THROMBOLYTIC COMPOSITION

Abstract: The invention disclosed relates to thrombolytic combination therapy by the administration of an agent capable of activating native plasminogen, and a non-native plasminogen analogue which is cleavable by native thrombin to generate plasmin activity.

Description: Thrombolytic Composition This invention relates to products and methods for improved thrombolytic treatment of patients having, or at risk of developing, a thrombus or thrombi. In particular, the invention relates to thrombolytic combination therapy by the administration of an agent capable of activating native plasminogen, and a non-native plasminogen analogue which is cleavable by native thrombin to generate plasmin activity. Background to the Invention Plasminogen Activators Agents capable of activating native plasminogen are known and are in use in thrombolytic therapy, are in clinical trial or have been proposed for that purpose. Examples of such compounds include tissue-type plasminogen activator (tPA), urokinase, streptokinase, and desmodus salivary plasminogen activator (DSPA). Intravenous treatment with tPA and streptokinase has been successful in reducing mortality from acute myocardial infarction. Despite this success, it is widely recognised that thrombolysis has major limitations which are due to the shortcomings of the agents available (reviewed by Marder and Sherry, New England Journal of Medicine 1989, 318: 1513-1520). For example, for tPA these are its rapid elimination from the body and its relative lack of thrombus specificity at clinically useful doses. The rapid clearance of tPA means that a large quantity of the protein has to be given by intravenous infusion, delaying the start of therapy until the patient is admitted to hospital. A further problem associated with the rapid clearance of tPA is that reocclusion of the reperfused blood vessel commonly occurs when tPA administration is stopped. Finally, the relative lack of thrombus specificity of therapeutic doses of tPA produces a risk of haemorrhage. Risk of haemorrhage is a problem common to current thrombolytics because they are not thrombus specific at clinically useful doses and they activate plasminogen to produce plasmin in the general circulation. Urokinase has a similar rapid plasma clearance and also requires administration by continuous infusion. Many attempts have been made to increase the half-life of tPA to overcome its rapid clearance, but tPA variants in clinical development appear to be cleared only 3-5 times more slowly than tPA (Thromb.Haemostas. 66: 569-574, 1991 ; Thromb. Haemostas. 70: 307-312, 1993); the plasma half-life of tPA is around five minutes in man (Bounameaux et al. in: "Contemporary issues in Haemostasis and Thrombosis" vol 1 p5-91 , 1985. Collen et al. eds, Churchill Livingstone). These tPA variants may well allow bolus administration and/or dose reduction but they are unlikely to remain in circulation long enough to be effective in preventing reocclusion. They are also unlikely to reduce the haemorrhagic risk significantly, and it may increase due to persistence in the circulation. Another approach to improving the clinical efficacy of plasminogen activators is via adjunctive therapy with anticoagulant and antiplatelet agents. There has been limited success in improving the therapeutic efficiency of tPA with the adjunct use of heparin and aspirin. However, such a therapeutic regime still has limitations of a 15-20% rate of failure to recanalize the infarct-related artery and by a reocclusion rate of 5-10%. As a result, the reinfarction rate at 30 days is 4-6%, cardiogenic shock and congestive heart failure occur in 5-7% and 15-17% of patients, respectively, and mortality is in the range of 5-8% (Am. J. Cardiol. 75: 7-13 1995). Both the initial failure of thrombolysis and reocclusion despite the use of heparin and aspirin are thought to be the result of ongoing thrombin activity. Hence, more potent and selective agents are under investigation. Hirudin is a potent inhibitor of thrombin which, in animal models has been shown to be superior to heparin in decreasing platelet deposition and thrombus formation (Circulation 79: 657-665, 1989) and in models of coronary thrombosis has been shown to both speed thrombolysis and decrease reocclusion (Circulation 83: 1048-1056 and Circulation Research 70: 829-834, 1992). US patent 4944943 discloses the use of thrombolytic agents such as tPA and antithrombotic agents, hirudin being the only suggested example, for adjunctive therapy. US patent 5126134 discloses the use of plasminogen activator such as tPA and hirudin, for adjunctive therapy. However, three clinical trials investigating hirudin as an adjunct to tPA were stopped in 1994 because of a high incidence of bleeding (Circulation 90: 1624-30, 1631-37 and 1638-42, 1994). In addition, these trials investigated a higher heparin dose than the previous norm and found that it too was associated with an increased haemorrhage incidence. Therefore it appears that intensification of adjunct antithrombotic therapy using agents which inhibit thrombin activity results in an unacceptable increase in bleeding. Thrombin Activatable Plasminogen Mutants. Patent publications WO 91/09118 and WO 94/10318 (both British Bio-technology Ltd) describe a new approach to the treatment of thrombotic conditions, based on the use of mutants of plasminogen which are activated to generate plasmin or plasmin-like activity by cleavage by an enzyme which is itself involved in the natural clotting cascade, particularly thrombin. One advantage of such agents lies in their thrombus specificity. Since activation occurs on exposure to thrombin, which is particularly concentrated at the site of the thrombus, thrombolytic plasmin activity is generated where it is required, thereby reducing the risk of systemic activation and haemorrhage. It is to be expected that such compounds will have an antithrombotic effect also, because the tendency to thrombus formation will be counteracted by the thrombolytic plasmin activity generated by thrombin cleavage of the agent at that site. Natural Glu-plasminogen has a plasma half-life of 2.2 days (Thromb. Haemostas. 43:77-89 1980), thus prolonged persistence in the circulation confers a further advantage on thrombin-activatable plasminogen which complements the thrombus selectivity of its action. The potency of the thrombin activatable plasminogen mutants of WO 91/09118 and WO 94/10318 may be enhanced by the further mutation disclosed in WO 94/03614 (British Bio-technology Ltd) which is designed to introduce resistance to antiplasmin, the cognate serine protease inhibitor of plasmin. Brief Description of the Invention This invention is based on the finding of the present inventors that thrombin activatable plasminogen analogues of the kind referred to above are capable of increasing the thrombolytic activity of plasminogen activating agents such as tPA without significantly increasing systemic plasmin production and therefore the risk of haemorrhage. This finding makes available a new more effective thrombolytic therapy by permitting bolus administration of the plasminogen activator and thus the earlier start of therapy; by reducing the effective dose of the plasminogen activator required, thereby reducing the haemorrhagic risk; and by reducing the incidence of reocclusion of opened vessels by reforming thrombi. Detailed Description of the Invention According to the present invention there is provided a product containing a plasminogen activator and a thrombin-activatable plasminogen analogue, for simultaneous, separate or sequential use in thrombolytic therapy. The invention also includes a method of treating a patient in need of thrombolytic or antithrombotic therapy, which comprises the simultaneous, separate or sequential intravenous administration of effective amounts of a plasminogen activator and a thrombin-activatable plasminogen analogue. According to another aspect of the invention there is provided for the use of a thrombin-activatable plasminogen analogue in the preparation of an agent for: a) treating a patient undergoing thrombolytic therapy with a plasminogen activator; and/or b) reducing the effective dose of a plasminogen activator required for a patient undergoing thrombolytic therapy with said plasminogen activator; and/or c) reducing the risk of haemorrhage in patients undergoing thrombolytic therapy with a plasminogen activator. Such adjunct antithrombotic therapy can be used for the treatment of acute vascular diseases such as: myocardial infarct, stroke, unstable angina, pulmonary embolism, deep vein thrombosis, peripheral arterial occlusion, extracorporeal circulation, arteriovenous shunts and other venous thromboses to produce accelerated removal of pathological thrombus. By the term "plasminogen activator" is meant a compound which activates plasminogen to generate plasmin-type thrombolytic activity. Examples of such compounds include those which directly cleave plasminogen to generate plasmin, such as tPA, DSPA, urokinase, and mutants of these proteins having sequence changes which do not destroy their ability to cleave plasminogen to release plasmin, as well as compounds which indirectly activate plasminogen, such as streptokinase, which forms a complex with plasminogen causing conformational changes which allow the complex to cleave plasminogen molecules to release plasmin. By the term "thrombin-activatable plasminogen analogue" is meant a molecule differing from wild type plasminogen by having sequence changes which render the molecule cleavable by thrombin to release plasmin or a molecule substantially homologous to plasmin which retains plasmin-type activity. Thrombin-activatable plasminogen analogues are inefficiently activated by plasminogen activators when compared to natural plasminogen. The thrombin-activatable plasminogen analogues may also have sequence changes relative to wild type plasminogen which either have no effect on the thrombin-cleavability of the molecules and the plasmin activity of the cleavage product, or confer an additional benefit on the molecules while retaining thrombin-cleavability and the plasmin activity of the cleavage product, for example mutations which confer antiplasmin resistance as described in WO 94/03614. Thrombin-activatable plasminogen analogues are disclosed in the British Bio¬ technology patent publications referred to above. The mutations which render the molecule cleavable by thrombin to generate plasmin activity, are preferably at or near the position in the molecule corresponding to the natural cleavage site of wild type plasminogen. In that connection, plasminogen was numbered as a result of the protein sequencing studies of Sottrup-Jensen et al. (in: Atlas of Protein Sequence and Structure (Dayhoff, M.O., ed.) 5 suppl. 3, p.95 (1978)) which indicated that plasminogen was a 790 amino acid protein and that the site of cleavage was the Arg(560)-Val(561) peptide bond. However, a suitable plasminogen cDNA useful as an intermediate in the synthesis of thrombin-activatable plasminogen analogues is that isolated by Forsgren et al (FEBS Letters 213: 254-260 (1987)), which codes for a 791 residue protein with an extra lie at position 65. In this specification, the numbering of the amino acids in plasminogen corresponds to that of the Forsgren cDNA. The presently preferred plasminogen activator for use in the present invention is tPA, but "second generation tPAs" such as that known as BM 06.022 (Martin. U. et al. Thromb. Haemostas. 66: 569-574, 1991) or that known as T103N.KHRR296- 299AAAA (Paoni .F.et al. Thromb. Haemostas. 70: 307-312, 1993) may become preferred as and when approved for human therapy by the regulatory authorities. Presently preferred thrombin-activatable plasminogen analogues for use in the present invention include those disclosed in WO 94/10318, which have a cleavage site sequence P4-P3-Pro-Arg-P1'-P2' where P3 is a basic amino acid residue, P4 is a hydrophobic amino acid residue and each of P1' and P2' is independently a non- acidic amino acid residue, said site being cleavable by thrombin between Arg and P1\ A particularly preferred thrombin-activatable plasminogen analogue for use in the invention is BB-10153, as described in example 2 of WO 94/10318, which is a plasminogen analogue in which, relative to wild type plasminogen, the amino acid residues Pro(559), Gly(560) are replaced by Thr-Thr-Lys-lle-Lys-Pro, and Val(562) is replaced by lie to produce a cleavage loop cleavable by thrombin; and two additional amino-acid substitutions Glu606 to Lys and Glu623 to Lys serve to impair binding of α2-antiplasmin. In the products of the invention, the plasminogen activator and the thrombin- activatable plasminogen analogue are, for reasons of regulatory requirements and/or product quality control, preferably packaged separately in unit dose form, particularly for separate intravenous bolus injection. Standard injectable protein formulation technology enables the preparation of suitable unit dose formulations. The unit dose concentration of tPA will generally be in the range of 0.05 - 1.5 mg/kg body weight, preferably 0.1 - 0.5 mg/kg body weight, and the unit dose concentration of thrombin- activatable plasminogen analogue will generally be in the range of 0.1 - 5 mg/kg body weight, preferably 0.5 - 3 mg/kg body weight, more preferably 2 mg/kg body weight. The maximum thrombin-activatable plasminogen analogue BB-10153 dose for man will generally be no more than 5mg/kg. As an alternative, the products of the invention may contain single unit doses of a mixture of the plasminogen activator and the thrombin-activatable plasminogen analogue, providing the formulation technology employed for its preparation ensures satisfactory stability and preservation of potency of the two components. For the treatment of human patients, as an individual therapeutic, tPA was originally given as a 100mg dose by intravenous infusion over 3 hours. This has now been superseded by an accelerated regime comprising an intravenous bolus dose of 15mg followed by an intravenous infusion of 0.75mg/kg of body weight over a 30 minute period (maximum 50mg) and then an infusion of 0.5mg/kg over 60 minutes (maximum 35mg) (J. Am. Coll. Cardiol. 14: 1566- 1569, 1989 and N. Eng. J. Med. 329: 673-682, 1993). tPA is not effective as a single i.v. bolus although it has recently been reported to be effective as two 50mg i.v. bolus injections (J. Am. Coll. Cardiol.23: 6-10, 1994). Reteplase (BM 06.022), long-acting tPA variant, has been administered as a double intravenous bolus of 10 million units (MU) followed 30 minutes later by 5MU (Am. J. Cardiol. 72: 518-524, 1993). Streptokinase is administered as a 1.5 million unit dose by intravenous infusion over 1 hour. The effective dosages of the plasminogen activator and thrombin activatable plasminogen analogues for administration can, based on the knowledge of current dosages and the potential reduction in tPA dose possible, be determined by the physician. The inventors have discovered, from animal studies, that a 3-fold or more reduction in tPA dose is generally possible with the adjunct thrombin-activatable plasminogen analogue BB-10153, both agents given as an i.v. bolus. A similar reduction would be expected using other plasminogen activators. Thrombin-activatable plasminogen analogue adjunct administration may therefore allow the plasminogen activator agents to be given as a single bolus. The maximum tPA dose in any current regime is 100mg. By co-administration of a thrombin activatable plasminogen analogue the effective total tPA dose may be reduced to 80mg, and preferably 70mg, 60mg, 50 mg, 40 mg, 35mg, 30mg 20mg or 10mg. By co-administration of a thrombin activatable plasminogen analogue the effective total Reteplase tPA dose may be reduced to 12MU, and preferably 10MU, 8MU, 7MU, 6MU, 5MU, 4MU, 3MU, 2MU or 1.5MU. A similar total dose reduction may be achieved for the other "second generation tPAs" including that known as T103N.KHRR296-299AAAA. By co-administration of a thrombin activatable plasminogen analogue the effective total streptokinase dose may be reduced to 1.2MU, and preferably 1 MU, 0.8MU, 0.7MU, 0.6MU, 0.5MU, 0.4MU, 0.3MU, 0.2MU or 0.15MU. Where the plasminogen activator and the thrombin-activatable plasminogen analogue are administered separately each by intravenous bolus injection, the order of administration is not critical. It may be preferable to administer the plasminogen activator first, followed by the thrombin-activatable plasminogen analogue. Where the thrombin-activatable plasminogen analogue and tPA agents are administered separately, it is contemplated that the the first agent may be administered 1 - 30 minutes, preferably about 10 minutes, more preferably about 5 minutes, after administration of the first agent. Administration of the plasminogen activator and the thrombin-activatable plasminogen analogue may also be by intravenous infusion, either from separate sources of the two components or (again providing the formulation technology employed for its preparation ensures satisfactory stability and preservation of potency of the two components) from a single source of the mixed components. Simultaneous administration may be affected using a devise capable of administering two substances simultaneously. Alternatively, simultaneous administration is also contemplated to include the administration of either the thrombin-activatable plasminogen analogue or tPA first, and the other component may be administered immediately afterwards. "Immediately" in this context meaning any period of time up to one minute after administration of the first component. Alternatively, administration of either the plasminogen activator or the thrombin- activatable plasminogen analogue may be by intravenous infusion and the other by intravenous bolus injection. One embodiment of the present invention is illustrated in the following non-limiting example. EXAMPLE Preparation of a thrombin-activatable plasminogen analogue The design, construction, expression and purification of the thrombin-activatable plasminogen analogue BB-10153 is described in WO 94/10318. BB10153 is a plasminogen analogue in which the amino acid residues Pro(559), Gly(560) are replaced by Thr-Thr-Lys-lle-Lys-Pro, and Val(562) is replaced by Me to produce a cleavage loop cleavable by thrombin; two additional amino-acid substitutions Glu606 to Lys and Glu623 to Lys serve to impair binding of α2- antiplasmin. Biological testing of Adjunctive effects of Intravenous tPA and BB-10153 The thrombolytic activities of tPA and thrombin activatable plasminogen BB-10153 were measured in a rabbit arterial thrombosis model in which thrombus formation in the femoral artery is induced by insertion of a coil of copper wire (copper is a potent stimulus for thrombus formation). Blood flow was monitored just distal to the coil by an ultrasonic flow probe and meter. Male New Zealand White rabbits, 2.5 - 3.0 kg, were anaesthetised by intravenous injection (ear vein) with a loading dose of 35mg/kg of a 17.5mg/ml pentobarbitone solution. Once the venous cannula was in place pentobarbitone was infused throughout the experiment at 18mg/kg/hr (infusion rate of 2ml/hr). The trachea of the anaesthetised rabbit was cannulated to allow the animal to be artificially respired. The end tidal CO2 was set to 6% and the inspired air was enriched with oxygen. Both jugular veins were cannulated, one for the anaesthetic infusion and the other for bolus doses of test compounds. The left carotid artery was cannulated to record blood pressure and heart rate. The femoral artery from both limbs was dissected free from surrounding tissue making sure no side branches were tied. A laparotomy was performed and the peritoneum opened above the position where the aorta bifurcates into the iliac arteries. A flow probe (2SB Transonic) was placed on the left femoral artery distal to the lateral circumflex artery and superficial epigastric artery (approx 2-3cm distal to the epigastric). Then approx. 5ml of bicarbonate was given to correct any acidosis. A blood sample was taken to check the pH (7.35-7.45) and the blood gases pθ2 (100-120mmHg) and pC0 (35-45mmHg). A copper coil made from 10 turns of 0.5 mm diameter wire wrapped around a 21 gauge needle was used to induce a thrombus. The coil was positioned in the left femoral artery just distal to the lateral circumflex artery and proximal to the flow probe by cannulation of the right femoral artery. Branches between the coil and probe were tied. A cannula was used to advance the coil up into the right iliac artery and then into the aorta where the blood carries it down to the left iliac artery to the femoral artery. The coil is finally positioned using forceps. Blood flow was monitored just distal to the coil in the femoral artery by an ultrasonic flow probe and meter. Blood flow through the left femoral artery ceased within 5 minutes of placing the coil in the vessel and treatment started 30 minutes after cessation of flow. For the combined treatment, BB-10153 was given first as an intravenous bolus injection and was followed 5 minutes later by tPA, also given as a bolus. 1.0ml blood samples were taken from a carotid artery for analysis before and at 0.5, 1 , 2, 3 and 4 hours after drug administration. The samples were anticoagulated with 3.8% w/v trisodium citrate (1 part in 10). The samples were spun at 14000 rev/min for 10 minutes and the plasma was then used for haemostatic protein determinations (see Methods). Thrombolytic activity of tPA. tPA (Actilyse, purchased from Boehringer Ingelheim) at 3mg/kg produced prolonged reperfusion in 4/6 animals and short periods of reperfusion in the remaining 2. tPA at 1 mg/kg induced significant periods of reperfusion in 2/8 animals but there was no reperfusion in the other 6. tPA at 0.3mg/kg did not induce any significant reperfusion. Thrombolytic activity of BB-10153 BB-10153 did not induce reperfusion of the occluded femoral artery when administered at doses up to 4mg/kg. Thrombolytic activity of combined treatment with tPA and BB-10153 The thrombolytic potency of tPA was increased significantly by co-administration of BB-10153. The combination of 1 mg/kg tPA and 2mg/kg BB-10153 induced prolonged reperfusion in 4/6 animals, a significant but shorter reperfusion in 1 animal and several short periods of flow in 1. This pattern was similar to that produced by 3mg/kg tPA. The combination of 0.3mg/kg tPA and 2mg/kg BB10153 induced substantial periods of flow in 3/4 animals. Effect of tPA and BB-10153 on plasma «2-antiplasmin and fibrinoαen levels Increasing the thrombolytic potency of tPA by co-administration of BB-10153 was not accompanied by a significant increase in the systemic generation of plasmin. tPA at 3mg/kg produced marked systemic plasmin generation as evidenced by reduction of the plasma α2-antiplasmin (α2-PI) level to less than 20% of control and reduction of the plasma fibrinogen level to approximately 25% of control. tPA at 1 mg/kg reduced the 0.2-PI and fibrinogen levels to around 60% and 75% of control respectively. BB- 10153 at 2mg/kg had no effect on plasma α2-PI and fibrinogen levels. The combination of 1 mg/kg tPA and 2mg/kg BB-10153 produced only a minor increase in systemic plasmin activity compared to that produced by 1 mg/kg tPA alone. tPA at 0.3mg/kg had little effect on the α2-PI and fibrinogen levels and this was unchanged with the thrombolytic combination of 0.3mg/kg tPA and 2mg/kg BB10153. METHODS Haemostatic proteins All determinations were performed on an ACL300R coagulometer from Instrumentation Laboratories; the coagulometer was supplied with a PC and relevant software (Research software). All reagents and kits for the coagulation tests were supplied by Instrumentation Laboratories. α2-antiplasmin The assay was performed using the standard kit supplied for the coagulometer and the default settings for the antiplasmin test. Fibrinogen A modification of the Clauss method was used (Clauss. A, Acta Haematol. 17:237 1957) A calibration curve was created using calibration plasma (the reciprocal of the fibrinogen concentration vs time to clot). Plasma for the calibration curves was obtained from Instrumentation Laboratories (IL). The concentrations were 2.95, 1.475, 0.98, 0.7375, 0.59 and 0.295 g/l (dilutions from stock are stock, 1 :2, 1 :3, 1 :4, 1 :5 and 1 :10). Fibrinogen in the test blood samples was determined from the calibration curve using the thrombin time assay results (see below). Analysis of the data was carried out on a PC using the Research software supplied by IL to go with the ACL 300R coagulometer. Thrombin time A standard kit was used with the modification that thrombin was made up with lOOmmol CaCl 2 to a cone of 3 NIHU/ml. The assay was performed using research mode (i.e clot cycle 1) settings - volumes of sample and reagent 75μl, activation time 180 sec, inter ramp interval 1 sec, acquisition time 300 sec, speed 1200rpm. Analysis using the Path matt.def (S/RX1 OO.S4.S4.threshold (3.50)).

Claims: Claims: 1. A product containing a plasminogen activator and a thrombin-activatable plasminogen analogue, for simultaneous, separate or sequential use in thrombolytic therapy. 2. A method of treating a patient in need of thrombolytic or antithrombotic therapy, which comprises the simultaneous, separate or sequential intravenous administration of effective amounts of a plasminogen activator and a thrombin-activatable plasminogen analogue. 3. The use of a thrombin-activatable plasminogen analogue in the preparation of an agent for: a) treating a patient undergoing thrombolytic therapy with a plasminogen activator; and/or b) reducing the effective dose of the plasminogen activator required for a patient undergoing thrombolytic therapy with said plasminogen activator; and/or c) reducing the risk of haemorrhage in patients undergoing thrombolytic therapy with a plasminogen activator. 4. A product as claimed in claim 1 , a method as claimed in claim 2 or a use as claimed in claim 3, wherein the plasminogen activator is tPA. 5. A product as claimed in claim 1 , a method as claimed in claim 2 or a use as claimed in claim 3, wherein the thrombin-activatable plasminogen analogue has a cleavage site sequence P4-P3-Pro-Arg-P1'-P2' where P3 is a basic amino acid residue, P4 is a hydrophobic amino acid residue and each of P1' and P2' is independently a non-acidic amino acid residue, said site being cleavable by thrombin between Arg and P1\ 6. A product, a method or a use as claimed in claim 5, wherein the thrombin- activatable plasminogen analogue for use in the invention is BB-10153

Inventors: COMER MICHAEL BERISFORD, DAWSON KEITH MARTYN, WOOD LARS MICHAEL, COMER, MICHAEL, BERISFORD, DAWSON, KEITH, MARTYN, WOOD, LARS, MICHAEL
Applicants: BRITISH BIOTECH PHARM, COMER MICHAEL BERISFORD, DAWSON KEITH MARTYN, WOOD LARS MICHAEL, BRITISH BIOTECH PHARMACEUTICALS LIMITED, COMER, MICHAEL, BERISFORD, DAWSON, KEITH, MARTYN, WOOD, LARS, MICHAEL
Application year: 1995
Main classification: A61K38
IPC codes: A61K38, A61P7