Development of small bisquaternary cholinesterase inhibitors as drugs for pre-treatment of nerve agent poisonings

Abstract

Background: Intoxication by nerve agents could be prevented by using small acetylcholinesterase inhibitors (eg, pyridostigmine) for potentially exposed personnel. However, the serious side effects of currently used drugs led to research of novel potent molecules for prophylaxis of organophosphorus intoxication.

Methods: The molecular design, molecular docking, chemical synthesis, in vitro methods (enzyme inhibition, cytotoxicity, and nicotinic receptors modulation), and in vivo methods (acute toxicity and prophylactic effect) were used to study bispyridinium, bisquinolinium, bisisoquinolinium, and pyridinium-quinolinium/isoquinolinium molecules presented in this study.

Results: The studied molecules showed non-competitive inhibitory ability towards human acetylcholinesterase in vitro that was further confirmed by molecular modelling studies. Several compounds were selected for further studies. First, their cytotoxicity, nicotinic receptors modulation, and acute toxicity (lethal dose for 50% of laboratory animals [LD₅₀]; mice and rats) were tested to evaluate their safety with promising results. Furthermore, their blood levels were measured to select the appropriate time for prophylactic administration. Finally, the protective ratio of selected compounds against soman-induced toxicity was determined when selected compounds were found similarly potent or only slightly better to standard pyridostigmine.

Conclusion: The presented small bisquaternary molecules did not show overall benefit in prophylaxis of soman-induced in vivo toxicity.

Keywords: AChE inhibitors; nerve agents; pre-treatment; prophylaxis; soman; toxicity.

Figure 1

Bisquaternary compounds tested or used for organophosphorus protection or reactivation.

Figure 2

Bispyridinium, bisquinolinium, bisisoquinolinium and pyridinium-quinolinium/isoquinolinium compounds designed as small cholinesterase inhibitors.

Figure 3

4-(tert-butyl)pyridinium or 4-positioned pyridinium analogs designed as small cholinesterase inhibitors.

Figure 4

Example of small inhibitor preparation technique. Notes: X = Cl, Br; A = (CH₂)_1–12; (E/Z)-CH2CH=CHCH₂; (CH₂)_1–2O(CH₂)_1–2. Abbreviations: DMF, dimethylformamide; MeCN, acetonitrile.

Figure 5

Selected promising small cholinesterase inhibitors. Abbreviations: hAChE, human acetylcholinesterase; IC₅₀, half maximal inhibitory concentration.

Figure 6

Example of molecular modeling result at human AChE active site for compound K524 (in blue; A) and K792 (in brown; B). Notes: Image A reproduced from Komloova M, Musilek K, Horova A, et al. Preparation, in vitro screening and molecular modelling of symmetrical bisquinolinium cholinesterase inhibitors – implications for early Myasthenia gravis treatment. Bioorg Med Chem Lett. 2011;21:2505–2509. Copyright © 2011 Elsevier Ltd. All rights reserved. Image B reproduced from Komloova M, Horova A, Hrabinova M, et al. Preparation, in vitro evaluation and molecular modelling of pyridinium-quinolinium/isoquinolinium non-symmetrical bisquaternary cholinesterase inhibitors. Bioorg Med Chem Lett. 2013;23(24):6663–6666. Copyright © 2013 Elsevier Ltd. All rights reserved. Abbreviation: AChE, acetylcholinesterase.