Development of an in-vivo active reversible butyrylcholinesterase inhibitor

Tryptophan-derived butyrylcholinesterase inhibitors as promising leads against Alzheimer's disease

We have identified tryptophan-based selective nanomolar butyrylcholinesterase (BChE) inhibitors. They are defined according to their chemical modularity, novel binding mode revealed by five solved crystal structures with human BChE, low cytotoxicity, and predicted permeability of the blood-brain barrier. Altogether, these factors indicate their potential as unique lead compounds for symptomatic therapy against Alzheimer's disease.

Efficient synthesis and preliminary biological evaluations of trifluoromethylated imidazo[1,2-a]pyrimidines and benzimidazo[1,2-a]pyrimidines

Fluoromethylated imidazo[1,2-a]pyrimidines and benzimidazo[1,2-a]pyrimidines were synthesized through Michael addition/intramolecular cyclization reaction by condensation of 2-amino imidazole derivatives with ethyl 4,4,4-trifluorobut-2-ynate and using C–O bond activation.

Contemporary medicinal-chemistry strategies for the discovery of selective butyrylcholinesterase inhibitors

Butyrylcholinesterase (BChE) is considered a promising drug target for the treatment of moderate to severe Alzheimer's disease (AD). Here, we review medicinal-chemistry strategies that are currently available for the discovery of selective BChE inhibitors.

Design, synthesis and biological evaluation of tricyclic pyrazolo[1,5-c][1,3]benzoxazin-5(5H)-one scaffolds as selective BuChE inhibitors

Based on the structural analysis of tricyclic scaffolds as butyrylcholinesterase (BuChE) inhibitors, a series of pyrazolo[1,5-c][1,3]benzoxazin-5(5H)-one derivatives were designed, synthesized and evaluated for their acetylcholinesterase (AChE) and BuChE inhibitory activity. Compounds with 5-carbonyl and 7- or/and 9-halogen substitutions showed potential BuChE inhibitory activity, among which compounds 6a, 6c and 6g showed the best BuChE inhibition (IC₅₀ = 1.06, 1.63 and 1.63 µM, respectively). The structure–activity relationship showed that the 5-carbonyl and halogen substituents significantly influenced BuChE activity. Compounds 6a and 6g were found nontoxic, lipophilic and exhibited remarkable neuroprotective activity and mixed-type inhibition against BuChE (K_i = 7.46 and 3.09 µM, respectively). Docking studies revealed that compound 6a can be accommodated into BuChE via five hydrogen bonds, one Pi–Sigma interaction and three Pi–Alkyl interactions.

Design and evaluation of selective butyrylcholinesterase inhibitors based on Cinchona alkaloid scaffold

This paper describes the synthesis and anticholinesterase potency of Cinchona-based alkaloids; ten quaternary derivatives of cinchonines and their corresponding pseudo-enantiomeric cinchonidines. The quaternization of quinuclidine moiety of each compound was carried out with groups diverse in their size: methyl, benzyl and differently meta- and para-substituted benzyl groups. All of the prepared compounds reversibly inhibited human butyrylcholinesterase and acetylcholinesterase with Ki constants within nanomolar to micromolar range. Five cinchonidine derivatives displayed 95-510 times higher inhibition selectivity to butyrylcholinesterase over acetylcholinesterase and four were potent butyrylcholinesterase inhibitors with Ki constants up to 100 nM, of which N-para-bromobenzyl cinchonidinium bromide can be considered a lead for further modifications and optimizations for possible use in the treatment of neurodegenerative diseases.

Synthesis and Biological Evaluation of New Cholinesterase Inhibitors for Alzheimer's Disease

Alzheimer’s disease (AD) is a neurodegenerative disorder mostly influencing the elderly, and causes death due to dementia. The main pathogenic feature connected with the progression of this multifactorial disease is the weakening of the cholinergic system in the brain. Cholinesterase (ChE) inhibitors are recognized as one of the choices in the treatment of AD. The inhibition of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) were approved as a therapeutic strategy to reduce the symptoms of AD and prevent its progression. The capacity of BChE is not completely known yet; rather, it is accepted to assume a part in a few disorders such as AD. Thus, BChE inhibitors may have a greater role for the treatment of AD in the future. In the present study, 2-(9-acridinylamino)-2-oxoethyl piperazine/piperidine/morpholinecarbodithioate derivatives were synthesized in order to investigate anticholinesterase activity. Eight derivatives demonstrated a specific and promising action against BChE. Furthermore, compound 4n showed inhibitory activity against both enzymes. It was found that the active compounds were well tolerated in the cytotoxicity test. Possible interactions between the lead compound, 4n, and the BChE enzyme were determined through a docking study. The findings obtained within this paper will contribute to the development of new and effective synthetic anti-Alzheimer compounds, and will ideally encourage future screening against AD.

Regulation of striatal cells and goal-directed behavior by cerebellar outputs

The cerebellum integrates descending motor commands and sensory information to generate predictions and detect errors during ongoing behaviors. Cerebellar computation has been proposed to control motor but also non-motor behaviors, including reward expectation and cognitive flexibility. However, the organization and functional contribution of cerebellar output channels are incompletely understood. Here, we elaborate the cell-type specificity of a broad connectivity matrix from the deep cerebellar nuclei (DCN) to the dorsal striatum in mice. Cerebello-striatal connections arise from all deep cerebellar subnuclei and are relayed through intralaminar thalamic nuclei (ILN). In the dorsal striatum, these connections target medium spiny neurons, but also ChAT-positive interneurons, a class of tonically active interneurons implicated in shifting and updating behavioral strategies. Chemogenetic silencing of cerebello-striatal connectivity modifies function of striatal ChAT-positive interneurons. We propose that cerebello-striatal connections relay cerebellar computation to striatal circuits for goal-directed behaviors.

Cerebellar outputs contribute to motor as well as cognitive behaviors. Here, the authors elucidate the connectivity between deep cerebellar nuclei and specific cell types in the striatum via the intralaminar thalamic nucleus and the participation of this circuit in striatum-dependent behavior.

Multi-target-directed ligands for treating Alzheimer's disease: Butyrylcholinesterase inhibitors displaying antioxidant and neuroprotective activities

The limited clinical efficacy of current symptomatic treatment and minute effect on progression of Alzheimer's disease has shifted the research focus from single targets towards multi-target-directed ligands. Here, a potent selective inhibitor of human butyrylcholinesterase was used as the starting point to develop a new series of multifunctional ligands. A focused library of derivatives was designed and synthesised that showed both butyrylcholinesterase inhibition and good antioxidant activity as determined by the DPPH assay. The crystal structure of compound 11 in complex with butyrylcholinesterase revealed the molecular basis for its low nanomolar inhibition of butyrylcholinesterase (Ki = 1.09 ± 0.12 nM). In addition, compounds 8 and 11 show metal-chelating properties, and reduce the redox activity of chelated Cu²⁺ ions in a Cu-ascorbate redox system. Compounds 8 and 11 decrease intracellular levels of reactive oxygen species, and are not substrates of the active efflux transport system, as determined in Caco2 cells. Compound 11 also protects neuroblastoma SH-SY5Y cells from toxic Aβ_1-42 species. These data indicate that compounds 8 and 11 are promising multifunctional lead ligands for treatment of Alzheimer's disease.

Design, Synthesis, and Biological Evaluation of 1-Benzylamino-2-hydroxyalkyl Derivatives as New Potential Disease-Modifying Multifunctional Anti-Alzheimer's Agents

The multitarget approach is a promising paradigm in drug discovery, potentially leading to new treatment options for complex disorders, such as Alzheimer's disease. Herein, we present the discovery of a unique series of 1-benzylamino-2-hydroxyalkyl derivatives combining inhibitory activity against butyrylcholinesterase, β-secretase, β-amyloid, and tau protein aggregation, all related to mechanisms which underpin Alzheimer's disease. Notably, diphenylpropylamine derivative 10 showed balanced activity against both disease-modifying targets, inhibition of β-secretase (IC_{50  hBACE-1} = 41.60 μM), inhibition of amyloid β aggregation (IC_50 Aβ = 3.09 μM), inhibition of tau aggregation (55% at 10 μM); as well as against symptomatic targets, butyrylcholinesterase inhibition (IC_{50  hBuChE} = 7.22 μM). It might represent an encouraging starting point for development of multifunctional disease-modifying anti-Alzheimer's agents.

Phencyclidine and Scopolamine for Modeling Amnesia in Rodents: Direct Comparison with the Use of Barnes Maze Test and Contextual Fear Conditioning Test in Mice

Nowadays cognitive impairments are a growing unresolved medical issue which may accompany many diseases and therapies, furthermore, numerous researchers investigate various neurobiological aspects of human memory to find possible ways to improve it. Until any other method is discovered, in vivo studies remain the only available tool for memory evaluation. At first, researchers need to choose a model of amnesia which may strongly influence observed results. Thereby a deeper insight into a model itself may increase the quality and reliability of results. The most common method to impair memory in rodents is the pretreatment with drugs that disrupt learning and memory. Taking this into consideration, we compared the activity of agents commonly used for this purpose. We investigated effects of phencyclidine (PCP), a non-competitive NMDA receptor antagonist, and scopolamine (SCOP), an antagonist of muscarinic receptors, on short-term spatial memory and classical fear conditioning in mice. PCP (3 mg/kg) and SCOP (1 mg/kg) were administrated intraperitoneally 30 min before behavioral paradigms. To assess the influence of PCP and SCOP on short-term spatial memory, the Barnes maze test in C57BL/J6 mice was used. Effects on classical conditioning were evaluated using contextual fear conditioning test. Additionally, spontaneous locomotor activity of mice was measured. These two tests were performed in CD-1 mice. Our study reports that both tested agents disturbed short-term spatial memory in the Barnes maze test, however, SCOP revealed a higher activity. Surprisingly, learning in contextual fear conditioning test was impaired only by SCOP.

Graphical Abstract

Structure-Activity Relationships and Computational Investigations into the Development of Potent and Balanced Dual-Acting Butyrylcholinesterase Inhibitors and Human Cannabinoid Receptor 2 Ligands with Pro-Cognitive in Vivo Profiles

The enzyme butyrylcholinesterase (BChE) and the human cannabinoid receptor 2 (hCB₂R) represent promising targets for pharmacotherapy in the later stages of Alzheimer's disease. We merged pharmacophores for both targets into small benzimidazole-based molecules, investigated SARs, and identified several dual-acting ligands with a balanced affinity/inhibitory activity and an excellent selectivity over both hCB₁R and hAChE. A homology model for the hCB₂R was developed based on the hCB₁R crystal structure and used for molecular dynamics studies to investigate binding modes. In vitro studies proved hCB₂R agonism. Unwanted μ-opioid receptor affinity could be designed out. One well-balanced dual-acting and selective hBChE inhibitor/hCB₂R agonist showed superior in vivo activity over the lead CB₂ agonist with regards to cognition improvement. The data shows the possibility to combine a small molecule with selective and balanced GPCR-activity/enzyme inhibition and in vivo activity for the therapy of AD and may help to rationalize the development of other dual-acting ligands.

Comparison of the Binding of Reversible Inhibitors to Human Butyrylcholinesterase and Acetylcholinesterase: A Crystallographic, Kinetic and Calorimetric Study

Acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) hydrolyze the neurotransmitter acetylcholine and, thereby, function as coregulators of cholinergic neurotransmission. Although closely related, these enzymes display very different substrate specificities that only partially overlap. This disparity is largely due to differences in the number of aromatic residues lining the active site gorge, which leads to large differences in the shape of the gorge and potentially to distinct interactions with an individual ligand. Considerable structural information is available for the binding of a wide diversity of ligands to AChE. In contrast, structural data on the binding of reversible ligands to BChE are lacking. In a recent effort, an inhibitor competition approach was used to probe the overlap of ligand binding sites in BChE. Here, we extend this study by solving the crystal structures of human BChE in complex with five reversible ligands, namely, decamethonium, thioflavin T, propidium, huprine, and ethopropazine. We compare these structures to equivalent AChE complexes when available in the protein data bank and supplement this comparison with kinetic data and observations from isothermal titration calorimetry. This new information now allows us to define the binding mode of various ligand families and will be of importance in designing specific reversible ligands of BChE that behave as inhibitors or reactivators.

Proline-Based Carbamates as Cholinesterase Inhibitors

Series of twenty-five benzyl (2S)-2-(arylcarbamoyl)pyrrolidine-1-carboxylates was prepared and completely characterized. All the compounds were tested for their in vitro ability to inhibit acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), and the selectivity of compounds to individual cholinesterases was determined. Screening of the cytotoxicity of all the compounds was performed using a human monocytic leukaemia THP-1 cell line, and the compounds demonstrated insignificant toxicity. All the compounds showed rather moderate inhibitory effect against AChE; benzyl (2S)-2-[(2-chlorophenyl)carbamoyl]pyrrolidine-1-carboxylate (IC₅₀ = 46.35 μM) was the most potent agent. On the other hand, benzyl (2S)-2-[(4-bromophenyl)-] and benzyl (2S)-2-[(2-bromophenyl)carbamoyl]pyrrolidine-1-carboxylates expressed anti-BChE activity (IC₅₀ = 28.21 and 27.38 μM, respectively) comparable with that of rivastigmine. The ortho-brominated compound as well as benzyl (2S)-2-[(2-hydroxyphenyl)carbamoyl]pyrrolidine-1-carboxylate demonstrated greater selectivity to BChE. The in silico characterization of the structure–inhibitory potency for the set of proline-based carbamates considering electronic, steric and lipophilic properties was provided using comparative molecular surface analysis (CoMSA) and principal component analysis (PCA). Moreover, the systematic space inspection with splitting data into the training/test subset was performed to monitor the statistical estimators performance in the effort to map the probability-guided pharmacophore pattern. The comprehensive screening of the AChE/BChE profile revealed potentially relevant structural and physicochemical features that might be essential for mapping of the carbamates inhibition efficiency indicating qualitative variations exerted on the reaction site by the substituent in the 3′-/4′-position of the phenyl ring. In addition, the investigation was completed by a molecular docking study of recombinant human AChE.

Bacterial Expression of Human Butyrylcholinesterase as a Tool for Nerve Agent Bioscavengers Development

Human butyrylcholinesterase is a performant stoichiometric bioscavenger of organophosphorous nerve agents. It is either isolated from outdated plasma or functionally expressed in eukaryotic systems. Here, we report the production of active human butyrylcholinesterase in a prokaryotic system after optimization of the primary sequence through the Protein Repair One Stop Shop process, a structure- and sequence-based algorithm for soluble bacterial expression of difficult eukaryotic proteins. The mutant enzyme was purified to homogeneity. Its kinetic parameters with substrate are similar to the endogenous human butyrylcholinesterase or recombinants produced in eukaryotic systems. The isolated protein was prone to crystallize and its 2.5-Å X-ray structure revealed an active site gorge region identical to that of previously solved structures. The advantages of this alternate expression system, particularly for the generation of butyrylcholinesterase variants with nerve agent hydrolysis activity, are discussed.

Evaluation of Novel Dual Acetyl- and Butyrylcholinesterase Inhibitors as Potential Anti-Alzheimer's Disease Agents Using Pharmacophore, 3D-QSAR, and Molecular Docking Approaches

DL0410, containing biphenyl and piperidine skeletons, was identified as an acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibitor through high-throughput screening assays, and further studies affirmed its efficacy and safety for Alzheimer’s disease treatment. In our study, a series of novel DL0410 derivatives were evaluated for inhibitory activities towards AChE and BuChE. Among these derivatives, compounds 6-1 and 7-6 showed stronger AChE and BuChE inhibitory activities than DL0410. Then, pharmacophore modeling and three-dimensional quantitative structure activity relationship (3D-QSAR) models were performed. The R² of AChE and BuChE 3D-QSAR models for training set were found to be 0.925 and 0.883, while that of the test set were 0.850 and 0.881, respectively. Next, molecular docking methods were utilized to explore the putative binding modes. Compounds 6-1 and 7-6 could interact with the amino acid residues in the catalytic anionic site (CAS) and peripheral anionic site (PAS) of AChE/BuChE, which was similar with DL0410. Kinetics studies also suggested that the three compounds were all mixed-types of inhibitors. In addition, compound 6-1 showed better absorption and blood brain barrier permeability. These studies provide better insight into the inhibitory behaviors of DL0410 derivatives, which is beneficial for rational design of AChE and BuChE inhibitors in the future.

Rapid Mechanistic Evaluation and Parameter Estimation of Putative Inhibitors in a Single-Step Progress-Curve Analysis: The Case of Horse Butyrylcholinesterase

Highly efficient and rapid lead compound evaluation for estimation of inhibition parameters and type of inhibition is proposed. This is based on a single progress-curve measurement in the presence of each candidate compound, followed by the simultaneous analysis of all of these curves using the ENZO enzyme kinetics suite, which can be implemented as a web application. In the first step, all of the candidate ligands are tested as competitive inhibitors. Where the theoretical curves do not correspond to the experimental data, minimal additional measurements are added, with subsequent processing according to modified reaction mechanisms.