Schisandrin B reverses doxorubicin resistance through inhibiting P-glycoprotein and promoting proteasome-mediated degradation of survivin.

Acquired drug resistance poses a great challenge in cancer therapy. Drug efflux and anti-apoptotic processes are the most two common mechanisms that confer cancer drug resistance. In this study, we found that Schisandrin B (Sch B), one of the major dibenzocyclooctadiene derivatives extracted from Chinese herbal medicine Schisandrae Chinensis Fructus, could significantly enhance the sensitivity of doxorubicin (DOX)-resistant breast cancer and ovarian cancer cells to DOX. Our results showed that Sch B increased the intracellular accumulation of DOX through inhibiting expression and activity of P-glycoprotein (P-gp). Meanwhile, Sch B could markedly downregulate the expression of anti-apoptotic protein survivin. Overexpression of survivin attenuated the sensitizing effects of Sch B, while silencing of survivin enhanced Sch B-mediated sensitizing effects. Furthermore, Sch B preferentially promoted chymotryptic activity of the proteasome in a concentration-dependent manner, and the proteasome inhibitor MG-132 prevented Sch B-induced survivin downregulation. Taken together, our findings suggest that Sch B could be a potential candidate for combating drug resistant cancer via modulating two key factors that responsible for cancer resistance.