Pharmacokinetic Evaluation of Brain Penetrating Morpholine-3-hydroxy-2-pyridine Oxime as an Antidote for Nerve Agent Poisoning

Nerve agents, the deadliest chemical warfare agents, are potent inhibitors of acetylcholinesterase (AChE) and cause rapid cholinergic crisis with serious symptoms of poisoning. Oxime reactivators of AChE are used in medical practice in the treatment of nerve agent poisoning, but the search for novel improved reactivators with central activity is an ongoing pursuit. For numerous oximes synthesized, in vitro reactivation is a standard approach in biological evaluation with little attention given to the pharmacokinetic properties of the compounds. This study reports a comprehensive physicochemical, pharmacokinetic, and safety profiling of five lipophilic 3-hydroxy-2-pyridine aldoximes, which were recently shown to be potent AChE reactivators with a potential to be centrally active. The oxime JR595 was singled out as highly metabolically stable in human liver microsomes, noncytotoxic oxime for SH-SY5Y neuroblastoma and 1321N1 astrocytoma cell lines, and its pharmacokinetic profile was determined after intramuscular administration in mice. JR595 was rapidly absorbed into blood after 15 min with simultaneous distribution to the brain at up to about 40% of its blood concentration; however, it was eliminated from both the brain and blood within an hour. In addition, the MDCKII-MDR1 cell line assay showed that oxime JR595 was not a P-glycoprotein efflux pump substrate. Finally, the preliminary antidotal study against multiple LD50 doses of VX and sarin in mice showed the potential of JR595 to provide desirable therapeutic outcomes with future improvements in its circulation time.