A New Class of Bi- and Trifunctional Sugar Oximes as Antidotes against Organophosphorus Poisoning

Abstract

Recent events demonstrated that organophosphorus nerve agents are a serious threat for civilian and military populations. The current therapy includes a pyridinium aldoxime reactivator to restore the enzymatic activity of acetylcholinesterase located in the central nervous system and neuro-muscular junctions. One major drawback of these charged acetylcholinesterase reactivators is their poor ability to cross the blood-brain barrier. In this study, we propose to evaluate glucoconjugated oximes devoid of permanent charge as potential central nervous system reactivators. We determined their in vitro reactivation efficacy on inhibited human acetylcholinesterase, the crystal structure of two compounds in complex with the enzyme, their protective index on intoxicated mice, and their pharmacokinetics. We then evaluated their endothelial permeability coefficients with a human in vitro model. This study shed light on the structural restrains of new sugar oximes designed to reach the central nervous system through the glucose transporter located at the blood-brain barrier.

Scheme 1. Alkyl Chain-Containing Aldoxime Synthetic Pathway

Scheme 2. Triazole-Containing Aldoxime Synthetic Pathway

Scheme 3. Triazole and Alkyne Glycoconjugate Synthetic Pathway

Scheme 4. Position 6-Substituted Alkyl-Triazole Glycoconjugate

Figure 1

Sugar oximes and synthetic product synthesized and tested.

Figure 2

Molecular docking of selected oximes in the active site of VX and GB-inhibited human acetylcholinesterase (respectively top and bottom panel). The binding energy determined by the scoring function of Autodock Vina and the distance between the phosphorus atom of VX or GB and the oxime oxygen atom are indicated in the top left corner of each docking pose.

Figure 3

Views of oximes 3 (PDB 7P1P) and 4 (PDB 7P1N) in complex with hAChE. Top: overall view of oximes 3 and 4 location inside the gorge of hAChE defined by the solvent accessible surface showing the sugar moiety outside the gorge. Bottom: closer view of oximes 3 and 4 inside the gorge of hAChE. A 1.0-σ feature-enhanced map is represented as a blue mesh. Key peripheral (Trp286) and active site (Trp86) tryptophan residues are represented in sticks with carbons in cyan. H-bonds are represented in black dashes and water molecules as red spheres.

Figure 4

Radar representation of protective index values of 100 μmol/kg intraperitoneal treatment of 2-PAM, HI-6, obidoxime, oximes 4 and 4′ 1 min after paraoxon, and NIMP or NEMP subcutaneous exposure. Protective indexes were determined by the up-and-down method.

Figure 5

Reactivation of VX-inhibited hAChE by oximes 4 and 4′ in mice plasma. The same dose of 100 μmol/kg of oxime 4 and 4′ was administered intraperitoneally to mice (n = 7). Blood samples were drawn at various time points (0, 2, 5, 10, 15, 30, 60, and 180 min) after treatment, and the levels of reactivation of VX-phosphylated hAChE were determined. Values are presented as percentages of maximum reactivation and points are means ± SEM. Fitting was performed on GraphPad Prism software.

Figure 6

Endothelial permeability coefficients (Pe) of control oximes (2-PAM, HI-6, obidoxime), glycoconjugate oximes (compounds 1, 2, 3, 4, 4′, 5, and 15), glycoconjugate intermediates (compounds 6, 7, 8, 9, 10, 11, 12, 13, and 14), and ¹⁴C d-glucose. Values are means ± SD, n = 3–9.