To test the usefulness of
immunotherapy in
organophosphate poisoning, two mouse
monoclonal antibodies were prepared to the
chemical warfare agent soman. The
antibodies bound reversibly to
soman and afforded considerable protection to
acetylcholinesterase in vitro. However, they were only marginally effective in preventing the consequences of
soman poisoning in mice (these data have been published elsewhere). Since potential for immunotherapeutic usefulness resides in antibody affinity and specificity, we conducted experiments to define these parameters to enable us to maximize them in the production of later
antibodies. Interaction of the
antibodies (CC1 and BE2) in affinity-purified form with a series of
soman analogs in a competitive inhibition
enzyme immunoassay was used to assess the contribution to binding affinity of each functional group on the
soman molecule. Neither antibody interacted with the -P = S analog of
soman or
methylphosphonic acid. A decrease in the number of methyl groups on the pinacolyl side chain reduced or eliminated binding with both
antibodies while increasing the size of this group had a mixed result. The major metabolite of
soman, its basic hydrolysis product, interacted weakly with BE2 and failed to interact with CC1. Alkyl
ester group substitution at the
fluorine position increased antibody binding up to the symmetrical dipinacolyl analog. Stereochemical specificity was determined by measuring the apparent decrease in the rate of inhibition of
cholinesterases (
acetylcholine acetylhydrolase, EC 3.1.1.7, or
acylcholine acylhydrolase, EC 3.1.1.8) by pure
soman stereoisomers in the presence of increasing concentrations of each antibody. CC1 demonstrated specificity that varied as C(+)P(+) less than C(-)P(+) less than C(-)P(-) less than C(+)P(-). Although affinities were much lower, BE2 also showed a preference for the more toxic P(-) isomers.