This study aimed to investigate the effects of cationic liposomes containing different cationic lipids （DC-Chol and DOTAP） and different pegylation ratios on siRNA transfection in human U251 glioma cells. The data showed that the transfection efficiency of DOTAP was much higher than that of DC-Chol and PEG at 2 mol% enhanced cellular uptake of siRNA. Cationic liposome-siRNA complexes with particle size around 100 nm were prepared. PEG modification could efficiently stabilize the liposome in the presence of serum, which might protect the siRNA from serum degradation and prolong the circulation time in vivo. Efficient intracellular uptake and lysosome release of siRNA in human U251 glioma cells were observed for pegylated DOTAP-based lipososomes compared with the control transfection reagent lipofectamine 2000. The results demonstrated that this cationic liposome might be a potential vehicle for the in vivo delivery of siRNA.
In this study, the novel RGD-modified stabilized cationic liposomes were developed as the delivery vehicle for siRNA targeting human MDR1 gene. The complex of cationic liposomes and siRNA, RGD-Lipo-siRNA, was prepared with a narrow size distribution below 200 nm. It was shown that the encapsulated siRNA in the liposomes could be effectively protected from serum degradation. Also, enhanced cell binding and intracellular uptake of siRNA in the doxorubicin-resistant human ova- rian cancer cell lines SKOV3/A were found in RGD-Lipo-siRNA preparation as compared to that of unmodified cationic lipsomes （Lipo-siRNA）. Using the post-insertion method for RGD modification, lysosome release of siRNA in pRGD-Lipo-siRNA was improved. From flow cytometry, significant increase of doxorubicin accumulation was observed in the SKOV3/A cells treated with pRGD-Lipo-siRNA targeting human MDR1 gene. In vitro cytotoxicity assay showed that the significant cell growth inhibition was achieved in the SKOV3/A cells after treating with the combined use of siRNA and doxorubicin. In conclusions, postinserted RGD modified lipoplex, pRGD-Lipo-siRNA, was successfully used for siRNA transfection and achieved drug resistance reversal in human ovarian cancer SKOV3/A （doxorubicin-resistant） cells. It suggested that this liposomes might be a potential vehicle for siRNA delivery in vivo.
