CCD-986Sk and WI-38 cells were seeded at 1 × 104 cells/well in 96-well plates containing 200 μL of medium for overnight culture, whereas SKOV-3 cells were cultured in the same manner but seeded at 5 × 103 cells/well. Then, the cells were treated with various concentrations of apigenin, α-mangostin, or doxorubicin, or the 0.1% (v/v) dimethyl sulfoxide (DMSO) solvent only (control). The SKOV-3 cells were treated for 24, 48, and 72 hr, whereas the CCD-986Sk and WI-38 cells were treated for 24 hr only. After the indicated incubation (exposure) time was reached, 10 μL of 5 mg/mL MTT solution was added to each well and the culture plates were incubated for 3 hr to allow for mazan formation. The culture medium was then removed, the formazan was solubilized by the addition of 150 μL of DMSO, and the absorbance at 560 nm (A560) was measured with a microplate reader. The cell viability (%) was calculated using Eq. (1) as follows:
The IC50 value of each compound was calculated from the graphical plot of the relative number of viable cells (%) vs. the test compound concentration.