ABSTRACT
West Nile virus (WNV) is a mosquito-borne member of flaviviruses that causes significant morbidity and mortality especially among children. There is currently no approved vaccine or antiviral therapeutic for human use. In a previous study, we described compounds containing the 8-hydroxyquinoline (8-HQ) scaffold as inhibitors of WNV serine protease (NS2B/NS3pro) in a high throughput screen (HTS) using the purified WNV NS2B/NS3pro as the target. In this study, we analyzed potencies of some commercially available as well as chemically synthesized derivatives of 8-HQ by biochemical assays. An insight into the contribution of various substitutions of 8-HQ moiety for inhibition of the protease activity was revealed. Most importantly, the substitution of the N1 of the 8-HQ ring by -CH- in compound 26 significantly reduced the inhibition of the viral protease by this naphthalen-1-ol derivative. The kinetic constant (K(i)) for the most potent 8-HQ inhibitor (compound 14) with an IC(50) value of 2.01 ± 0.08 µM using the tetra-peptide substrate was determined to be 5.8 µM. This compound inhibits the WNV NS2B/NS3pro by a competitive mode of inhibition which is supported by molecular modeling.
Subject(s)
Oxyquinoline/pharmacology , Serine Proteinase Inhibitors/pharmacology , Viral Proteins/antagonists & inhibitors , West Nile Fever/virology , West Nile virus/enzymology , Binding Sites , Humans , Kinetics , Models, Molecular , Oxyquinoline/chemistry , Serine Proteases/chemistry , Serine Proteases/genetics , Serine Proteases/metabolism , Serine Proteinase Inhibitors/chemistry , Viral Proteins/chemistry , Viral Proteins/genetics , Viral Proteins/metabolism , West Nile virus/chemistry , West Nile virus/drug effects , West Nile virus/geneticsABSTRACT
Detergents such as Triton X-100 are often used in drug discovery research to weed out small molecule promiscuous and non-specific inhibitors which act by aggregation in solution and undesirable precipitation in aqueous assay buffers. We evaluated the effects of commonly used detergents, Triton X-100, Tween-20, Nonidet-40 (NP-40), Brij-35, and CHAPS, on the enzymatic activity of West Nile virus (WNV) protease. Unexpectedly, Triton X-100, Tween-20, and NP-40 showed an enhancement of in vitro WNV protease activity from 2 to 2.5-fold depending on the detergent and its concentration. On the other hand, Brij-35, at 0.001% enhanced the protease activity by 1.5-fold and CHAPS had the least enhancing effect. The kinetic analysis showed that the increase in protease activity by Triton X-100 was dose-dependent. Furthermore, at Triton X-100 and Tween-20 concentrations higher than 0.001%, the inhibition of compound B, one of the lead compounds against WNV protease identified in a high throughput screen (IC(50) value of 5.7+/-2.5 microM), was reversed. However, in the presence of CHAPS, compound B still showed good inhibition of WNV protease. Our results, taken together, indicate that nonionic detergents, Triton X-100, Tween, and NP-40 are unsuitable for the purpose of discrimination of true versus promiscuous inhibitors of WNV protease in high throughput assays.
