A structure-based design approach to the development of novel, reversible AChE inhibitors

Discovery and biological characterization of a novel mesoionic insecticide fenmezoditiaz

BACKGROUND

Many piercing-sucking insects have developed resistance or cross-resistance to many insecticides targeting insect neural nicotinic acetylcholine receptor (nAChR). Here we are aiming to present the discovery of a novel mesoionic insecticide, fenmezoditiaz, by BASF through structure-based drug design (SBDD) approaches. It has recently been added to the Insecticide Resistance Action Committee mode of classification (IRAC 4E). It is being developed for plant protection against piercing-sucking pests, especially rice hopper complex.

RESULTS

The soluble acetylcholine binding protein (AChBP) from the sea slug Aplysia californica was modified using site-directed mutagenesis and based on putative aphid nAChR subunit sequences to create soluble insect-like AChBPs. Among them, insect-like β1 AChBP and native aphid membrane preparation showed the highest correlated biochemical affinity toward structurally diverse ligands. This mutant AChBP was used to understand how insect nAChRs structurally interact with mesoionics, which was then utilized to design novel mesoionics including fenmezoditiaz. It is an excellent systemic insecticide with diverse application methods and has a broad insecticidal spectrum, especially against piercing/sucking insects. It lacks cross-resistance for neonicotinoid resistant plant hoppers. Field-collected brown plant hopper populations from Asian countries showed high susceptibility.

CONCLUSIONS

Fenmezoditiaz is a systemic insecticide with a broad spectrum, lack of cross-resistance and it could be an additional tool for integrated pest management and insecticide resistance management, especially for the rice hopper complex. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

In silico identification and study of potential anti-mosquito juvenile hormone binding protein (MJHBP) compounds as candidates for dengue virus - Vector insecticides

Dengue has become a huge global health burden. It is currently recognized as the most rapidly spreading mosquito-borne viral disease. Yet, there are currently no licensed vaccines or specific therapeutics to manage the virus, thus, scaling up vector control approaches is important in controlling this viral spread. This study aimed to identify and study in silico, potential anti-mosquito compounds targeting Juvenile hormone (JH) mediated pathways via the Mosquito Juvenile Hormone Binding Protein (MJHBP). The study was implemented using series of computational methods. The query compounds included pyrethroids and those derived from ZINC and ANPDB databases using a simple pharmacophore model in Molecular Operating Environment (MOE). Molecular docking of selected compounds' library was implemented in MOE. The resultant high-score compounds were further validated by molecular dynamics simulation via Maestro 12.3 module and the respective Prime/Molecular Mechanics Generalized Born Surface Area (Prime/MM-GBSA) binding energies computed. The study identified compounds-pyrethroids, natural and synthetic - with high docking energy scores (ranging from 10.91-12.34 kcal/mol). On further analysis of the high-ranking (in terms of docking scores) compounds using MD simulation, the compounds - Ekeberin D4, Maesanin, Silafluofen and ZINC16919139- revealed very low binding energies (-122.99, -72.91 -104.50 and,-74.94 kcal/mol respectively), fairly stable complex and interesting interaction with JH-binding site amino acid residues on MJHBP. Further studies can explore these compounds in vitro/in vivo in the search for more efficient mosquito vector control.

Enantioseparation, in vitro testing, and structural characterization of triple-binding reactivators of organophosphate-inhibited cholinesterases

The enantiomers of racemic 2-hydroxyimino-N-(azidophenylpropyl)acetamide-derived triple-binding oxime reactivators were separated, and tested for inhibition and reactivation of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibited with tabun (GA), cyclosarin (GF), sarin (GB), and VX. Both enzymes showed the greatest affinity toward the methylimidazole derivative (III) of 2-hydroxyimino-N-(azidophenylpropyl)acetamide (I). The crystal structure was determined for the complex of oxime III within human BChE, confirming that all three binding groups interacted with active site residues. In the case of BChE inhibited by GF, oximes I (kr = 207 M-1 min-1) and III (kr = 213 M-1 min-1) showed better reactivation efficiency than the reference oxime 2-PAM. Finally, the key mechanistic steps in the reactivation of GF-inhibited BChE with oxime III were modeled using the PM7R6 method, stressing the importance of proton transfer from Nε of His438 to Oγ of Ser203 for achieving successful reactivation.

Structural and kinetic evidence of aging after organophosphate inhibition of human Cathepsin A

Human Cathepsin A (CatA) is a lysosomal serine carboxypeptidase of the renin-angiotensin system (RAS) and is structurally similar to acetylcholinesterase (AChE). CatA can remove the C-terminal amino acids of endothelin I, angiotensin I, Substance P, oxytocin, and bradykinin, and can deamidate neurokinin A. Proteomic studies identified CatA and its homologue, SCPEP1, as potential targets of organophosphates (OP). CatA could be stably inhibited by low µM to high nM concentrations of racemic sarin (GB), soman (GD), cyclosarin (GF), VX, and VR within minutes to hours at pH 7. Cyclosarin was the most potent with a kinetically measured dissociation constant (K_I) of 2 µM followed by VR (K_I = 2.8 µM). Bimolecular rate constants for inhibition by cyclosarin and VR were 1.3 × 10³ M^-1sec^-1 and 1.2 × 10³ M^-1sec^-1, respectively, and were approximately 3-orders of magnitude lower than those of human AChE indicating slower reactivity. Notably, both AChE and CatA bound diisopropylfluorophosphate (DFP) comparably and had K_I^DFP = 13 µM and 11 µM, respectively. At low pH, greater than 85% of the enzyme spontaneously reactivated after OP inhibition, conditions under which OP-adducts of cholinesterases irreversibly age. At pH 6.5 CatA remained stably inhibited by GB and GF and <10% of the enzyme spontaneously reactivated after 200 h. A crystal structure of DFP-inhibited CatA was determined and contained an aged adduct. Similar to AChE, CatA appears to have a "backdoor" for product release. CatA has not been shown previously to age. These results may have implications for: OP-associated inflammation; cardiovascular effects; and the dysregulation of RAS enzymes by OP.

Therapeutic Potential of Multifunctional Tacrine Analogues

Abstract: Tacrine is a potent inhibitor of cholinesterases (acetylcholinesterase and butyrylcholinesterase) that shows limiting clinical application by liver toxicity. In spite of this, analogues of tacrine are considered as a model inhibitor of cholinesterases in the therapy of Alzheimer’s disease. The interest in these compounds is mainly related to a high variety of their structure and biological properties. In the present review, we have described the role of cholinergic transmission and treatment strategies in Alzheimer’s disease as well as the synthesis and biological activity of several recently developed classes of multifunctional tacrine analogues and hybrids, which consist of a new paradigm to treat Alzheimer’s disease. We have also reported potential of these analogues in the treatment of Alzheimer’s diseases in various experimental systems.

Computer-Aided Drug Discovery in Plant Pathology

Control of plant diseases is largely dependent on use of agrochemicals. However, there are widening gaps between our knowledge on plant diseases gained from genetic/mechanistic studies and rapid translation of the knowledge into target-oriented development of effective agrochemicals. Here we propose that the time is ripe for computer-aided drug discovery/design (CADD) in molecular plant pathology. CADD has played a pivotal role in development of medically important molecules over the last three decades. Now, explosive increase in information on genome sequences and three dimensional structures of biological molecules, in combination with advances in computational and informational technologies, opens up exciting possibilities for application of CADD in discovery and development of agrochemicals. In this review, we outline two categories of the drug discovery strategies: structure- and ligand-based CADD, and relevant computational approaches that are being employed in modern drug discovery. In order to help readers to dive into CADD, we explain concepts of homology modelling, molecular docking, virtual screening, and de novo ligand design in structure-based CADD, and pharmacophore modelling, ligand-based virtual screening, quantitative structure activity relationship modelling and de novo ligand design for ligand-based CADD. We also provide the important resources available to carry out CADD. Finally, we present a case study showing how CADD approach can be implemented in reality for identification of potent chemical compounds against the important plant pathogens, Pseudomonas syringae and Colletotrichum gloeosporioides.

Discovery of Species-selective and Resistance-breaking Anticholinesterase Insecticides for the Malaria Mosquito

Great reductions in malaria mortality have been accomplished in the last 15 years, in part due to the widespread roll-out of insecticide-treated bednets across sub-Saharan Africa. To date, these nets only employ pyrethroids, insecticides that target the voltage-gated sodium ion channel of the malaria vector, Anopheles gambiae. Due to the growing emergence of An. gambiae strains that are resistant to pyrethroids, there is an urgent need to develop new public health insecticides that engage a different target and possess low mammalian toxicity. In this review, we will describe efforts to develop highly species-specific and resistance-breaking inhibitors of An. gambiae acetylcholinesterase (AgAChE). These efforts have been greatly aided by advances in knowledge of the structure of the enzyme, and two major inhibitor design strategies have been explored. Since AgAChE possesses an unpaired Cys residue not present in mammalian AChE, a logical strategy to achieve selective inhibition involves design of compounds that could ligate that Cys. A second strategy involves the design of new molecules to target the catalytic serine of the enzyme. Here the challenge is not only to achieve high inhibition selectivity vs human AChE, but also to demonstrate toxicity to An. gambiae that carry the G119S resistance mutation of AgAChE. The advances made and challenges remaining will be presented. This review is part of the special issue "Insecticide Mode of Action: From Insect to Mammalian Toxicity".

Superacidic Cyclization of Activated Anthranilonitriles into 2-Unsubstituted-4-aminoquinolines

4-Aminoquinolines were prepared in a three-step synthesis starting from substituted anthranilonitriles. The condensation on 1,1,1-trichloro-4-ethoxybut-3-enone proceeded efficiently either neat or in refluxing EtOH. Cyclization in superacidic trifluoromethanesulfonic acid provided unstable intermediate, which upon treatment with NaOEt in ethanol, afforded the expected esters. Theoretical investigations pointed out a monoprotonated nitrilium as the reactive species during the cyclization process.

Novel bipharmacophoric inhibitors of the cholinesterases with affinity to the muscarinic receptors M1 and M2

A set of hybrid compounds composed of the fragment of allosteric modulators of the muscarinic receptor, i.e. W84 and naphmethonium, and the well-known AChE inhibitor tacrine on the one hand, and the skeletons of the orthosteric muscarinic agonists, iperoxo and isox, on the other hand, were synthesized. The two molecular moieties were connected via a polymethylene linker of varying length. These bipharmacophoric compounds were investigated for inhibition of AChE (from electric eel) and BChE (from equine serum) as well as human ChEs in vitro and compared to previously synthesized dimeric inhibitors. Among the studied hybrids, compound 10-C10, characterized by a 10 carbon alkylene linker connecting tacrine and iperoxo, proved to be the most potent inhibitor with the highest pIC₅₀ values of 9.81 (AChE from electric eel) and 8.75 (BChE from equine serum). Docking experiments with compounds 10-C10, 7b-C10, and 7a-C10 helped to interpret the experimental inhibitory power against AChE, which is affected by the nature of the allosteric molecular moiety, with the tacrine-containing hybrid being much more active than the naphthalimido- and phthalimido-containing analogs. Furthermore, the most active AChE inhibitors were found to have affinity to M₁ and M₂ muscarinic receptors. Since 10-C10 showed almost no cytotoxicity, it emerged as a promising lead structure for the development of an anti-Alzheimer drug.

Design, synthesis and biological evaluation of bisthiazole-based trifluoromethyl ketone derivatives as potent HDAC inhibitors with improved cellular efficacy

Histone deacetylases (HDACs) are a class of epigenetic modulators with complex functions in histone post-translational modifications and are well known targets for antineoplastic drugs. We have previously developed a series of bisthiazole-based hydroxamic acids as novel potent HDAC inhibitors. In the present work, a new series of bisthiazole-based compounds with different zinc binding groups (ZBGs) have been designed and synthesized. Among them is compound 7, containing a trifluoromethyl ketone as the ZBG, which displays potent inhibitory activity towards human HDACs and improved antiproliferative activity in several cancer cell lines.

Difluoromethyl ketones: Potent inhibitors of wild type and carbamate-insensitive G119S mutant Anopheles gambiae acetylcholinesterase

Malaria is a devastating disease in sub-Saharan Africa, and current vector control measures are threatened by emerging resistance mechanisms. With the goal of developing new, selective, resistance-breaking insecticides we explored α-fluorinated methyl ketones as reversible covalent inhibitors of Anopheles gambiae acetylcholinesterase (AgAChE). Trifluoromethyl ketones 5 demonstrated remarkable volatility in microtiter plate assays, but 5c,e-h exhibited potent (1-100 nM) inhibition of wild type (WT) AgAChE and weak inhibition of resistant mutant G119S mutant AgAChE. Fluoromethyl ketones 10c-i exhibited submicromolar to micromolar inhibition of WT AgAChE, but again only weakly inhibited G119S AgAChE. Interestingly, difluoromethyl ketone inhibitors 9c and 9g had single digit nanomolar inhibition of WT AgAChE, and 9g had excellent potency against G119S AgAChE. Approach to steady-state inhibition was quite slow, but after 23 h incubation an IC50 value of 25.1 ± 1.2 nM was measured. We attribute the slow, tight-binding G119S AgAChE inhibition of 9g to a balance of steric size and electrophilicity. However, toxicities of 5g, 9g, and 10g to adult A. gambiae in tarsal contact, fumigation, and injection assays were lower than expected based on WT AgAChE inhibition potency and volatility. Potential toxicity-limiting factors are discussed.

Spectroscopic analysis and charge transfer interaction studies of 4-benzyloxy-2-nitroaniline insecticide: a density functional theoretical approach

A widespread exploration on the intra-molecular charge transfer interaction through an efficient π-conjugated path from a strong electron-donor group (amino) to a strong electron-acceptor group (nitro) has been carried out using FTIR, FT-Raman, UV-Vis, fluorescence and NMR spectra on insecticide compound 4-benzyloxy-2-nitroaniline. Density functional theory method is used to determine optimized molecular geometry, harmonic vibrational wavenumbers and intensities using 6-311G(d,p) basis set by means of Gaussian 09W program suit. A comprehensive investigation on the sp(2) to sp(3) hybridization and non-planarity property has been performed. Natural bond orbital analysis is used to study the existence of C-H⋯O, N-H⋯O and C-H⋯π proper and improper hydrogen bonds. The HOMO and LUMO analysis reveals the possibility of charge transfer within the molecule. A complete assignment of the experimental absorption peaks in the ultraviolet region has also been performed. Isotropic chemical shifts of (13)C, (1)H, (15)N and (18)O NMR and nuclear spin-spin coupling constants have been computed using the gauge-invariant atomic orbital method. The biological activity of substituent amino and nitro groups are evident from the hydrogen bonds through which the target amino acids are linked to the drug as evidenced from molecular docking.

Conformational analysis and parallel QM/MM X-ray refinement of protein bound anti-Alzheimer drug donepezil

The recognition and association of donepezil with acetylcholinesterase (AChE) has been extensively studied in the past several decades because of the former's use as a palliative treatment for mild Alzheimer disease. Herein we examine the conformational properties of donepezil and we re-examine the donepezil-AChE crystal structure using combined quantum mechanical/molecular mechanical (QM/MM) X-ray refinement tools. Donepezil's conformational energy surface was explored using the M06 suite of density functionals and with the MP2/complete basis set (CBS) method using the aug-cc-pVXZ (X = D and T) basis sets. The donepezil-AChE complex (PDB 1EVE) was also re-refined through a parallel QM/MM X-ray refinement approach based on an in-house ab initio code QUICK, which uses the message passing interface (MPI) in a distributed SCF algorithm to accelerate the calculation via parallelization. In the QM/MM re-refined donepezil structure, coordinate errors that previously existed in the PDB deposited geometry were improved leading to an improvement of the modeling of the interaction between donepezil and the aromatic side chains located in the AChE active site gorge. As a result of the re-refinement there was a 93% reduction in the donepezil conformational strain energy versus the original PDB structure. The results of the present effort offer further detailed structural and biochemical inhibitor-AChE information for the continued development of more effective and palliative treatments of Alzheimer disease.

Molecular docking and receptor-specific 3D-QSAR studies of acetylcholinesterase inhibitors

The reversible inhibition of acetylcholinesterase (AChE) has become a promising target for the treatment of Alzheimer's disease (AD) which is mainly associated with low in vivo levels of acetylcholine (ACh). The availability of AChE crystal structures with and without a ligand triggered the effort to find a structure-based design of acetylcholinesterase inhibitors (AChEIs) for AD. The major problem observed with the structure-based design was the feeble robustness of the scoring functions toward the correlation of docking scores with inhibitory potencies of known ligands. This prompted us to develop new prediction models using the stepwise regression analysis based on consensus of different docking and their scoring methods (GOLD, LigandFit, and GLIDE). In the present investigation, a dataset of 91 molecules belonging to 9 different structural classes of heterocyclic compounds with an activity range of 0.008 to 281,000 nM was considered for docking studies and development of AChE-specific 3D-QSAR models. The model (M1) developed using consensus of docking scores of scoring functions viz. Glide score, Gold score, Chem score, ASP score, PMF score, and DOCK score was found to be the best (R(2) = 0.938, Q(2) = 0.925, R(pred)(2) = 0.919, R(2)m((overall)) = 0.936) compared to other consensus models. Docking studies revealed that the molecules with proper alignment in the active site gorge and the ability to interact with all the crucial amino acid residues, in particular by forming π-π stacking interactions with Trp84 at the catalytic anionic site (CAS) and Trp279 at peripheral anionic site (PAS), showed augmented potencies with consequent improvement in patient cognition and reduced the formation of senile plaques associated with AD. Further, the descriptors that signify the association of the ligands with the receptor as well as ADME properties of the ligands were also analyzed by means of the set of ligands that have been pre-positioned with respect to a receptor after docking analysis and considered as independent variables to generate a linear model (M3 and M4) using a stepwise multiple linear regression method to get additional insight into the physicochemical requirements for effective binding of ligands with AChE as well as for prediction of AChE inhibition. The developed AChE-specific prediction models (M1-M4) satisfactorily reflect the structure-activity relationship of the existing AChEIs and have all the potential to facilitate the process of design and development of new potent AChEIs.

Backdoor opening mechanism in acetylcholinesterase based on X-ray crystallography and molecular dynamics simulations

The transient opening of a backdoor in the active-site wall of acetylcholinesterase, one of nature's most rapid enzymes, has been suggested to contribute to the efficient traffic of substrates and products. A crystal structure of Torpedo californica acetylcholinesterase in complex with the peripheral-site inhibitor aflatoxin is now presented, in which a tyrosine at the bottom of the active-site gorge rotates to create a 3.4-Å wide exit channel. Molecular dynamics simulations show that the opening can be further enlarged by movement of Trp84. The crystallographic and molecular dynamics simulation data thus point to the interface between Tyr442 and Trp84 as the key element of a backdoor, whose opening permits rapid clearance of catalysis products from the active site. Furthermore, the crystal structure presented provides a novel template for rational design of inhibitors and reactivators, including anti-Alzheimer drugs and antidotes against organophosphate poisoning.

The evolution of new enzyme function: lessons from xenobiotic metabolizing bacteria versus insecticide-resistant insects

Here, we compare the evolutionary routes by which bacteria and insects have evolved enzymatic processes for the degradation of four classes of synthetic chemical insecticide. For insects, the selective advantage of such degradative activities is survival on exposure to the insecticide, whereas for the bacteria the advantage is simply a matter of access to additional sources of nutrients. Nevertheless, bacteria have evolved highly efficient enzymes from a wide variety of enzyme families, whereas insects have relied upon generalist esterase-, cytochrome P450- and glutathione-S-transferase-dependent detoxification systems. Moreover, the mutant insect enzymes are less efficient kinetically and less diverged in sequence from their putative ancestors than their bacterial counterparts. This presumably reflects several advantages that bacteria have over insects in the acquisition of new enzymatic functions, such as a broad biochemical repertoire from which new functions can be evolved, large population sizes, high effective mutation rates, very short generation times and access to genetic diversity through horizontal gene transfer. Both the insect and bacterial systems support recent theory proposing that new biochemical functions often evolve from 'promiscuous' activities in existing enzymes, with subsequent mutations then enhancing those activities. Study of the insect enzymes will help in resistance management, while the bacterial enzymes are potential bioremediants of insecticide residues in a range of contaminated environments.

Medicinal chemistry of competitive kainate receptor antagonists

Kainic acid (KA) receptors belong to the group of ionotropic glutamate receptors and are expressed throughout in the central nervous system (CNS). The KA receptors have been shown to be involved in neurophysiological functions such as mossy fiber long-term potentiation (LTP) and synaptic plasticity and are thus potential therapeutic targets in CNS diseases such as schizophrenia, major depression, neuropathic pain and epilepsy. Extensive effort has been made to develop subtype-selective KA receptor antagonists in order to elucidate the physiological function of each of the five subunits known (GluK1-5). However, to date only selective antagonists for the GluK1 subunit have been discovered, which underlines the strong need for continued research in this area. The present review describes the structure-activity relationship and pharmacological profile for 10 chemically distinct classes of KA receptor antagonists comprising, in all, 45 compounds. To the medicinal chemist this information will serve as reference guidance as well as an inspiration for future effort in this field.

Discovery of a new class of ionotropic glutamate receptor antagonists by the rational design of (2S,3R)-3-(3-carboxyphenyl)-pyrrolidine-2-carboxylic acid

The kainic acid (KA) receptors belong to the class of glutamate (Glu) receptors in the brain and constitute a promising target for the treatment of neurological and/or psychiatric diseases such as schizophrenia, major depression, and epilepsy. Five KA subtypes have been identified and named GluK1-5. In this article, we present the discovery of (2S,3R)-3-(3-carboxyphenyl)-pyrrolidine-2-carboxylic acid (1) based on a rational design process. Target compound 1 was synthesized by a stereoselective strategy in 10 steps from commercially available starting materials. Binding affinities of 1 at native ionotropic Glu receptors were determined to be in the micromolar range (AMPA, 51 μM; KA, 22 μM; NMDA 6 μM), with the highest affinity for cloned homomeric KA receptor subtypes GluK1,3 (3.0 and 8.1 μM, respectively). Functional characterization of 1 by two electrode voltage clamp (TEVC) electrophysiology at a nondesensitizing mutant of GluK1 showed full competitive antagonistic behavior with a K(b) of 11.4 μM.

Inactivation of acetylcholinesterase by various fluorophores

The inhibition of recombinant mouse acetylcholinesterase (rMAChE) and electric eel acetylcholinesterase (EEAChE) by seven, structurally different chromophore-based (dansyl, pyrene, dabsyl, diethylamino- and methoxycoumarin, Lissamine rhodamine B, and Texas Red) propargyl carboxamides or sulfonamides was studied. Diethylaminocoumarin, Lissamine, and Texas Red amides inhibited rMAChE with IC50 values of 1.00 microM, 0.05 microM, and 0.70 microM, respectively. Lissamine and Texas Red amides inhibited EEAChE with IC50 values of 3.57 and 10.4 microM, respectively. The other chromophore amides did not inhibit either AChE. The surprising inhibitory potency of Lissamine was examined in further detail against EEAChE and revealed a mixed-type inhibition with Ki = 11.7 microM (competitive) and Ki' = 24.9 microM (noncompetitive), suggesting that Lissamine binds to free enzyme and enzyme-substrate complex.

Molecular interactions of cholinesterases inhibitors using in silico methods: current status and future prospects

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by a low amount of acetylcholine (ACh) in hippocampus and cortex. Acetylcholinesterase (AChE) is one of the most important enzymes in many living organisms including human being and other vertebrates, insects like mosquitoes, among others. Several reports have been published where it has been clearly shown that the genesis of amyloid protein plaques associated with AD is connected to modifications of both AChE and butyrylcholinesterase (BChE), since the plaque is significantly decreased in AD patients using cholinesterase inhibitors (ChEIs). This review gives some examples of these inhibitors discovered during past couple of years that have shown very prominent interactions at the active site triad of the proteins as well as different other parts of the active site like, peripheral anionic site (PAS), oxyanionic hole, anionic subsite or acyl binding pocket (ABP). Most of the inhibition and their interactions have been visualized by X-ray crystallography, but some of the other inhibitors have been studied either by molecular docking or molecular dynamic (MD) simulations or by both the in silico methods. Some of these prominent studies have been crucially observed and reported here.

Virtual Screening, Molecular Interaction Field, Molecular Dynamics, Docking, Density Functional, and ADMET Properties of Novel AChE Inhibitors in Alzheimer's Disease

Alzheimer's disease (AD) affects approximately 10% of the world's population with 65 years of age, being the most common form of dementia in adults and is characterized by senile plaquets and cholinergic deficits. Many drugs currently used for the treatment of the AD are based on the improvement of cholinergic neurotransmission achieved by Acetylcholinesterase (AChE) inhibition, the enzyme responsible for acetylcholine hydrolysis. We have focused in this work on the usage of computer-aided molecular design by virtual screening, molecular dynamics with implicit and explicit water solvation, density functional, molecular interaction field studies, docking procedures, ADMET predictions in order to propose novel potential AChE inhibitor for the treatment of Alzheimer's disease.

Medicinal Studies of Dimeric Phenols with Multiple Quaternary-Ammonium Pendant Arms

A series of biphenol-derived quaternary ammonium salts, originally developed as DNA-cross-linking agents, and carrying either two (i.e., 1) or four (i.e., 2) net positive charges, were investigated for their in vitro DNA-transcription- and acetylcholinesterase (AChE)-inhibitory activities. The effects of charge and type of linker between the two phenolic residues were systematically investigated. Several compounds showed good activities in both tests, which makes them potential lead candidates for drug design.

Synthesis of tricyclic 1,3-oxazin-4-ones and kinetic analysis of cholesterol esterase and acetylcholinesterase inhibition

A series of thieno[1,3]oxazin-4-ones and thieno[1,3]thiazin-4-ones were synthesized and investigated as inhibitors of the alpha/beta hydrolases cholesterol esterase (CEase) and acetylcholinesterase (AChE). The introduction of a cycloaliphatic five- or six-membered ring fused at the thiophene was favorable for CEase inhibition. Such compounds were analyzed as true alternate substrate inhibitors. 6,7-Dihydro-2-(dimethylamino)-4H,5H-cyclopenta[4,5]thieno[2,3-d][1,3]oxazin-4-one (33) exhibited a K(i) value of 630 nM and excelled in its low susceptibility to CEase-catalyzed degradation. Compound 33 and its analogues did not inhibit AChE. The introduction of a tetrahydropyrido ring with bulky hydrophobic substituents at the basic nitrogen provided inhibitors of AChE which were completely inactive toward CEase. 7-Benzyl-5,6,7,8-tetrahydro-2-(N-3,4-dimethoxybenzyl-N-methylamino)-4H-pyrido[4',3':4,5]thieno[2,3-d][1,3]oxazin-4-one (21) had the IC(50) value of 330 nM for AChE inhibition. A residual enzymatic activity at an infinite inhibitor concentration and thus a catalytically active ternary enzyme-substrate-inhibitor complex was concluded. To specify kinetic parameters of inhibition, a new method was derived to characterize selected thieno[1,3]oxazin-4-ones as hyperbolic mixed-type inhibitors of AChE.

Antibacterial, anti-inflammatory, anti-cholinesterase and mutagenic effects of extracts obtained from some trees used in South African traditional medicine

Extracts obtained from 10 trees used in South African traditional medicine were screened for antibacterial, anti-inflammatory (COX-1 and COX-2) and anti-cholinesterase activities and investigated for potential mutagenic effects using the Ames test. Antibacterial activity was detected using the disc-diffusion and micro-dilution assays. The extracts were tested against Gram-positive bacteria: Bacillus subtilis, Staphylococcus aureus, Micrococcus luteus and Gram-negative bacteria: Escherichia coli and Klebsiella pneumoniae. Of the 78 different plant extracts investigated, 80% showed activity against both Gram-positive and Gram-negative bacteria in the disc-diffusion assay. In the micro-dilution assay, 60% of the plant extracts showed minimum inhibitory concentration (MIC) values < or =1.56 mg ml(-1). The lowest MIC value (0.092 mg ml(-1)) was recorded for an ethyl acetate root extract of Acacia sieberiana against Staphylococcus aureus and Escherichia coli. In the anti-inflammatory assay, 70% of the investigated plant extracts (0.25 mg ml(-1)) inhibited both COX-1 and COX-2 activity (>50% and 70% for water and organic solvent extracts, respectively). An ethyl acetate leaf extract of Trichilia dregeana showed selective inhibition of COX-2 (81%). In the acetylcholinesterase inhibitory test, 21% of the plant extracts were active at a concentration < or =1 mg ml(-1) using the micro-dilution assay. The lowest IC(50) value was 0.04 mg ml(-1) obtained with an ethanol bark extract of Combretum kraussii. None of the investigated plants showed any potential mutagenic effects.

Alaternin and emodin with hydroxyl radical inhibitory and/or scavenging activities and hepatoprotective activity on tacrine-induced cytotoxicity in HepG2 cells

The antioxidative and hepatoprotective potentials of two anthraquinones, alaternin (2-hydroxyemodin) and emodin, to scavenge and/or inhibit hydroxyl radicals generated by the Fenton reaction and to protect tacrine-induced cytotoxicity in human liver derived HepG2 cells were evaluated, respectively. The inhibitory activity on hydroxyl radical generated in a cell-free chemical system (FeSO4/H2O2) was investigated by a fluorescence spectrophotometer using a highly fluorescent probe, 2',7'-dichlorofluorescein. The hydroxyl radical scavenging activity was determined by electron spin resonance spectroscopy using 5,5-dimethy-1-pyrroline-N-oxide as hydroxyl radicals trapping agents. Tacrine-induced HepG2 cell toxicity was determined by a 3-[4,5-dimethylthiazole-2yl]-2,5-diphenyltertrazolium bromide assay. Although the scavenging activity of alaternin on hydroxyl radical was similar to that of emodin in dose-dependent patterns, the inhibitory activity exhibited by the former on hydroxyl radical generation was stronger than that of the latter, with IC50 values of 3.05 +/- 0.26 microM and 13.29 +/- 3.20 microM, respectively. In addition, the two anthraquinones, alaternin and emodin showed their hepatoprotective activities on tacrine-induced cytotoxicity, and the EC50 values were 4.02 microM and 2.37 microM, respectively. Silymarin, an antihepatotoxic agent used as a positive control exhibited the EC50 value of 2.00 microM. These results demonstrated that both alaternin and emodin had the simultaneous antioxidant and hepatoprotective activities.

Characterization of acetylcholinesterases, and their genes, from the hemipteran species Myzus persicae (Sulzer), Aphis gossypii (Glover), Bemisia tabaci (Gennadius) and Trialeurodes vaporariorum (Westwood)

Gene sequences encoding putative acetylcholinesterases have been reported for four hemipteran insect species. Although acetylcholinesterase insensitivity occurs in insecticide-resistant populations of each of these species, no mutations were detected in the gene sequences from the resistant insects. This, coupled with a series of experiments using novel reversible inhibitors to compare the biochemical characteristics of acetylcholinesterase from a range of insect species, showed that the cloned cDNA fragments are unlikely to encode the hemipteran synaptic acetylcholinesterases, and there is likely to be a second ace locus.

The genesis of high-throughput structure-based drug discovery using protein crystallography

Over the past 12 years, drugs have been developed using structure-based drug design relying upon traditional crystallographic methods. Established successes, such as the drugs designed against HIV-1 protease and neuraminidase, demonstrate the utility of a structure-based approach in the drug-discovery process. However, the approach has historically lacked throughput and reliability capabilities; these bottlenecks are being overcome by breakthroughs in high-throughput structural biology. Recent technological innovations such as submicroliter high-throughput crystallization, high-performance synchrotron beamlines and rapid binding-site analysis of de novo targets using virtual ligand screening and small molecule co-crystallization have resulted in a significant advance in structure-based drug discovery.

Crystal structure of a squalene cyclase in complex with the potential anticholesteremic drug Ro48-8071

Squalene-hopene cyclase (SHC) catalyzes the conversion of squalene into pentacyclic compounds. It is the prokaryotic counterpart of the eukaryotic oxidosqualene cyclase (OSC) that catalyzes the steroid scaffold formation. Because of clear sequence homology, SHC can serve as a model for OSC, which is an attractive target for anticholesteremic drugs. We have established the crystal structure of SHC complexed with Ro48-8071, a potent inhibitor of OSC and therefore of cholesterol biosynthesis. Ro48-8071 is bound in the active-center cavity of SHC and extends into the channel that connects the cavity with the membrane. The binding site of Ro48-8071 is largely identical with the expected site of squalene; it differs from a previous model based on photoaffinity labeling. The knowledge of the inhibitor binding mode in SHC is likely to help develop more potent inhibitors for OSC.