Drug – bio-affecting and body treating compositions – Enzyme or coenzyme containing – Hydrolases
Patent
1989-05-24
1991-06-11
Stone, Jacqueline
Drug, bio-affecting and body treating compositions
Enzyme or coenzyme containing
Hydrolases
435219, 514 56, 514822, A61K 37547, A61K 31725, C12N 950
Patent
active
050230786
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a chemical modification of biologically active thrombolytic agents. More specifically, the invention relates to selective conjugation of plasminogen activators to heparin fragments to increase the half-life of the resulting conjugate.
BACKGROUND OF THE INVENTION
The formation of blood clots in blood vessels of major organs in the body is one of the leading causes of human mortality in Western industrialized society. Myocardial infarction--heart attack--primarily caused by blood clot formation or thrombosis in the coronary artery, is the leading cause of death in the United States among adult males. Emboli, blood clots traveling in the circulatory system, which lodge in the blood vessels of the lung, brain, or heart are also significant causes of death in patients following surgery, dialysis and traumatic injury. Phlebitis, a condition in which thrombi, stationary blood clots, block circulation through the large blood vessels, particularly of the lower extremities, is also a serious threatening disease.
The mechanism of blood clot dissolution or fibrinolysis is complex. At least three components are involved; plasminogen, plasminogen activators and plasmin inhibitors. Plasminogen is one of the circulating plasma proteins incorporated into a blood clot as it forms. Plasminogen is an inactive precursor or proenzyme form of the protein plasmin, a proteolytic enzyme that digests fibrin threads, as well as other substances involved in the activation of blood clot formation such as fibrinogen, factor V, factor VIII, prothrombin, and factor XII. Limited proteolysis of plasminogen yields plasmin. Plasminogen can be proteolytically activated to form plasmin by a number of enzymatically active proteins known as plasminogen activators. Plasminogen has a specific binding affinity for fibrin and thus a portion of the circulating plasminogen accumulates in the blood clot in association with the fibrin reticulum of the clot.
There are a number of commercially known plasminogen activators presently available for use in thrombolytic therapy including streptokinase, urokinase, recombinant tissue type plasminogen activator and acylated streptokinase-plasminogen. Streptokinase does not specifically bind to fibrin and as a result, it activates both circulating plasminogen and plasminogen in the blood clot. Two-chain urokinase is similar to streptokinase in its pattern of activity and the generalized, rather than local manner in which they exert their plasminogen activation, is a major drawback in therapeutic use.
Single-chain urokinase (scuPA) and tissue plasminogen activator (tPA) are fibrin-specific thrombolytic agents and are thus expected to cause less bleeding complications resulting from a systemic fibrinogenolysis at doses that are therapeutically effective. While these plasminogen activators are more fibrin-specific, tPA has a short half-life in the patient, on the order of two to five minutes (Matsuo, (1982) Throm Haemostas 48:242) and the half-life of scuPA is similarly limited (Stump et al (1987) J Pharm Exp Therap 242(1):245-250).
Modification of these therapeutically useful plasminogen activators to increase the half-life while maintaining desired biological activities of the activators would allow the use of these activators in the mammalian fibrinolytic system in lower dosages to achieve comparable thrombolytic efficacy with the concomitant potential advantages of reduced proteolysis of plasma proteins, prevention of reocclusion for longer periods, and reduced production cost per therapeutic dose.
The problems of short half-life mentioned above and other undesirable properties of certain activators are well recognized and various modifications of the activators have been undertaken to solve them. These include the modification of tissue plasminogen activator (tPA) to prevent site specific N-glycosylation (Lau et al, (1987) Biotechnology 5:953-957) and identifying the function of the structural domains of tPA in order to construct second generation plasminogen ac
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Halluin Albert P.
Halluin Albert P.
Murphy Lisabeth F.
Stone Jacqueline
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