(+)-Catechin inhibits the invasion of malignant fibrosarcoma cells into chick heart in vitro.

(+)-Catechin, a flavonoid extractable from higher plants and trees, inhibits the invasion of malignant MO4 fibrosarcoma cells into embryonic chick heart fragments in vitro. This inhibition is maximal at a drug concentration of 0.5 mM. The growth of the MO4 cells is only partly inhibited at such a concentration, and the effect can hardly be ascribed to an irreversible cytotoxicity of the drug to the host tissue. Pretreatment of the host tissue with the drug seems to be a prerequisite for the inhibitory action, which suggests that the anti-invasive effect is at least partly mediated by the condition of the heart tissue. We hypothesize that the collagen-stabilizing effect of (+)-catechin is the key to the explanation of its anti-invasive properties.