In vivo evaluation of cholinesterase activity, oxidative stress markers, cyto- and genotoxicity of K048 oxime–a promising antidote against organophosphate poisoning

K048 is a member of K-oximes, a new oxime class that has recently been confirmed effective against poisoning by the nerve agent tabun and several pesticides. The toxicity profile of the K048 oxime has not been fully characterized and its optimal therapeutic dose has not yet been established. Earlier studies report excellent results with K048 in reactivating tabun-phosphorylated AChE and in the therapy of tabun-poisoned mice. It possesses a low acute toxicity and exerts an acceptable toxicity profile on isolated human peripheral blood lymphocytes in vitro. Intraperitoneal administration of K048 in rats resulted in an LD50 of 238.3 mg/kg. In this in vivo study, we investigated cholinesterase (ChE) activity and oxidative stress marker levels (lipid peroxidation and superoxide dismutase activity) in the plasma of exposed rats after administering the compound at 25% of its LD50. Lymphocyte viability was evaluated using an acridine orange/ethidium bromide in situ fluorescent assay. The levels of primary DNA damage in rat white blood cells were measured using the alkaline comet assay. The compound applied at 25% of its LD50 did not significantly affect ChE activity and lipid peroxidation and did not cause significant changes in the SOD activity in plasma. The cytotoxicity profile of K048 in the tested dose was also acceptable, and it did not possess significant DNA-damaging potential. The obtained results are promising for further evaluations of the K048 oxime, which should include tests on a broader concentration range and longer incubation times.

Oxime K027: novel low-toxic candidate for the universal reactivator of nerve agent- and pesticide-inhibited acetylcholinesterase

Oxime K027 is a low-toxic bisquaternary compound originally developed as a reactivator of acetylcholinesterase (AChE) inhibited by nerve agents. The reactivation potency of K027 has been tested as a potential reactivator of AChE inhibited by tabun, sarin, cyclosarin, soman, VX, Russian VX, paraoxon, methylchlorpyrifos, and DDVP. The results show that oxime K027 reactivated AChE inhibited by almost all tested inhibitors to more than 10%, which is believed to be enough for saving the lives of intoxicated organisms. In the case of cyclosarin- and soman-inhibited AChE, oxime K027 did not reach sufficient reactivation potency.

Reactivation of VX-inhibited AChE by novel oximes having two oxygen atoms in the linker

Two newly developed AChE reactivators possessing two oxime groups in 4-position of the pyridinium rings with linkers CH(2)O(CH(2))(2)OCH(2) and CH(2)O(CH(2))(4)OCH(2) were tested for their potency to reactivate VX-inhibited AChE. Their reactivation potency was compared with currently available oximes such as pralidoxime, obidoxime and HI-6. Appropriate constants (affinity towards the intact and inhibited enzyme, reactivation rate) characterizing the reactivation process were determined. According to the data obtained, a new oxime with CH(2)O(CH(2))(2)OCH(2) linker reached as high reactivation potency as HI-6. The percentage of reactivation of the oxime with CH(2)O(CH(2))(2)OCH(2) linker was comparable to that of obidoxime at a concentration 10(-3)M. Hence, these oximes may be worthy of future development for the treatment of nerve agent intoxications, especially, with lipophilic agents such as soman and cyclosarin.

Monooxime reactivators of acetylcholinesterase with (E)-but-2-ene linker—Preparation and reactivation of tabun- and paraoxon-inhibited acetylcholinesterase

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.

New oxime reactivators connected with CH2O(CH2)nOCH2 linker and their reactivation potency for organophosphorus agents-inhibited acetylcholinesterase

New bis-pyridinium oxime reactivators 6 with CH(2)O(CH(2))(2)OCH(2) and CH(2)O(CH(2))(4)OCH(2) linkers between the two pyridinium rings were designed and synthesized. In the in vitro test of their potency to reactivate AChE inhibited by organophosphorus agents at 5 x 10(-3)M concentration, the reactivation ability of 1,2-dimethoxy-ethylene-bis-N,N'-4-pyridiumaldoxime dichloride (6a) was 63% for housefly (HF) AChE inhibited by diisopropyl fluorophosphates (DFP), 51% for bovine red blood cell (RBC) AChE inhibited by DFP, 67% for HF-AChE inhibited by paraoxon, and 81% for RBC-AChE inhibited by paraoxon. Except in the case of DFP-inhibited HF AChE test of 2-PAM, the activities of 6a are much higher than the activities of 2-PAM and HI-6 which are AChE reactivators currently in use.

Targeted synthesis of 1-(4-hydroxyiminomethylpyridinium)-3-pyridiniumpropane dibromide--a new nerve agent reactivator

Preparation of 1-(4-hydroxy-iminomethylpyridinium)-3-pyridiniumpropane dibromide is described. This compound represents a new acetylcholinesterase (AChE) reactivator, which has no substituents on the second pyridinium ring as found in other commonly used AChE reactivators. The reactivation ability of this reactivator was tested on tabun- and cyclosarin-inhibited AChE. According to the results obtained, the new compound (without substitution and with decreased molecule size) showed increased reactivation potency in case of cyclosarin inhibited AChE. A potent oxime for treatment of tabun and cyclosarin-caused intoxications was thus obtained via slight modification of the reactivator structure (compared to trimedoxime and K027).