Abstract: Objective To construct eukaryotic expression plasmids containing siMDR1, which can inhibit the expression of MDR1 in yolk sac carcinoma cells, and to study on the changes of vincristine resistance with MDR1 inhibition. Methods Four pairs of synthetical siMDR1 were reconstructed into pSES-HUS vector to obtain 4 pSES-siMDR1s, which were transfected into L2RYC, a rat yolk sac tumor cell line, by using Lipofectamine 2000, respectively. Then, the expression of MDR1 gene and protein were detected by real-time PCR and Western blot. MTT assay was performed to check the drug resistance of pSES-siMDR1 transfeced L2RYC cultured in the medium containing different concentration of Vincristine. Result The expression of MDR1 gene and protein in L2RYC were inhibited by four pairs of siMDR1s respectively, especially by pool siMDR1s. IC50 of vincristine in L2RYC was decreased with the inhibition of MDR1 expression and the most significant changes were observed in siMDR1s pool group. Conclusion Successfully constructed siRNAs which can inhibit the expression of MDR1. The sensitivity to vincristine was increased in L2RYC when MDR1 was repressed by siMDR1s.

Key words: RNAi, MDR1, Yolk sac tumor, chemotherapy, vincristine