rhinacanthin-c enhances chemosensitivity of breast cancer cells via the downregulation of p-glycoprotein through inhibition of akt/nf-kappa b signaling pathway

Introduction: high expression of p-glycoprotein (p-gp) has been linked to multidrug resistance (mdr) and chemotherapeutic failure. previously, we demonstrated that rhinacanthin-c, a naphthoquinone from rhinacanthus nasutus, was able to enhance the cytotoxicity of doxorubicin against breast cancer mcf-7 cells via direct p-gp inhibition. in this study, we looked at its effect on p-gp downregulation and the mechanism involved in the resistance of mcf-7 cells to doxorubicin. methods: doxorubicin-resistant mcf-7 (mcf-7/dox) cells were exposed to rhinacanthin-c for 24-48 hours prior to the assessment of their chemosensitivity via mtt assay, p-gp activity via calcein-am uptake assay, p-gp expression, and signaling via qrt-pcr and western blot analyses. results: pretreatment with 1 μm of rhinacanthin-c for 48 hours significantly enhanced cytotoxicity of doxorubicin, as well as camptothecin and etoposide, to mcf-7/dox cells. in the rhinacanthin-c-treated cells, reduction of mdr1 mrna and p-gp levels and increased intracellular calcein were observed. moreover, phosphorylation of akt, nf-ᴋb and iκb-α, along with yb-1 expression, significantly decreased after 24-hour treatment with rhinacanthin-c. in contrast, the naphthoquinone had no effect on expression levels of erk1/2 and phosphorylated erk1/2 under similar conditions. conclusion: rhinacanthin-c, at a non-cytotoxic concentration (1 μm), could downregulate p-gp expression in mcf-7/dox cells via the inhibition of the akt/nf-ᴋb signaling pathway and yb-1 expression. long-term exposure to this natural naphthoquinone may increase chemosensitivity of cancer cells with mdr phenotype.