IMMUNOTARGETING OF ANTIOXIDANT ENZYMES TO THE PULMONARY ENDOTHELIUM

Oxidative injury to the pulmonary endothelium has pathological signifi cance for a spectrum of diseases. Administration of antioxidant enzyme s, superoxide dismutase (SOD) and catalase (Cat), has been proposed as a method to protect endothelium. However, neither these enzymes nor t heir derivatives possess specific affinity to endothelium and do not a ccumulate in the lung. Previously we have described a monoclonal antib ody to angiotensin-converting enzyme (ACE) that accumulates selectivel y in the lung after systemic injection in rats, hamsters, cats, monkey s, and humans. In the present work we describe a system for selective intrapulmonary delivery of CuZn-SOD and Cat conjugated with biotinylat ed anti-ACE antibody mAb 9B9 (b-mAb 9B9) by a streptavidin (SA)-biotin bridge. Both enzymes biotinylated with biotin ester at biotin/enzyme ratio 20 retain enzymatic activity and bind SA without loss of activit y. We have constructed tri-molecular heteropolymer complexes consistin g of b-mAb 9B9, SA, and biotinylated SOD or biotinylated Cat and have studied biodistribution and pulmonary uptake of these complexes in the rat after i.v. injection. Biodistribution of biotinylated enzymes was similar to that of nonmodified enzymes. Binding of SA markedly prolon ged lifetime of biotinylated enzymes in the circulation. In contrast t o enzymes conjugated with nonspecific IgG, other enzyme derivatives, a nd nonmodified enzymes, biotinylated enzymes conjugated with b-mAb 9B9 accumulated specifically in the rat lung (9% of injected SOD/g of lun g tissue and 7.5% of injected Cat/g of lung tissue). Pulmonary uptake of nonmodified enzymes or derivatives with nonspecific IgG did not exc eed 0.5% of injected dose/g. Both SOD and Cat conjugated with b-mAb 9B 9 were retained in the rat lung for at least several hours. Trichlorac etic acid-precipitable radiolabeled Cat was associated with microsomal and plasma membrane fractions of the lung tissue homogenate. Thus, mo dification of antioxidant enzymes with biotin and SA-mediated conjugat ion with b-mAb 9B9 prolongs the circulation of enzymes resulting in se lective accumulation in the lung and intracellular delivery of enzymes to the pulmonary endothelium. These results provide the background fo r an approach to provide protection of pulmonary endothelium against o xidative insults.