Thrombolytic therapy has not been widely used for pulmonary embolism due to less than optimal results with conventional plasminogen activators. We propose a new approach to deliver plasminogen activators to the luminal surface of the pulmonary vasculature to potentially improve dissolution of pulmonary thromboemboli. Our previous studies have documented that a monoclonal antibody (mAb) to angiotensin-converting enzyme (anti- angiotensin-converting enzyme mAb 9B9) accumulates in the lungs of various animal species after systemic administration. We coupled 125I-labeled biotinylated plasminogen activators (single-chain urokinase plasminogen activator, tissue-type plasminogen activator and streptokinase) to biotinylated mAb 9B9, using streptavidin as a cross-linker. The fibrinolytic activity of plasminogen activators was not changed significantly by either biotinylation or by coupling to streptavidin. Antibody-conjugated plasminogen activators bind to the antigen immobilized in plastic wells and provide lysis of fibrin clots formed in these wells. Therefore, antibody-conjugated plasminogen activators bound to their target antigen retain their capacity to activate plasminogen. One hour after i.v. injection of mAb 9B9-conjugated radiolabeled biotinylated single-chain urokinase plasminogen activator, biotinylated tissue-type plasminogen activator or biotinylated-streptokinase in rats, the level of radiolabel was 7.4 ± 0.8, 5.9 ± 0.4 and 3.6 ± 0.4% of injected dose/g (ID/g) of lung tissue vs. 0.5 ± 0.01,0.3 ± 0.01 and 0.6 ± 0.3% ID/g after injection of the same activators conjugated with control mouse IgG (P <.01 in all cases). Injection of mAb 9B9-conjugated radiolabeled plasminogen activator led to its rapid pulmonary uptake with a peak value 6.2 ± 1.2% ID/g attained 3 hr after injection. One day later, 2.2 ± 0.5% of the injected radioactivity was found per gram of lung tissue, although the blood level was 0.13 ± 0.03% ID/g (lung/blood ratio 16.7 ± 0.3). Therefore, conjugation of plasminogen activators with anti- angiotensin-converting enzyme mAb 9B9 provides their specific targeting to and prolonged association with the pulmonary vasculature. These results provide a basis for study of the local pulmonary fibrinolysis by mAb 9B9- conjugated plasminogen activators.
|Number of pages||9|
|Journal||Journal of Pharmacology and Experimental Therapeutics|
|Publication status||Published - Nov 1996|
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