Anti-tumor effects of pNEgr-mIL-12 recombinant plasmid induced by X-irradiation and its mechanisms.

ABSTRACT

OBJECTIVE: To study the effect of gene radiotherapy combining injection of recombinant plasmid pNEgr-mIL-12 with local X-irradiation on cancer growth and to elucidate the mechanisms of tumor inhibition. METHODS: Alkaline lysis was used to extract the plasmid and polyethylene glycol 8000 (PEG 8000) was applied for further purification of plasmids. Enzyme-linked immunosorbent assay (ELISA) was used to detect the expression of IL-12 protein. C57BL/6J mice were subcutaneously inoculated with B16 melanoma cells and the plasmid was injected directly into the tumor. Gene-radiotherapy combining pNEgr-mIL-12 recombinant plasmid with X-irradiation was given three times to C57BL/6J mice bearing B16 melanoma. Changes in immunologic parameters of tumor-bearing mice were detected with relevant immunologic assays. RESULTS: Results showed a significant decrease in tumor growth rate (P<0.05-0.001) after 3 times of gene-radiotherapy with IL-12 and X-irradiation. Immunologic studies showed a significant increase in CTL and NK cytolytic activity (P<0.05-0.001) and an up-regulated secretion of IFN-gamma and TNF-alpha (P<0.01-0.001). Moreover, the expression of mIL-12 in B16 melanoma cells of the treated tumor-bearing mice was found to be higher than that of control. CONCLUSION: pNEgr-mIL-12 plasmid combined with X-irradiation can increase tumor control and the mechanism of increased tumor inhibition is related to the enhancement of anticancer immunity in tumor-bearing mice.