Inhibitory effects of newly synthesized active center-directed trypsin-like serine protease inhibitors on the complement system

Abstract.

Objective: To obtain a synthetic anti-complement inhibitor which has stronger activity than FUT-175 (nafamostat mesilate), as a synthetic ester derivative containing amidino and guanidino groups.¶Methods: We synthesized several modified compounds of FUT-175. The anti-complement activities were measured using synthetic substrates and complement-mediated hemolysis in vitro. The anti-complement activity in vivo was evaluated via Forssman systemic shock in guinea pigs.¶Results: FUT-175 inhibited C1r^- and C1s^- with IC_50s of 1.7 × 10^-6 and 3.2 × 10^-7 M, respectively. Inhibitory activities were decreased by substitution of the amidino group with a hydrogen atom (compound 2), but not the guanidino group with a hydrogen atom (compound 3). Compound 6, in which the benzene ring of compound 3 was substituted with a furan ring, inhibited C1r^- and the complement-mediated hemolysis in high-diluted serum with higher potency than FUT-175. The inhibitory activity of compound 6 in hemolysis was weakened in low diluted serum. Compound 7 had a guanidino group inserted into compound 6; however, Compound 7 strongly inhibited hemolysis even in low-diluted serum, and suppressed Forssman systemic shock more potently than both FUT-175 and compound 6.¶Conclusions: These data suggest that the 2-furylcarboxylic acid derivatives have a strong potential for inhibiting the activities of the complement, and the guanidino group was required to retain high inhibitory activities in vivo, and compound 7 is a hopeful anti-complement agent.¶