[Combining FCU/5-FU suicide gene/prodrug system and radiation in treating nasopharyngeal carcinoma: an experimental study].

OBJECTIVE: To explore the in vitro, in situ and in vivo killing effects to CNE-2 cells of human nasopharyngeal carcinoma (NPC) by FCU/5-FC system combined with gamma irradiation for predicting the treatment effect on NPC. METHODS: Plasmid pcDNA3.1(-)CMVe.Egr-1. FCU was introduced into CNE-2 cells by electroporation. The transfected cells were selected by G418 (600 microg/ml) for 14 days to yield cells expressing FCU stably. The FCU protein in transfected CNE-2 cells was tested by Western blotting. In vitro response of FCU-expressing CNE-2 cells to 5-FC or gamma irradiation, alone or in combination was detected by MTT assay. Furthermore, A NPC model was employed by inoculating CNE-2 cells in the right flank of nude mice for in situ gene therapy, and after 12 days of inoculation, those rats were randomized to seven groups, then the suppression of NPC growth in model was observed after giving different treatments. Finally, FCU-expressing CNE-2 cells were inoculating in the right flank of nude mice to generate NPC xenografts for in vivo gene therapy, and after 5-day of implantation, those rats were randomized to seven groups, then the delaying of tumour growth was observed in xenografts treated with different conditions. RESULTS: A anticipated relative molecular quality 42,000 protein was obtained from total protein of FCU-expressing CNE-2 cells. The growth of FCU-positive CNE-2 cells were inhibited by 5-FC or gamma irradiation, alone or in combination, but cells treated with both 5-FC and gamma irradiation resulted in enhanced cell killing when compared with cells treated with gamma irradiation or 5-FC alone. In vitro study showed that the relative survival rates of FCU-expressing CNE-2 cells treated with gamma irradiation were 15.85% - 97.88%, while that of gamma irradiation + 5-FC (100 microg/ml) group were 6.58% - 50.00%, and there was a significant difference (P < 0.01). The MTT results also demonstrated that the relative survival rate has a striking different (P < 0.01) between 5-FC group (12.11% - 99.51%) and 5-FC + gamma irradiation (1.0 Gy) group (2.37% - 35.87%). Not only in situ but also in vivo, potent growth inhibition on the explanted NPC tumours was observed in mice treated with 5-FC or gamma irradiation, alone or in combination, among which interference of both 5-FC and gamma irradiation leaded to most distinct suppression of tumour growth. Tumour volumes in groups interfered by 5-FC and or gamma irradiation were extinctly different with the control group and PBS treatment group (P < 0.05). CONCLUSION: CNE-2 cells or nasopharyngeal carcinoma venograph could be killed by FCU/5-FC suicide gene prodrug system or gamma irradiation, and there is a synergistic therapeutic effect on NPC between FCU/5-FC and gamma irradiation.