Developing peptide inhibitors to thrombin activation of platelets from bradykinin analogs

Investigations identified peptide, platelet-selective thrombin inhibitors. Three peptides (MAP4-RPPGF, RGKWc and RCDWC) were relatively selective inhibitors of thrombin-induced platelet activation and calcium mobilization. MAP4-RPPGF at 35.5+/-0.03 muM inhibits gamma-thrombin-induced platelet aggregation 100% and a-thrombin-induced calcium mobilization in fibroblasts 84%. RGKWc at 800+/-400 muM inhibits gamma-thrombin-induced platelet aggregation 100% and calcium mobilization 63%. RGDWC at 140 +/- 100 muM inhibits gamma-thrombin-induced platelet aggregation 100% and calcium mobilization 32%. RGDWC also inhibits ADP-induced platelet aggregation, whereas MAP4-RPPGF and RCKWC do not. RGKWC prolongs the activated partial thromboplastin time (APTT) but not the prothrombin time (PT) or thrombin clotting time (TCT). RGKWC uniquely inhibits a-thrombin activation of human factor XI. Single amino acid substitutions in peptide pentamers result in differences in potency and mechanism(s) of inhibition of platelet and fibroblast activation by thrombin. (C) 2001 Elsevier Science Ltd. All rights reserved.