingly, Glu197 needs to be protonated to have the structures simulated appropriately. It should be noted that Glu197 has been commonly considered as deprotonated in diverse analyses due to its low pKa in aqueous solution, for which some interpretations are inconsistent or unclear. Our further investigation shows that the protonated Glu197 plays a very important role in preserving His438 within the catalytic triad through stabilizing a highly conserved water molecule. Interestingly, the catalytic triad and Glu197 have been long recognized for possibly deviating largely from the crystal structure, which might be catalytically deficient and is generally considered to result from the difference between the crystal and aqueous environment. Herein, our results suggest that the large deviations of the catalytic triad and Glu197 from the crystal structure are caused by the inappropriate protonation state of Glu197. This finding shall provide an important clue that has been long missing for a better understanding of BChE-related puzzles or even reconsideration of some BChE-catalyzed reaction mechanisms.

Catalytic Reaction Mechanism for Drug Metabolism in Human Carboxylesterase-1: Cocaine Hydrolysis Pathway

Carboxylesterase-1 (CE-1) is a crucial enzyme responsible for metabolism/activation/inactivation of xenobiotics (therapeutic agents, prodrugs, abused drugs, and organophosphorus nerve agents etc.) and also involved in many other biological processes. In this study, we performed extensive computational modeling and simulations to understand the fundamental reaction mechanism of cocaine hydrolysis catalyzed by CE-1, revealing that CE-1-catalyzed cocaine hydrolysis follows a novel reaction pathway with only two reaction steps: a single-step acylation process and a single-step deacylation process. In the transition states of both single-step processes, the cocaine NH group joins the oxyanion hole to form an additional hydrogen bond with the negatively charged carbonyl oxygen atom of the cocaine. Thus, the transition states are stabilized by both intermolecular and intramolecular hydrogen bonds with the methyl ester of cocaine, specifically the carbonyl oxygen atom. The rate-limiting transition state is associated with the acylation process, and the activation free energy barrier was predicted to be 20.1 kcal/mol. Further, in vitro experimental kinetic analysis was performed for human CE-1-catalyzed cocaine hydrolysis. For CE-1-catalyzed cocaine hydrolysis, the computationally predicted free energy barrier (20.1 kcal/mol) is reasonably close to the experimentally derived turnover number ( k_cat = 0.058 min^-1), indicating the reasonability of the computational results. The obtained novel mechanistic insights are expected to benefit not only CE-1 related rational drug discovery but also future research on the catalytic mechanism of other esterases.

Kinetic characterization of cholinesterases and a therapeutically valuable cocaine hydrolase for their catalytic activities against heroin and its metabolite 6-monoacetylmorphine

As the most popularly abused one of opioids, heroin is actually a prodrug. In the body, heroin is hydrolyzed/activated to 6-monoacetylmorphine (6-MAM) first and then to morphine to produce its toxic and physiological effects. It has been known that heroin hydrolysis to 6-MAM and morphine is accelerated by cholinesterases, including acetylcholinesterase (AChE) and/or butyrylcholinesterase (BChE). However, there has been controversy over the specific catalytic activities and functional significance of the cholinesterases, which requires for the more careful kinetic characterization under the same experimental conditions. Here we report the kinetic characterization of AChE, BChE, and a therapeutically promising cocaine hydrolase (CocH1) for heroin and 6-MAM hydrolyses under the same experimental conditions. It has been demonstrated that AChE and BChE have similar k_cat values (2100 and 1840 min^-1, respectively) against heroin, but with a large difference in K_M (2170 and 120 μM, respectively). Both AChE and BChE can catalyze 6-MAM hydrolysis to morphine, with relatively lower catalytic efficiency compared to the heroin hydrolysis. CocH1 can also catalyze hydrolysis of heroin (k_cat = 2150 min^-1 and K_M = 245 μM) and 6-MAM (k_cat = 0.223 min^-1 and K_M = 292 μM), with relatively larger K_M values and lower catalytic efficiency compared to BChE. Notably, the K_M values of CocH1 against both heroin and 6-MAM are all much larger than previously reported maximum serum heroin and 6-MAM concentrations observed in heroin users, implying that the heroin use along with cocaine will not drastically affect the catalytic activity of CocH1 against cocaine in the CocH1-based enzyme therapy for cocaine abuse.

TV-1380 attenuates cocaine-induced changes in cardiodynamic parameters in monkeys and reduces the formation of cocaethylene

BACKGROUND

TV-1380 is a rationally mutated, human BChE fused to human serum albumin that has high hydrolytic enzymatic activity against cocaine and as well as an extended elimination half-life.

OBJECTIVE

The present studies examined the safety of TV-1380 and its protective effect when given to monkeys alone or concomitantly with cocaine and ethanol.

METHODS

A set of studies was conducted in monkeys with TV-1380. The parameters tested included telemetric assessment of cardiovascular parameters, clinical pathology, plasma analysis of cardiac troponin I, ex-vivo analyses of cocaethylene and PK analysis of serum concentrations of TV-1380, cocaine and its metabolites, and histopathological examinations.

RESULTS

TV-1380 treatment in monkeys was well tolerated. TV-1380 pretreatment prior to cocaine significantly attenuated the cardiac effects of cocaine and reduced cocaine-induced elevations in serum cardiac troponin I. TV-1380 changed the metabolic fate of cocaine resulting in decreased exposure to benzoylecgonine, while increasing the exposure to ecgonine methyl ester in plasma.TV-1380 reduced the plasma levels of the toxic metabolite cocaethylene formed after co-administration of ethanol and cocaine.

CONCLUSION

The results of this study demonstrate that TV-1380 not only accelerates the elimination of cocaine, but also protects the treated animal from the cardiac effects of cocaine, and inhibits the formation of the toxic cocaethylene metabolite when cocaine is given together with ethanol, supporting further clinical development of modified BChE products as possible treatments for cocaine abuse.

Development of Fc-Fused Cocaine Hydrolase for Cocaine Addiction Treatment: Catalytic and Pharmacokinetic Properties

Cocaine abuse is a worldwide public health and social problem without a US Food and Drug Administration (FDA)-approved medication. Accelerating cocaine metabolism that produces biologically inactive metabolites by administration of an efficient cocaine hydrolase (CocH) has been recognized as a promising strategy for cocaine abuse treatment. However, the therapeutic effects of CocH are limited by its short biological half-life (e.g., 8 h or shorter in rats). In this study, we designed and prepared a set of Fc-fusion proteins constructed by fusing Fc(M3) with CocH3 at the N-terminus of CocH3. A linker between the two protein domains was optimized to improve both the biological half-life and catalytic activity against cocaine. It has been concluded that Fc(M3)-G₆S-CocH3 not only has fully retained the catalytic efficiency of CocH3 against cocaine but also has the longest biological half-life (e.g., ∼ 136 h in rats) among all of the long-acting CocHs identified so far. A single dose (0.2 mg/kg, IV) of Fc(M3)-G₆S-CocH3 was able to significantly attenuate 15 mg/kg cocaine-induced hyperactivity for at least 11 days (268 h) after the Fc(M3)-G₆S-CocH3 administration.

Effectiveness of a Cocaine Hydrolase for Cocaine Toxicity Treatment in Male and Female Rats

Development of a truly effective medication for treatment of cocaine abuse has been a grand challenge. There is no FDA-approved therapeutic agent specific for cocaine addiction or overdose. An enzyme therapy using an efficient cocaine-metabolizing enzyme could be a promising treatment strategy for cocaine overdose and addiction. One of our previously designed cocaine hydrolases (CocHs), known as CocH1, was fused with human serum albumin (HSA) to prolong the biological half-life. The fusion protein CocH1-HSA is an investigational new drug (IND) approved by the FDA for clinical trials in cocaine addiction treatment, but not in cocaine overdose/toxicity treatment. In the present study, we aimed to evaluate the pharmacokinetic profile of CocH1-HSA and its effectiveness for cocaine toxicity treatment in male and female rats and demonstrate the clinical potential. The data demonstrate that enzyme CocH1-HSA has very similar pharmacokinetic profile in male and female rats. For both male and female rats, the enzyme can rapidly eliminate cocaine even if the cocaine dose is as high as 180 mg/kg (LD₁₀₀). Based on the animal data, whenever the enzyme is given to a living subject, the remaining cocaine in the body will be converted rapidly to physiologically inactive metabolites and, thus, reverse the cocaine toxicity and help the subject to recover. So, an enzyme therapy using CocH1-HSA can effectively treat cocaine toxicity and prevent the subject from further damage by cocaine. The data obtained clearly demonstrate the promising clinical potential of CocH1-HSA in cocaine overdose treatment for both genders.

Clinical Potential of an Enzyme-based Novel Therapy for Cocaine Overdose

It is a grand challenge to develop a truly effective medication for treatment of cocaine overdose. The current available, practical emergence treatment for cocaine overdose includes administration of a benzodiazepine anticonvulsant agent (e.g. diazepam) and/or physical cooling with an aim to relieve the symptoms. The inherent difficulties of antagonizing physiological effects of drugs in the central nervous system have led to exploring protein-based pharmacokinetic approaches using biologics like vaccines, monoclonal antibodies, and enzymes. However, none of the pharmacokinetic agents has demonstrated convincing preclinical evidence of clinical potential for drug overdose treatment without a question mark on the timing used in the animal models. Here we report the use of animal models, including locomotor activity, protection, and rescue experiments in rats, of drug toxicity treatment with clinically relevant timing for the first time. It has been demonstrated that an efficient cocaine-metabolizing enzyme developed in our previous studies can rapidly reverse the cocaine toxicity whenever the enzyme is given to a living rat, demonstrating promising clinical potential of an enzyme-based novel therapy for cocaine overdose as a successful example in comparison with the commonly used diazepam.

Computational Design of Protein Function

The computational design of enzymes is a tremendous challenge for both chemistry and biochemistry. The ability to design stable and functional biocatalysts that could operate under different conditions to perform chemical reactions without precedent in nature, allowing the large-scale production of chemicals à la carte, would revolutionise both synthetic, pharmacologic and materials chemistry. Despite the great advances achieved, this highly multidisciplinary area of research is still in its infancy. This chapter describes the ‘inside-out’ protocol for computational enzyme design and both the achievements and limitations of the current technology are highlighted. Furthermore, molecular dynamics simulations have proved to be invaluable in the enzyme design process, constituting an important tool for discovering elusive catalytically relevant conformations of the engineered or designed enzyme. As a complement to the ‘inside-out’ design protocol, different examples where hybrid QM/MM approaches have been directly applied to discover beneficial mutations in rational computational enzyme design are described.

Plant-expressed cocaine hydrolase variants of butyrylcholinesterase exhibit altered allosteric effects of cholinesterase activity and increased inhibitor sensitivity

Butyrylcholinesterase (BChE) is an enzyme with broad substrate and ligand specificities and may function as a generalized bioscavenger by binding and/or hydrolyzing various xenobiotic agents and toxicants, many of which target the central and peripheral nervous systems. Variants of BChE were rationally designed to increase the enzyme’s ability to hydrolyze the psychoactive enantiomer of cocaine. These variants were cloned, and then expressed using the magnICON transient expression system in plants and their enzymatic properties were investigated. In particular, we explored the effects that these site-directed mutations have over the enzyme kinetics with various substrates of BChE. We further compared the affinity of various anticholinesterases including organophosphorous nerve agents and pesticides toward these BChE variants relative to the wild type enzyme. In addition to serving as a therapy for cocaine addiction-related diseases, enhanced bioscavenging against other harmful agents could add to the practicality and versatility of the plant-derived recombinant enzyme as a multivalent therapeutic.

Catalytic Mechanisms for Cofactor-Free Oxidase-Catalyzed Reactions: Reaction Pathways of Uricase-Catalyzed Oxidation and Hydration of Uric Acid

First-principles quantum mechanical/molecular mechanical (QM/MM)-free energy calculations have been performed to uncover how uricase catalyzes metabolic reactions of uric acid (UA), demonstrating that the entire reaction process of UA in uricase consists of two stages-oxidation followed by hydration. The oxidation consists of four steps: (1) chemical transformation from 8-hydroxyxythine to an anionic radical via a proton transfer along with an electron transfer, which is different from the previously proposed electron-transfer mechanism that involves a dianion intermediate (UA^2-) during the catalytic reaction process; (2) proton transfer to the O₂^- anion (radical); (3) diradical recombination to form a peroxo intermediate; (4) dissociation of H₂O₂ to generate the dehydrourate. Hydration, for the most favorable pathway, is initiated by the nucleophilic attack of a water molecule on dehydrourate, along with a concerted proton transfer through residue Thr69 in the catalytic site. According to the calculated free energy profile, the hydration is the rate-determining step, and the corresponding free energy barrier of 16.2 kcal/mol is consistent with that derived from experimental kinetic data, suggesting that the computational insights into the catalytic mechanisms are reasonable. The mechanistic insights not only provide a mechanistic base for future rational design of uricase mutants with improved catalytic activity against uric acid as an improved enzyme therapy, but also are valuable for understanding a variety of other cofactor-free oxidase-catalyzed reactions involving an oxygen molecule.

Plant expression of cocaine hydrolase-Fc fusion protein for treatment of cocaine abuse

BACKGROUND

A recently reported cocaine hydrolase (CocH3) fused with fragment crystallizable (Fc) region of human immunoglobulin G1, denoted as CocH3-Fc, is known as a promising therapeutic candidate for the treatment of cocaine overdose and addiction. A challenge for practical therapeutic use of this enzyme exists in the large-scale protein production and, therefore, it is interesting to identify a low-cost and feasible, sustainable source of CocH3-Fc production.

RESULTS

CocH3-Fc was transiently expressed in plant Nicotiana benthamiana leaves. The plant-expressed protein, denoted as pCocH3-Fc, was as active as that expressed in mammalian cells both in vitro and in vivo. However, compared to the mammalian-cell expressed CocH3-Fc protein, pCocH3-Fc had a shorter biological half-life, probably due to the lack of protein sialylation in plant. Nevertheless, the in vivo half-life was significantly extended upon the PEGylation of pCocH3-Fc. The Fc fusion did not prolong the biological half-life of the plant-expressed enzyme pCocH3-Fc, but increased the yield of the enzyme expression in the plant under the same experimental conditions.

CONCLUSIONS

It is feasible to express pCocH3-Fc in plants. Further studies on the pCocH3-Fc production in plants should focus on the development of vectors with additional genes/promoters for the complete protein sialylation and for a better yield.

Metabolic Enzymes of Cocaine Metabolite Benzoylecgonine

Cocaine is one of the most addictive drugs without a U.S. Food and Drug Administration (FDA)-approved medication. Enzyme therapy using an efficient cocaine-metabolizing enzyme is recognized as the most promising approach to cocaine overdose treatment. The actual enzyme, known as RBP-8000, under current clinical development for cocaine overdose treatment is our previously designed T172R/G173Q mutant of bacterial cocaine esterase (CocE). The T172R/G173Q mutant is effective in hydrolyzing cocaine but inactive against benzoylecgonine (a major, biologically active metabolite of cocaine). Unlike cocaine itself, benzoylecgonine has an unusually stable zwitterion structure resistant to further hydrolysis in the body and environment. In fact, benzoylecgonine can last in the body for a very long time (a few days) and, thus, is responsible for the long-term toxicity of cocaine and a commonly used marker for drug addiction diagnosis in pre-employment drug tests. Because CocE and its mutants are all active against cocaine and inactive against benzoylecgonine, one might simply assume that other enzymes that are active against cocaine are also inactive against benzoylecgonine. Here, through combined computational modeling and experimental studies, we demonstrate for the first time that human butyrylcholinesterase (BChE) is actually active against benzoylecgonine, and that a rationally designed BChE mutant can not only more efficiently accelerate cocaine hydrolysis but also significantly hydrolyze benzoylecgonine in vitro and in vivo. This sets the stage for advanced studies to design more efficient mutant enzymes valuable for the development of an ideal cocaine overdose enzyme therapy and for benzoylecgonine detoxification in the environment.

Free energy profiles of cocaine esterase-cocaine binding process by molecular dynamics and potential of mean force simulations

The combined molecular dynamics (MD) and potential of mean force (PMF) simulations have been performed to determine the free energy profile of the CocE)-(+)-cocaine binding process in comparison with that of the corresponding CocE-(-)-cocaine binding process. According to the MD simulations, the equilibrium CocE-(+)-cocaine binding mode is similar to the CocE-(-)-cocaine binding mode. However, based on the simulated free energy profiles, a significant free energy barrier (∼5 kcal/mol) exists in the CocE-(+)-cocaine binding process whereas no obvious free energy barrier exists in the CocE-(-)-cocaine binding process, although the free energy barrier of ∼5 kcal/mol is not high enough to really slow down the CocE-(+)-cocaine binding process. In addition, the obtained free energy profiles also demonstrate that (+)-cocaine and (-)-cocaine have very close binding free energies with CocE, with a negligible difference (∼0.2 kcal/mol), which is qualitatively consistent with the nearly same experimental K_M values of the CocE enzyme for (+)-cocaine and (-)-cocaine. The consistency between the computational results and available experimental data suggests that the mechanistic insights obtained from this study are reasonable.

Effects of a cocaine hydrolase engineered from human butyrylcholinesterase on metabolic profile of cocaine in rats

Accelerating cocaine metabolism through enzymatic hydrolysis at cocaine benzoyl ester is recognized as a promising therapeutic approach for cocaine abuse treatment. Our more recently designed A199S/F227A/S287G/A328W/Y332G mutant of human BChE, denoted as cocaine hydrolase-3 (CocH3), has a considerably improved catalytic efficiency against cocaine and has been proven active in blocking cocaine-induced toxicity and physiological effects. In the present study, we have further characterized the effects of CocH3 on the detailed metabolic profile of cocaine in rats administrated intravenously (IV) with 5 mg/kg cocaine, demonstrating that IV administration of 0.15 mg/kg CocH3 dramatically changed the metabolic profile of cocaine. Without CocH3 administration, the dominant cocaine-metabolizing pathway in rats was cocaine methyl ester hydrolysis to benzoylecgonine (BZE). With the CocH3 administration, the dominant cocaine-metabolizing pathway in rats became cocaine benzoyl ester hydrolysis to ecgonine methyl ester (EME), and the other two metabolic pathways (i.e. cocaine methyl ester hydrolysis to BZE and cocaine oxidation to norcocaine) became insignificant. The CocH3-catalyzed cocaine benzoyl ester hydrolysis to EME was so efficient such that the measured maximum blood cocaine concentration (∼38 ng/ml) was significantly lower than the threshold blood cocaine concentration (∼72 ng/ml) required to produce any measurable physiological effects.

Activity and polymorphisms of butyrylcholinesterase in a Polish population

Butyrylcholinesterase (BChE) activity assay and inhibitor phenotyping can help to identify individuals at risk of prolonged paralysis following the administration of neuromuscular blocking agents, like succinylcholine, pesticides and nerve agents. In this study, the activity of BChE and its sensitivity to inhibition by dibucaine and fluoride was evaluated in 1200 Polish healthy individuals. In addition, molecular analysis of all exons, exon-intron boundaries and the 3'UTR sequence of the BCHE gene was performed in a group of 72 subjects with abnormal BChE activity (<2000 U/L and >5745 U/L) or with DN (Dibucaine Number) or FN (Fluoride-Number) values outside the reference range (DN < 78 and FN < lower than wild type). In a studied group, BChE activity range was similar to those observed in other populations. BChE activity screening allowed to detect UA and UF phenotypes in 26 (2.2%) and 15 (1.2%) individuals, respectively. Observed UA or UF phenotypes were confirmed by direct sequencing and heterozygous c.293A > G or c.1253G > T substitutions were identified in all cases. Nine out of 18 (50%) individuals with BChE activity below 2000 U/L had a mutation in 5'UTR (32G/A), intron 2 (c.1518-121T/C) or exon 4 (c.1699G/A; the K variant mutation). Majority of the individuals with BChE activity ≥6000 U/L were wild type. To summarize, the range of BChE activity in a Polish population is similar to those observed in other countries. We conclude that the BChE phenotyping assay is a reliable method for identification of individuals with the UA and UF genotypes.

Biologic Approaches to Treat Substance-Use Disorders

In contrast to traditional pharmacodynamic approaches to treat substance-use disorders (SUDs), the use of biologics (vaccines, monoclonal antibodies, and genetically modified enzymes) is based on a pharmacokinetic principle: reduce the amount of (and, ideally, eliminate) abused drug entering the central nervous system (CNS). Preclinical studies indicate that biologics are effective in both facilitating abstinence and preventing relapse to abused substances ranging from nicotine to heroin. While data are still emerging, the results from multiple clinical trials can best be described as mixed. Nonetheless, these clinical studies have already provided important insights using 'first-generation' tools that may inform the development of effective and commercially viable biologics to treat tobacco-, cocaine-, and methamphetamine-use disorders.

Long-Term Blockade of Cocaine Self-Administration and Locomotor Activation in Rats by an Adenoviral Vector-Delivered Cocaine Hydrolase

A promising approach in treating cocaine abuse is to metabolize cocaine in the blood using a mutated butyrylcholinesterase (BChE) that functions as a cocaine hydrolase (CocH). In rats, a helper-dependent adenoviral (hdAD) vector-mediated delivery of CocH abolished ongoing cocaine use and cocaine-primed reinstatement of drug-seeking for several months. This enzyme also metabolizes ghrelin, an effect that may be beneficial in maintaining healthy weights. The effect of a single hdAD-CocH vector injection was examined in rats on measures of anxiety, body weight, cocaine self-administration, and cocaine-induced locomotor activity. To examine anxiety, periadolescent rats were tested in an elevated-plus maze. Weight gain was then examined under four rodent diets. Ten months after CocH-injection, adult rats were trained to self-administer cocaine intravenously and, subsequently, cocaine-induced locomotion was tested. Viral gene transfer produced sustained plasma levels of CocH for over 13 months of testing. CocH-treated rats did not differ from controls in measures of anxiety, and only showed a transient reduction in weight gain during the first 3 weeks postinjection. However, CocH-treated rats were insensitive to cocaine. At 10 months postinjection, none of the CocH-treated rats initiated cocaine self-administration, unlike 90% of the control rats. At 13 months postinjection, CocH-treated rats showed no cocaine-induced locomotion, whereas control rats showed a dose-dependent enhancement of locomotion. CocH vector produced a long-term blockade of the rewarding and behavioral effects of cocaine in rats, emphasizing its role as a promising therapeutic intervention in cocaine abuse.

Unexpected Reaction Pathway for butyrylcholinesterase-catalyzed inactivation of "hunger hormone" ghrelin

Extensive computational modeling and simulations have been carried out, in the present study, to uncover the fundamental reaction pathway for butyrylcholinesterase (BChE)-catalyzed hydrolysis of ghrelin, demonstrating that the acylation process of BChE-catalyzed hydrolysis of ghrelin follows an unprecedented single-step reaction pathway and the single-step acylation process is rate-determining. The free energy barrier (18.8 kcal/mol) calculated for the rate-determining step is reasonably close to the experimentally-derived free energy barrier (~19.4 kcal/mol), suggesting that the obtained mechanistic insights are reasonable. The single-step reaction pathway for the acylation is remarkably different from the well-known two-step acylation reaction pathway for numerous ester hydrolysis reactions catalyzed by a serine esterase. This is the first time demonstrating that a single-step reaction pathway is possible for an ester hydrolysis reaction catalyzed by a serine esterase and, therefore, one no longer can simply assume that the acylation process must follow the well-known two-step reaction pathway.

Reaction Pathway for Cocaine Hydrolase-Catalyzed Hydrolysis of (+)-Cocaine

A recently designed and discovered cocaine hydrolase (CocH), engineered from human butyrylcholinesterase (BChE), has been proven promising as a novel enzyme therapy for treatment of cocaine overdose and addiction because it is highly efficient in catalyzing hydrolysis of naturally occurring (-)-cocaine. It has been known that the CocH also has a high catalytic efficiency against (+)-cocaine, a synthetic enantiomer of cocaine. Reaction pathway and the corresponding free energy profile for the CocH-catalyzed hydrolysis of (+)-cocaine have been determined, in the present study, by performing first-principles pseudobond quantum mechanical/molecular mechanical (QM/MM)-free energy (FE) calculations. Acordingt to the QM/MM-FE results, the catalytic hydrolysis process is initiated by the nucleophilic attack on carbonyl carbon of (-)-cocaine benzoyl ester via hydroxyl oxygen of S198 side chain, and the second reaction step (i.e. dissociation of benzoyl ester) is rate-determining. This finding for CocH-catalyzed hydrolysis of (+)-cocaine is remarkably different from that for the (+)-cocaine hydrolysis catalyzed by bacterial cocaine esterase in which the first reaction step of the deacylation is associated with the highest free energy barrier (~17.9 kcal/mol). The overall free energy barrier (~16.0 kcal/mol) calculated for the acylation stage of CocH-catalyzed hydrolysis of (+)-cocaine is in good agreement with the experimental free energy barrier of ~14.5 kcal/mol derivated from the experimental kinetic data.

Long-acting cocaine hydrolase for addiction therapy

Cocaine abuse is a world-wide public health and social problem without a US Food and Drug Administration-approved medication. An ideal anticocaine medication would accelerate cocaine metabolism, producing biologically inactive metabolites by administration of an efficient cocaine-specific exogenous enzyme. Our recent studies have led to the discovery of the desirable, highly efficient cocaine hydrolases (CocHs) that can efficiently detoxify and inactivate cocaine without affecting normal functions of the CNS. Preclinical and clinical data have demonstrated that these CocHs are safe for use in humans and are effective for accelerating cocaine metabolism. However, the actual therapeutic use of a CocH in cocaine addiction treatment is limited by its short biological half-life (e.g., 8 h or shorter in rats). Here we demonstrate a novel CocH form, a catalytic antibody analog, which is a fragment crystallizable (Fc)-fused CocH dimer (CocH-Fc) constructed by using CocH to replace the Fab region of human IgG1. The CocH-Fc not only has a high catalytic efficiency against cocaine but also, like an antibody, has a considerably longer biological half-life (e.g., ∼107 h in rats). A single dose of CocH-Fc was able to accelerate cocaine metabolism in rats even after 20 d and thus block cocaine-induced hyperactivity and toxicity for a long period. Given the general observation that the biological half-life of a protein drug is significantly longer in humans than in rodents, the CocH-Fc reported in this study could allow dosing once every 2-4 wk, or longer, for treatment of cocaine addiction in humans.

Assessment of Pharmacokinetic and Pharmacodynamic Interactions Between Albumin-Fused Mutated Butyrylcholinesterase and Intravenously Administered Cocaine in Recreational Cocaine Users

Cocaine dependence presents a major public health issue, and to date, no pharmacotherapies are approved for its treatment. TV-1380 is a novel recombinant albumin-fused mutated butyrylcholinesterase (Albu-BChE) that has increased catalytic efficiency for cocaine compared with wild-type BChE and therefore has the potential to facilitate abstinence in cocaine-dependent subjects by decreasing exposure to cocaine and its reinforcing effects.

METHODS

This randomized, double-blind, placebo-controlled, parallel-group study in nondependent cocaine users was conducted to evaluate the effect of a single intramuscular dose of Albu-BChE (50, 100, and 300 mg) on the pharmacokinetic and metabolic profile of intravenous cocaine infusions (40 mg) administered at baseline and at 24, 96, and 168 hours after Albu-BChE dosing, to assess safety of coadministering Albu-BChE and cocaine, and to explore the subjective responses to cocaine infusions after Albu-BChE dosing.

RESULTS

Administration of Albu-BChE resulted in significant dose-dependent reductions in cocaine exposure (maximum concentration, area under the curve) and half-life. Effects were greatest at 24 hours after Albu-BChE dose, but were sustained up to 168 hours. Spearman correlations indicated a significant negative relationship between Albu-BChE concentration and cocaine clearance and exposure. Consistent with its mechanism of action, Albu-BChE also shifted cocaine metabolism toward preferential formation of ecgonine methyl ester. Administration of Albu-BChE was associated with modest decreases in subjective reports of feeling high and willingness to take cocaine again after cocaine infusion. Coadministration of Albu-BChE and cocaine was safe and well tolerated.

CONCLUSIONS

Administration of Albu-BChE at single doses of 50, 100, and 300 mg safely resulted in long-lasting decreases in cocaine exposure in recreational cocaine users.