Multidrug-resistance (MDR) is a major hindrance to successful chemotherapy. Among different mechanisms responsible for MDR, cellular over-expression of P-glycoprotein (Pgp) plays an important role. Pgp is an energy dependent drug efflux pump that effectively transports a broad of commonly used chemotherapeutic drug out of the cells and leads to resistance to the chemotherapeutic drugs. Use of modulators is main approach to overcome MDR. Although, in vitro and in vivo preclinical studies have yielded encouraging results, the clinical reversal of resistance by common modulators such as verapamil, quinine, and cyclosporine A has been difficult due to the toxic side effects. Antisense technology offers an alternative approach to overcome MDR. RNA interference (RNAi) is the best one of all antisense technologies. RNAi acts through a post-transcriptional targeting of mRNA for degradation, resulting in sequence-specific post-transcriptional gene silencing. Short hairpin RNA (shRNA) vectors can be transfected into the cells to stably express siRNA. In our preliminary study, eukaryotic shRNA expression vectors aimed at mdr1 mRNA target sequences were cloned and transfected into drug resistance cell line K562/A02 by liposome-induced gene transfection. The mdr1 mRNA was identified by real time RT-PCR, the function of P-gp was measured by a daunorubicin (DNR) efflux assay, and the sensitivity of cell lines to doxorubicin (ADM) was detected by an MTT assay. Our results showed that two mdr1-targeted shRNAs could down-regulate mdr1 mRNA and P-gp expression, with mdr1 mRNA reduced by 86% and 88%. The intracellular DNR increased after RNAi treatment, with the daunorubicin efflux ratio at 60min were 13% and 22%, compared with control (40%~45%) (P<0.05). The MTT assay demonstrated the relative reversing efficiency to doxorubicin to be 84% and 77%.

Conclusion: RNA interference can effectively reverse mdr1-mediated multidrug resistance in resistant leukemic cell line.

Disclosure: No relevant conflicts of interest to declare.

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