Structure–Activity Relationship Analysis on Antioxidant and Anticancer Actions of Theaflavins on Human Colon Cancer Cells

The roles of natural products as effective cancer prevention and therapeutic agents have been documented by various studies in recent years, but the action mechanisms and structure–activity relationship need more elucidation. The present study showed that theaflavins (theaflavin and its derivatives, TFs) from black tea caused an inhibitory effect on the proliferation of human colon adenocarcinoma cancer SW480 cells and human colon cancer SW620 cells [half maximal inhibitory concentration (IC50) < 32.0 μM] by the induction of cell cycle arrest but exerted lower toxicity against normal cells with a high safety index (1.89–6.26). Moreover, TFs triggered a decrease in reactive oxygen species in SW480 cells as a result of their excellent radical-scavenging ability (e.g., the IC50 value of TF4 to ABTS• + was 1.91 ± 0.21 μM). More importantly, the structure–activity relationship analysis of TFs exhibited that the galloyl group was an important factor to affect these activities. Taken together, we revealed that t...