Kinetic interactions of a homologous series of bispyridinium monooximes (HGG oximes) with native and phosphonylated human acetylcholinesterase

Inhibition of acetylcholinesterase (AChE) is the main toxic mechanism of organophosphorus compounds (OP) and reactivation of OP-inhibited AChE by oximes is a mainstay of antidotal treatment. The inadequate efficacy of clinically used oximes led to the synthesis of numerous new compounds in the past decades to identify more effective reactivators. Despite of extensive in vitro reactivation studies the structural features for the development of effective oximes are not well understood. In the present study we investigated the kinetic interactions of a homologous series of bispyridinium monoximes bearing C1 to C12 alkylketone groups on the second pyridinium ring with native and cyclosarin-inhibited human AChE. We observed a correlation of the length of the alkyl side chain with an up to 20-fold increased affinity towards native AChE. The effect of the alkyl side chain on the affinity and reactivity towards phosphonylated AChE was moderate, except of a markedly reduced reactivity of C10 and C12 oximes. In comparison to the reference oxime HI-6 all HGG oximes had a lower reactivating potency and these oximes are not considered as promising compounds for the reactivation of cyclosarin-inhibited AChE.