The in silico and in vitro analysis of donepezil derivatives for Anopheles acetylcholinesterase inhibition.

Current studies on Anopheles anticholinesterase insecticides are focusing on identifying agents with high selectivity towards Anopheles over mammalian targets. Acetylcholinesterase (AChE) from electric eel is often used as the bioequivalent enzyme to study ligands designed for activity and inhibition in human. In this study, previously identified derivatives of a potent AChE, donepezil, that have exhibited low activity on electric eel AChE were assessed for potential AChE-based larvicidal effects on four African malaria vectors; An. funestus, An. arabiensis, An. gambiae and An. coluzzii. This led to the identification of four larvicidal agents with a lead molecule, 1-benzyl-N-(thiazol-2-yl) piperidine-4-carboxamide 2 showing selectivity for An. arabiensis as a larvicidal AChE agent. Differential activities of this molecule on An. arabiensis and electric eel AChE targets were studied through molecular modelling. Homology modelling was used to generate a three-dimensional structure of the An. arabiensis AChE for this binding assay. The conformation of this molecule and corresponding interactions with the AChE catalytic site was markedly different between the two targets. Assessment of the differences between the AChE binding sites from electric eel, human and Anopheles revealed that the electric eel and human AChE proteins were very similar. In contrast, Anopheles AChE had a smaller cysteine residue in place of bulky phenylalanine group at the entrance to the catalytic site, and a smaller aspartic acid residue at the base of the active site gorge, in place of the bulky tyrosine residues. Results from this study suggest that this difference affects the ligand orientation and corresponding interactions at the catalytic site. The lead molecule 2 also formed more favourable interactions with An. arabiensis AChE model than other Anopheles AChE targets, possibly explaining the observed selectivity among other assessed Anopheles species. This study suggests that 1-benzyl-N-(thiazol-2-yl) piperidine-4-carboxamide 2 may be a lead compound for designing novel insecticides against Anopheles vectors with reduced toxic potential on humans.

Discovery of Novel Acetylcholinesterase Inhibitors by Virtual Screening, In Vitro Screening, and Molecular Dynamics Simulations.

Alzheimer's disease is the most common neurodegenerative disease and currently poses a significant socioeconomic problem. This study describes the uses of computer-aided drug discovery techniques to identify novel inhibitors of acetylcholinesterase, a target for Alzheimer's disease. High-throughput virtual screening was employed to predict potential inhibitors of acetylcholinesterase. Validation of enrichment was performed with the DUD-E data set, showing that an ensemble of binding pocket conformations is critical when a diverse set of ligands are being screened. A total of 720 compounds were submitted for in vitro screening, which led to 25 hits being identified with IC50 values of less than 50 µM. The majority of these hits belonged to two scaffolds: 1-ethyl-3-methoxy-3-methylpyrrolidine and 1H-pyrrolo[3,2-c]pyridin-6-amine both of which are noted to be promising compounds for further optimization. As various possible binding poses were suggested from molecular docking, molecular dynamics simulations were employed to validate the poses. In the case of the most active compounds identified, a critical, stable water bridge formed deep within the binding pocket was identified potentially explaining in part the lack of activity for subsets of compounds that are not able to form this water bridge.

A Cytotoxic Bis(1,2,3-triazol-5-ylidene)carbazolide Gold(III) Complex Targets DNA by Partial Intercalation.

The syntheses of bis(triazolium)carbazole precursors and their corresponding coinage metal (Au, Ag) complexes are reported. For alkylated triazolium salts, di- or tetranuclear complexes with bridging ligands were isolated, while the bis(aryl) analogue afforded a bis(carbene) AuI -CNC pincer complex suitable for oxidation to the redox-stable [AuIII (CNC)Cl]+ cation. Although the ligand salt and the [AuIII (CNC)Cl]+ complex were both notably cytotoxic toward the breast cancer cell line MDA-MB-231, the AuIII complex was somewhat more selective. Electrophoresis, viscometry, UV-vis, CD and LD spectroscopy suggest the cytotoxic [AuIII (CNC)Cl]+ complex behaves as a partial DNA intercalator. In silico screening indicated that the [AuIII (CNC)Cl]+ complex can target DNA three-way junctions with good specificity, several other regular B-DNA forms, and Z-DNA. Multiple hydrophobic π-type interactions involving T and A bases appear to be important for B-form DNA binding, while phosphate O⋅⋅⋅Au interactions evidently underpin Z-DNA binding. The CNC ligand effectively stabilizes the AuIII ion, preventing reduction in the presence of glutathione. Both the redox stability and DNA affinity of the hit compound might be key factors underpinning its cytotoxicity in vitro.