| Introduction. Activation of HER-2 receptor initiates growth, survival and invasion promoting signaling mechanisms in breast cancer cells. Compared to normal cells, cancer cell biology is sustained at higher intracellular levels of reactive oxygen species (ROS). ROS like hydrogen peroxide (H2O2) can mediate activation of receptors, downstream signaling pathways and matrix degrading enzymes regulating cellular growth, survival and invasion. Epidemiological studies indicate that consumption of diet rich in fruits and vegetables is correlated with reduced incidence of breast cancer. Such a diet is rich in antioxidants (isoflavones) and essential trace elements (manganese). Therefore, we hypothesized that "dietary antioxidant agents like biochanin A and manganese could be used alone or in combination to selectively inhibit breast cancer cell survival and ROS regulated pathways in HER-2 positive SK-BR-3 breast cancer cells". Methods. HER-2-positive SK-BR-3 breast cancer cells, MCF-10A immortalized normal breast epithelial cells and NIH-3T3 normal fibroblast cells were treated with biochanin A and manganese for 72 hrs. Subsequently cell viability assays, western blotting, gelatin zymography, spectrophotometeric antioxidant enzyme activity assays and fluorescence evaluation of hydrogen peroxide were carried out. Results. The data indicate that 50 muM biochanin A inhibits cell viability, signaling pathways (p-HER-2, p-Erk, p-Akt, p-mTOR, NFkappaB) and invasive enzyme expression (MT1-MMP) and activity (MMP-9) in SK-BR-3 breast cancer cells. Biochanin A did not inhibit MCF-10A and NIH-3T3 cellular viability. Biochanin A (50 muM) treatment inhibited cytoplasmic and mitochondrial superoxide dismutase activities, induced glutathione peroxidase activity, reduced intracellular level of H2O2 and blocked H2O2 induced signaling pathways (p-HER-2 & p-Erk) in SK-BR-3 cells. Additionally, biochanin A (50 muM) and manganese (0.5 muM) in combination induced increased inhibition of cellular viability, p-Erk, p-Akt and H2O2 level in SK-BR-3 cells. Conclusions. Biochanin A could be a unique anticancer agent which can selectively target cancer cells and inhibit multiple signaling pathways in HER-2-positive SK-BR-3 breast cancer cells. The data suggest that biochanin A and manganese mediated decrease in intracellular level of H2O2 could be a mechanism which can partly contribute towards inhibition of cellular viability and signaling pathways in SK-BR-3 breast cancer cells. |
