Mutidrug resistance reversal (MDR Reversal) of rhinacanthin-c in mcf-7 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 and antiviral agent. The purpose of this study was to determine the capability of RN-C to enhance cytotoxicity of doxorubicin (DOX) in a breast cancer cell line MCF-7 and the involvement of the ABC drug efflux transporters. The cytotoxicity was assessed by an MTT assay. RN-C at the non-cytotoxic concentration (0.1 µM) was able to significantly enhance DOX-mediated cytotoxicity in the MCF-7. The apparent IC50 of DOX at 48 hr-treatment in the presence of RN-C decreased by 38-fold. The interaction between RN-C and DOX was strong synergism with the combination index (CI) value of 0.2. The degree of synergy between RN-C and DOX was time-and concentration-dependent. In addition, intracellular DOX accumulation in the MCF-7 increased in the presence of RN-C. Furthermore, the interference of RN-C on the ABC drug transporters (MRP1 and MRP2) was evaluated by a substrate accumulation assay, using fluorescence spectroscopy technique. RN-C at 0.1 µM after 12-hr treatment could increase intracellular accumulation of transporter substrate in the MCF-7 cells [i.e., DCDF by 1.20-fold (MRP1) and CDCF by 1.90-fold (MRP2)]. Rhinacanthin-C was able overcome MDR in DOX resistant MCF-7 (MCF-7/DOX) cells, which expressed high level of P-gp and MRP2. The combination between DOX and RN-C at their non-cytotoxic concentrations when giving each compound alone significantly reduced cell viability. The findings suggested that RN-C was able to increase DOX-mediated cytotoxicity and overcome MDR effectively, possibly through interference on MRP2 and P-gp functions. The nature of interaction between RN-C and DOX was synergism. Another potential mechanism of the synergy between rhinacanthin-C and doxorubicin would be investigated further