Caspase-dependent and caspase-independent induction of apoptosis in breast cancer by fucoidan via the PI3K/AKT/GSK3β pathway in vivo and in vitro.

Purpose Fucoidan, a complex, sulfated polysaccharide obtained from brown seaweed, exerted anticancer activity through the down-regulation of β-catenin signaling in mouse breast cancer cells in our previous study. This study examines the anti-cancer effects of fucoidan as well as its underlying molecular mechanisms in the human triple negative breast cancer (TNBC) cell line and in 7,12-dimethylbenz[a]anthracene (DMBA)-induced experimental mammary carcinogenesis in rats. Methods in vitro studies, fluorescent staining, flow cytometry and Western blotting were performed to analyze apoptosis and protein expression in human breast cancer MDA-MB-231 cells. In vivo intervention experiments were conducted with Sprague Dawley (SD) rats with DMBA-induced breast cancer. Tumor volumes and weights were measured. Results in vitro fucoidan treatment inhibited proliferation and induced apoptosis in MDA-MB-231 cells. Western blotting detected that Cyt C and Smac were released into the cell cytoplasm and that caspase-3 and caspase-9 were activated in MDA-MB-231 cells. The levels of AIF and EndoG were significantly increased in the cytoplasm and in the nuclei by fucoidan. These data show that fucoidan induced caspase-dependent and caspase-independent apoptosis. Moreover, fucoidan treatment down-regulated the expression of Bid, Bcl-2 and Bcl-xl and up-regulated the level of Bax. In vivo, fucoidan supplementation decreased the mean tumor weight. DISCUSSION: Results from the in vivo and in vitro experiments both showed that fucoidan decreased the levels of p-PI3K, p-AKT and p-GSK-3β (Ser9) in breast cancer. The level of β-catenin was also decreased. These results suggest that fucoidan can inhibit MDA-MB-231 human breast cancer cells and DMBA-induced tumors in rats by down-regulating the PI3 K/AKT/GSK3β pathway. This study provides experimental evidence that elucidates the mechanism of antitumor effect of fucoidan and clarifies the mechanism of the effect of fucoidan on the regulation of β-catenin.