OBJECTIVETo explore the effect of small interfering RNA(siRNA) on silence of mdr1 gene and reversal of apoptosis resistance in multidrug-resistant (MDR) human leukemia K562/ADM cell.

METHODSHuman MDR leukemia cell line K562/ADM was used as the target cells. Two siRNAs (mdr1 siRNA-1 and mdr1 siRNA-2) targeted mdr1 gene were chemically synthesized and transfected into K562/ADM cells with liposome. Expression of mdr1 mRNA was determined by real-time PCR, P-glycoprotein (P-gp) expression and caspase-3 activity were measured with flow cytometry (FCM), and the cell apoptosis was observed by optical and electronic microscopy for morphology and Annexin V/PI staining.

RESULTSThe mdr1 siRNA-1 and mdr1 siRNA-2 could markedly down-regulate the expression of mdr1 gene in K562/ADM cells, the expression of mdr1 mRNA decreased by 91.2% and 82.0% , and the P-gp by 74.1% and 84.4%, respectively. The caspase-3 activity was markedly enhanced, and the active caspase-3 in K562/ADM cells increased by about 40% compared to liposome alone and non-silencing controls. the sensitivity of K562/ADM cells to adriamycin-induced apoptosis was significantly augmented, the apoptotic rate of the cells treated with siRNA plus adriamycin increased by about 60% compared to adriamycin alone.

CONCLUSIONsiRNAs silence the expression of mdr1/P-gp to overcome the P-gp-mediated apoptosis resistance in drug-resistant K562/ADM cells.