DISCOVERY OF A NOVEL, POTENT, AND SPECIFIC FAMILY OF FACTOR XA INHIBITORS VIA COMBINATORIAL CHEMISTRY

A series of low molecular weight peptide inhibitors of factor Xa, unre lated to any previously described, was identified by screening a combi natorial peptide library composed of L-amino acids. The minimal inhibi tory sequence is a tripeptide, L-tyrosinyl-L-isoleucyl-L-arginyl, whic h competitively inhibits the hydrolysis of small chromogenic substrate s by factor Xa but binds in an orientation which prevents a productive nucleophilic attack by serine 195 of the catalytic triad on the carbo nyl carbon of the carboxy-terminal arginine. The initial leads identif ied in an octamer combinatorial peptide library ranged in potency from 4 to 15 mu M. These peptides were modified into peptide mimetics with a greater than 1000-fold increase in potency while retaining unusual selectivity for factor Xa over the related serine proteases thrombin, factor VIIa/tissue factor, plasmin, activated protein C, kallikrein, a nd trypsin. One of the most potent analogues, SEL 2711, with a K-i of 0.003 mu M for factor Xa and 40 mu M for thrombin, is active in in vit ro and ex vivo coagulation assays, suggesting the potential applicatio n of these inhibitors in anticoagulant therapy.