AMPLIFICATION OF THE EFFECTIVENESS OF ACETYLCHOLINESTERASE FOR DETOXIFICATION OF ORGANOPHOSPHORUS COMPOUNDS BY BIS-QUATERNARY OXIMES

Pretreatment of rhesus monkeys with fetal bovine serum acetylcholinest erase (FBS AChE) provides complete protection against 5 LD(50) of orga nophosphate (OF) without any signs of toxicity or performance decremen ts as measured by serial probe recognition tests or primate equilibriu m platform performance (Maxwell ct al., Toxicol Appl Pharmacol 115: 44 -49, 1992; Wolfe et al., Toxicol Appl Pharmacol 117: 189-193, 1992). A lthough such use of enzyme as a single pretreatment drug for OP toxici ty is sufficient to provide complete protection, a relatively large (s toichiometric) amount of enzyme was required in vivo to neutralize OP. To improve the efficacy of cholinesterases as pretreatment drugs, we have developed an approach in which the catalytic activity of OF-inhib ited FBS AChE was rapidly and continuously restored, thus detoxifying the OP and minimizing enzyme aging by having sufficient amounts of app ropriate oxime present. The efficacy of FBS AChE to detoxify several O Ps was amplified by addition of bis-quaternary oximes, particularly 1- (2-hydroxyiminomethyl-1-pyridinium) 1-(4-carboxyaminopyridinium)-dimet hyl ether hydrochloride (HI-6). When mice were pretreated with suffici ent amounts of FBS AChE and HI-6 and challenged with repeated doses of O-isopropyl methylphosphonofluoridate (sarin), the OP was continuousl y detoxified so long as the molar concentration of the sarin dose was less than the molar concentration of AChE in circulation. The in vitro experiments showed that the stoichiometry of sarin:FBS AChE was highe r than 3200:1 and in vivo stoichiometry with mice was as high as 57:1. Addition of HI-6 to FBS AChE as a pretreatment drug amplified the eff icacy of enzyme as a scavenger of nerve agents.