Abstract： Objective:Recurrent ovarian cancer is often resistant to drugs such as paclitaxel.Short hairpin RNA (shRNA) targeting MDR1,a gene involved in the process of drug resistance,may be a promising strategy to overcome drug resistance.Methods:Construction and identification of eukaryotic expression plasmid of shRNA targeting on MDR1 gene.The plasmid was transiently transfected into human ovarian cancer cell line A2780/Taxol.Apoptosis was determined by flow cytometry using annexin V-FITC/PI double labeling.Expression of MDR1 mRNA was detected by quantitative polymerase chain reaction (qPCR) and P-glycoprotein expression was detected using Western blot.Results:The IC50 of paclitaxel in MDR1 shRNA-transfected group was significantly reduced (1.986±0.153) μmol/ml as compared with that in negative control (5.246±0.107)μmol/ml and empty vector-transfected group (5.212±0.075)μmol/ml (P＜0.05).The percent of the relative reverse sensitivity to paclitaxel on A2780/Taxol cells was 67.1％,and the apoptotic rate was significantly increased [(6.977±0.333)％] compared with control [(1.637±0.111)％] and empty vector-transfected group [(1.663±0.114)％] (P＜0.05).Expressions of MDR1 mRNA and P-glycoprotein were significantly reduced compared with control (P＜0.05).Conclusion:The present study demonstrated that the eukaryotic expression plasmid of shRNA targeting on MDR1 inhibited the expression of MDR1 effectively,thus enhance the sensitivity of A2780/Taxol cells to paclitaxel.