Synergistic effects of tea polyphenols and ascorbic acid on human lung adenocarcinoma SPC-A-1 cells

Tea polyphenols have been shown to have anticancer activity in many studies. In the present study, we investigated effects of theaflavin-3-3′-digallate (TF3), one of the major theaflavin monomers in black tea, in combination with ascorbic acid (AA), a reducing agent, and (−)-epigallocatechin-3-gallate (EGCG), the main polyphenol presented in green tea, in combination with AA on cellular viability and cell cycles of the human lung adenocarcinoma SPC-A-1 cells. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay showed that the 50% inhibition concentrations (IC50) of TF3, EGCG, and AA on SPC-A-1 cells were 4.78, 4.90, and 30.62 μmol/L, respectively. The inhibitory rates of TF3 combined with AA (TF3+AA) and EGCG combined with AA (EGCG+AA) at a molar ratio of 1:6 on SPC-A-1 cells were 54.4% and 45.5%, respectively. Flow cytometry analysis showed that TF3+AA and EGCG+AA obviously increased the cell population in the G0/G1 phase of the SPC-A-1 cell cycle from 53.9% to 62.8% and 60.0%, respectively. TF3-treated cells exhibited 65.3% of the G0/G1 phase at the concentration of its IC50. Therefore, TF3+AA and EGCG+AA had synergistic inhibition effects on the proliferation of SPC-A-1 cells, and significantly held SPC-A-1 cells in G0/G1 phase. The results suggest that the combination of TF3 with AA or EGCG with AA enhances their anticancer activity.