Abstract
The antitumor agent flavone-8-acetic acid (FAA) is remarkable because it induces hemorrhagic necrosis, altered tumor blood flow, and cytokine synthesis. We show here that FAA and structurally related analogues increase plasma nitrite plus nitrate (NO2-/NO3-) levels in mice. Dose-dependent increases in plasma NO2-/NO3- concentrations, which reached maximum levels at 12 h, were found following administration of FAA. Furthermore, the presence of a palpable s.c. Colon 38 tumor significantly enhanced the response. Tumor-dependent increases were also observed with the active FAA analogues xanthenone-4-acetic acid, 5-methyl XAA, and 5,6-dimethyl XAA, while the inactive analogue 8-methyl XAA failed to increase plasma NO2-/NO3- concentrations substantially above basal levels. Increased plasma NO2-/NO3- levels were also observed in response to endotoxin (100 μg/mouse) and to recombinant human tumor necrosis factor α (4 to 16 μg/mouse). NO2-/NO3- levels may signify nitric oxide production as a result of stimulation of the l-arginine-dependent pathway in activated macrophages. The tumor dependence of the response may reflect the immunological stimulus imposed by tumor implantation. A clear relationship was found between increased plasma NO2-/NO3- levels and tumor growth delays induced by FAA and xanthenone-4-acetic acid analogues. It is suggested that nitric oxide may contribute to tumor cell death by two mechanisms, alteration of blood flow contributing to tumor ischemia and direct tumor cell killing. Plasma NO2-/NO3- concentrations may be a sensitive indication of the antitumor response to this class of compounds.
Footnotes
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↵1 Supported by the Ruth Spencer Medical Research Fellowship Trust, the Auckland Division of the Cancer Society of New Zealand, the Medical Research Council of New Zealand, and a Warner-Lambert Laboratory Fellowship.
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↵2 To whom requests for reprints should be addressed, at Cancer Research Laboratory, University of Auckland Medical School, Private Bag, Auckland, New Zealand.
- Received August 3, 1990.
- Accepted October 9, 1990.
- ©1991 American Association for Cancer Research.