Selenium nanoparticles coupling with Astragalus Polysaccharides exert their cytotoxicities in MCF-7 cells by inhibiting autophagy and promoting apoptosis

Astragalus Polysaccharides (APS) had been reported to exhibit antitumor activities. Given that nanoparticles possessed unique advantages in cancer treatment, APS was used as the modifier to prepare gold, silver and selenium nanoparticles (APS-Au, APS-Ag and APS-Se NPs) in the present study.The three nanoparticles were synthesized via a green approach and characterized by DLS, TEM, XRD, FT-IR and UV-Vis. The inhibitory effects of these nanoparticles on various tumor cells proliferation were examined by MTT assay in vitro. Reactive oxygen species (ROS), mitochondrial membrane potential (MMP) and the expression of apoptosis and autophagy-related proteins were also detected.Among these, APS-Se NPs displayed the most potent antitumor activities against MCF-7 cells in vitro. Flow cytometric analysis suggested that after cells were exposed to elevated concentrations of APS-Se NPs (10, 20 and 40 μmol/L), the rate of apoptosis was increasing (16.63 ± 0.89, 38.60 ± 3.46 and 44.38 ± 2.62%, respectively). Further analysis by immunofluorescence revealed an increase in intracellular ROS and a loss of MMP. This was accompanied by increased LC3-I to LC3-II conversion. Also, western blot analysis demonstrated that the ratios of Bax/Bcl-2 and cleaved caspase9/caspase 9 rose, and LC3-II and p62 protein levels increased. The addition of chloroquine, an inhibitor of autophagy, further enhanced protein expression of p62 and LC3-II.APS-Se NPs exerted their cytotoxic activity in MCF-7 cells by blocking autophagy and facilitating mitochondrial pathway-mediated apoptosis.