Gene-Delivered Butyrylcholinesterase Is Prophylactic against the Toxicity of Chemical Warfare Nerve Agents and Organophosphorus Compounds

Gene delivery using an adenoviral system has been effective in introducing therapeutic proteins in vitro and in vivo. This study tested the feasibility of using adenovirus to deliver clinically relevant amounts of butyrylcholinesterase (BChE), a proven bioscavenger of nerve agents. The adenovirus construct expressed full-length mouse BChE. Mice were injected with a single dose of adenovirus (1.5 x 10(10) infectious units) in the tail vein; plasma was collected through day 11 and assayed for BChE activity. Maximum activity, representing a 300- to 3400-fold increase over baseline, was found on day 4. Expression levels returned to baseline by day 10. Nondenaturing gel electrophoresis showed the recombinant BChE was a dimer that could be converted to tetramers by addition of polyproline. The toxic compounds chosen for protection studies were positively charged organophosphorus agents, echothiophate, and O-ethyl-S-2-N,N-diisopropylaminoethyl methylphosphonothiolate (VX). Mice containing elevated blood levels of BChE (300- to 3,000-fold over the control mice) were challenged with incremental doses of echothiophate or VX. Mice showed no signs of toxicity and were protected from up to 30 x LD50 dose of echothiophate and 5 x LD50 dose of VX. A good correlation was observed between tolerated echothiophate dose and plasma BChE levels at time of challenge. The absolute increases in levels of circulating BChE and the sustained nature of the response resulted in a very high enzyme concentration, deemed critical in acute toxicity (5 x LD50 or more) scenarios. These results suggest that gene-delivered BChE is a prophylactic and affords protection equivalent to that of a multimilligram injection of the same.