Potency determinations of acetylcholinesterase inhibitors using Ellman's reaction-based assay in screening: Effect of assay variants

In primary drug discovery screenings and potency determinations of active acetylcholinesterase (AChE) inhibitors, different variations of the Ellman's reaction-based assay are extensively applied. However, these are prone to produce variable results. Here we studied how assay variants differing in the order of reagent addition and substrate concentrations influence potency measurements of AChE inhibitors. Three model compounds were used: tacrine, physostigmine, and a newly reported inhibitor, 1-[5-[4-[(hexahydro-1H-azepin-1-yl)carbonyl]-1-piperidinyl]-1,3,4-thiadiazol-2-yl]-2-pyrrolidinone. Different patterns of potency changes related to the different inhibition mechanisms of the compounds were detected. Recognizing this, better judgment can be applied when publishing results and selecting optimal screening assays.