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Urokinase-type plasminogen activator (uPA) plays a crucial role in the regulation of plasminogen activation, tumor cell adhesion and migration. The inhibition of uPA activity is a promising mechanism for anti-cancer therapy. Most current uPA inhibitors employ a highly basic group (either amidine or guanidine group) to target the S1 pocket of uPA active site, which leads to poor oral bioavailability. Here we study the possibility of using less basic 2-aminobenzothiazole (ABT) as S1 pocket binding group. We report the crystal structures of uPA complexes with ABT or 2-amino-benzothiazole-6-carboxylic acid ethyl ester (ABTCE). The inhibitory constants of these two inhibitors were measured by a chromogenic competitive assay, and it was found that ABTCE is a better inhibitor for uPA (Ki = 656 μM) than ABT (Ki = 5.03 mM). This work shows that 2-amniobenzothiazole can be used as P1 group which may have better oral bioavailability than the commonly used amidine or guanidine group. We also found the ethyl ester group occupies the characteristic oxyanion hole and contacts to uPA 37- and 60-loops. Such work provides structural information for further improvements of potency and selectivity of this new class of uPA inhibitor.
The inhibition of uPA activity is a promising mechanism for anti-cancer therapy. Most inhibition of uPA inhibitors employ a highly basic group ( either amidine or guanidine group) to target the S1 pocket of uPA active site, which leads to poor oral bioavailability. Here we study the possibility of using less basic 2-aminobenzothiazole (ABT) as S1 pocket binding group. We report the crystal structures of uPA complexes with ABT or 2-amino-benzothiazole-6-carboxylic acid ethyl ester (ABTCE). The inhibitory constants of these two inhibitors were measured by a chromogenic competitive assay, and it was found that ABTCE is a better inhibitor for uPA = 656 μM) than ABT (Ki = 5.03 mM). This work shows that 2-amniobenzothiazole can be used as P1 group which may have better oral bioavailability than the commonly used amidine or guanidine group. We also foun d the ethyl ester group occupies the characteristic oxyanion hole and contacts to uPA 37- and 60-loops. Such work provides structural information for further improvements of potency and selectivity of this new class of uPA inhibitors.