Inhibitory activities of FUT-187 on trypsin-like serine proteases were compared using camostat mesilate (camostat), and 4-(4-guanidino benzoyloxy)-phenyl acetic acid methanesulfonate (GBPA) known as an active metabolite of camostat in the blood. Ki values of FUT-187 on the competitive inhibition mechanism were 0.097 μM for trypsin, 0.029 μM for pancreatic kallikrein, 0.61 μM for plasma kallikrein, 0.57 μM for plasmin, 2.5 μM for thrombin, 20.4 μM for factor Xa and 6.4 μM for Clr. However, FUT-187 acted as a noncompetitive inhibitor for factor XIIa and an uncompetitive inhibitor for Cls, and Ki values for these proteases were 0.021 and 0.18 μM, respectively. Ki values of camostat for these proteases were in the range of 0.037 to 96.4 μM, and those of GBPA for the above proteases except trypsin and plasma kallikrein were higher than those of FUT-187. The inhibitory activity of FUT-187 on trypsin was not reduced by the addition of the serum at 10%, whereas, that of GBPA was reduced (4.3 fold) in terms of IC50 values. The concentration of FUT-187 required to double APTT (activated partial thromboplastin time) was 1.09 μM, while GBPA, by concentrations up to 1 mM failed to double APTT. The kinin formation by glandular kallikrein in the rat plasma was inhibited by FUT-187 with IC50 value of 0.024 μM, while camostat revealed no inhibition by concentrations up to 1 μM. The complement-mediated hemolyses in the classical and alternative pathways were also inhibited by FUT-187 with IC50 values of 0.17 and 3.5 μM, respectively, the corresponding values for camostat being 350 and 150 μM, respectively. It is concluded that FUT-187 is a potent and selective inhibitor of trypsin-like serine proteases, and its inhibitory activities are stronger than those of camostat on glandular kallikrein, factor XIIa and Cls in complement pathway.
