Oximes: inhibitors of human recombinant acetylcholinesterase. A structure-activity relationship (SAR) study

Carltonine-derived compounds for targeted butyrylcholinesterase inhibition

The investigation into human butyrylcholinesterase (hBChE) inhibitors as therapeutic agents for Alzheimer's disease (AD) holds significant promise, addressing both symptomatic relief and disease progression. In the pursuit of novel drug candidates with a selective BChE inhibition pattern, we focused on naturally occurring template structures, specifically Amaryllidaceae alkaloids of the carltonine-type. Herein, we explored a series of compounds implementing an innovative chemical scaffold built on the 3- and 4-benzyloxy-benzylamino chemotype. Notably, compounds 28 (hBChE IC50 = 0.171 ± 0.063 μM) and 33 (hBChE IC50 = 0.167 ± 0.018 μM) emerged as top-ranked hBChE inhibitors. In silico simulations elucidated the binding modes of these compounds within hBChE. CNS availability was predicted using the BBB score algorithm, corroborated by in vitro permeability assessments with the most potent derivatives. Compound 33 was also inspected for aqueous solubility, microsomal and plasma stability. Chemoinformatics analysis validated these hBChE inhibitors for oral administration, indicating favorable gastrointestinal absorption in compliance with Lipinski's and Veber's rules. Safety assessments, crucial for the chronic administration typical in AD treatment, were conducted through cytotoxicity testing on human neuroblastoma (SH-SY5Y) and hepatocellular carcinoma (HepG2) cell lines.

Morphing cholinesterase inhibitor amiridine into multipotent drugs for the treatment of Alzheimer's disease

The search for novel drugs to address the medical needs of Alzheimer's disease (AD) is an ongoing process relying on the discovery of disease-modifying agents. Given the complexity of the disease, such an aim can be pursued by developing so-called multi-target directed ligands (MTDLs) that will impact the disease pathophysiology more comprehensively. Herewith, we contemplated the therapeutic efficacy of an amiridine drug acting as a cholinesterase inhibitor by converting it into a novel class of novel MTDLs. Applying the linking approach, we have paired amiridine as a core building block with memantine/adamantylamine, trolox, and substituted benzothiazole moieties to generate novel MTDLs endowed with additional properties like N-methyl-d-aspartate (NMDA) receptor affinity, antioxidant capacity, and anti-amyloid properties, respectively. The top-ranked amiridine-based compound 5d was also inspected by in silico to reveal the butyrylcholinesterase binding differences with its close structural analogue 5b. Our study provides insight into the discovery of novel amiridine-based drugs by broadening their target-engaged profile from cholinesterase inhibitors towards MTDLs with potential implications in AD therapy.

In Vitro Evaluation of Oxidative Stress Induced by Oxime Reactivators of Acetylcholinesterase in HepG2 Cells

Oxime reactivators of acetylcholinesterase (AChE) are used as causal antidotes for intended and unintended poisoning by organophosphate nerve agents and pesticides. Despite all efforts to develop new AChE reactivators, none of these drug candidates replaced conventional clinically used oximes. In addition to the therapeutic efficacy, determining the safety profile is crucial in preclinical drug evaluation. The exact mechanism of oxime toxicity and the structure-toxicity relationship are subjects of ongoing research, with oxidative stress proposed as a possible mechanism. In the present study, we investigated four promising bispyridinium oxime AChE reactivators, K048, K074, K075, and K203, and their ability to induce oxidative stress in vitro. Cultured human hepatoma cells were exposed to oximes at concentrations corresponding to their IC50 values determined by the MTT assay after 24 h. Their potency to generate reactive oxygen species, interfere with the thiol antioxidant system, and induce lipid peroxidation was evaluated at 1, 4, and 24 h of exposure. Reactivators without a double bond in the four-carbon linker, K048 and K074, showed a greater potential to induce oxidative stress compared with K075 and K203, which contain a double bond. Unlike oximes with a three-carbon-long linker, the number of aldoxime groups attached to the pyridinium moieties does not determine the oxidative stress induction for K048, K074, K075, and K203 oximes. In conclusion, our results emphasize that the structure of oximes plays a critical role in inducing oxidative stress, and this relationship does not correlate with their cytotoxicity expressed as the IC50 value. However, it is important to note that oxidative stress cannot be disregarded as a potential contributor to the side effects associated with oximes.

Inhibitory Activity of 4-Benzylidene Oxazolones Derivatives of Cinnamic Acid on Human Acetylcholinesterase and Cognitive Improvements in a Mouse Model

We synthesized seven (Z)-benzylidene-2-(E)-styryloxazol-5(4H)-ones derivatives of cinnamic acid and evaluated the ability of these compounds to inhibit human acetylcholinesterase (hAChE). The most potent compound was evaluated for cognitive improvement in short-term memory. The seven compounds reversibly inhibited the hAChE between 51 and 75% at 300 μM, showed an affinity (Ki) from 2 to 198 μM, and an IC50 from 9 to 246 μM. Molecular docking studies revealed that all binding moieties are involved in the non-covalent interactions with hAChE for all compounds. In addition, in silico pharmacokinetic analysis was carried out to predict the compounds' blood-brain barrier (BBB) permeability. The most potent inhibitor of hAChE significantly improved cognitive impairment in a modified Y-maze test (5 μmol/kg) and an Object Recognition Test (10 μmol/kg). Our results can help the rational design of hAChE inhibitors to work as potential candidates for treating cognitive disorders.

Inhibition of Human Cholinesterases and in vitro β-Amyloid Aggregation by Rationally Designed Peptides

The multifactorial nature of Alzheimer's disease (AD) is now widely recognized, which has increased the interest in compounds that can address more than one AD-associated targets. Herein, we report the inhibitory activity on the human cholinesterases (acetylcholinesterase, hAChE and butyrylcholinesterase, hBChE) and on the AChE-induced β-amyloid peptide (Aβ) aggregation by a series of peptide derivatives designed by mutating aliphatic residues for aromatic ones. We identified peptide W3 (LGWVSKGKLL-NH2 ) as an interesting scaffold for the development of new anti-AD multitarget-directed drugs. It showed the lowest IC50 value against hAChE reported for a peptide (0.99±0.02 μM) and inhibited 94.2 %±1.2 of AChE-induced Aβ aggregation at 10 μM. Furthermore, it inhibited hBChE (IC50 , 15.44±0.91 μM), showed no in vivo toxicity in brine shrimp and had shown moderated radical scavenging and Fe2+ chelating capabilities in previous studies. The results are in line with multiple reports showing the utility of the indole moiety for the development of cholinesterase inhibitors.

Structure-Guided Design of N-Methylpropargylamino-Quinazoline Derivatives as Multipotent Agents for the Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is a complex disease with an unknown etiology. Available treatments, limited to cholinesterase inhibitors and N-methyl-d-aspartate receptor (NMDAR) antagonists, provide symptomatic relief only. As single-target therapies have not proven effective, rational specific-targeted combination into a single molecule represents a more promising approach for treating AD, and is expected to yield greater benefits in alleviating symptoms and slowing disease progression. In the present study, we designed, synthesized, and biologically evaluated 24 novel N-methylpropargylamino-quinazoline derivatives. Initially, compounds were thoroughly inspected by in silico techniques determining their oral and CNS availabilities. We tested, in vitro, the compounds' effects on cholinesterases and monoamine oxidase A/B (MAO-A/B), as well as their impacts on NMDAR antagonism, dehydrogenase activity, and glutathione levels. In addition, we inspected selected compounds for their cytotoxicity on undifferentiated and differentiated neuroblastoma SH-SY5Y cells. We collectively highlighted II-6h as the best candidate endowed with a selective MAO-B inhibition profile, NMDAR antagonism, an acceptable cytotoxicity profile, and the potential to permeate through BBB. The structure-guided drug design strategy applied in this study imposed a novel concept for rational drug discovery and enhances our understanding on the development of novel therapeutic agents for treating AD.

Highly selective butyrylcholinesterase inhibitors related to Amaryllidaceae alkaloids - Design, synthesis, and biological evaluation

Butyrylcholinesterase (BChE) is one of the most frequently implicated enzymes in the advanced stage of Alzheimer's disease (AD). As part of our endeavors to develop new drug candidates for AD, we have focused on natural template structures, namely the Amaryllidaceae alkaloids carltonine A and B endowed with high BChE selectivity. Herein, we report the design, synthesis, and in vitro evaluation of 57 novel highly selective human BChE (hBChE) inhibitors. Most synthesized compounds showed hBChE inhibition potency ranging from micromolar to low nanomolar scale. Compounds that revealed BChE inhibition below 100 nM were selected for detailed biological investigation. The CNS-targeted profile of the presented compounds was confirmed theoretically by calculating the BBB score algorithm, these data were corroborated by determining the permeability in vitro using PAMPA-assay for the most active derivatives. The study highlighted compounds 87 (hBChE IC₅₀ = 3.8 ± 0.2 nM) and 88 (hBChE IC₅₀ = 5.7 ± 1.5 nM) as the top-ranked BChE inhibitors. Compounds revealed negligible cytotoxicity for the human neuroblastoma (SH-SY5Y) and hepatocellular carcinoma (HepG2) cell lines compared to BChE inhibitory potential. A crystallographic study was performed to inspect the binding mode of compound 87, revealing essential interactions between 87 and hBChE active site. In addition, multidimensional QSAR analyses were applied to determine the relationship between chemical structures and biological activity in a dataset of designed agents. Compound 87 is a promising lead compound with potential implications for treating the late stages of AD.

FDA-Approved Oximes and Their Significance in Medicinal Chemistry

Despite the scientific advancements, organophosphate (OP) poisoning continues to be a major threat to humans, accounting for nearly one million poisoning cases every year leading to at least 20,000 deaths worldwide. Oximes represent the most important class in medicinal chemistry, renowned for their widespread applications as OP antidotes, drugs and intermediates for the synthesis of several pharmacological derivatives. Common oxime based reactivators or nerve antidotes include pralidoxime, obidoxime, HI-6, trimedoxime and methoxime, among which pralidoxime is the only FDA-approved drug. Cephalosporins are β-lactam based antibiotics and serve as widely acclaimed tools in fighting bacterial infections. Oxime based cephalosporins have emerged as an important class of drugs with improved efficacy and a broad spectrum of anti-microbial activity against Gram-positive and Gram-negative pathogens. Among the several oxime based derivatives, cefuroxime, ceftizoxime, cefpodoxime and cefmenoxime are the FDA approved oxime-based antibiotics. Given the pharmacological significance of oximes, in the present paper, we put together all the FDA-approved oximes and discuss their mechanism of action, pharmacokinetics and synthesis.

The Influence of Seasonality on Secondary Metabolite Profiles and Neuroprotective Activities of Moss Hypnum cupressiforme Extracts: In Vitro and In Silico Study

Numerous representatives of mosses, including Hypnum cupressiforme, have been used to alleviate different inflammation-related conditions. However, the mode of action underlying this anti-inflammatory potential has been poorly understood. Moreover, the influence of seasonality on the chemical composition and biological activity of mosses is generally overlooked. This study aimed to investigate the influence of seasonal changes (spring, summer, and autumn) on secondary metabolite composition and biological activities of ethyl acetate H. cupressiforme extracts. Antioxidant activity was measured using β-carotene bleaching assay, while MTT, NBT, ELISA, and Griess assays were carried out to explore the anti-neuroinflammatory and neuroprotective potential of extracts. Inhibitory activities on acetylcholinesterase and tyrosinase were assessed experimentally and by docking analysis. The highest content of secondary metabolites and antioxidant activity were observed in moss during the summer. Extracts inhibited the secretion of ROS, NO, TNF-α, and IL-6, alleviating the inflammatory potential of H₂O₂ and LPS in microglial and neuronal cells. Strong inhibitory effects on acetylcholinesterase and tyrosinase were observed in vitro. Docking analyses revealed high-affinity interactions of secondary metabolites present in H. cupressiforme with important enzyme residues. Altogether, these results reveal the neuroprotective potential and the significance of seasonal fluctuations on secondary metabolite content and biological activities in moss H. cupressiforme.

Rational design and synthesis of modified natural peptides from Boana pulchella (anura) as acetylcholinesterase inhibitors and antioxidants

The use of acetylcholinesterase (AChE) inhibitors, antioxidants or multitarget compounds are among the main strategies against Alzheimer's disease (AD). Between AChE inhibitors, those targeting the peripheral anionic site (PAS) are of special interest. Here, we describe the rational design and synthesis of peptide analogs of a natural PAS-targeting sequence that we recently discovered, aiming at increasing its activity against AChE. We also tested their radical scavenging and metal chelating properties. Our design strategy was based on the position-specific, computer-aided insertion of aromatic residues. The analog named as W3 showed a 30-fold higher inhibitory activity than the original sequence and an improved antioxidant activity. W3 is the most potent modified natural peptide against Electrophorus electricus AChE ever reported with an IC₅₀ of 10.42 μM (± 1.02). In addition, it showed a radical scavenging activity of 47.00% ± 3.11 at 50 μM and 93.47% ± 1.53 at 400 μM. Since peptides are receiving increasing interest as drugs, we propose the W3 analog as an attractive sequence for the development of new peptide-based multitarget drugs for AD. Besides, this work sheds light on the importance of the aromatic residues in the modulation of AChE activity and their effect on the radical scavenging activity of a peptide.

Design and synthesis of novel tacrine-indole hybrids as potential multitarget-directed ligands for the treatment of Alzheimer's disease

The authors report on the synthesis and biological evaluation of new compounds whose structure combines tacrine and indole moieties. Tacrine-indole heterodimers were designed to inhibit cholinesterases and β-amyloid formation, and to cross the blood-brain barrier. The most potent new acetylcholinesterase inhibitors were compounds 3c and 4d (IC₅₀ = 25 and 39 nM, respectively). Compound 3c displayed considerably higher selectivity for acetylcholinesterase relative to human plasma butyrylcholinesterase in comparison to compound 4d (selectivity index: IC₅₀ [butyrylcholinesterase]/IC₅₀ [acetylcholinesterase] = 3 and 0.6, respectively). Furthermore, compound 3c inhibited β-amyloid-dependent amyloid nucleation in the yeast-based prion nucleation assay and displayed no dsDNA destabilizing interactions with DNA. Compounds 3c and 4d displayed a high probability of crossing the blood-brain barrier. The results support the potential of 3c for future development as a dual-acting therapeutic agent in the prevention and/or treatment of Alzheimer's disease.

Pursuing the Complexity of Alzheimer's Disease: Discovery of Fluoren-9-Amines as Selective Butyrylcholinesterase Inhibitors and N-Methyl-d-Aspartate Receptor Antagonists

Alzheimer’s disease (AD) is a complex disorder with unknown etiology. Currently, only symptomatic therapy of AD is available, comprising cholinesterase inhibitors and N-methyl-d-aspartate (NMDA) receptor antagonists. Drugs targeting only one pathological condition have generated only limited efficacy. Thus, combining two or more therapeutic interventions into one molecule is believed to provide higher benefit for the treatment of AD. In the presented study, we designed, synthesized, and biologically evaluated 15 novel fluoren-9-amine derivatives. The in silico prediction suggested both the oral availability and permeation through the blood–brain barrier (BBB). An initial assessment of the biological profile included determination of the cholinesterase inhibition and NMDA receptor antagonism at the GluN1/GluN2A and GluN1/GluN2B subunits, along with a low cytotoxicity profile in the CHO-K1 cell line. Interestingly, compounds revealed a selective butyrylcholinesterase (BChE) inhibition pattern with antagonistic activity on the NMDARs. Their interaction with butyrylcholinesterase was elucidated by studying enzyme kinetics for compound 3c in tandem with the in silico docking simulation. The docking study showed the interaction of the tricyclic core of new derivatives with Trp82 within the anionic site of the enzyme in a similar way as the template drug tacrine. From the kinetic analysis, it is apparent that 3c is a competitive inhibitor of BChE.

Exploring Structure-Activity Relationship in Tacrine-Squaramide Derivatives as Potent Cholinesterase Inhibitors

Tacrine was the first drug to be approved for Alzheimer’s disease (AD) treatment, acting as a cholinesterase inhibitor. The neuropathological hallmarks of AD are amyloid-rich senile plaques, neurofibrillary tangles, and neuronal degeneration. The portfolio of currently approved drugs for AD includes acetylcholinesterase inhibitors (AChEIs) and N-methyl-d-aspartate (NMDA) receptor antagonist. Squaric acid is a versatile structural scaffold capable to be easily transformed into amide-bearing compounds that feature both hydrogen bond donor and acceptor groups with the possibility to create multiple interactions with complementary sites. Considering the relatively simple synthesis approach and other interesting properties (rigidity, aromatic character, H-bond formation) of squaramide motif, we combined this scaffold with different tacrine-based derivatives. In this study, we developed 21 novel dimers amalgamating squaric acid with either tacrine, 6-chlorotacrine or 7-methoxytacrine representing various AChEIs. All new derivatives were evaluated for their anti-cholinesterase activities, cytotoxicity using HepG2 cell line and screened to predict their ability to cross the blood-brain barrier. In this contribution, we also report in silico studies of the most potent AChE and BChE inhibitors in the active site of these enzymes.

Interspecies and intergender differences in acute toxicity of K-oximes drug candidates

K-oximes were developed as modern drug candidates acting as AChE reactivators. In this study, it has been investigated which interspecies and intergender differences changes could be observed in Wistar rats and Swiss mice, both genders, after the treatment with increasing doses of selected acetylcholinesterase reactivators - asoxime, obidoxime, K027, K048, and K075. After the 24 h, a number of died animals was counted and the median lethal dose (LD₅₀) for each oxime was calculated. By using the intramuscular route of administration, asoxime and K027 had the least toxicity in female rats (640.21 mg/kg and 686.08 mg/kg), and in female mice (565.75 mg/kg and 565.74 mg/kg), respectively. Moreover, asoxime and K027 showed 3, 4 or 8 times less acute toxicity in comparison to K048, obidoxime and K075, respectively. Beyond, K075 had the greatest toxicity in male rats (81.53 mg/kg), and in male mice (57.34 mg/kg), respectively. Our results can help to predict likely adverse toxic effects, target organ systems and possible outcome in the event of massive human overexposure, and in establishing risk categories or in dose selection for the initial repeated dose toxicity tests to be conducted for each oxime.

Reactivation potency of two novel oximes (K456 and K733) against paraoxon-inhibited acetyl and butyrylcholinesterase: In silico and in vitro models

Organophosphates (OPs) irreversibly inhibit acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes. The reactivation of these inhibited enzymes is paramount for their normal function. Present study evaluates reactivation potency of two newly developed oximes, K456 and K733, against paraoxon (POX)-inhibited human-RBC-AChE and human-plasma-BChE in comparison to reported reactivator, pralidoxime (2-PAM). In vitro studies showed higher intrinsic toxicities of both oximes than 2-PAM for AChE. No substantial reactivation of hBChE was noted by tested concentration. Contrary to 2-PAM, the in silico study predicted lower binding free energies for both oximes. However, the detailed interaction study revealed inability of oximes to interact with catalytic anionic site of AChE and hBChE in contrast to 2-PAM. Both in vitro and in silico studies conclude that K456 and K733 are unlikely to be used as reactivators of paraoxon-inhibited AChE or BChE.

Synthesis and in vitro evaluation of neutral aryloximes as reactivators of Electrophorus eel acetylcholinesterase inhibited by NEMP, a VX surrogate

Casualties caused by nerve agents, potent acetylcholinesterase inhibitors, have attracted attention from media recently. Poisoning with these chemicals may be fatal if not correctly addressed. Therefore, research on novel antidotes is clearly warranted. Pyridinium oximes are the only clinically available compounds, but poor penetration into the blood-brain barrier hampers efficient enzyme reactivation at the central nervous system. In searching for structural factors that may be explored in SAR studies, we synthesized and evaluated neutral aryloximes as reactivators for acetylcholinesterase inhibited by NEMP, a VX surrogate. Although few tested compounds reached comparable reactivation results with clinical standards, they may be considered as leads for further optimization.

Kinetics of acetylcholinesterase inhibition by hemp seed protein-derived peptides

The aim of this work was to enhance the acetylcholinesterase (AChE)-inhibitory activity of a pepsin-produced hemp seed protein hydrolysates (HPH) through reverse-phase HPLC separation followed by identification of peptide sequences present in the most active fraction. The HPH was separated into eight fractions (F1-F8) with F7 exhibiting significantly (p < 0.05) the strongest (97.5%) in vitro inhibition of electric eel AChE (eeAChE) activity in comparison to 53.8% for HPH. The HPH consisted mostly of low molecular weight peptides of < 11 amino acid residues and most contained at least one hydrophobic amino acid. Kinetics of enzyme inhibition revealed a mixed-type inhibition of eeAChE activity by HPH whereas F7 acted through an uncompetitive mode; in contrast inhibition of human AChE by HPH and F7 was uncompetitive. The stronger inhibitory potency of the F7 peptides fraction against both enzymes was confirmed through reduced maximal velocity, catalytic efficiency, and inhibition constant values when compared to the HPH. PRACTICAL APPLICATIONS: The use of natural products for the prevention or treatment of human diseases continues to be an area of intense research activities. Food protein-derived peptides obtained through enzymatic hydrolysis of hemp seed proteins were shown in vitro to be strong inhibitors of activities of both the eel and human forms of acetylcholinesterase (AChE). AChE is an important therapeutic target because excessive activity of this enzyme is a causative factor of neurodegenerative diseases such as dementia and Alzheimer's. This work showed that peptides in the most active fraction are small in sizes, which may favor their absorption into blood circulation and possible permeation of the blood-brain barrier. Therefore, the hemp seed peptides are potential agents that can be used to formulate functional foods and nutraceuticals against neurodegenerative diseases.

Prediction of Ligands Binding Acetylcholinesterase with Potential Antidotal Activity: A Virtual Screening Approach

Intoxications caused by organophosphorus compounds (OPs) are associated with the reversible, and sometimes irreversible interaction with acetylcholinesterase (AChE). OPs are commonly used as pesticides mainly in developing countries, where the associated poisoning is a major health problem related to suicidal attempts, careless manipulation, and chemical warfare. The current antidotes are oxime-based drugs that can regenerate the AChE catalytic activity. Nevertheless, challenges associated with lack of efficiency and difficulties for crossing blood-brain barrier have motivated the design of novel alternatives. We used a validated molecular docking approach for the virtual screening of 579,890 synthetic ligands and 478 drugs against a human AChE in its apo conformation, and a murine AChE conjugated with the OP tabun. After filtering, 7 hits were selected as potential competitors due to the formation of key interactions within the active site gorge of the AChE structure, and potential reactivators based on interactions with amino acids of the catalytic triad in the presence of organophosphorus compounds. The selected candidates will be further evaluated through in vitro and in vivo assays.

Toxic Injury to Muscle Tissue of Rats Following Acute Oximes Exposure

Therapeutic application of newly developed oximes is limited due to their adverse effects on different tissues. Within this article, it has been investigated which morphological changes could be observed in Wistar rats after the treatment with increasing doses of selected acetyl cholinesterase reactivators - asoxime, obidoxime, K027, K048, and K075. Subsequently, heart, diaphragm and musculus popliteus were obtained for pathohistological and semiquantitative analysis 24 hrs and 7 days after im administration of a single dose of 0.1 LD₅₀, 0.5 LD₅₀, and 1.0 LD₅₀ of each oxime. Different muscle damage score was based on an estimation scale from 0 (no damage) to 5 (strong damage). In rats treated with 0.1 LD₅₀ of each oxime, muscle fibres did not show any change. The intensive degeneration was found in all muscles after treatment with 0.5 LD₅₀ of asoxime and obidoxime, respectively. Acute toxic muscle injury was developed within 7 days following treatment with 0.5 LD₅₀ and 1.0 LD₅₀ of each oxime, with the highest values in K048 and K075 group (P < 0.001 vs. control and asoxime), respectively. The early muscle alterations observed in our study seem to contribute to the pathogenesis of the oxime-induced toxic muscle injury, which probably manifests as necrosis and/or inflammation.

Oxime K203: a drug candidate for the treatment of tabun intoxication

For over 60 years, researchers across the world have sought to deal with poisoning by nerve agents, the most toxic and lethal chemical weapons. To date, there is no efficient causal antidote with sufficient effect. Every trialed compound fails to fulfil one or more criteria (e.g. reactivation potency, broad reactivation profile). In this recent contribution, we focused our attention to one of the promising compounds, namely the bis-pyridinium reactivator K203. The oxime K203 is very often cited as the best reactivator against tabun poisoning. Herein, we provide all the available literature data in comprehensive and critical review to address whether K203 could be considered as a new drug candidate against organophosphorus poisoning with the stress on tabun. We describe its development from the historical point of view and review all available in vitro as well as in vivo data to date. K203 is easily accessible by a relatively simple two-step synthesis. It is well accommodated in the enzyme active gorge of acetylcholinesterase providing suitable interactions for reactivation, as shown by molecular docking simulations. According to a literature survey, in vitro data for tabun-inhibited AChE are extraordinary. However, in vivo efficiency remains unconvincing. The K203 toxicity profile did not show any perturbations compared to clinically used standards; on the other hand versatility of K203 does not exceed currently available oximes. In summary, K203 does not seem to address current issues associated with the organophosphorus poisoning, especially the broad profile against all nerve agents. However, its reviewed efficacy entitles K203 to be considered as a backup or tentative replacement for obidoxime and trimedoxime, currently only available anti-tabun drugs.

The concept of hybrid molecules of tacrine and benzyl quinolone carboxylic acid (BQCA) as multifunctional agents for Alzheimer's disease

Novel tacrine-benzyl quinolone carboxylic acid (tacrine-BQCA) hybrids were designed based on multi-target directed ligands (MTLDs) paradigm, synthesized and evaluated in vitro as inhibitors of human acetylcholinesterase (hAChE) and human butyrylcholinesterase (hBChE). Tacrine moiety is represented herein as 7-methoxytacrine, 6-chlorotacrine or unsubstituted tacrine forming three different families of seven members, i.e. 21 compounds in overall. Introducing BQCA, a positive modulator of M1 muscarinic acetylcholine receptors (mAChRs), the action of novel compounds on M1 mAChRs was evaluated via Fluo-4 NW assay on the Chinese hamster ovarian (CHO-M1WT2) cell line. All the novel tacrine-BQCA hybrids were able to block the action of hAChE and hBChE in micromolar to nanomolar range. The hAChE kinetic profile of 5p was found to be mixed-type which is consistent with our docking experiments. Moreover, selected ligands were assessed for their potential hepatotoxicity on HepG2 cell line and presumable permeation through the blood-brain barrier by PAMPA assay. Expected agonistic profile towards M1 mAChRs delivered by BQCA moiety was not confirmed. From all the hybrids, 5o can be highlighted as non-selective cholinesterase inhibitor (hAChE IC₅₀ = 74.5 nM; hBChE IC₅₀ = 83.3 nM) with micromolar antagonistic activity towards M1 mAChR (IC₅₀ = 4.23 μM). A non-selective pattern of cholinesterase inhibition is likely to be valuable during the onset as well as later stages of AD.

Anti-acetylcholinesterase activity of essential oils and their major constituents from four Ocimum species

Ocimum is a genus of considerable importance in traditional medicine worldwide. The goal of this study was to examine the anti-acetylcholinesterase activity of Ocimum essential oils and to correlate the activity with their chemical profiles using a metabolome based GC-MS approach coupled to chemometrics. Further, molecular docking was adopted to rationalize the activity of some essential oil isolates. Essential oil prepared from the four species O. basilicum, O. africanum, O. americanum, and O. minimum exhibited significant anti-acetylcholinesterase activity with (IC50 0.22, 0.175, 0.57 and 0.152 mg/mL, respectively) comparable to that of physostigmine (IC50 0.27 mg/mL). The phenylpropanoids (i.e. estragole) constituted the most dominant chemical group in O. basilicum (sweet basil) and O. minimum, whereas camphor (a ketone) was the most abundant in O. africanum and O. americanum. Supervised and unsupervised multivariate data analyses clearly separated O. africanum and O. americanum from other accessions, with estragole, camphor and, to less extent, β-linalool contributing to species segregation. Estragole was found the most active AchE inhibitor (IC50 0.337 µM) followed by cineole (IC50 2.27 µM), camphor (IC50 21.43 µM) and eugenol (IC50 40.32 µM). Molecular docking revealed that these compounds bind to key amino acids in the catalytic domain of AchE, similar to standard drugs.

Development of 2-Methoxyhuprine as Novel Lead for Alzheimer's Disease Therapy

Tacrine (THA), the first clinically effective acetylcholinesterase (AChE) inhibitor and the first approved drug for the treatment of Alzheimer’s disease (AD), was withdrawn from the market due to its side effects, particularly its hepatotoxicity. Nowadays, THA serves as a valuable scaffold for the design of novel agents potentially applicable for AD treatment. One such compound, namely 7-methoxytacrine (7-MEOTA), exhibits an intriguing profile, having suppressed hepatotoxicity and concomitantly retaining AChE inhibition properties. Another interesting class of AChE inhibitors represents Huprines, designed by merging two fragments of the known AChE inhibitors—THA and (−)-huperzine A. Several members of this compound family are more potent human AChE inhibitors than the parent compounds. The most promising are so-called huprines X and Y. Here, we report the design, synthesis, biological evaluation, and in silico studies of 2-methoxyhuprine that amalgamates structural features of 7-MEOTA and huprine Y in one molecule.

Novel Organophosphate Ligand O-(2-Fluoroethyl)-O-(p-Nitrophenyl)Methylphosphonate: Synthesis, Hydrolytic Stability and Analysis of the Inhibition and Reactivation of Cholinesterases

The organophosphate O-(2-fluoroethyl)-O-(p-nitrophenyl) methyphosphonate 1 is the first-in-class, fluorine-18 radiolabeled organophosphate inhibitor ([18F]1) of acetylcholinesterase (AChE). In rats, [18F]1 localizes in AChE rich regions of the brain and other tissues where it likely exists as the (CH3)(18FCH2CH2O)P(O)-AChE adduct (ChE-1). Characterization of this adduct would define the inhibition mechanism and subsequent postinhibitory pathways and reactivation rates. To validate this adduct, the stability (hydrolysis) of 1 and ChE-1 reactivation rates were determined. Base hydrolysis of 1 yields p-nitrophenol and (CH3) (FCH2CH2O)P(O)OH with pseudo first order rate constants (kobsd) at pH 7.4 (PBS) of 3.25 × 10-4 min-1 (t1/2 = 35.5 h) at 25 °C and 8.70 × 10-4 min-1 (t1/2 = 13.3 h) at 37 °C. Compound 1 was a potent inhibitor of human acetylcholinesterase (HuAChE; ki = 7.5 × 105 M-1 min-1), electric eel acetylcholinesterase (EEAChE) (ki = 3.0 × 106 M-1 min-1), and human serum butyrylcholinesterase (HuBChE; 1.95 × 105 M-1 min-1). Spontaneous and oxime-mediated reactivation rates for the (CH3) (FCH2CH2O)P(O)-serine ChE adducts using 2-PAM (10 μM) were (a) HuAChE 8.8 × 10-5 min-1 (t1/2 = 131.2 h) and 2.41 × 10-2 min-1 (t1/2 = 0.48 h), (b) EEAChE 9.32 × 10-3 min-1 (t1/2 = 1.24 h) and 3.33 × 10-2 min-1 (t1/2 = 0.35 h), and (c) HuBChE 1.16 × 10-4 min-1 (t1/2 = 99.6 h) and 4.19 × 10-2 min-1 (t1/2 = 0.27 h). All ChE-1 adducts undergo rapid and near complete restoration of enzyme activity following addition of 2-PAM (30 min), and no aging was observed for either reactivation process. The fast reactivation rates and absence of aging of ChE-1 adducts are explained on the basis of the electron-withdrawing fluorine group that favors the nucleophilic reactivation processes but disfavors cation-based dealkylation aging mechanisms. Therefore, the likely fate of radiolabeled compound 1 in vivo is the formation of (CH3)(FCH2CH2O)P(O)-serine adducts and monoacid (CH3)(FCH2CH2O)P(O)OH from hydrolysis and reactivation.

Primary Investigation for the Mechanism of Biatractylolide from Atractylodis Macrocephalae Rhizoma as an Acetylcholinesterase Inhibitor

Biatractylolide was isolated from ethyl acetate extract of dried Atractylodis Macrocephalae Rhizoma root by multistep chromatographic processing. Structure of biatractylolide was confirmed by (1)H-NMR and (13)C-NMR. The IC50 on acetylcholinesterase (AChE) activity was 6.5458 μg/mL when the control IC50 value of huperzine A was 0.0192 μg/mL. Molecular Docking Software (MOE) was used to discover molecular sites of action between biatractylolide and AChE protein by regular molecular docking approaches. Moreover, biatractylolide downregulated the expression of AChE of MEF and 293T cells in a dose-dependent manner. These results demonstrated that the molecular mechanisms of inhibitory activities of biatractylolide on AChE are not only through binding to AChE, but also via reducing AChE expression by inhibiting the activity of GSK3β.

Synthesis and inhibitory properties of some carbamates on carbonic anhydrase and acetylcholine esterase

A series of carbamate derivatives were synthesized and their carbonic anhydrase I and II isoenzymes and acetylcholinesterase enzyme (AChE) inhibitory effects were investigated. All carbamates were synthesized from the corresponding carboxylic acids via the Curtius reactions of the acids with diphenyl phosphoryl azide followed by addition of benzyl alcohol. The carbamates were determined to be very good inhibitors against for AChE and hCA I, and II isoenzymes. AChE inhibition was determined in the range 0.209-0.291 nM. On the other hand, tacrine, which is used in the treatment of Alzheimer's disease possessed lower inhibition effect (Ki: 0.398 nM). Also, hCA I and II isoenzymes were effectively inhibited by the carbamates, with inhibition constants (Ki) in the range of 4.49-5.61 nM for hCA I, and 4.94-7.66 nM for hCA II, respectively. Acetazolamide, which was clinically used carbonic anhydrase (CA) inhibitor demonstrated Ki values of 281.33 nM for hCA I and 9.07 nM for hCA II. The results clearly showed that AChE and both CA isoenzymes were effectively inhibited by carbamates at the low nanomolar levels.

Discovery of New Classes of Compounds that Reactivate Acetylcholinesterase Inhibited by Organophosphates

Acetylcholinesterase (AChE) that has been covalently inhibited by organophosphate compounds (OPCs), such as nerve agents and pesticides, has traditionally been reactivated by using nucleophilic oximes. There is, however, a clearly recognized need for new classes of compounds with the ability to reactivate inhibited AChE with improved in vivo efficacy. Here we describe our discovery of new functional groups--Mannich phenols and general bases--that are capable of reactivating OPC--inhibited AChE more efficiently than standard oximes and we describe the cooperative mechanism by which these functionalities are delivered to the active site. These discoveries, supported by preliminary in vivo results and crystallographic data, significantly broaden the available approaches for reactivation of AChE.