Abstract: To construct the shRNA plasmids which targeting the MDR1 Gene and to investigate their reversal effect on human breast cancer cell line MCF-7/ADR. MethodsThe oligonucleotides of the MDR-1 gene were designed based on that of the Gene Bank, and the MDR-1 shRNA expression plasmid pRNATU6.1/Neo-mdr1 was constructed. Human breast cancer cell line MCF-7/ADR was tranfected with the MDR-1-shRNA expression plasmids by lipofectamine 2000, and positive clone was selected by G418. MDR-1mRNA was assayed by RT-PCR and protein expression was determined by Western blotting. The P-gp function was determined by rhodamine 123 retention and the efficiency of MCF7/ADR to ADM was determined by MTT method. ResultsThe MDR-1 shRNA expression plasmids were successfully constructed .The MDR1mRNA and protein expressions were significantly decreased 48 hours after transfection, 1 month and 2 months after selection by G418， and that the sensitivity to P-gp-transportable drugs was restored. The transporting function of P-gp was increased and the efficiency of MCF-7/ADR to ADM significantly reversed. Conclusion The shRNA expression plasmid pRNATU6.1/Neo-mdr1 can inhibit the MDR-1 gene stably and permanently. The sensitivity of MCF-7/ADR to adriamycin is reversed.

Key words: RNA intrference, Gene, MDR-1, Drug resistance, neoplasm, Cell line, MCF-7/ADR