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Background and Objective:Adenovirus vectors were widely used in gene therapy for tumors. We used adenovirus vector to transfer small interfering RNA (siRNA) against vascular epithelium growth factor A (VEGF-A)molecules to mouse lung adenoma LA795 cells and used low dose of chemotherapeutic drugs to further elevate the infection efficiency of adenovirus vector in and therapeutic effect of RNAi on tumor cells. Methods:LA795 cells were infected by Ad/EGFP and treated with different dosages of gemcitabin, epirubicin, cisplatin, or 5-fluorouracil (5-FU). Cells were observed under fluorescence microscope continuously using green fluorescent protein (GFP) as the reporter gene.The percentage of GFP-positive cells and fluorescent intensity were tested by flow cytometry to determine optimum concentrations of drugs. Ad/siVEGF-A containing VEGF-A siRNA was constructed. Real-time PCR and ELISA were applied to measure the expression level of VEGF-A after LA795 cells were infected by Ad/siVEGF-A and treated with 5-FU. The combination of Ad/siVEGF-A and 5-FU was also applied in treating subcutaneous tumor in mice. Results:Low dose of 5-FU elevated the Ad/EGFP infection in LA795 cells significantly, and also enhanced the effect of Ad/siVEGF-A in downregulating VEGF-A mRNA and protein levels in tumor cells. When used in tumor in vivo, the combination strategy repressed tumor growth effectively. Conclusion:Low dose of 5-FU can enhance the capability of adenovirus infecting tumor cells and promote the efficiency of gene therapy by adenovirus.