Curcumin increases anti-cancer activity of tamoxifen in MCF-7 breast cancer cells through the suppression of MDR1 mRNA expression

Introduction: A major limitation in cancer treatment is the development of multidrug resistance (MDR). Tamoxifen is a substrate of multidrug resistance protein 1 (MDR1) or P-glycoprotein, while curcumin is known as MDR1 inhibitor. The objective of this study was to analyze cell viability and MDR1 mRNA expressions in breast cancer cells, treated with tamoxifen alone or in combination with curcumin. Method: MCF-7 breast cancer cells lines were treated with tamoxifen 1 μM alone or in combination with curcumin at 10, 20 and 35 μM, while tamoxifenverapamil (50 μM) was used as positive control for MDR1 inhibitor. The cells were harvested and counted for their viability and extracted for total RNA. MDR1 mRNA expressions were quantified using quantitative reverse transcriptase polymerase chain reaction (qRT-PCR). Results: MCF-7 cells viability were decreased in concomitant treatment of tamoxifen + curcumin compared with tamoxifen alone, and appeared to be dosedependent. The expressions of MDR1 mRNA were shown to be suppressed in MCF-7 cells co-treated with tamoxifen and curcumin. Conclusion: Concomitant administration of tamoxifen and curcumin resulted in an increased anticancer activity compared with tamoxifen alone. This effect is thought to be via the suppression of MDR1 mRNA expressions.