Induction of STAT and NF kappa B activation by the antitumor agents 5,6-dimethylxanthenone-4-acetic acid and flavone acetic acid in a murine macrophage cell line

The antitumor agents flavone-8-acetic acid (FAA) and its dose-potent analog ue 5,6-dimethyl-xanthenone di-acetic acid (DMXAA), currently in clinical tr ials, have a novel mechanism of action that is mediated through their abili ty to induce a spectrum of cytokines. Since NF kappa B and STAT transcripti on factors participate in the regulation of a number of genes involved in i mmune and cytokine responses, we investigated whether these transcription f actors were activated in the ANA-1 murine macrophage cell line by DMXAA and FAA compared with lipopolysaccharide (LPS), a bacterial component that ind uces an overlapping spectrum of cytokines. Activation of STAT1 and STAT3 wa s observed distinctly 4 hr after DMXAA and FAA stimulation. DMXAA and FAA, induced NF kappa B translocation with slower kinetics of activation compare d with LPS. STAT activation by DMXAA and FAA was inhibited by cycloheximide , indicating a requirement for de novo protein synthesis. The ANA-1 cells p roduced high titres of interferons (IFNs) in the culture supernatant after stimulation with DMXAA and FAA, and the addition of antibodies to IFN alpha /beta inhibited STAT activation, indicating that IFNs mediated STAT activat ion. NF kappa B activation, on the other hand, was not inhibitable with cyc loheximide or with antibodies to IFN alpha/beta. NF kappa B activation appe ared to be a direct action of the anticancer agents, whereas activation of the STAT proteins was due, in part, to the high titres of IFNs induced. The se results demonstrate the significance of the IFN response in initiating t he cascade of secondary events that may contribute to the overall antitumor efficacy of DMXAA and FAA in murine models. (C) 1999 Elsevier Science Inc.