Chemico-Biological Interactions 175 (2008) 413–416 Contents lists available at ScienceDirect Chemico-Biological Interactions journal homepage: www.elsevier.com/locate/chembioint New bispyridinium oximes: In vitro and in vivo evaluation of their biological efficiency in soman and tabun poisoning Suzana Berend a,∗ , Ana Luci ´ c Vrdoljak a , Boˇ zica Radi ´ c a , Kamil Kuˇ ca b a Institute for Medical Research and Occupational Health, Ksaverska c. 2, P.O. Box 291, HR-10001 Zagreb, Croatia b Department of Toxicology, Faculty of Military Health Sciences, University of Defence, Trebesska 1575, 500 01 Hradec Kralove, Czech Republic article info Article history: Available online 3 May 2008 Keywords: Acetylcholinesterase Soman Tabun Oxime Antidotal efficacy abstract Improving the efficacy of antidotal treatment of poisonings with nerve agents is still a challenge for the scientific community. This study investigated the interactions of four bispyridinium oximes with human erythrocyte acetylcholinesterase (AChE) and their effects on soman- and tabun-poisoned mice. Oximes HI-6 and TMB-4 were used for comparison. These oximes inhibited AchE with inhibitory potency (IC 50 ) ranging from 0.02 to 1.0mM. The best reactivating potency (%R) was obtained with K074, when AChE was inhibited by tabun. The protective potency (P 50 ) of all oximes in human erythrocyte AChE inhibited by soman and tabun could not be determined. In tabun-poisoned mice very good antidotal efficacy was obtained with K027, K048, and K074, which makes them interesting for future investigation. The combination of HI-6 and atropine is the therapy of choice for soman poisoning. © 2008 Elsevier Ireland Ltd. All rights reserved. 1. Introduction Organophosphorous (OP) compounds are widely used as pesticides, as drugs in the treatment of cholinergic disorders, and as nerve agents in chemical warfare [1,2]. Irreversible inhibition of acetylcholinesterase (AChE, EC 3.1.1.7) by these compounds results in acethylcholine accu- mulation in the synaptic cleft with consequences to the central and peripheral nervous system. The clinical signs of AChE inhibition manifest as hypersalivation, lacrima- tion, diarrhea, tremor, respiratory distress, convulsions, and seizures. Signs are dose-dependent, leading to severe incapacitation and rapid death. Presently, OP poisoning is treated with a combination of an antimuscarinic agent, e.g. atropine and an AChE reactivator oxime [3,4]. Pyri- dinium compounds, with or without the oxime group, are reversible inhibitors of AChE; they bind to either the cat- alytic or allosteric (substrate inhibition) enzyme binding ∗ Corresponding author. Tel.: +385 1 46 73 188; fax: +385 1 46 73 303. E-mail address: suzana@imi.hr (S. Berend). site or both, and they also protect AChE from phospho- rylation [5]. Their primary action is attributed to the nucleophilic displacement of the compounds’ moiety from the phosphorylated enzyme [6]. Unfortunately, OP such as soman phosphorylate AChE and rapidly “age” into a form that cannot be reactivated by oximes [7]. On the other hand, tabun-phosphorylated AChE is resistant to oxime reactivation due to an electron pair located on the amidic group that makes the nucleophilic attack almost impossible [8–10]. The inability of the standard therapy to provide adequate protection against these compounds calls for a synthesis of new compounds with the charac- teristic oxime group. This study investigated four oximes with a similar basic structure, but differing in the length of the linker between two pyridinium rings and in the posi- tion of the oxime group in the pyridinium ring. The aim was to determine their in vitro toxicity and protective and reactivating potency in human erythrocyte AChE. We also tested their in vivo antidotal efficacy in soman- and tabun- poisoned mice. Currently used oximes were included for comparison; HI-6 for soman and TMB-4 for tabun poison- ing. 0009-2797/$ – see front matter © 2008 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.cbi.2008.04.031