METHODS: Metastatic mammary
tumors induced by inoculation in BALB/c female mice were treated by intratumoral
injections of either a plasmid vector containing
IL-12 or empty vector and then subjected to in vivo electrogene transfer once a week for 8 weeks.
RESULTS: Treatment with
IL-12 resulted in elevation of both
IL-12 and IFNgamma levels in mammary
tumors and in serum and intratumoral levels of CD4 and CD8
proteins were also increased.
Tumor volumes and lymphatic and pulmonary
metastases were significantly reduced. The histopathological changes induced by
IL-12 characteristically included marked
inflammation, increased apoptosis, decreased
DNA synthesis, peripheral influx of significantly greater numbers of active macrophages, and reduced blood microvessel density, and apoptotic vascular endothelial cells were frequently seen. Western blotting showed decreases in
VEGFR-3 of
tumors exposed to
IL-12 gene therapy. In adjuvant immunofluorescence studies, the CD31-positive endothelial cells of microvessels showed decreased
VEGFR-3 expression in IL-12-treated
tumors. However, apparent alterations in
VEGFR-3 expression of podoplanin-positive lymphatic endothelial cells were not observed in IL-12-treated
tumors. Although recombinant
IL-12 did not inhibit tubular formation of human umbilical vein endothelial cells in a
Matrigel assay, recombinant IFNgamma did completely suppress the tubular formation.
CONCLUSIONS: In vivo electrogene transfer of
IL-12 exerts strong anti-tumorigenic and anti-metastatic effects likely due to T-cell-mediated immune responses as well as anti-angiogenic action.