Interleukin-18 is a novel
cytokine identified as a strong inducer of
interferon-gamma.
Interleukin-18 has been shown to have similar bioactivities to
interleukin-12 and to have antitumor efficacy in experimental models. In this study, we investigated whether the introduction of the
interleukin-18 gene to B16F10
melanoma cells can induce antitumor response or not. Before the transfection, we modified the
interleukin-18 gene to enable transfected
tumor cells to secrete bioactive
interleukin-18, because
interleukin-18 does not have a
signal sequence and requires processing by the
interleukin-1 converting enzyme to attain the mature form. We found that
B16 melanoma cells transduced with hybrid
cDNA consisting of the
interferon-beta signal sequence and mature
interleukin-18 sequence, but not native
interleukin-18, secreted a large amount of
interleukin-18 and exhibited retarded
tumor growth when injected in syngeneic mice. The antitumor effect was mostly abrogated by administration of anti-
interferon-gamma antibody, but was not affected by in vivo depletion of CD8+ T cells or natural killer cells. Histologic analysis revealed that vascularization was markedly reduced and that
necrosis was extensively induced in interleukin-18-secreting B16F10
melanoma (B16/
IL18) tissues, whereas abundant
tumor vessel formation was observed in B16/
IL18 tissues of
interferon-gamma-neutralized mice. We also found that
chemokines,
interferon-inducible protein-10 and monokine induced by
interferon-gamma, were produced in B16/
IL18 tissues and that the expression of both
chemokines was dependent on that of
interferon-gamma in the
tumor tissues. Further, we showed that
B16 melanoma cells secreted both
chemokines in response to
interferon-gamma. In addition, the expression of
angiogenin, an
angiogenic factor of
melanoma, in
B16 melanoma cells was reduced by
interferon-gamma treatment. These results indicate that gene transfer of secreted-type
interleukin-18 to B16F10
melanoma cells is a useful method of triggering an antitumor response without any systemic adverse effects and that the antitumor efficacy is mainly mediated by antiangiogenic activity, which is possibly involved in at least two dynamic changes induced by
interferon-gamma inside
B16 melanoma cells: the upregulation of antiangiogenic
chemokines,
interferon-inducible protein-10 and monokine induced by
interferon-gamma, and the downregulation of
angiogenic factor,
angiogenin.