Background: Interleukin 12 (IL-12) is a proinflammatory cytokine with antitumor activity. Plasmid-based intratumoral gene therapy for treating malignancy with IL-12 or other genes is safe, inexpensive, and simple to carry out. However, effective delivery methods for injecting DNA plasmid into a tumor to generate therapeutic levels of gene product are lacking. To overcome this obstacle, we used electroporation to deliver the IL-12 gene intratumorally in a murine squamous cell carcinoma (SCC) model, SCCVII.
Methods: Plasmids with or without mouse IL-12 gene were injected into SCCVII tumors of C3H/HeJ mice (n = 5 per group). Electric pulses were then applied to the tumors, a process termed electro-gene therapy. The first treatment was administered when the tumor reached 4-6 mm in diameter, and the second treatment followed a week later. The tumor size, survival, and ability to generate systemic antitumor memory were assessed at various time intervals. Changes in gene expression were measured using northern blot analysis, and vessel density and T-cell infiltration were examined by immunostaining. The results were analyzed by two-sided Student's t tests.
Results: Electroporation of 20 microg or 40 microg of IL-12 DNA plasmid eradicated tumors in 40% of mice (P =.031 and.022, respectively). A total of six mice from two separate experiments with regressed tumors were challenged with homologous SCCVII tumor cells multiple times; three of six mice showed no tumor growth for more than 11 months and thus indicated the generation of antitumor memory in these mice. IL-12 electro-gene therapy was associated with increased expression of IL-12, interferon-gamma, monokine induced by interferon-gamma, and interferon-inducible protein 10. IL-12 electro-gene therapy was also associated with decreased vessel density and increased infiltration of CD8(+) T cells after the second administration (P =.02 and.03, respectively).
Conclusion: IL-12 electro-gene therapy appears to be effective in reducing tumor growth by triggering both antiangiogenic effects and an immune response. The antitumor memory was seen to last more than 11 months. Because IL-12 electro-gene therapy is easy to administer and is effective, it could potentially be applicable in the treatment of electrode-accessible malignancies, such as head and neck SCCs.