Soy-derived isoflavones inhibit HeLa cell growth by inducing apoptosis

Isoflavones are among the major bioactive compounds found in a wide variety of plant-derived foods, especially in soybeans and soy-based foods. In this study, the effect of a soy-derived isoflavone mixture (designated as SI-I, containing 71% daidzein, 14.3% genistein and 14.7% glycitein) on HeLa cells and its mechanism were investigated. SI-I in concentration range 5-80 μg/ml significantly reduced the survival rate of HeLa cells by MTT assay, whereas showed no side effect on that of L929 cells. After HeLa cells were exposed to 10, 20 and 40 μg/ml SI-I for 4 days, typical apoptotic morphological changes, including nuclear fragmentation, cytoplasm shrinkage and decrease of cell volume, were observed by fluorescence microscope and CLSM, respectively. FCM analysis revealed that the percentages of early apoptotic cells with lost Δψm increased by 2.27, 2.74 and 4.05 folds respectively, compared with control. The results showed that SI-I inhibited HeLa cell growth through inducing apoptosis via the mitochondrial pathway and comparisons with reported data indicated that synergistic effect existed between the isoflavone species contained in SI-I. It is proposed that natural soy-derived isoflavones are potential candidates as chemotherapeutic agents against human cervical cancer.