Biol. Pharm. Bull. 30(1) 200—204 (2007)

tients, and its blockade is believed to enable cancer patients to live longer. Thus, it is important to find promising antimetastatic agents. A variety of compounds have been shown to be benefitial for the inhibition of cancer metastasis. Some of them involve mechanisms based on the invasive inhibition of tumor cells by interfering with tumor adhesion to extracellular matrix components, inhibiting tumor cell-associated protease activity, or reducing the motile activity of tumor cells. Other compounds work through immunostimulation or through the inhibition of tumor-endothelial or -platelet interaction. Although these antimetastatic compounds have great potential for clinical applications, it remains critical to find compounds which may be much more effective. Antioxidants includes a variety of compounds having the ability of capturing reactive oxygen species; which are such as antioxidative vitamins and polyphenols. Antioxidants therefore have been proposed to have potential benefits for the prevention and treatment of diseases associated with reactive oxygen species. Especially in the cancer research field, antioxidants have been demonstrated to be effective in reducing the risk of carcinogenesis partly based on their antioxdative activity. Some antioxidants have also been shown to have other anti-cancer properties, which are inhibitory activities on cancer cell-derived proteases, cancer cell invasion and growth, and angiogenesis. Inhibitory activities on cancer metastasis have also been reported for some antioxidative vitamins, their analogues and some polyphenols in animal models; and their inhibitory mechanisms have been suggested to involve the inhibition of cancer cell invasion or angiogenesis, or the induction of apoptosis of cancer cells. It is important to note here that most of the in vivo experiments showing the efficacy of the compounds have been conducted in an experimental design evaluating their effect on the development of tumor micrometastasis, which suggests therapeutic values of compounds. In contrast, preventive activity of those compounds on the formation of tumor metastasis has not fully understood. The present comparative study examined the inhibitory activities against the in vitro invasion, growth and experimental lung metastasis of murine colon carcinoma cells of 20 antioxidants, including antioxidative vitamins and polyphenols.