rnai induced inhibition of mrp1 expression and reversal of drug resistance in human promyelocytic hl60 cell line

multidrug resistance (mdr) is a complex phenomenon in which many different genes regulating drug transport, cellular repair, detoxification and drug metabolism are involved. nevertheless, in most drug resistant cell lines and cancer patients up-regulation of abc-transporter genes such as mdr associated protein (mrp1) gene could be at the basis of the drug resistance phenotype. we aimed to decrease mrp1 expression at the mrna level to modulate drug resistance phenotype in the methotrexate-resistant hl60 cell line. we designed a small interfering rna (sirna) molecule against mrp1 and applied it to hl60 cell line in a 0 to 72 hours time range. sirna could specifically inhibit gene expression by 80% of the initial mrna level with in 36 to 48 hours. the sirna-treated cells demonstrated 100-fold reduction in methotrexate (mtx) resistance compared to untreated cells. the data indicate that this approach may be applicable to the study of mrp1 expression and development of future strategies to reverse the mrp1 dependent drug-resistance phenotype in tumors back to a drug-sensitive one.