Schisandrin A enhances the cytotoxicity of doxorubicin by the inhibition of nuclear factor-kappa B signaling in a doxorubicin-resistant human osteosarcoma cell line

Abstract

The emergence of multidrug resistance (MDR) is a significant challenge in osteosarcoma chemotherapy. The central element of the MDR phenomenon is P-glycoprotein (P-gp, also called MDR1), an efflux transporter. Schisandrin A (SchA) extracted from Fructus schisandra has been reported to potently reverse MDR. However, the effect of SchA on osteosarcoma and the mechanism through which it inhibits MDR capacity remain unclear. In this study, SchA was tested for its potential to modulate the MDR phenotype and the function of P-gp in MG-63 doxorubicin-resistant (MG-63/DOX) cells. SchA increased the accumulation and retention of intracellular doxorubicin (DOX) in MG-63/DOX cells. Furthermore, it increased the accumulation of rhodamine 123 and decreased its efflux, indicating that SchA blocked P-gp. Furthermore, SchA enhanced DOX-induced apoptosis, reduced the expression of P-gp, and inhibited MDR1 transcription. P-gp overexpression in MG-63 cells resulted in an increase in the IC₅₀ value in response to DOX. Knockdown of P-gp in MG-63/DOX cells resulted in a decrease in IC₅₀ value in response to DOX. Furthermore, P-gp overexpression in MG-63 cells or knockdown in MG-63/DOX cells resulted in changes in both cleaved-PARP and cleaved-Caspase-7 levels in response to DOX. SchA reduced the IC₅₀ of DOX and increased cleaved-PARP and cleaved-Caspase-7 levels in MG-63 cells transfected with the MDR1 expression vector. In addition, SchA inhibited NF-κB signaling, TNF-α-induced p-IκB-α and P-gp levels, and the TNF-α-induced increase in the IC₅₀ values of DOX. Taken together, these results support the potential therapeutic value of SchA as an MDR-reversing agent in chemotherapy for osteosarcoma.