Reactivator Report for: K203

DDVP-inhibited rat diaphragm AChE reactivation by oxime K027/K203 was dose-dependent. Dose-response relationships were described by 4-parameter exponential and Hill models. Maximum size of DDVP-inhibited AChE reactivation by K-oximes was 2.1-fold. Oxime K027 had 5-fold higher relative reactivating potency compared to oxime K203. ***LongTextEnd*** Paper "Arens_2019_J.Med.Toxicol_15_184" Author "Arens AM" Author "Kearney T" Year "2019" Title "Adverse Effects of Physostigmine" Journal "J Med Toxicol" Volume "15" Page "184" "191" Medline "30747326" Abstract "Arens_2019_J.Med.Toxicol_15_184" LongText "Arens_2019_J.Med.Toxicol_15_184" INTRODUCTION: Physostigmine is a tertiary amine carbamate acetylcholinesterase inhibitor. Its ability to cross the blood-brain barrier makes it an effective antidote to reverse anticholinergic delirium. Physostigmine is underutilized following the publication of patients with sudden cardiac arrest after physostigmine administration in patients with tricyclic antidepressant (TCA) overdoses. We completed a narrative literature review to identify reported adverse effects associated with physostigmine administration. DISCUSSION: One hundred sixty-one articles and a total of 2299 patients were included. Adverse effects occurred in 415 (18.1%) patients. Hypersalivation (206; 9.0%) and nausea and vomiting (96; 4.2%) were the most common adverse effects. Fifteen (0.61%) patients had seizures, all of which were self-limited or treated successfully without complication. Symptomatic bradycardia occurred in 8 (0.35%) patients including 3 patients with bradyasystolic arrests. Ventricular fibrillation occurred in one (0.04%) patient with underlying coronary artery disease. Of the 394 patients with TCA overdose, adverse effects were described in 14 (3.6%). Adverse effects occurred in 7.7% of patients treated with an overdose of an anticholinergic agent compared with 20.6% of patients with non-anticholinergic agents. Five (0.22%) fatalities were identified. CONCLUSIONS: In conclusion, significant adverse effects associated with the use of physostigmine were infrequently reported. Seizures were self-limited or resolved with benzodiazepines, and all patients recovered neurologically intact. Physostigmine should be avoided in patients with QRS prolongation on EKG, and caution should be used in patients with a history of coronary artery disease and overdoses with QRS prolonging medications. Based upon our review, physostigmine is a safe antidote to treat anticholinergic overdose.

Studies with oximes have been extensively developed to design new reactivators with better efficiency, and greater spectrum of action. In this study, we aimed to analyze the influence of the Carbamoyl group position change in two isomeric oximes, K203 and K206, on the reactivation percentage of Mus musculus Acetylcholinesterase (MmAChE), inhibited by different nerve agents. Theoretical calculations were performed to assess the difference for the oxime activity with inhibited AChE-complexes and the factors that govern this difference. Comparing theoretical and experimental data, it is possible to observe that this change between the oximes results in different reactivation percentage for the same nerve agent, due to the different interaction modes and activation energy for the studied systems.

Six AChE monooxime-monocarbamoyl reactivators with an (E)-but-2-ene linker were synthesized using modification of currently known synthetic pathways. Their potency to reactivate AChE inhibited by the nerve agent tabun and insecticide paraoxon was tested in vitro. The reactivation efficacies of pralidoxime, HI-6, obidoxime, K048, K075 and the newly prepared reactivators were compared. According to the results obtained, one reactivator seems to be promising against tabun-inhibited AChE and two reactivators against paraoxon-inhibited AChE. The best results were obtained for bisquaternary substances with at least one oxime group in position four.

DDVP-inhibited rat diaphragm AChE reactivation by oxime K027/K203 was dose-dependent. Dose-response relationships were described by 4-parameter exponential and Hill models. Maximum size of DDVP-inhibited AChE reactivation by K-oximes was 2.1-fold. Oxime K027 had 5-fold higher relative reactivating potency compared to oxime K203. ***LongTextEnd*** Paper "Arens_2019_J.Med.Toxicol_15_184" Author "Arens AM" Author "Kearney T" Year "2019" Title "Adverse Effects of Physostigmine" Journal "J Med Toxicol" Volume "15" Page "184" "191" Medline "30747326" Abstract "Arens_2019_J.Med.Toxicol_15_184" LongText "Arens_2019_J.Med.Toxicol_15_184" INTRODUCTION: Physostigmine is a tertiary amine carbamate acetylcholinesterase inhibitor. Its ability to cross the blood-brain barrier makes it an effective antidote to reverse anticholinergic delirium. Physostigmine is underutilized following the publication of patients with sudden cardiac arrest after physostigmine administration in patients with tricyclic antidepressant (TCA) overdoses. We completed a narrative literature review to identify reported adverse effects associated with physostigmine administration. DISCUSSION: One hundred sixty-one articles and a total of 2299 patients were included. Adverse effects occurred in 415 (18.1%) patients. Hypersalivation (206; 9.0%) and nausea and vomiting (96; 4.2%) were the most common adverse effects. Fifteen (0.61%) patients had seizures, all of which were self-limited or treated successfully without complication. Symptomatic bradycardia occurred in 8 (0.35%) patients including 3 patients with bradyasystolic arrests. Ventricular fibrillation occurred in one (0.04%) patient with underlying coronary artery disease. Of the 394 patients with TCA overdose, adverse effects were described in 14 (3.6%). Adverse effects occurred in 7.7% of patients treated with an overdose of an anticholinergic agent compared with 20.6% of patients with non-anticholinergic agents. Five (0.22%) fatalities were identified. CONCLUSIONS: In conclusion, significant adverse effects associated with the use of physostigmine were infrequently reported. Seizures were self-limited or resolved with benzodiazepines, and all patients recovered neurologically intact. Physostigmine should be avoided in patients with QRS prolongation on EKG, and caution should be used in patients with a history of coronary artery disease and overdoses with QRS prolonging medications. Based upon our review, physostigmine is a safe antidote to treat anticholinergic overdose.

For over 60 years, researchers across the world have sought to deal with poisoning by nerve agents, the most toxic and lethal chemical weapons. To date, there is no efficient causal antidote with sufficient effect. Every trialed compound fails to fulfil one or more criteria (e.g. reactivation potency, broad reactivation profile). In this recent contribution, we focused our attention to one of the promising compounds, namely the bis-pyridinium reactivator K203. The oxime K203 is very often cited as the best reactivator against tabun poisoning. Herein, we provide all the available literature data in comprehensive and critical review to address whether K203 could be considered as a new drug candidate against organophosphorus poisoning with the stress on tabun. We describe its development from the historical point of view and review all available in vitro as well as in vivo data to date. K203 is easily accessible by a relatively simple two-step synthesis. It is well accommodated in the enzyme active gorge of acetylcholinesterase providing suitable interactions for reactivation, as shown by molecular docking simulations. According to a literature survey, in vitro data for tabun-inhibited AChE are extraordinary. However, in vivo efficiency remains unconvincing. The K203 toxicity profile did not show any perturbations compared to clinically used standards; on the other hand versatility of K203 does not exceed currently available oximes. In summary, K203 does not seem to address current issues associated with the organophosphorus poisoning, especially the broad profile against all nerve agents. However, its reviewed efficacy entitles K203 to be considered as a backup or tentative replacement for obidoxime and trimedoxime, currently only available anti-tabun drugs.

Studies with oximes have been extensively developed to design new reactivators with better efficiency, and greater spectrum of action. In this study, we aimed to analyze the influence of the Carbamoyl group position change in two isomeric oximes, K203 and K206, on the reactivation percentage of Mus musculus Acetylcholinesterase (MmAChE), inhibited by different nerve agents. Theoretical calculations were performed to assess the difference for the oxime activity with inhibited AChE-complexes and the factors that govern this difference. Comparing theoretical and experimental data, it is possible to observe that this change between the oximes results in different reactivation percentage for the same nerve agent, due to the different interaction modes and activation energy for the studied systems.

BACKGROUND: Based on in vitro and in vivo rat experiments, the newly developed acetylcholinesterase (AChE) reactivator, K203, appears to be much more effective in the treatment of tabun poisonings than currently fielded oximes. METHODS: To determine if this reactivating efficacy would extend to humans, studies were conducted in vitro using human brain homogenate as the source of AChE. The efficacy of K203 was compared with commercially available oximes; pralidoxime, obidoxime and asoxime (HI-6). RESULTS: Reactivation studies showed that K203 was the most effective reactivator with a second order kinetic constant (kr) of 2142 min(- 1). M(- 1), which was 51 times higher than that obtained for obidoxime (kr = 42 min(- 1). M(- 1)). Both pralidoxime and asoxime (HI-6) failed to significantly reactivate tabun-inhibited human AChE. DISCUSSION: According to these results and previous studies, using K203, it appears that oxime K203 is the most effective reactivator of tabun-inhibited cholinesterase in several species including humans and should be considered as a possible medical countermeasure to tabun exposure.

Standard treatment of organophosphorus compounds (OPs) poisoning includes administration of an anti-muscarinic (atropine), anticonvulsive (diazepam) and acetylcholinesterase reactivator (oxime). From a wide group of newly synthesized oximes, oxime K027 and oxime K203 seem to be perspective compounds in some specific OPs intoxication. The available in vitro and in vivo preclinical data indicate that both oximes may be considered for potential human use. The main aim of this study was to establish plasmatic concentration curves of both oximes after intramuscular (i.m.) and intragastric (i.g.) application with subsequent pharmacokinetic analysis and study distribution after (i.m.) application on a non-rodent animal model (experimental pigs; 1500mg/animal). According to the results, both oximes had similar Cmax (K027: 106+/-19mug/mL and K203: 111+/-8mug/mL) in Tmax 19+/-5min, respectively, in 22+/-3min. Bioavailability of oxime K027 calculated as AUCtotal (8389+/-1024minmug/mL) was halved compared to oxime K203 (16938+/-795minmug/mL). The highest concentration from peripheral tissues was found in the kidney and lung, but the brain concentrations stay very low, the plasma/brain ratio being approximately 1%. The applied doses were derived from the recommendation where it is possible to use three autoinjectors to save human life. The results provide us with knowledge about the pharmacokinetics and distribution of these new oximes and may help us to better estimate the human pharmacokinetic profile.

As oxime-based structures are the only causal antidotes to organophosphate (OP)-inhibited acetylcholinesterase (AChE), the majority of studies on these have been directed towards their synthesis and testing. In this study, experimental bispyridinium oximes K027 and K203, which have shown promising results in the last decade of research, were examined in vivo for their therapeutic and reactivating ability in acute poisoning by the direct AChE-inhibitor dichlorvos (DDVP), used as a dimethyl OP structural model. Additionally, the efficacy of oximes K027 and K203 was compared with the efficacy of four oximes (pralidoxime, trimedoxime, obidoxime and HI-6), already used in efficacy experiments and human medicine. To evaluate therapeutic efficacy, groups of Wistar rats were treated with equitoxic doses of oximes (5% LD50, i.m.) and/or atropine (10mg/kg, i.m.) immediately after s.c. DDVP challenge (4-6 doses). Using the same antidotal protocol, AChE activity was measured in erythrocytes, diaphragm and brain 60min after s.c. DDVP exposure (75% LD50). The oxime K027 was the most efficacious in reducing the DDVP induced lethal effect in rats, while the oxime K203 was more efficacious than trimedoxime, pralidoxime and HI-6. Significant reactivation of DDVP inhibited AChE was achieved only with oxime K027 or its combination with atropine in erythocytes and the diaphragm. Moreover, the acute i.m. toxicity of oxime K027 in rats was lower than all other tested oximes. The results of this study support previous studies considering the oxime K027 as a promising experimental oxime structure for further testing against structurally-different OP compounds.

The reactivating and therapeutic efficacy of three original bispyridinium oximes (K727, K733 and K203) and one currently available oxime (trimedoxime) was evaluated in tabun-poisoned rats and mice. The oxime-induced reactivation of tabun-inhibited acetylcholinesterase was measured in diaphragm and brain of tabun-poisoned rats. The results showed that the reactivating efficacy of two recently developed oximes (K727 and K733) does not achieve the level of the reactivation of tabun-inhibited acetylcholinesterase induced by oxime K203 and trimedoxime. While all oximes studied were able to increase the activity of tabun-inhibited acetylcholinesterase in diaphragm, oxime K733 was not able to reactivate tabun-inhibited acetylcholinesterase in the brain. The therapeutic efficacy of all oximes studied roughly corresponds to their reactivating efficacy. While both recently developed oximes were able to reduce acute toxicity of tabun less than 1.5-fold, another original oxime K203 and commonly used trimedoxime reduced the acute toxicity of tabun almost two times. In conclusion, the reactivating and therapeutic potency of both newly developed oximes does not prevail the effectiveness of oxime K203 and trimedoxime, and therefore, they are not suitable for their replacement of commonly used oximes for the antidotal treatment of acute tabun poisoning.

Oxime K203 seems to be the most promising oxime in case of reactivation of tabuninhibited acetylcholinesterase (AChE). Although it was originally developed for treatment of tabun intoxications, it is able to reactivate cholinesterases inhibited by other nerve agents. This study is aimed at the evaluation of its potency in vitro against other nerve agents. For this purpose, sarin, tabun, cyclosarin, soman, VX, Russian VX and DFP were selected as members of the nerve agent family to check its universality. At high concentrations (10(-3) M), oxime K203 reached promising reactivation activity. At low concentrations, relevant for human use (10(-5) M), promising reactivation potency was obtained only with tabun. In conclusion, oxime K203 reactivates other nerve agents-inhibited cholinesterases, however its broad-spectrum reactivation is limited at high, for human not attainable, concentrations only.

Oxime-assisted reactivation of organophosphate (OP)-inhibited acetylcholinesterase (AChE) is a crucial step in the post-inhibitory treatment of OP intoxication. The limited efficacy of oxime reactivators for all OP nerve agents and pesticides led to the development of various novel oximes and their thorough kinetic investigations. Hence, in the present investigation, we have tested 10 structurally different pyridinium oxime-based reactivators for their in vitro potency to reactivate paraoxon- and DFP-inhibited electric eel AChE. From structure activity relationship point of view, various oximes such as mono-quaternary (2-PAM, K100, K024) and bis-quaternary symmetric (obidoxime, TMB-4(Trimedoxime)) and asymmetric (K027, K048, K203, K618, K628) oximes bearing different connecting linkers (oxybismethylene, trimethylene, propane, butane, butene, and xylene) have been studied. The observed kinetic data demonstrate that not only the position of oxime group is decisive for the increased reactivation ability of oximes, but the role of connecting linker is also significant. Oximes with aliphatic linkers are superior reactivators than the oximes with unsaturated and aromatic linkers. The optimal chain length for plausible reactivation ability for paraoxon- and DFP-inhibited AChE is 3 or 4 carbon-carbon connecting linker between prydinium rings.

Abstract The potency of two newly developed oximes (K361 and K378) to reactivate tabun-inhibited cholinesterase and to reduce acute toxicity of tabun was compared with the oxime K203 and trimedoxime using in vivo methods. The study determining percentage of reactivation of tabun-inhibited diaphragm cholinesterase in poisoned rats showed that the reactivating efficacy of the oxime K378 is slightly lower than the reactivating potency of the oxime K203 and trimedoxime while the ability of the oxime K361 to reactivate tabun-inhibited cholinesterase is markedly lower compared with the oxime K203 and trimedoxime. In the brain, the potency of both newly developed oximes to reactivate tabun-inhibited cholinesterase was negligible. The therapeutic efficacy of both newly developed oximes roughly corresponds to their weak reactivating efficacy. Their potency to reduce acute toxicity of tabun was significantly lower compared with the oxime K203 as well as trimedoxime. In conclusion, the reactivating and therapeutic potency of both newly developed oximes does not prevail the effectiveness of the oxime K203 and trimedoxime and, therefore, they are not suitable for their replacement of commonly used oximes for the treatment of acute tabun poisoning.

The potency of three newly developed bispyridinium compounds (K454, K456, K458) to reactivate tabun-inhibited acetylcholinesterase and reduce tabun-induced lethal toxic effects was compared with the oxime K203 and trimedoxime using in vivo methods. The study determining percentage of reactivation of tabun-inhibited diaphragm and brain acetylcholinesterase in poisoned rats showed that the reactivating efficacy of all newly developed oximes is comparable with K203 but lower than the reactivating potency of trimedoxime in diaphragm. In the brain, their potency to reactivate tabun-inhibited acetylcholinesterase is lower compared with trimedoxime and the oxime K203. All three newly developed oximes were also found to be relatively effective in reducing lethal toxic effects in tabun-poisoned mice. Their therapeutic efficacy is consistent with the therapeutic potency of the oxime K203. On the other hand, their potency to reduce acute toxicity of tabun is significantly lower compared with trimedoxime. In conclusion, the reactivating and therapeutic potency of all three newly developed oximes does not prevail the effectiveness of the oxime K203 and trimedoxime and, therefore, they are not suitable for their replacement of commonly used oximes for the treatment of acute tabun poisoning.

Reactivation effects of K203 and currently available oximes (obidoxime, HI-6) in combination with atropine on acetylcholinesterase activities in the brain parts of rats poisoned with tabun were studied. The activity was determined by quantitative histochemical and biochemical methods correlating between them very well. The tabun-induced changes in acetylcholinsterase activity as well as in reactivation potency of reactivators used were different in various parts of the brain. Pontomedullar area seems to be important for observed changes following tabun intoxication and its treatment. From the oximes studied, the reactivation effect of K203 was comparable with obidoxime; HI-6 was ineffective. Combination of bio- and histochemical methods allow fine differentiation among the action of different oximes following tabun poisoning.

The reactivating and therapeutic efficacy of two combinations ofoximes (HI-6 + trimedoxime and HI-6 + K203) was compared with the effectiveness of antidotal treatment involving single oxime (HI-6, trimedoxime, K203) using in vivo methods. In vivo determined percentage of reactivation of cyclosarin-inhibited blood and tissue acetylcholinesterase in poisoned rats showed that the reactivating efficacy of both combinations of oximes is slightly higher than the reactivating efficacy of the most effective individual oxime in blood, diaphragm as well as in brain. Moreover, both combinations of oximes were found to be slightly more efficacious in the reduction of acute lethal toxic effects in cyclosarin-poisoned mice than the antidotal treatment involving single oxime. Based on the obtained data, we can conclude that the antidotal treatment involving chosen combinations of oximes brings a beneficial effect for its ability to counteract the acute poisoning with cyclosarin.

Highly toxic organophosphorus inhibitors of acetylcholinesterase referred as nerve agents are considered to be among the most dangerous chemical warfare agents. The oximes represent very important part of medical countermeasures of nerve agent poisonings. They are used to reactivate the nerve agent-inhibited acetylcholinesterase. Despite long-term research activities, there is no single, broad-spectrum oxime suitable for the antidotal treatment of poisoning with all organophosphorus agents. There are two approaches how to increase and broaden the effectiveness of antidotal treatment of poisoning with nerve agents - to develop new structural analogues of currently available oximes and/or to combine currently available or newly developed oximes. The review describes the evaluation of the potency of newly developed oximes (especially the oxime K203) or combinations of oximes to reactivate nerve agent-inhibited acetylcholinesterase and to counteract the acute toxicity of nerve agents in comparison with single commonly used oxime (obidoxime, trimedoxime or HI-6).

The influence of the combinations of oximes on the reactivating and therapeutic efficacy of antidotal treament of acute sarin poisoning was evaluated in this study. The ability of two combinations of oximes (HI-6 + trimedoxime and HI-6 + K203) to reactivate sarin-inhibited acetylcholinesterase and reduce acute toxicity of sarin was compared with the reactivating and therapeutic efficacy of antidotal treatment involving single oxime (HI-6, trimedoxime, K203) using in vivo methods. Studies determining percentage of reactivation of sarin-inhibited blood and tissue acetylcholinesterase in poisoned rats showed that the reactivating efficacy of the combination of oximes involving HI-6 and K203 is slightly higher than the reactivating efficacy of the most effective individual oxime in diaphragm and brain but the difference between them is not significant. The ability of combination of oximes involving HI-6 and trimedoxime to reactivate sarin-inhibited acetylcholinesterase roughly corresponds to the reactivating effects of the most effective individual oxime in blood as well as tissues. Moreover, both combinations of oximes were found to be as efficacious in the reduction of acute lethal toxic effects in sarin-poisoned mice as the most effective individual oxime. A comparison of reactivating and therapeutic efficacy of individual oximes showed that the oxime HI-6 is markedly more effective than the oxime K203 and trimedoxime. Based on the obtained data, we conclude that the antidotal treatment involving chosen combinations of oximes does not significantly influence the ability of the most effective individual oxime (HI-6) to reactivate sarin-inhibited rat acetylcholinesterase and to reduce acute toxicity of sarin in mice.

The ability of 2 combinations of oximes (HI-6 + trimedoxime and HI-6 + K203) to reactivate VX-inhibited acetylcholinesterase and reduce acute toxicity of VX was compared with the reactivating and therapeutic efficacy of antidotal treatment involving a single oxime (HI-6, trimedoxime, K203) in rats and mice. Our results showed that the reactivating efficacy of both combinations of oximes studied in rats is significantly higher than the reactivating efficacy of all individual oximes in diaphragm and roughly corresponds to the most effective individual oxime in blood and brain. Both combinations of oximes were found to be more effective in the reduction of acute lethal toxicity of VX in mice than the antidotal treatment involving the most efficacious individual oxime although the difference is not significant. Based on the obtained data, we can conclude that the antidotal treatment involving the chosen combinations of oximes brings benefit for the reactivation of VX-inhibited acetylcholinesterase in rats and for the antidotal treatment of VX-induced acute poisoning in mice.

The treatment of organophosphorus (OP) poisoning consists of the administration of a parasympatholytic agent (e.g., atropine), an anticonvulsant (e.g., diazepam) and an acetylcholinesterase (AChE) reactivator (e.g., obidoxime). The AChE reactivator is the causal treatment of OP exposure, because it cleaves the OP moiety covalently bound to the AChE active site. In this paper, fourteen novel AChE reactivators are described. Their design originated from a former promising compound K027. These compounds were synthesized, evaluated in vitro on human AChE (hAChE) inhibited by tabun, paraoxon, methylparaoxon and DFP and then compared to commercial hAChE reactivators (pralidoxime, HI-6, trimedoxime, obidoxime, methoxime) or previously prepared compounds (K027, K203). Three of these novel compounds showed a promising ability to reactivate hAChE comparable or better than the used standards. Consequently, a molecular docking study was performed for three of these promising novel compounds. The docking results confirmed the apparent influence of pi-pi or cation-pi interactions and hydrogen bonding for reactivator binding within the hAChE active site cleft. The SAR features concerning the non-oxime part of the reactivator molecule are also discussed.

OBJECTIVE: The present experiment is based on biochemical assessment of nerve agent soman intoxication and atropine, respectively atropine and HI-6, trimedoxime or K203 treatment in rats. BACKGROUND: Nerve agents are toxic substances irreversibly inhibiting enzyme acetylcholinesterase (AChE). Treatment is typically based on application of atropine and oxime reactivator. Atropine is able to protect overstimulation of muscarinic acetylcholine receptors. Application of oxime reactivator enable return of AChE activity and full suppression of intoxication. METHODS: In a total, fifteen biochemical markers were assayed in plasma or blood of intoxicated animals. 42 rats were divided into 7 groups each 6 individuals. The first group was exposed to atropine; the second group was exposed to one LD50 of soman and atropine. The groups 3-5 were exposed in a same way as the second group and were treated with oxime reactivators: HI-6 (group 3), trimedoxime (4) and K203 (5). The sixth group was control treated with saline solution only. The last (seventh) group was intoxicated with soman only. RESULTS: The most striking shifts were found for blood acetylcholinesterase and plasma creatinine, glucose, inorganic phosphate as well as uric acid. Lactate dehydrogenase and aspartate aminotransferase assays were useless due to soman interference. CONCLUSION: It was demonstrated that treatment was able to protect poisoned animals from metabolic disorder represented by hyperglycemia and nephropathy represented by hyperuricemia and elevated creatinine. Soman exposure and treatment with the oxime reactivators and/or atropine contains quite complex and still not well understood side mechanisms (Tab. 2, Fig. 1, Ref. 25).

The antidotal treatment of organophosphorus poisoning is still a problematic issue since no versatile antidote has been developed yet. In our study, we focused on an interesting property, which does not relate to the reactivation of inhibited acetylcholinesterase (AChE) of some oximes, but refers to their anti-muscarinic effects which may contribute considerably to their treatment efficacy. One standard reactivator (HI-6) and two new compounds (K027 and K203) have been investigated for their antimuscarinic properties. Anti-muscarinic effects were studies by means of an in vitro stimulated atrium preparation (functional test), the [(3)H]-QNB binding assay and G-protein coupled receptor assay (GPCR, beta-Arrestin Assay). Based on the functional data HI-6 demonstrates the highest anti-muscarinic effect. However, only when comparing [(3)H]-QNB binding results and GPCR data, K203 shows a very promising compound with regard to anti-muscarinic potency. The therapeutic impact of these findings has been discussed.

Current treatment of organophosphorus poisoning, resulting in overstimulation and desensitization of muscarinic and nicotinic receptors by acetylcholine (ACh), consists of the administration of atropine and oxime reactivators. However, no versatile oxime reactivator has been developed yet and some mortality still remains after application of standard atropine treatment, probably due to its lack of antinicotinic action. In our study, we focused on the interesting non-acetylcholinesterase property of oximes, i.e. antinicotinic effect of reactivators. Two standard reactivators (HI-6, obidoxime) and two new compounds (K027 and K203) were chosen for in vitro (patch clamp) and in vivo (nerve-evoked muscle contraction) testings. Both examinations showed antinicotinic effects of the reactivators. In vitro inhibition of acetylcholine-evoked currents by obidoxime, HI-6 and K203 was equivalent while K027 was less potent. Similar order of potency was observed by the in vivo examinations. We thus confirm previous in vitro results, which describe antinicotinic effects of oxime reactivators, and furthermore, we show in vivo antagonism of oxime reactivators exerted by the inhibition of ACh effect on the nicotinic receptor in the neuromuscular junction. Taking together, the effects of tested oxime reactivators indicate an antagonism on both embryonic and adult form of the muscle nicotinic receptors.

The ability of the newly developed bispyridinium compound K203 and its fluorinated analogue KR-22836 to reduce tabun-induced acute neurotoxic signs and symptoms was compared with the currently available reactivator of acetylcholinesterase-obidoxime. Tabun-induced neurotoxicity and the neuroprotective effects of all tested oximes in combination with atropine in rats poisoned with tabun at a sublethal dose (200 ug/kg intramuscularly (i.m.); 80% of LD(50) value) were monitored by a functional observational battery at 24 hr after tabun challenge. The results indicate that all tested oximes combined with atropine were able to survive tabun-poisoned rats 24 hr after tabun challenge while one non-treated tabun-poisoned rat died within 24 hr after tabun poisoning. All tested oximes combined with atropine were able to decrease tabun-induced neurotoxicity in the case of sublethal poisoning but they did not eliminate all tabun-induced acute neurotoxic signs and symptoms. While the ability to reduce tabun-induced acute neurotoxicity of obidoxime and K203 was similar, the neuroprotective efficacy of KR-22836 was slightly higher compared to other tested oximes. Thus, the newly developed fluorinated analogue of K203, called KR-22836, is able to slightly increase the neuroprotective effectiveness of antidotal treatment of acute tabun poisonings compared to K203 and currently available obidoxime.

The potency of newly developed bispyridinium compound K203 and its fluorinated analog KR-22836 in reactivating tabun-inhibited acetylcholinesterase and reducing tabun-induced lethal toxic effects was compared with commonly used oximes (obidoxime, trimedoxime, the oxime HI-6) using in vivo methods. Studies determining the percentage of reactivation of tabun-inhibited blood and tissue acetylcholinesterase in rats showed that the reactivating efficacy of K203 is higher than the reactivating efficacy of its fluorinated analog KR-22836 as well as currently available oximes studied. The therapeutic efficacy of the oxime K203 and its fluorinated analog corresponds to their potency to reactivate tabun-inhibited acetylcholinesterase. According to the results, the oxime K203 is more suitable than KR-22836 for the replacement of commonly used oximes for the antidotal treatment of acute tabun poisoning due to its relatively high potency to counteract the acute toxicity of tabun.

The influence of the combination of oximes on the reactivating and therapeutic efficacy of antidotal treament of acute tabun poisoning was evaluated. The ability of two combinations of oximes (HI-6 + obidoxime and HI-6 + K203) to reactivate tabun-inhibited acetylcholinesterase and reduce acute toxicity of tabun was compared with the reactivating and therapeutic efficacy of antidotal treatment involving single oxime (HI-6, obidoxime, K203) using in vivo methods. Studies determining percentage of reactivation of tabun-inhibited blood and tissue acetylcholinesterase in poisoned rats showed that the reactivating efficacy of both combinations of oximes is higher than the reactivating efficacy of the most effective individual oxime in blood and diaphragm and comparable with the reactivating effects of the most effective individual oxime in brain. Moreover, both combinations of oximes were found to be slightly more efficacious in the reduction of acute lethal toxic effects in tabun-poisoned mice than the antidotal treatment involving individual oxime. A comparison of reactivating and therapeutic efficacy of individual oximes showed that the newly developed oxime K203 is slightly more effective than commonly used obidoxime and both of them are markedly more effective than the oxime HI-6. Based on the obtained data, we can conclude that the antidotal treatment involving chosen combinations of oximes brings beneficial effects for the potency of antidotal treatment to reactivate tabun-inhibited acetylcholinesterase in rats and to reduce acute toxicity of tabun in mice.

Acetylcholinesterase (AChE) reactivators are crucial antidotes to organophosphate intoxication. A new series of 26 monooxime-monocarbamoyl xylene-linked bispyridinium compounds was prepared and tested in vitro, along with known reactivators (pralidoxime, HI-6, obidoxime, trimedoxime, methoxime, K107, K108 and K203), on a model of tabun- and paraoxon-, methylparaoxon- and DFP-inhibited human erythrocyte AChE. Although their ability to reactivate tabun-inhibited AChE did not exceed that of the previously known compounds, some newly prepared compounds showed promising reactivation of pesticide-inhibited AChE. The acute toxicity of the novel compounds was also determined. Docking studies using tabun-inhibited AChE were performed for three compounds of interest. The structure-activity relationship (SAR) study confirmed the apparent influence of the xylene linkage and carbamoyl moiety on the reactivation ability and toxicity of the agents.

Catalytic activity of acetylcholinesterase (AChE; EC 3.1.1.7) was studied in the presence of oximes HI-6, K114, K127 and K203, and inhibition constants were determined for the reversible enzyme-inhibitor complex (K(I)). Based on the mixed inhibition model, inhibition constants were 0.020 mM for HI-6, 0.0021 mM for K114, 0.175 mM for K127, and 0.036 mM for K203. Molecular modelling of AChE-oxime complexes was used to determine amino acid residues of the active site involved in the interactions. Bis-oxime K114 achieved the best stabilization in the active site due to pi-pi interaction between its three aromatic rings and Tyr124, Tyr341 and Trp86, and hydrogen bonds formed by its oxime groups with Gly121 and Glu285. Mono-oximes HI-6 and K203, which inhibited the enzyme with similar potency, showed similar positions of their pyridinium rings in the active site. The weakest inhibitor, K127, also formed several hydrogen bonds with the active site residues, but due to its long linker it was more likely stabilized at the peripheral site (Tyr124), which could explain lower AChE affinity for this oxime.

Seven new oxime-based acetylcholinesterase reactivators were compared with three currently available ones (obidoxime, trimedoxime, HI-6) for their ability to lessen cholinesterase inhibition in blood and brain of cyclosarin-treated rats. Oximes were given at doses of 5% their LD(50) along with 21 mg/kg atropine five min before the LD(50) of cyclosarin (120 ug/kg) was administered. Blood and brain samples were collected 30 minutes later. The greatest difference between acetylcholinesterase inhibition in blood of cyclosarin-treated rats was found after administration of HI-6 (40%), compared to 22% for trimedoxime and 6% for obidoxime. Only two of the seven newly synthesized oximes had any effect (K203 at 7%, K156 at 5%). Effective oximes against cyclosarin-inhibited plasma butyrylcholinesterase were HI-6 (42%), trimedoxime (11%), and K156 (4%). The oximes were less effective in brain than in blood, with reactivation values for HI-6 30% against acetylcholinesterase and 10% against butyrylcholinesterase. Values for newly synthesized oximes were less than 10% for K206, K269 and K203.

A potency of newly-developed oximes (K156, K203) and commonly used oximes (obidoxime, HI-6) to reactivate cyclosarin-inhibited acetylcholinesterase and to reduce cyclosarin-induced acute toxic effects was evaluated in this study. In vivo determined percentage of reactivation of cyclosarin-inhibited blood and tissue acetylcholinesterase in poisoned rats showed that the potency of a newly-developed oxime (K203) to reactivate cyclosarin-inhibited acetylcholinesterase and to reduce the acute lethal effects of cyclosarin, corresponding to the relatively low reactivating and therapeutic efficacy of obidoxime. The potency of another newly-developed oxime (K156) to counteract the inhibitory and acute clinical effects of cyclosarin is almost negligible. On the other hand, the oxime HI-6 is a very efficient reactivator of cyclosarin-inhibited acetylcholinesterase in the peripheral (blood, diaphragm) as well as central (brain) compartment, and it is able to reduce the acute toxicity of cyclosarin more than three times. Although the reactivating and therapeutic efficacy of the oxime K203 is higher compared to another newly-developed oxime K156, the reactivating and therapeutic potency of both newly-developed oximes is significantly lower in comparison with the oxime HI-6 and, therefore, none of them is suitable for replacement of HI-6 in the case of the treatment of cyclosarin poisoning.

We studied bispyridinium oxime K203 [(E)-1-(4-carbamoylpyridinium)-4-(4-hydroxyiminomethylpyridinium)-but-2-ene dibromide] with tabun-inhibited human acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) in vitro, and its antidotal effect on tabun-poisoned mice and rats in vivo. We compared it with oximes K048 and TMB-4, which have proven the most efficient oxime antidotes in tabun poisoning by now. Tabun-inhibited AChE was completely reactivated by K203, with the overall reactivation rate constant of 1806 L mol(-1) min(-1). This means that K203 is a very potent reactivator of tabun-inhibited AChE. In addition, K203 reversibly inhibited AChE (Ki = 0.090 mmol L(-1)) and BChE (K(i) = 0.91 mmol L(-1)), and exhibited its protective effect against phosphorylation of AChE by tabun in vitro. In vivo, a quarter of the LD50 K203 dose insured survival of all mice after the application of as many as 8 LD50 doses of tabun, which is the highest dosage obtained compared to K048 and TMB-4. Moreover, K203 showed high therapeutic potency in tabun-poisoned rats, preserving cholinesterase activity in rat plasma up to 60 min after poisoning. This therapeutic improvement obtained by K203 in tabun-poisoning places this oxime in the spotlight for further development.

The potency of newly developed monoxime bispyridinium compounds (K156, K203) in reactivating tabun-inhibited acetylcholinesterase and reducing tabun-induced lethal toxic effects was compared with commonly used oximes (obidoxime, trimedoxime, the oxime HI-6) using in vivo methods. Studies determining percentage of reactivation of tabun-inhibited blood and tissue acetylcholinesterase in poisoned rats showed that the reactivating efficacy of newly developed oxime K203 is comparable with obidoxime and trimedoxime in blood and higher than the reactivating potency of trimedoxime and obidoxime in diaphragm and brain, where the difference in reactivating efficacy of obidoxime, trimedoxime and K203 is significant. On the other hand, the potency of newly developed K156 to reactivate tabun-inhibited acetylcholinesterase is comparable with obidoxime or trimedoxime in diaphragm and brain. It is significantly lower than the reactivating efficacy of trimedoxime and obidoxime in blood. Moreover, both newly developed oximes were found to be relatively efficacious in the reduction of lethal toxic effects in tabun-poisoned mice. Especially, the oxime K203 is able to decrease the acute toxicity of tabun nearly two times. The therapeutic efficacy of K156 and K203 corresponds to their potency to reactivate tabun-inhibited acetylcholinesterase, especially in diaphragm and brain. In contrast to obidoxime and trimedoxime, the oxime HI-6 is not effective in reactivation of tabun-inhibited acetycholinesterase and in reducing tabun lethality. While the oxime K156 does not improve the reactivating and therapeutic effectiveness of currently available obidoxime and trimedoxime, the newly developed oxime K203 is markedly more effective in reactivation of tabun-inhibited acetylcholinesterase in rats, especially in brain, and in reducing lethal toxic effects of tabun in mice and, therefore, it is suitable for the replacement of commonly used oximes for the antidotal treatment of acute tabun poisoning.

Six AChE monooxime-monocarbamoyl reactivators with an (E)-but-2-ene linker were synthesized using modification of currently known synthetic pathways. Their potency to reactivate AChE inhibited by the nerve agent tabun and insecticide paraoxon was tested in vitro. The reactivation efficacies of pralidoxime, HI-6, obidoxime, K048, K075 and the newly prepared reactivators were compared. According to the results obtained, one reactivator seems to be promising against tabun-inhibited AChE and two reactivators against paraoxon-inhibited AChE. The best results were obtained for bisquaternary substances with at least one oxime group in position four.

Acetylcholinesterase reactivators are crucial antidotes for the treatment of organophosphate intoxication. Among the organophosphates, with the exception of soman, tabun (GA) intoxications are the least responsive to treatment with commercially available therapeutics. A rational design was used to increase reactivation ability and decrease the toxicity of the novel reactivator. (E)-1-(4-carbamoylpyridinium)-4-(4-hydroxyiminomethylpyridinium)-but-2-ene dibromide (K203) has better properties than previously tested compounds in vitro and, therefore, is a potential candidate for the treatment of GA intoxication in vivo.

Acetylcholinesterase reactivators are crucial antidotes for the treatment of organophosphate intoxication. Fifteen new monooxime reactivators of acetylcholinesterase with a (E)-but-2-ene linker were developed in an effort to extend the properties of K-oxime (E)-1-(4-carbamoylpyridinium)-4-(4-hydroxyiminomethylpyridinium)-but-2-ene dibromide (K203). The known reactivators (pralidoxime, HI-6, obidoxime, K075, K203) and the new compounds were tested in vitro on a model of tabun- and paraoxon-inhibited AChE. Monooxime reactivators were not able to exceed the best known compounds for tabun poisoning, but some of them did show reactivation comparable with known compounds for paraoxon poisoning. However, extensive differences were found by a SAR study for various substitutions on the non-oxime part of the reactivator molecule.