Anti-SARS coronavirus 3C-like protease effects of Isatis indigotica root and plant-derived phenolic compounds

The 3C-like protease (3CL(pro),) of SARS-coronavirus mediates the proteolytic processing of replicase polypeptides 1 a and 1 ab into functional proteins, becoming an important target for the drug development. In this study, Isatis indigotica root extract, five major compounds of I indigotica root, and seven plant-derived phenolic compounds were tested for anti-SARS-CoV 3CL(pro) effects using cell-free and cell-based cleavage assays. Cleavage assays with the 3CL(pro) demonstrated that IC50 values were in micromolar ranges for I indigotica root extract, indigo, sinigrin, aloe emodin and hesperetin. Sinigrin (IC50: 217 mu M) was more efficient in blocking the cleavage processing of the 3CL(pro), than indigo (IC50: 752 mu M) and beta-sitosterol (IC50: 1210 mu M) in the cell-based assay. Only two phenolic compounds aloe emodin and hesperetin dose-dependently inhibited cleavage activity of the 3CL(pro), in which the IC50 was 366 mu M for aloe emodin and 8.3 mu M for hesperetin in the cell-based assay. (c) 2005 Elsevier B.V. All rights reserved.