Quercetin Induces Apoptosis via the Mitochondrial Pathway in KB and KBv200 Cells

In this study, anticancer activities of six compounds of flavonoids were investigated in human epidermoid carcinoma KB and ICBv200 cells. Among these compounds, quercetin and acacetin showed strong inhibition of cell growth in KB and KBv200 cells. IC50 values of quercetin against KB and KBv200 cells were 17.84 +/- 4.14 and 18.94 +/- 4.75 mu M, respectively. The IC50 values of acacetin against KB and KBv200 cells were 41.33 +/- 6.05 and 49.04 +/- 3.64 mu M. The IC50 values of apigenin, kaempferol, kaempferol 3-O-rhamnoside, and quercetin 3-O-rhamnoside were more than 100 mu M. Furthermore, quercetin was found to induce apoptosis in KB and KBv200 cells via the mitochondrial pathway, including a decrease of the reactive oxygen species level, loss of mitochondrial membrane potential, release of cytochrome c, activation of caspase-9 and caspase-3, and cleavage of poly (ADP-ribose) polymerase. The apoptosis induced by quercetin was not related to the regulation of Bcl-2 or Bax in KB and KBv200 cells.