Objective    To explore the reversing effect of antisense oligodeoxynucleotide (ASOND) mediated by nanometer particle against multidrug resistance genes mdr-1 and mrp on the multidrug resistance of breast cancer cell line MCF-7/ADR.     Methods    ASOND of mdr-1 and ASODN of mrp were respectively transfected into MCF-7/ADR cells by nanometer particle. Their sense oligodeoxynucleotides were also transduced to serve as control. The changes of mdr-1 and mrp expressions were detected by reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting in 48 h after transfection. MTT assay were performed to evaluate the sensibility of the transfected cells to adriamycin

epirubicin

5-fluorouracil and paclitaxel respectively.     Results    After 48 hours’ exposure to mdr-1-ASODN or mrp-ASODN mediated by nanometer particle

MCF-7/ADR cells significantly reduced the expressions of mdr-1 and mrp in mRNA and protein levels (P0.05)

and enhanced drug sensitivity to adriamycin

epirubicin

5-fluorouracil and paclitaxel respectively (P0.05).     Conclusion    ASOND enhances the drug sensitivity of breast cancer cell line MCF-7/ADR by inhibiting the expressions of drug resistance genes. Nanometer particle is a valid tool to mediate ASOND in vitro.