A synthetic flavonoid with vascular targeting properties. Flavone acetic acid exhibits an antiproliferative effect on endothelial cells as a result of a superoxide-dependent mechanism, which induces changes in permeability of the vasculature of the tumor. This agent may stimulate tumor necrosis and promote shunting of blood flow to viable regions of the tumor, increasing their oxygenation and rendering them more susceptible to the antitumor effects of hyperthermia and ionizing radiation. (NCI04)