2.3. MTT assay for cell viability

The effect of oridonin on cell viability was assessed using the MTT assay. Briefly, cells (1 × 10⁴ cells/well) were plated in 96‐well culture plates. After being incubated overnight, the cells were treated with oridonin (0, 2.5, 5, 10, 20 and 40 μmol/L) for 24 and 48 hours. 10 μL MTT solution (5 mg/mL) was added to each well, and after 4 hours of incubation, the medium was discarded. DMSO (150 μL) was added to dissolve the resulting formazan crystals. The absorbance value at 570 nm was measured using an enzyme‐linked immunosorbent assay reader (Labsystems, Finland). The cell viability rate was calculated as follows: cell viability rate (%) = OD of test group/OD of control group × 100%.