Highly toxic
organophosphorus compounds that irreversibly inhibit the
enzyme acetycholinesterase (AChE), including
nerve agents like
tabun,
sarin, or
soman, still pose a credible threat to civilian populations and military personnel. New
therapeutics that can be used as a pretreatment or after
poisoning with these compounds, complementing existing treatment schemes such as the use of
atropine and AChE reactivating
oximes, are currently the subject of intense research. A prominent role among potential candidates is taken by
enzymes that can detoxify
nerve agents by hydrolysis.
Diisopropyl fluorophosphatase (
DFPase) from the squid Loligo vulgaris is known to effectively hydrolyze
DFP and the range of G-type
nerve agents including
sarin and
soman. In the present work,
DFPase was PEGylated to increase
biological half-life, and to lower or avoid an immunogenic reaction and proteolytic digest. Addition of linear
polyethylene glycol (PEG) chains was achieved using
mPEG-NHS
esters and conjugates were characterized by electrospray ionization--time of flight--mass specrometry (ESI-ToF-MS). PEGylated wildtype
DFPase and a mutant selective for the more toxic stereoisomers of the agents were tested in vivo with rats that were challenged with a subcutaneous 3x LD(50) dose of
soman. While wildtype
DFPase prevented death only at extremely high doses, the mutant was able keep the animals alive and to minimize or totally avoid symptoms of
poisoning. The results serve as a proof of principle that engineered variants of
DFPase are potential candidates for in vivo use if substrate affinity can be improved or the turnover rate enhanced to lower the required
enzyme dose.