Streptavidin facilitates internalization and pulmonary targeting of an anti-endothelial cell antibody (platelet-endothelial cell adhesion molecule 1): A strategy for vascular immunotargeting of drugs

Conjugation of drugs with antibodies to surface endothelial antigens is a potential strategy for drug delivery to endothelium. We studied antibodies to platelet-endothelial adhesion molecule 1 (PECAM-1, a stably expressed endothelial antigen) as carriers for vascular immunotargeting. Although ¹²⁵I-labeled anti-PECAM bound to endothelial cells in culture, the antibody was poorly internalized by the cells and accumulated poorly after intravenous administration in mice and rats. However, conjugation of biotinylated anti-PECAM (b-anti-PECAM) with streptavidin (SA) markedly stimulated uptake and internalization of anti-PECAM by endothelial cells and by cells expressing PECAM. In addition, conjugation with streptavidin markedly stimulated uptake of ¹²⁵I-labeled b-anti-PECAM in perfused rat lungs and in the lungs of intact animals after either intravenous or intraarterial injection. The antioxidant enzyme catalase conjugated with b- anti-PECAM/SA bound to endothelial cells in culture, entered the cells, escaped intracellular degradation, and protected the cells against H₂O₂- induced injury. Anti-PECAM/SA/¹²⁵I, catalase accumulated in the lungs after intravenous injection or in the perfused rat lungs and protected these lungs against H₂O₂-induced injury. Thus, modification of a poor carrier antibody with biotin and SA provides an approach for facilitation of antibody-mediated drug targeting. Anti-PECAM/SA is a promising Candidate for vascular immunotargeting of bioactive drugs.