BIOTINYLATED ISOCOUMARINS, NEW INHIBITORS AND REAGENTS FOR DETECTION, LOCALIZATION, AND ISOLATION OF SERINE PROTEASES

Eight new biotinylated, mechanism-based isocoumarin serine protease inhibitors have been designed and synthesized to detect, localize, and isolate serine proteases. Isocoumarins that contain a 4-chloro group, a biotinylated substituent at the 7-position, and different 3-alkoxy groups are inhibitors of various serine proteases including human leukocyte elastase (HLE), porcine pancreatic elastase (PPE), trypsin, human recombinant granzyme A, chymotrypsin, and cathepsin G. Insertion of spacers between the isocoumarin moiety and the biotin moiety enhanced enzyme inhibitory potency and may also promote binding of the enzyme-inhibitor complex to avidin. The 3-alkoxy groups conferred selectivity toward different serine proteases with chymotrypsin being inhibited effectively by compounds with 3-phenylethoxy groups while derivatives with 3-methoxy, ethoxy, or propoxy groups were potent inhibitors of HLE and moderate inhibitors of PPE. Full enzymatic activity was regained after the immediate addition of hydroxylamine to the inactivated chymotrypsin and PPE derivatives, which indicated that a simple acyl enzyme derivative is formed initially in the inhibition reaction. Egg avidin did not effect the rate of spontaneous enzyme reactivation rate while streptavidin accelerated the reactivation reaction. PPE inhibited by 7-[[6-(biotinylamino)caproyl]amino]-4-chloro-3-ethoxyisocoumarin (BIC 5) or 7-[[6-[[6-(biotinylamino)caproyl]amino]caproyl]amino]-4-chloro-3-methoxyisocoumarin (BIC 7) was bound to immobilized avidin columns. Most of inhibited PPE could be eluted from the monomeric or tetrameric avidin columns but only a portion (40-70 %) of the enzyme was active due to the partial formation of a stable alkylated enzyme derivative during the isolation process. Under ideal circumstances and formation of a simple acyl enzyme derivative, BICs should be useful for the isolation of new active serine proteases. Biotinylated isocoumarins should also have wide applicability for the detection, quantitation, and histochemical localization of stable biotinylated serine protease derivatives in a variety of physiological situations.