siRNA Targeting of MDR1 Reverses Multidrug Resistance in a Nude Mouse Model of Doxorubicin-resistant Human Hepatocellular Carcinoma

Aim: To investigate the effects of vector-based small interfering RNA (siRNA) targeting MDR1 on the reversal of multidrug resistance in a mouse model of doxorubicin (DOX)-resistant human hepatocellular carcinoma. Materials and Methods: Three siRNAs plasmid vectors (MDR1 siRNA1, MDR1 siRNA2 and MDR1 siRNA3) targeting MDR1 were constructed and transfected into DOX-resistant human hepatocellular carcinoma Bel-7402/ADM cells. The expression of MDR1 mRNA and P-glycoprotein (P-gp) was detected with RT-PCR and western blotting, respectively. A nude mouse model of DOX-resistance was established with untransfected Bel-7402/ADM or Bel-7402/ADM transfected with MDR1 siRNA (Bel-7402/ADMsi). The nude mice with tumors from untransfected Bel-7402/ADM cells were treated with either saline (Group 1); intravenous DOX (Group 2); or the combination of intra-tumoral MDR1 siRNA and intravenous DOX (Group 3). The nude mice with tumors from Bel-7402/ADMsi cells were treated with intravenous DOX (Group 4). DOX and MDR1 siRNA were administered twice a week at 20 mg/kg/dose and 9.8 mg/kg/dose, respectively. Tumor growth was measured to assess reversal of multidrug resistance by MDR1 siRNA. Results: MDRl mRNA and P-gp expression of Bel-7402/ADM cells was reduced by transfection of three siRNAs with different silencing efficiency (p<0.05). DOX treatment (Group 4) resulted in significant reduction in tumor size in the Bel-7402/ADMsi tumor model (p<0.05), indicating reversal of multidrug resistance in tumor by MDR1 siRNA. However, the combination treatment of intratumoral MDR1 siRNA and DOX (Group 3) showed no significant anti-tumor efficacy in the untransfected Bel-7402/ADM (p>0.05) tumor model, suggesting poor in vivo transfection efficiency of MDR1 siRNA. Analysis of the tumor samples showed the reduced expression level of MDR1 mRNA and P-gp was due to efficacy of MDR1 siRNA. Conclusion: In vitro transfection of siRNAs' vectors targeting the MDR1 gene can effectively silence MDR1 mRNA and P-gp expression in DOX-resistant human hepatocellular carcinoma Bel-7402/ADM cells that resulted in reversal of multidrug resistance to DOX in the xenograft tumor model.

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