Synthesis and in vitro assessment of the reactivation profile of clinically available oximes on the acetylcholinesterase model inhibited by A-230 nerve agent surrogate.

The risk of the use of toxic chemicals for unlawful acts has been a matter of concern for different governments and multilateral agencies. The Organisation for the Prohibition of Chemical Weapons (OPCW), which oversees the implementation of the Chemical Weapons Convention (CWC), considering recent events employing chemical warfare agents as means of assassination, has recently included in the CWC "Annex on Chemicals" some organophosphorus compounds that are regarded as acting in a similar fashion to the classical G- and V-series of nerve agents, inhibiting the pivotal enzyme acetylcholinesterase. Therefore, knowledge of the activity of the pyridinium oximes, the sole class of clinically available acetylcholinesterase reactivators to date, is plainly justified. In this paper, continuing our research efforts in medicinal chemistry on this class of toxic chemicals, we synthesized an A-230 nerve agent surrogate and applied a modified Ellman's assay to evaluate its ability to inhibit our enzymatic model, acetylcholinesterase from Electrophorus eel, and if the clinically available antidotes are able to rescue the enzyme activity for the purpose of relating the findings to the previously disclosed in silico data for the authentic nerve agent and other studies with similar A-series surrogates. Our experimental data indicates that pralidoxime is the most efficient compound for reactivating acetylcholinesterase inhibited by A-230 surrogate, which is the opposite of the in silico data previously disclosed.

Are the current commercially available oximes capable of reactivating acetylcholinesterase inhibited by the nerve agents of the A-series?

The misuse of novichok agents in assassination attempts has been reported in the international media since 2018. These relatively new class of neurotoxic agents is claimed to be more toxic than the agents of the G and V series and so far, there is no report yet in literature about potential antidotes against them. To shed some light into this issue, we report here the design and synthesis of NTMGMP, a surrogate of A-242 and also the first surrogate of a novichok agent useful for experimental evaluation of antidotes. Furthermore, the efficiency of the current commercial oximes to reactivate NTMGMP-inhibited acetylcholinesterase (AChE) was evaluated. The Ellman test was used to confirm the complete inhibition of AChE, and to compare the subsequent rates of reactivation in vitro as well as to evaluate aging. In parallel, molecular docking, molecular dynamics and MM-PBSA studies were performed on a computational model of the human AChE (HssAChE)/NTMGMP complex to assess the reactivation performances of the commercial oximes in silico. Experimental and theoretical studies matched the exact hierarchy of efficiency and pointed to trimedoxime as the most promising commercial oxime for reactivation of AChE inhibited by A-242.