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

Oxime reactivators of acetylcholinesterase (AChE) are used as causal antidotes for intended and unintended poisoning by organophosphate nerve agents and pesticides. Despite all efforts to develop new AChE reactivators, none of these drug candidates replaced conventional clinically used oximes. In addition to the therapeutic efficacy, determining the safety profile is crucial in preclinical drug evaluation. The exact mechanism of oxime toxicity and the structure-toxicity relationship are subjects of ongoing research, with oxidative stress proposed as a possible mechanism. In the present study, we investigated four promising bispyridinium oxime AChE reactivators, K048, K074, K075, and K203, and their ability to induce oxidative stress in vitro. Cultured human hepatoma cells were exposed to oximes at concentrations corresponding to their IC50 values determined by the MTT assay after 24 h. Their potency to generate reactive oxygen species, interfere with the thiol antioxidant system, and induce lipid peroxidation was evaluated at 1, 4, and 24 h of exposure. Reactivators without a double bond in the four-carbon linker, K048 and K074, showed a greater potential to induce oxidative stress compared with K075 and K203, which contain a double bond. Unlike oximes with a three-carbon-long linker, the number of aldoxime groups attached to the pyridinium moieties does not determine the oxidative stress induction for K048, K074, K075, and K203 oximes. In conclusion, our results emphasize that the structure of oximes plays a critical role in inducing oxidative stress, and this relationship does not correlate with their cytotoxicity expressed as the IC50 value. However, it is important to note that oxidative stress cannot be disregarded as a potential contributor to the side effects associated with oximes.

• MeSH
• Acetylcholinesterase metabolism   MeSH
• Antidotes pharmacology   MeSH
• Hep G2 Cells MeSH
• Cholinesterase Inhibitors toxicity   MeSH
• Humans MeSH
• Organophosphates toxicity   MeSH
• Oxidative Stress MeSH
• Oximes pharmacology   chemistry   MeSH
• Pyridinium Compounds pharmacology   chemistry   MeSH
• Cholinesterase Reactivators * pharmacology   chemistry   MeSH
• Carbon MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Acetylcholinesterase MeSH
• Antidotes MeSH
• Cholinesterase Inhibitors MeSH
• Organophosphates MeSH
• Oximes MeSH
• Pyridinium Compounds MeSH
• Cholinesterase Reactivators * MeSH
• Carbon MeSH