Effects of rhinacanthin-C in multidrug-resistance breast cancer cells

Abstract

Rhinacanthin-C (RN-C) is a major bioactive naphthoquinone ester found in Rhinacanthus nasutus Kurz (Acanthaceae). This compound has potential therapeutic value as an anticancer agent. Rhinacanthin-C was reported to enhance doxorubicin cytotoxicity in breast cancer cells through direct inhibition of P-gp activity. However, its ability in reversing multidrug resistance (MDR) in cancer cells through the down-regulation of P-gp expression, alteration of detoxification system, and increase in apoptosis proteins remains unreported. Thus, this study was to investigate the potential MDR reversal effect of rhinacanthin-C and its underlying mechanisms in MCF-7/DOX. In this study, rhinacanthin-C (1 µM, 48 h) significantly enhanced cytotoxicity of camptothecin, doxorubicin, and etoposide. Apparently, the loss of P-gp function in the rhinacanthin-C-treated for 24- h in MCF-7/DOX cells was associated with the reduction of MDR1 mRNA expression and P-gp protein levels. In addition, the down-regulation effect of rhinacanthin-C on P-gp expression involved with suppressions of the Akt/NF-kB signaling pathway and YB-1 expression, but not the MAPK/ERK1/2 signaling pathway. The result also demonstrated that rhinacanthin-C (up to 3 µM, 24-h) was able to produce intracellular ROS and potentiate H2O2 toxicity, leading to increased apoptosis in MCF-7/DOX cells. Moreover, this compound inhibited the MAPKs signaling, resulting in changes in the Bax/Bcl-2 ratios and a decrease in the expression of PARP protein. In addition, rhinacanthin-C might increase cellular stress and promote apoptosis via inhibition of the Akt/GSK-3β/Nrf2 pathway, leading to the down-regulation of antioxidant and detoxifying enzymes such as NQO1 and HO-1. Taken together, rhinacanthin-C displayed its MDR reversal effect in MCF-7/DOX cells through down-regulation of MDR1 and P-gp expression by inhibiting Akt/NF-kB signaling pathway and YB-1 expression. In addition, rhincanthin-C was able to induce apoptosis through ROS production and suppression of the cell survival systems mediated by the MAPKs and Akt/GSK-3β/Nrf2 signaling pathways.