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 (TF(3)), 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 (IC(50)) of TF(3), EGCG, and AA on SPC-A-1 cells were 4.78, 4.90, and 30.62 mu mol/L, respectively. The inhibitory rates of TF(3) combined with AA (TF(3)+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 TF(3)+AA and EGCG+AA obviously increased the cell population in the G(0)/G(1) phase of the SPC-A-1 cell cycle from 53.9% to 62.8% and 60.0%, respectively. TF(3)-treated cells exhibited 65.3% of the G(0)/G(1) phase at the concentration of its IC(50). Therefore, TF(3)+AA and EGCG+AA had synergistic inhibition effects on the proliferation of SPC-A-1 cells, and significantly held SPC-A-1 cells in G(0)/G(1) phase. The results suggest that the combination of TF(3) with AA or EGCG with AA enhances their anticancer activity.