Growth Inhibition and Cell Cycle Arrest Effects of Oolong Tea Polyphenol Extract on Human Hepatoma and Prostate Cancer Cells

The antioxidant activities of polyphenolic antioxidants in green tea, jasmine, pu-erh and Oolong tea were compared. The anti-proliferative effects of tea polyphenol extract on human prostate cancer cells DU145, hepatocellular carcinoma cells HepG2 and hepatic carcinoma cells WRL68 were evaluated. Results indicated that, Oolong tea exhibited the highest antioxidant activities compared to other teas. The growth of cancer cells was effi ciently suppressed by the polyphenolic components in the extract after 48 h of incubation, showing dose dependency. According to the results of MTT assay, IC50 was 45.8 μg/mL in DU145, 31.2 μg/mL in HepG2 and 18.8 μg/mL in WRL68, respectively. Higher concentration of Oolong tea polyphenol extract (over IC50) induced typical apoptosis morphological changes, and triggered cell cycle arrest at S phase and G2/M phase in DU145 cells, S phase in HepG2 cells and G2/M phase in WRL68 cells, respectively. The apoptosis inducing effects were confi rmed by Annexin V/PI and JC-1 flow cytometry analyses. After Oolong tea polyphenol treatment (at concentration equal to IC80), the proportion of early apoptotic cells increased from 4.18 to slightly over 75% in HepG2 cells, 7.5 to 45.61% in WRL68 cells and 2.78 to 9.68% in DU145 cells, respectively. Collapse of mitochondrial membrane potential was observed in all three types of cancer cells, indicating one of the earliest features of apoptosis. In conclusion, higher concentration (over IC50) of Oolong tea polyphenols extract could effi ciently inhibit or slow down the growth of human hepatoma and prostate cancer cells, via the induction of cell cycle arrest and apoptosis.