Abstract:    Background and purpose: The effects of tumor after radiotherapy and chemotherapy with tumor cell apoptosis have positive correlation. Survivin is an apoptosis suppressor gene, which is overexpressed in lung cancer. The reduction of its expression can increase lung cancer cell apoptosis. RNA interference can specifically and effectively blocked the expression of this gene. After accepting a dose of radiation, tumor tissues can raise the rate of gene transduction. The purpose of this study was to investigate the effects of the expression of Survivin gene suppressed by intratumor injection siRNA and radiation in lung cancer. Methods: Mouse subcutaneous transplanted with tumors were randomly divided into four groups: untreated group (group A), group with intratumor injection siRNA (group B), group with radiation (group C), group 4 Gy pre-irradiation combination with intratumor injection siRNA (group D). Two days later, mouse with different treatments were executed by cervical dislocation and stripped the subcutaneous tumors. mRNA and protein levels of Survivin gene were detected by quantitative real-time PCR (qRTPCR) and Western blot; Cell cycle and cell apoptosis were assayed by flow cytometry (FCM). Results: The expression of Survivin gene in mRNA and protein levels in group B, C, and D were significantly reduced compared with group A. The differences of Survivin expression in mRNA level between group A and group D were statistically significant. Compared with the other 3 groups, the expression of Survivin gene in group D was significantly reduced, the differences were statistically significant (P=0.036)；The proportion of cells in S-phase of group D was (2.70±0.34)%, compared with group B [(8.93±0.75)%] and group C [(6.71±0.51)%], that was significantly reduced. The differences of the proportion of S-phase cells in group A and group D were statistically significant (P=0.034)；The rate of cell apoptosis in group D was (25.67 ± 0.65)%, which was significantly increased compared with the rate of cell apoptosis in the other 3 groups, the differences were statistically significant (F=78.82, P<0.05). Conclusion: Pre-irradiation can enhance the transduction rate of siRNA, reduce the expression of Survivin gene in lung cancer, promote cell apoptosis, and increase the sensitivity of the radiotherapy.

Key words: Lung cancer, Survivin gene, Cell apoptosis, RNA interference