The combined effects of TNP-470 (TNP), a semisynthetic analogue of fumagillin, and 5-fluorouracil (5FU), a representative chemotherapeutic agent for colorectal cancer, were investigated using murine colon 26 adenocarcinoma (CT 26) cells. In a cell-proliferation study in vitro, 50% inhibitory concentrations (IC50) were determined to be 5.2 microg/ml and 240 ng/ml for TNP and 5FU, respectively. When CT 26 cells were treated with TNP and 5FU in combination, a remarkable cytotoxic effect was obtained. Isobologram analysis revealed synergism of these two agents in inhibition of the cell growth. In vivo, using a dorsal air sac assay, we found that TNP significantly inhibited the CT 26-induced angiogenesis. In addition, the combination of TNP and 5FU exerted a synergistic anti-tumor effect in a model of hepatic metastasis by portal injection of CT 26 cells. Since TNP is known to exert inhibitory effects on tumor cell growth through suppression of cell cycle progress from the G1 to S phases as well as neovascularization, it is speculated that the treatment with TNP enhanced the anti-tumor effect of 5FU through suppression of the cell cycle and tumor-derived angiogenesis. Taken together, these results suggest that combined treatment with TNP and 5FU is potentially useful for inhibition of tumor cell growth and liver metastasis of colorectal cancer.