The investigational antitumor agent, 5,6-dimethylxanthenone-4-acetic acid (5,6-MeXAA; NSC 640488) induced greater expression of tumor necrosis factor-α (TNF-α) mRNA in murine spleen cells in vivo at its optimal dose of 27.5 mg/kg than flavone acetic acid (FAA; NSC 347512) at its optimal dose of 220 mg/kg. Up-regulation of TNF-α mRNA was obtained using 5,6-MeXAA in vitro in cultures of murine splenocytes, the murine J774 macrophage cell line, and the human HL-60 myelomonocytic leukemia cell line. Maximal induction occurred at a 5,6-MeXAA concentration of 200µg/ml for both murine J774 and human HL-60 cells. A direct comparison of FAA and 5,6-MeXAA (100-600µg/ml) to stimulate TNF-α mRNA in HL-60 cells showed activity by 5,6-MeXAA at all doses but minimal activity with FAA. The results demonstrate that 5,6-MeXAA is equally potent in up-regulating TNF-α mRNA in human and murine cells of the monocyte/macrophage lineage, whereas FAA has demonstrable activity in murine cells only. The results suggest that 5,6-MeXAA would be a more active clinical agent than FAA because TNF-α induction appears to be a critical factor in the antitumor effects of this class of compounds.

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This work was supported by the Auckland Division of the Cancer Society of New Zealand and the Health Research Council of New Zealand.

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