Nerve agents are organophosphates (OPs) that act as potent inhibitors of acetylcholinesterase (AChE), the enzyme responsible for the hydrolysis of acetylcholine. After inhibition, a dealkylation reaction of the phosphorylated serine, known as the aging of AChE, can occur. When aged, reactivators of OP-inhibited AChE are no longer effective. Therefore, the realkylation of aged AChE may offer a pathway to reverse AChE aging. In this study, molecular modeling was conducted to propose new ligands as realkylators of aged AChE. We applied a methodology involving docking and quantum mechanics/molecular mechanics (QM/MM) calculations to evaluate the resurrection kinetic constants and ligand interactions with OP-aged AChE, comparing them to data found in the literature. The results obtained confirm that this method is suitable for predicting kinetic and thermodynamic parameters of ligands, which can be useful in the design and selection of new and more effective ligands for AChE realkylation.

• Keywords
• acetylcholinesterase, mechanistic studies, nerve agents, realkylation, resurrection,
• MeSH
• Acetylcholinesterase * chemistry   metabolism   MeSH
• Cholinesterase Inhibitors * chemistry   pharmacology   MeSH
• Indolequinones * chemistry   MeSH
• Kinetics MeSH
• Humans MeSH
• Ligands MeSH
• Models, Molecular MeSH
• Molecular Dynamics Simulation MeSH
• Molecular Docking Simulation MeSH
• Thermodynamics MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Acetylcholinesterase * MeSH
• Cholinesterase Inhibitors * MeSH
• Indolequinones * MeSH
• Ligands MeSH
• quinone methide MeSH Browser

The organophosphorus antidotes, so-called oximes, are able to restore the enzymatic function of acetylcholinesterase (AChE) or butyrylcholinesterase (BChE) via cleavage of organophosphate from the active site of the phosphylated enzyme. In this work, the charged pyridinium oximes containing thiocarboxamide moiety were designed, prepared and tested. Their stability and pKa properties were found to be analogous to parent carboxamides (K027, K048 and K203). The inhibitory ability of thiocarboxamides was found in low µM levels for AChE and high µM levels for BChE. Their reactivation properties were screened on human recombinant AChE and BChE inhibited by nerve agent surrogates and paraoxon. One thiocarboxamide was able to effectively restore function of NEMP- and NEDPA-AChE, whereas two thiocarboxamides were able to reactivate BChE inhibited by all tested organophosphates. These results were confirmed by reactivation kinetics, where thiocarboxamides were proved to be effective, but less potent reactivators if compared to carboxamides.

• Keywords
• Cholinesterase, inhibition, organophosphate, oxime, reactivation,
• MeSH
• Acetylcholinesterase metabolism   MeSH
• Butyrylcholinesterase metabolism   MeSH
• Cholinesterase Inhibitors chemical synthesis   chemistry   pharmacology   MeSH
• Humans MeSH
• Molecular Structure MeSH
• Organophosphates chemical synthesis   chemistry   pharmacology   MeSH
• Oximes chemical synthesis   chemistry   pharmacology   MeSH
• Pyridinium Compounds chemical synthesis   chemistry   pharmacology   MeSH
• Sulfhydryl Compounds chemical synthesis   chemistry   pharmacology   MeSH
• Dose-Response Relationship, Drug MeSH
• Structure-Activity Relationship MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Acetylcholinesterase MeSH
• Butyrylcholinesterase MeSH
• Cholinesterase Inhibitors MeSH
• Organophosphates MeSH
• Oximes MeSH
• Pyridinium Compounds MeSH
• Sulfhydryl Compounds MeSH

Organophosphorus (OP) compounds are used as both chemical weapons and pesticides. However, these agents are very dangerous and toxic to humans, animals, and the environment. Thus, investigations with reactivators have been deeply developed in order to design new antidotes with better efficiency, as well as a greater spectrum of action in the acetylcholinesterase (AChE) reactivation process. With that in mind, in this work, we investigated the behavior of trimedoxime toward the Mus musculus acetylcholinesterase (MmAChE) inhibited by a range of nerve agents, such as chemical weapons. From experimental assays, reactivation percentages were obtained for the reactivation of different AChE-OP complexes. On the other hand, theoretical calculations were performed to assess the differences in interaction modes and the reactivity of trimedoxime within the AChE active site. Comparing theoretical and experimental data, it is possible to notice that the oxime, in most cases, showed better reactivation percentages at higher concentrations, with the best result for the reactivation of the AChE-VX adduct. From this work, it was revealed that the mechanistic process contributes most to the oxime efficiency than the interaction in the site. In this way, this study is important to better understand the reactivation process through trimedoxime, contributing to the proposal of novel antidotes.

• Keywords
• acetylcholinesterase, computational methods, mechanistic studies, nerve agents, reactivation, trimedoxime,
• MeSH
• Acetylcholinesterase metabolism   MeSH
• Antidotes pharmacology   MeSH
• Cholinesterase Inhibitors metabolism   pharmacology   MeSH
• Rats MeSH
• Humans MeSH
• Mice MeSH
• Nerve Agents chemistry   MeSH
• Organophosphorus Compounds chemistry   MeSH
• Oximes chemistry   MeSH
• Cholinesterase Reactivators chemistry   pharmacology   MeSH
• Trimedoxime pharmacology   therapeutic use   MeSH
• Computational Biology methods   MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Humans MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Acetylcholinesterase MeSH
• Antidotes MeSH
• Cholinesterase Inhibitors MeSH
• Nerve Agents MeSH
• Organophosphorus Compounds MeSH
• Oximes MeSH
• Cholinesterase Reactivators MeSH
• Trimedoxime MeSH