Differential anti‐proliferative activity of isoflavones against Src‐activated human adenocarcinoma cells

Abstract

Src oncogene has been strongly implicated in the development, growth, progression, and metastasis of a variety of human cancers. Although many studies reported that soy isoflavones have potential anticancer activity, the role of isoflavones in oncogenic activity of Src remains unknown. Using HAG‐1 human adenocarcinoma cells transfected with v‐Src, we investigated here the functional role of Src in anti‐proliferative activity of isoflavones including genistein, daidzein, glycitin and equol. The growth inhibitory activities of those isoflavones against Src‐transfected cells (HAG/src) and vehicle‐transfected control cells (HAG/neo) were investigated using WST‐1 cell proliferation assay. Effects of those isoflavones on apoptosis and cell cycle perturbation were evaluated by FACS analyses. The growth of HAG/neo cells were inhibited potently by genistein and equol, but modestly by daidzein and glycitin. Activation of Src conferred resistance to either daidzein, glycitin or equol, but rendered the cells more sensitive to genistein, compared to vehicle‐transfected cells; Genistein strongly inhibited the growth of HAG/src cells in a dose–dependent manner with IC50 approximately 25 μM, whereas in other three isoflavone components, the inhibitory effects were minimal without reaching an IC50 even at a dose of 100 μM. Upon treatment with 50 μM genistein for 72 h, HAG/src cells were significantly arrested at the G2/M compared to HAG/neo control cells (37.7% versus 7.0%). By contrast, the same concentration of either daidzein, glycitin or equol could not arrest HAG/src cells at any checkpoint of the cell cycle. The sub‐G0/G1 apoptotic cell population were not increased after 72 h exposure with either isoflavones. Therefore, it appears that growth inhibition by genistein in Src‐activated cells would be mediated mainly by the G2/M arrest of cell cycle rather than apoptosis induction. These data suggest that genistein would be the only isoflavone component that may potentially suppress oncogenic activity driven by Src, providing a mechanistic rationale for the potential use of genistein in the prevention and treatment of human cancers with activated Src. Studies for the effects of genistein on cell cycle‐related proteins are underway.