Cell viability assay

Cell viability was examined using the cell counting kit-8 (CCK-8) assay (YEASEN China). In brief, cells (1 × 10⁴ cells/well) in confluent 96-well cell culture plates were treated with different concentrations of coumarin derivative (1, 5, 10, 25, 50, 100, 200, and 400 μg/mL) for 48 h. Then 10 μL CCK-8 reagents were added into every well for 2 h of incubation. Optical density (OD) was detected using the microplate reader (BioTek, Germany). The values were then fit into a non-linear regression curve and the IC₅₀ was calculated using GraphPad Prism.