Zn II /pyridyloxime complexes as potential reactivators of OP-inhibited acetylcholinesterase: In vitro and docking simulation studies Konstantis F. Konidaris a,b, ⁎, Georgios A. Dalkas c , Eugenia Katsoulakou a , George Pairas c , Catherine P. Raptopoulou d , Fotini N. Lamari c , Georgios A. Spyroulias c , Evy Manessi-Zoupa a, ⁎⁎ a Department of Chemistry, University of Patras, 265 04 Patras, Greece b Institute of Nanotechnology, Karlsruhe Institute of Technology, Hermann-von-Helmholtz Platz 1, 76344 Eggenstein-Leopoldshafen, Germany c Department of Pharmacy, University of Patras, 26504 Patras, Greece d Institute of Materials Science, NCSR “Demokritos”, 153 10 Aghia Paraskevi Attikis, Greece abstract article info Article history: Received 17 July 2013 Received in revised form 26 December 2013 Accepted 26 December 2013 Available online 7 January 2014 Keywords: Acetylcholinesterase reactivators Docking simulations Zinc complexes Organophosphorus compounds Crystal structures Pyridyl oximes In order to investigate the ability of metal complexes to act as reactivators of organophosphorus compounds (OP)-inhibited acetylcholinesterase (AChE), we have synthesized and crystallographically characterized three novel mononuclear Zn II complexes formulated as [ZnCl 2 {(4-py)CHNOH} 2 ](1), [ZnBr 2 {(4-py)CHNOH} 2 ](2) and [Zn(O 2 CMe) 2 {(4-py)CHNOH} 2 ]∙2MeCN (3∙ 2MeCN), where (4-py)CHNOH is 4-pyridinealdoxime. Their reactiva- tion potency was tested in vitro with a slight modification of the Ellman's method using Electric eel acetylcholin- esterase and the insecticide paraoxon (diethyl 4-nitrophenyl phosphate) as inhibitor. The activity of the already reported complex [Zn 2 (O 2 CPh) 2 {(4-py)CHNOH} 2 ]·2MeCN (4·2MeCN) and of the clinically used drug obidoxime 1,1′-[oxybis(methylene)]bis{4-[(E)- (hydroxyimino)methyl]pyridinium} was also examined. The results of the in vitro experiments demonstrate moderate reactivation of the metal complexes compared to the drug obidoxime. On the other hand, it is clearly shown that the metal complex is the responsible molecular entity for the observed activity, as the reactivation efficacy of the organic ligand (4-pyridinealdoxime) is found to be inconsequential. Docking simulation studies were performed in the light of predicted complex-enzyme interac- tions using the paraoxon-inhibited enzyme along with the four Zn II complexes and obidoxime as a reference reactivator. The results showed that the three mononuclear metal complexes possess the required characteristics to be accommodated into the active site of AChE, while the entrance of the dinuclear Zn II compound is unsuccessful. An interesting outcome of docking simulations is the fact that the mononuclear compounds accommodate into the active site of AChE in a similar mode as obidoxime. © 2014 Elsevier Inc. All rights reserved. 1. Introduction Acetylcholinesterase (AChE, EC 3.1.1.7) is a serine hydrolase whose principal role is the termination of nerve impulse transmission at cholinergic synapses by rapid hydrolysis of the neurotransmitter acetyl- choline (ACh). AChE is irreversibly inhibited by organophosphorus compounds (OPs) [1], which include the toxic insecticides (parathion, paraoxon, chlorpyrifos, methamidophos) and the lethal chemical warfare agents (sarin, soman, tabun). Intoxication by OP-based insecticides is a serious public health problem, causing the death of more than 200,000 people per year [2], while the possible use of nerve agents by terrorists poses increasing threat for humans. OPs exert their acute toxicity through full inhibition of AChE, by forming covalently attached phos- phorus conjugates with the hydroxyl group of the catalytic serine residue [3]. Phosphylated (phosphorylated or phosphonylated) AChE can be reactivated by strong nucleophilic agents such as oximes. The family of cationic pyridinium oximes has been proven the most efficient among other oxime-type substances. The reactivator is able to cleave the covalent bond between the OP and AChE, restoring the enzyme activity. This reactivation process proceeds via a nucleophilic attack of the oximate anion on the P\O bond (Fig. 1). During the last 50 years, a plethora of substituted pyridyloxime analogs has been synthesized by many groups worldwide for their efficacy as AChE reactivators [4,5]. Nowadays, the most effective antidotes used for treatment of OPs poisoning are the monopyridinium oxime 2-PAM (pralidoxime) and the bispyridinium mono- or bis-oximes (obidoxime, HI-6, trimedoxime, etc) (Fig. 2). Unfortunately, none of known pyridinium oximes is able to satisfactorily reactivate AChE inhibited by various types of OPs, due to the broad structural Journal of Inorganic Biochemistry 134 (2014) 12–19 ⁎ Correspondence to: K.F. Konidaris, Institute of Nanotechnology, Karlsruhe Institute of Technology, Hermann-von-Helmholtz Platz 1, 76344 Eggenstein-Leopoldshafen, Germany. Tel.: +49 721 608 28922. ⁎⁎ Corresponding author. Tel.: +30 2610 997 147. E-mail addresses: konstantis.konidaris@partner.kit.edu, konstantis.konidaris@gmail.com (K.F. Konidaris), emane@upatras.gr (E. Manessi-Zoupa). 0162-0134/$ – see front matter © 2014 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jinorgbio.2013.12.011 Contents lists available at ScienceDirect Journal of Inorganic Biochemistry journal homepage: www.elsevier.com/locate/jinorgbio