Flavonoid-mediated tumor growth suppression demonstrated by in vivo study

Many of flavonoids as well as bioflavonoids extracted from higher plants, which were earlier revealed to have tumor cell growth suppression activity in vitro, were examined for their effect on tumors in vivo. Balb/c mice were inoculated i.p. with syngeneic tumor cells, meth/a, and then provided with flavonoids dissolved in their drinking water during the course of their survival time. Many flavonoids were effective in prolonging the survival period. Furthermore, flavonoids that did not show suppressive activities in the in vitro experiments were effective in the in vivo assay. The data suggested that sugar bonded to the A ring, which suppresses tumor growth inhibition in vitro, plays an important role. Many aglycones that were effective in the in vitro assay on the tumor growth suppression were not effective in the in vivo assay. The reason for this seems to be that most aglycones are unstable and thus break down in vivo. No acute nor chronic toxicity of flavonoids was observed in the mice.