OBJECTIVETo 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.

METHODSAlkaline 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.

RESULTSResults 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.

CONCLUSIONpNEgr-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.