Single-chain urokinase plasminogen activator (scu-PA) that had been modified with Nsuccinimidyl-3-(2-pyridyldithio)propionate was covalently linked by disulfide bonds to the Fab' of a monoclonal antibody specific for the P-chain of fibrin (antibody 59D8). scu-PA-59D8 Fab' conjugate was separated from free scu-PA and two-chain urokinase coupled to 59D8 Fab' by two-step affinity chromatography. First, the reaction mixture was chromatographed on a column containing Sepharose linked to the peptide that had been used as immunogen for antibody 59D8; scu-PA-59D8 Fab' conjugate and unconjugated 59D8 Fab' were retained but not unconjugated scu-PA. Then, the eluate from the peptide-Sepharose column was chromatographed on a column containing Sepharose linked to benzamidine, which acts as a ligand for two-chain urokinase. The molecular weight of the scu-PA-59D8 Fab' conjugate was approximately 100 kDa when electrophoresed on a nonreducing sodium dodecylsulfate-polyacrylamide gel. Enzymatic assay after purification revealed that more than 97% of the scu-PA present in the conjugate retained the single-chain form. The Fab' portion of the conjugate functioned in a manner indistinguishable from that of native antibody 59D8. In an in vitro assay for lysis of fibrin monomer, the fibrinolytic potency of scu-PA-59D8 Fab' was 33-fold more than that of tissue plasminogen activator (p<0.001), 230-fold more than that of unconjugated scu-PA (p<0.0001), and 420-fold more than that of urokinase (p<0.0001). In a human plasma clot assay, scu-PA-59D8 Fab' was significantly more potent than native scu-PA in clot lysis and consumed less fibrinogen at equipotent fibrinolytic concentrations. Potency in vivo, measured in the rabbit jugular vein thrombus model, increased by 29-fold. Thus, conjugation to a fibrin-specific Fab' appears to increase the fibrin affinity and fibrinolytic potency of scu-PA. (Circulation 1990:81;1974-1980 W hen plasminogen activator therapy is instituted within 4-6 hours of the onset of symptoms of acute myocardial infarction, there is a significant reduction in morbidity and mortality.1 2 The first generation of plasminogen activators, streptokinase and urokinase, are effective but lack. fibrin and hence clot specificity. Secondgeneration plasminogen activators tissue-type plasminogen activator (t-PA) and single-chain urokinase plasminogen activator (scu-PA) are relatively fibrin One approach to improving the specificity of currently available thrombolytic agents is to increase their fibrin affinity by conjugation to an antifibrin antibody. We have studied conjugates between antifibrin monoclonal antibody 59D8 and urokinase8,9 and between 59D8 and t-PA.l0,1l Conjugation markedly enhances the thrombolytic potency of the two plasminogen activators, both in vitro and in vivo.scu-PA is perhaps the most promising plasminogen activator to which direct fibrin specificity could be added. Native scu-PA is fibrin selective, but this selectivity derives from the activation of fibrin-bound plasminogen. Although the mechanism of activ...

The complement-mediated lysis is inefficient when complement and target cells are homologous with regard to the species. In erythrocytes from patients suffering from paroxysmal nocturnal hemoglobinuria (PNH), the species restriction is lost: PNHerythrocytes (PNH-E) are susceptible to lysis by human complement. In human erythrocytes (huE) the species restriction is ascribed to an integral membrane protein, designated C8-binding protein (Cgbp). In the present study, we tested membranes of PNH-E type III for the presence of C8bp. A protein with C8-binding capacity could not be detected. C8bp, which was isolated from the membrane of huE, inhibited the lysis of PNH-E by C5b-9 as well as the C9 polymerization. Thus, addition of C8bp restored the species restriction in PNH-E. In conclusion, we propose that lack of C8bp might represent the defect in PNH-E type III membranes, which is responsible for their enhanced lytic susceptibility towards lysis by the late complement components.

The effects of simultaneous intravenous infusions of 12 mg recombinant tissue-type plasminogen activator (rt-PA) over 30 minutes and 48 mg single-chain urokinase-type plasminogen activator (scuPA) over 40 minutes were studied in 38 patients with acute myocardial infarction. Coronary arterial patency was assessed angiographically 60 minutes and 90 minutes after initiation of treatment. Patency was achieved in 19 of 31 patients (61.3%) (95% confidence limits, 42-78%) at 60 minutes and in 27 of 33 patients (81.8%) (95% confidence limits, 65-93%) at 90 minutes. Nonspecific plasminogen activation was monitored by measuring relevant plasma parameters. At 60 minutes and 120 minutes, the fibrinogen concentration decreased slightly to 82.8±24.3% and 91.2±17.4% of the preinfusion level, and the plasminogen concentration to 66.3+± 15.2% and 65.3+13.4%, respectively. A greater consumption of ,2-antiplasmin was observed, which decreased to 30.7+22.8% and 32.2+±21.2% of the preinfusion level at 60 and 120 minutes, respectively. No bleeding necessitating transfusion was observed. Two patients (5.3%) died during hospitalization. The findings suggest that the combined intravenous infusion of rt-PA and scuPA at appropriate doses induces highly effective coronary thrombolysis equal to the best results obtained with either rt-PA or scuPA alone. This efficacy is coupled with high specificity. Thus, the data support the potential use of combinations of rt-PA and scuPA in place of monotherapy. (Circulation 1990;81:907-913 possible with certain combinations of rt-PA and scuPA to induce more effective thrombolysis without compromising specificity. By lowering the overall dose requirements, it might be additionally possible to reduce the cost of therapy.The present study was designed to evaluate this concept. A dosage combination was chosen that was estimated to be just below the threshold at which fibrinogen degradation would be anticipated. Methods MaterialHuman scuPA was highly purified from the conditioned medium of the transformed kidney cellline TCL-598. PatientsInclusion criteria consisted of chest pain typical of myocardial infarction lasting for more than 30 minutes, diagnostic electrocardiographic ST segment elevation of 2 mm in at least three leads or 1 mm in at least three leads accompanied by ST segment depression in three corresponding leads, presentation within 6 hours after the onset of pain, age less than 75 years, and informed consent.Exclusion criteria were recent (<3 months) trauma, stroke or major surgery, previous myocardial damage in the infarct territory, cardiopulmonary resuscitation, cardiogenic shock (systolic blood pressure, <80 mm Hg), hypertension (systolic blood pressure, >200 mmHg; diastolic blood pressure, >110 mmHg; or both) unresponsive to therapy within 10 minutes, or evidence of recent or active bleeding (e.g., peptic ulcer and hemoptysis). The study protocol had been approved by the institutional ethics committee. TreatmentPatients were anticoagulated with 5,000 units heparin at the start of treatme...

An intrinsic membrane protein with a m.w. of 65,000 that can bind human C8 has been identified after separation of human erythrocyte membrane proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and electrotransfer to nitrocellulose sheets. The protein, tentatively designated as the C8-binding protein (C8bp) could be isolated from papain-treated erythrocyte (E) membranes by phenol-water extraction and isoelectric focusing. In a functional assay, with chicken (ch) E as target cells, C8bp inhibited the lysis of ch E C5b67 intermediates by human C8 and C9, whereas the lysis by rabbit C8 and C9 was not affected. Because the decay accelerating factor (DAF) from human erythrocyte membranes also inhibits the activity of C3/C5 convertases in an homologous system, we tested whether or not a DAF activity was present in C8bp. C8bp, however, did not accelerate the decay of the classic C3 convertases. Thus, it appears that C8bp and DAF are two different factors of E membranes with a similar molecular size inhibiting different sites of the activation cascade of complement while they can function synergistically to minimize the self-inflicted damage by complement.

No abstract

No abstract