Abstract
INTRODUCTION: There have been no reports describing successful drug resistance reversal in tumors in the clinic until now. Conversion of drug resistance reversal studies to drug resistance prevention studies may assist in the development of more efficient anti-tumor strategies. The present study demonstrates the prevention of doxorubicin-induced drug resistance by tetrandrine on leukemia cells. MATERIALS AND METHODS: K562 cells were either solely treated with doxorubicin (0.6 mg/ml) or pretreated with tetrandrine of different concentrations (0.5, 1.0 and 2.0 microg/ml) for 24 h followed by combined-treatment with doxorubicin (0.6 microg/ml). RESULTS: The results showed that doxorubicin treatment only resulted in elevated levels of mdr1 mRNA/P-gp expression. Doxorubicin also induced up-regulation of P-gp functional activities, as intracellular retention of rhodamine was decreased; however, 2.0 microg/ml tetrandrine significantly inhibited the overexpression of doxorubicin-induced mdr1 mRNA/P-gp. Consistently, the functional activity of P-gp was also inhibited, which led to increased intracellular drug retention and the recovery of cell sensitivity to chemotherapeutic drugs in combined treatment groups. Both mRNA and protein levels of NF-kappaB were up-regulated in the cells treated with doxorubicin only. Results from an electrophoretic mobility shift assay and a chromatin immunoprecipitation assay demonstrated the enhanced binding to the promoter region of mdr1 gene compared to the control group. However, tetrandrine could markedly inhibit the doxorubicin-induced expression of NF-kappaB mRNA and protein. In addition, it also attenuated the NF-kappaB DNA-binding activity. CONCLUSION: In summary, tetrandrine can prevent doxorubicin-induced mdr1 mRNA/P-gp expression and P-gp functions in a dose-dependent manner through a mechanism that may involve inhibition of doxorubicin-induced NF-kappaB mRNA expression and protein activity.