Reversal of cancer multidrug resistance by green tea polyphenols.

The aim of this study was to examine the effect and mechanism of green tea polyphenols (TP) on reversal of multidrug resistance (MDR) in a carcinoma cell line. Using the MTT assay, TP was examined for its modulating effects on the drug-resistant KB-A-1 cells and drug-sensitive KB-3-1 cells. When 10 microg mL(-1) (-)-epigallocatechin gallate (EGCG) or 40 microg mL(-1) TP were present simultaneously with doxorubicin (DOX), the IC50 of DOX on KB-A-1 cells decreased from 10.3 +/- 0.9 microg mL(-1) to 4.2 +/- 0.2 and 2.0 +/- 0.1 microg mL(-1), respectively. TP and EGCG enhanced the DOX cytotoxicity on KB-A-1 cells by 5.2- and 2.5-times, respectively, but did not show a modulating effect on KB-3-1 cells. This indicated that both TP and EGCG had reversal effects on the MDR phenotype in-vitro. A KB-A-1 cell xenograft model was established, and the effect of TP on reversing MDR in-vivo was determined. Mechanistic experiments were conducted to examine the uptake, efflux and accumulation of DOX. Cloning and expression of the nucleotide binding domain of the human MDR1 gene in Escherichia coli was established, and by using colorimetry to examine the activity of ATPase to hydrolyse ATP, the ATPase activity of target nucleotide binding domain protein was determined. TP exerted its reversal effects through the inhibition of ATPase activity, influencing the function of P-glycoprotein, and causing a decreased extrusion of anticancer drug and an increased accumulation of anticancer drug in drug resistant cells. Using reverse transcription-polymerase chain reaction, the inhibitory effect of TP on MDR1 gene expression was investigated. Down-regulation of MDR1 gene expression was the main effect, which resulted in the reversal effect of TP on the MDR phenotype. TP is a potent MDR modulator with potential in the treatment of P-glycoprotein mediated MDR cancers.