The investigational chemotherapeutic
drug flavone acetic acid (FAA) acts as an
immunomodulator by augmenting natural killer activity in both humans and rodents after in vivo administration. The accumulated data derived from a series of experiments also demonstrates that FAA synergizes with
interleukin 2 (IL-2) for the treatment of murine
renal cancer. The immunomodulatory and immunotherapeutic effects of FAA are strictly dose dependent with doses of FAA greater than 150 mg/kg effectively synergizing with
IL-2, and doses less than 150 mg/kg exhibiting very little
therapeutic effect. The antitumor and immunomodulatory effects of FAA are more pronounced in vivo than in vitro. Collectively, these results suggested that
cytokines induced by FAA may contribute to these effects, and that the induction of such
cytokines may also be very dose dependent. Studies were therefore initiated to investigate whether the in vivo administration of FAA would alter the expression of
cytokine mRNA in leukocytes. Splenic leukocytes or liver nonparenchymal cells from untreated and FAA-treated mice were used as a source of
RNA for Northern blot analysis.
Interferon alpha and
interferon gamma mRNA in the spleen was upregulated within 1.5 h after FAA administration, with peak induction occurring by about 2 h. An upregulation of
tumor necrosis factor alpha mRNA was detected in the spleen by 0.5-1 h
after treatment with peak induction occurring by 1-1.5 h. Induction of
tumor necrosis factor alpha mRNA was also detected in hepatic nonparenchymal cells. No up-regulation of splenic
mRNA for
tumor necrosis factor beta,
IL-1 alpha or beta, or
IL-2 was detected after FAA administration. IFN and TNF activities were detectable in the serum by bioassay immediately following the appearance of
mRNA in FAA mice. The observed up-regulation by FAA of
cytokine mRNA and the corresponding
serum protein was strictly dose dependent with substantial induction of both
mRNA and
proteins occurring only at FAA doses greater than or equal to 150 mg/kg, a dose range also shown to be the minimum required for immunomodulatory and immunotherapeutic effects. In summary, these results demonstrate that FAA acts as a potent inducer of at least three
cytokines in vivo, and suggest that the immunomodulatory and immunotherapeutic effects of FAA may be partially mediated by these induced
cytokines.