MTT Assay and Synergy Analyses

To validate chemosensitivity of A549/DDP cells to cisplatin, the MTT assay was firstly performed. In summary, cells were seed into 96-well plates (5 × 10³ cells/well), and cultured overnight for adherence. Cells were exposed to different concentrations of cisplatin (0.625, 1.25, 2.5, 5, 10, and 20 μg/ml), scutellarin (10, 20, 40, 80, 120, and 160 μM), or their combination. After treatment for 24 or 48 h, 20 μL MTT (5 mg/ml) was added to each well and incubated for another 4 h. Subsequently, the medium was discarded and replaced with 150 μL DMSO. The absorbance at 490 nm wavelength was measured using a multiwell spectrophotometer (Bio-Rad, Hercules, CA, United States). To calculate the combination index (CI) of cisplatin and scutellarin, CalcuSyn software package (version 2.1) was used (Omar et al., 2016).