Organophosphorus compounds are highly toxic irreversible inhibitors of cholinesterases, causing the disruption of cholinergic functions. Treatment of poisoning includes causal antidotes (oximes) used as reactivators of inhibited cholinesterases, such as pralidoxime. In this work, new halogenated oxime reactivators derived from pralidoxime were developed. The oximes were designed with a halogen substituent that lowers the pK a and enhances oximate formation. Their synthesis, stability, physicochemical properties, inhibition of native cholinesterases, and in vitro reactivation of organophosphate-inhibited cholinesterases were investigated. A series of C4 and C6 halogenated oximes showed instability and their degradation products were identified, while C3 and C5 oximes exhibited sufficient stability for the evaluation. C3 oximes displayed overall low inhibition of cholinesterases and high reactivation ability of organophosphate-inhibited cholinesterases compared to pralidoxime, indicating the significant impact of halogen substitution on reactivation ability.

• Publication type
• Journal Article MeSH

Six novel brominated bis-pyridinium oximes were designed and synthesized to increase their nucleophilicity and reactivation ability of phosphorylated acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Their pKa was valuably found lower to parent non-halogenated oximes. Stability tests showed that novel brominated oximes were stable in water, but the stability of di-brominated oximes was decreased in buffer solution and their degradation products were prepared and characterized. The reactivation screening of brominated oximes was tested on AChE and BChE inhibited by organophosphorus surrogates. Two mono-brominated oximes reactivated AChE comparably to non-halogenated analogues, which was further confirmed by reactivation kinetics. The acute toxicity of two selected brominated oximes was similar to commercially available oxime reactivators and the most promising brominated oxime was tested in vivo on sarin- and VX-poisoned rats. This brominated oxime showed interesting CNS distribution and significant reactivation effectiveness in blood. The same oxime resulted with the best protective index for VX-poisoned rats.

• Keywords
• Cholinesterase, Nerve agent, Nucleophile, Organophosphate, Oxime, Reactivation,
• MeSH
• Acetylcholinesterase * metabolism   drug effects   MeSH
• Butyrylcholinesterase * metabolism   MeSH
• Chemical Warfare Agents toxicity   MeSH
• Cholinesterase Inhibitors * toxicity   pharmacology   MeSH
• Halogenation MeSH
• Rats MeSH
• Nerve Agents * toxicity   MeSH
• Organothiophosphorus Compounds * toxicity   MeSH
• Oximes * pharmacology   chemistry   MeSH
• Rats, Wistar MeSH
• Pyridinium Compounds pharmacology   MeSH
• Cholinesterase Reactivators * pharmacology   chemistry   MeSH
• Sarin * toxicity   MeSH
• Drug Stability MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Male MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Acetylcholinesterase * MeSH
• Butyrylcholinesterase * MeSH
• Chemical Warfare Agents MeSH
• Cholinesterase Inhibitors * MeSH
• Nerve Agents * MeSH
• Organothiophosphorus Compounds * MeSH
• Oximes * MeSH
• Pyridinium Compounds MeSH
• Cholinesterase Reactivators * MeSH
• Sarin * MeSH
• VX MeSH Browser

Organophosphorus poisoning caused by some pesticides and nerve agents is a life-threating condition that must be swiftly addressed to avoid casualties. Despite the availability of medical countermeasures, the clinically available compounds lack a broad spectrum, are not effective towards all organophosphorus toxins, and have poor pharmacokinetics properties to allow them crossing the blood-brain barrier, hampering cholinesterase reactivation at the central nervous system. In this work, we designed and synthesised novel isatin derivatives, linked to a pyridinium 4-oxime moiety by an alkyl chain with improved calculated properties, and tested their reactivation potency against paraoxon- and NEMP-inhibited acetylcholinesterase in comparison to the standard antidote pralidoxime. Our results showed that these compounds displayed comparable in vitro reactivation also pointed by the in silico studies, suggesting that they are promising compounds to tackle organophosphorus poisoning.

• Keywords
• Isatin, antidotes, cholinesterase reactivators, nerve agents, organophosphorus poisoning, pyridine oximes,
• MeSH
• Acetylcholinesterase drug effects   MeSH
• Isatin pharmacology   MeSH
• Computer Simulation MeSH
• Pyridines pharmacology   MeSH
• Cholinesterase Reactivators pharmacology   MeSH
• In Vitro Techniques MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Acetylcholinesterase MeSH
• Isatin MeSH
• pyridine MeSH Browser
• Pyridines MeSH
• Cholinesterase Reactivators MeSH

The pyridinium-2-carbaldoximes with quinolinium carboxamide moiety were designed and synthesised as cholinesterase reactivators. The prepared compounds showed intermediate-to-high inhibition of both cholinesterases when compared to standard oximes. Their reactivation ability was evaluated in vitro on human recombinant acetylcholinesterase (hrAChE) and human recombinant butyrylcholinesterase (hrBChE) inhibited by nerve agent surrogates (NIMP, NEMP, and NEDPA) or paraoxon. In the reactivation screening, one compound was able to reactivate hrAChE inhibited by all used organophosphates and two novel compounds were able to reactivate NIMP/NEMP-hrBChE. The reactivation kinetics revealed compound 11 that proved to be excellent reactivator of paraoxon-hrAChE better to obidoxime and showed increased reactivation of NIMP/NEMP-hrBChE, although worse to obidoxime. The molecular interactions of studied reactivators were further identified by in silico calculations. Molecular modelling results revealed the importance of creation of the pre-reactivation complex that could lead to better reactivation of both cholinesterases together with reducing particular interactions for lower intrinsic inhibition by the oxime.

• Keywords
• Organophosphate, acetylcholinesterase, butyrylcholinesterase, oxime, reactivator,
• MeSH
• Acetylcholinesterase metabolism   MeSH
• Butyrylcholinesterase metabolism   MeSH
• Quinolinium Compounds chemical synthesis   chemistry   pharmacology   MeSH
• Cholinesterase Inhibitors chemical synthesis   chemistry   pharmacology   MeSH
• Humans MeSH
• Molecular Structure MeSH
• Pyridinium Compounds chemical synthesis   chemistry   pharmacology   MeSH
• Recombinant Proteins metabolism   MeSH
• Molecular Docking Simulation 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
• Quinolinium Compounds MeSH
• Cholinesterase Inhibitors MeSH
• Pyridinium Compounds MeSH
• Recombinant Proteins MeSH