[An in vitro study on radiation-induced TNF gene therapy of cancer].

TNF has certain radioprotective effect on host tissues and can enhance the antitumor effect of radiotherapy. In addition, the promoter region of Egr-1 gene can be activated by radiation. So a radiation-inducible, double copy retroviral vector expressing TNF named pETDC was constructed by fusing of Egr-1 promoter to hTNF-alpha gene. After packaged with Psi-2 and Crip cells, the virus titer in the supermatant was 4 x 10(5) CFU/ml. By infection with the virus supermatant and by G418 resistant selection, positive clones from murine fibroblast cells NIH3T3 and murine melanoma cells B16.F10 were obtained and found to secrete 2.1 ng/ml and 1.1 ng/ml TNF respectively. After 20 Gy radiation of the cells, the TNF levels secreted by the two positive clones were elevated to 13.8 ng/ml (6.6-fold) and 5.7 ng/ml (5.2-fold). Furthermore, hTNF-alpha expression was confirmed with RT-PCR. These in vitro data provide an experimental basis for the in vivo use of combination TNF gene therapy with local radiotherapy in cancer patients.