OBJECTIVETo investigate the effect of cationic liposome-mediated RNA interference (RNAi) in silencing epidermal growth factor (EGF) receptor (EGFR) gene in breast cancer cells in vivo.

METHODSA small interfering RNA (siRNA) targeting EGFR gene was constructed and transfected into human breast cancer cell in vitro via cationic liposome. The transfected cells were inoculated into nude mice, and the tumor growth inhibition rate was calculated. The tumors were then removed for immunohistochemistry and Western blotting to examine the expression of EGFR protein. Quantitative RT-PCR was used to detect the mRNA expression of the EGF receptor gene, and enzyme-linked immunosorbent assay (ELISA) performed to assess the EGF level in both the serum and tumor extraction.

RESULTSIn athymic nude mice, MDA-MB-231 cells had obviously lower tumor formation rate than ZR-75 cells (30.00% and 88.89%). Transfection of the cells with EGFR siRNA significantly inhibited tumor formation capacity of the cells in vivo as compared with the cells transfected with empty vector or irrelevant siRNA. The results of ELISA demonstrated that in mice bearing the tumors grown from EGFR siRNA-transfected cells, the EGF levels in the serum and tumor extraction were lowered by 16.77% and 12.59%, respectively. Real-time RT-PCR showed that EGFR siRNA transfection caused a specific downregulation of EGFR mRNA expression by 21.05% in the tumor.

CONCLUSIONChemically synthesized 21-nucleotide siRNA duplexes can be effectively delivered via lipofectamine 2000 into breast cancer cells in vivo to induce a longer-lasting gene silencing effect than in vitro transfection. RNAi of EGFR gene may indicate a promising approach for management of lung cancers, especially those nodular ones with easy access.