Cytopathic Effect (CPE) Inhibition Assay

The antiviral activity of CoPP against PRV was determined via the CPE inhibition assay. Briefly, PK-15 or ST cells were seeded into 96-well plates at a density of 1 × 10⁴ cells/well about 24 h before infecting with equal volumes of PRV (0.01 MOI), following by the addition of twofold serial dilutions of CoPP to each well. The MNCC was set as the highest concentration for this experiment. Following cell culture for 72 h at 37°C, the CPE was observed in each well. PRV-infected PK-15 or ST cells without CoPP treatment were used as the control. The CoPP concentration decreasing CPE by 50%, compared with the control group, was estimated using GraphPad Prism software and defined as the half maximal inhibitory concentration (IC₅₀), expressed in μmol/l. The selectivity index (SI) was calculated from the ratio of CC₅₀ to IC₅₀.