Erythro-austrobailignan-6 down-regulates HER2/EGFR/integrinβ3 expression via p38 activation in breast cancer

Despite the benefits from different options of therapy for breast cancer, resistance of the disease to these therapies is rising and a novel agent is needed. Erythro-austrobailignan-6 (EA6) exhibits anti-cancer activity. However, the detailed anti-tumor mechanisms by which EA6 inhibits 4T-1 and MCF-7 cell growth have not been well studied.

In this study, we investigated the anti-proliferative and anti-tumor properties of EA6 on breast carcinoma and its accompanying mechanisms.

The cytotoxic and apoptotic effect of EA6 were measured in breast cancer cell lines of 4T-1 and MCF-7. The role of EA6 on cell proliferation and migration was examined by immunoblotting. The anti-tumor activity of EA6 was assessed in mice inoculated with 4T-1 breast cancer cells.

EA6 increased the number of Annexin V-positive apoptotic bodies and cleaved form of caspase-3 in a dose-dependent manner and phosphorylated JNK and p38 in both cells. Moreover, EA6 down-regulated cell cycle dependent proteins of CDK-4 and cyclin D1, and increased G0/G1 population in both cells. EA6-induced apoptosis is mediated by p38 MAPK and caspase-3 activation in both cells. EA6 significantly reduced HER2/EGFR/integrin β3 expression and Src phosphorylation, which was dependent on p38 MAPK activation in 4T-1 and MCF-7 cells. Furthermore, we confirmed the down-regulation of topoisomerases by EA6 treatment, but the overall effects of EA6 on topoisomerase isotype were cell type specific. Finally, EA6 (20mg/kg/day) significantly reduced mammary tumor volume in 4T-1 bearing mice by down-regulating HER2/EGFR/integrin β3 expression in tumor tissues.

Our results offer a novel insight into the mechanism of EA6-induced apoptosis in breast cancer cells. We propose that EA6 treatment resulted in the activation of p38 MAPK and caspase-3, which eventually participated in regulating apoptosis in 4T-1 and MCF-7 cells.