Inhibitory Effect of Nafamostat Mesilate on Metastasis into the Livers of Mice and on Invasion of the Extracellular Matrix by Cancer Cells

Although many agents that interfere with clotting mechanisms have been investigated for their potential to inhibit metastasis, their toxicity has prevented administration of sufficiently high doses to achieve inhibition of metastasis in clinical trials. Nafamostat mesilate (FUT-175), a synthetic serine protease inhibitor, inhibited liver metastasis in a CDF1 mice model with colon 26 adenocarcinoma cells. The apparently dose-dependent inhibitory effect was seen 21 days after all of the doses tested (0.3, 1.0, 3.0 and 10.0 nig/kg for 7 days) but the effect was only statistically significant (P < 0.01) at the highest dose. The blood concentrations 3 min after dosing were less than 10⁻⁶ M for all of the doses tested. At a concentration of 10⁻⁵ M or less nafamostat mesilate was not cytotoxic towards colon 26 cells in vitro. The results indicate that it may not be difficult to achieve blood nafamostat mesilate concentrations that inhibit metastasis in mouse liver. Possible mechanisms of nafamostat mesilate are inhibition of extravasation and invasion of cancer cells, inactivation of collagenase due to inhibition of plasmin activity and inhibition of the formation of the cancer cell thrombus, and arrest in the capillaries through inhibition of thrombin activity. These preliminary results suggest that peri-operative administration of nafamostat mesilate may prevent metastasis into the liver after surgery for gastrointestinal malignancies.