Comparison of affinities of urokinase and tissue plasminogen activator for fibrin clots

Preservation of Thrombolytic Activity of Urokinase Modified with Monomethoxypoly(ethylene glycol

A method is described to modify urokinase by covalent binding of monomethoxypoly(ethylene glycol) (mPEG) without impairing its catalytic ac tivity towards high molecular weight substrates. The urokinase active site is protected by an inhibitor, benzamidine, bound to Sepharose during the mPEG modification in order to avoid binding mPEG chains to the active site or to the surrounding area. The mPEG modified urokinase had increased activity towards small molecular weight substrates (acetyl-Gly-methyl ester) as com pared to the unmodified enzyme, while the activity towards the high molecular weight plasminogen and the insoluble substrate fibrin clot was preserved. This did not occur when the enzyme was modified in the absence of active site pro tection. The polymer modification increased the enzyme's thermostability and the stability in plasma in vitro and prolonged in vivo retention after in travenous injection in rats.

Insertion of fibrin peptides into urokinase enhances fibrin affinity

Low molecular weight two-chain urokinase is a 33-kD plasminogen activator, which has no innate affinity for fibrin and consequently, its use to facilitate lysis of blood clots may lead to systemic activation of plasminogen. In order to impart clot affinities to this urokinase form (UK) we have generated two novel fibrin-binding derivatives by partially reducing UK and exchanging the native disulfide-linked peptide A with peptide A analogs. The peptide A analogs contained the fibrin-adherent fibrin-derived sequences, GPRP (derived from positions 17-20 of the fibrinogen alpha chain) or QAGDV (407-411 sequence of the fibrinogen gamma chain), each coupled through amino-hexanoic acid to a synthetic peptide, LKFQCGQK, containing the Leu 144-Lys 158 sequence of the urinary plasminogen activator A Chain. The resultant derivatives contained about 0.4 moles peptide analog/mole UK, were 75% active toward synthetic UK substrates, and were recovered in a nearly 80% yield. The two fibrin peptide derivatives had a five-fold greater affinity for the clots.