Staphylococcal entorotoxin B anchored exosome induces apoptosis in negative esterogen receptor breast cancer cells

Exosomes (EXO) are acellular vehicles used for cancer immunotherapy due to their immune inducing properties. To identify whether designed structure based on tumoral EXO have a cytotoxic effect together with a potent immunological property, we synthesized a novel structure based on EXO and staphylococcal entrotoxin B (SEB), two immune inducer substances, and surveyed its cytostatic effect on the breast cancer cell line. EXO were purified from tumor cells and SEB was anchored on it by protein transfer method. To determine the cytotoxic and apoptosis inducing effect of this structure, treated cells with different concentrations of EXO/SEB were examined by MTT assay and Hoechst staining method. In addition, the expression rate of bcl-2, bax, bak, fas, bcl-xl and the activity of caspase-3 and caspase-9 were assessed. We observed that EXO/SEB significantly decreased the cell proliferation and stimulated apoptosis (P < 0.001) at all concentration after 24 h (P < 0.001). Furthermore, EXO/SEB raised the expression rate of bax and bak (P < 0.001) but no impact on fas and bcl-xl after 48 h. We observed reducing effect of EXO/SEB on the mRNA expression of bcl-2. After 24 h of exposing the cell with the EXO/SEB, a significant increase was found in the activity of caspase at the concentration of 2.5, 5 and 10 μg/100 μl for caspase-9 and at all concentrations for caspase-3 (P < 0.001). Our designed structure, the EXO/SEB, is a novel model for apopto-immunotherapy being able to induce apoptosis in ER⁻ breast cancer cells.