Determination of the half maximal inhibitory concentration (IC50)

A total of 100 µl containing 5×10⁴/ml cells was seeded into 96-well plates. Cells were subsequently incubated for 12 h with different concentrations of DDP (batch number: 100401-201302; 99.8%; Chinese Research Institute of Food and Drug Inspection); the DDP concentrations were 1, 2, 4, 8, 16, 32 and 64 µg/ml in 100 µl total volume per well, and three replicates were made for each concentration of the drug, using the same medium as that used in the negative control wells. Following culture for 48 h, the cells were treated with 20 µl MTT solution (5 mg/ml) in each well. After 4 h of incubation, the cell medium was removed, 150 µl DMSO was added, and cells were oscillated for 10 min. The absorbance value (A) was measured at 490 nm absorbance with automatic enzyme immunoassay. The cell growth inhibition rate (%) = (1 - A value of the experimental group/A value of the control group) ×100. The IC₅₀ of DDP in the human GC MKN-28 and MKN-45 cell lines was calculated.