Interleukin 12 gene transfer into skin distant from the tumor site elicits antimetastatic effects equivalent to local gene transfer

We have reported that particle-mediated interleukin 12 (IL-12) gene transfer into the skin overlying the local tumor inhibits systemic metastases. To further characterize this effect, we compared the antitumor and antimetastatic effects of IL-12 cDNA delivered at the local tumor site versus at a site distant from the primary tumor, in a spontaneous metastasis model of LLC-F5 tumor. Local IL-12 gene delivery into the skin overlying the intradermal tumor (local IL-12 treatment) on days 7, 9, and 11 after tumor implantation resulted in the most suppression of the growth of the primary LLC-F5 tumor, whereas IL-12 gene transfer into the skin distant from the tumor (distant IL-12 treatment) was less effective. In contrast, both local IL-12 and distant IL-12 treatment, followed by tumor excision, inhibited lung metastases to a similar extent, resulting in significantly extended survival of test mice. The results of in vivo studies using depleting anti-asialo GM1 antibody and anti-CD4/anti-CD8 monoclonal antibodies, or neutralizing anti-interferon γ (IFN-γ) monoclonal antibody demonstrated that natural killer (NK) cells, CD8⁺ T cells, and IFN-γ contributed to the antimetastatic effects in both treatment groups. Furthermore, the levels of mRNA expression of vascular endothelial growth factor and matrix methalloproteinase 9 at the tumor microenvironment were suppressed after both local and distant IL-12 treatment. These results suggest that the current particle-mediated IL-12 gene delivery in the spontaneous LLC-F5 metastasis model can confer antimetastatic activities, irrespective of the gene transfection site, via a combination of several mechanisms involving CD8⁺ T cells, NK cells, IFN-γ, and antiangiogenesis.