Cell-selective intracellular delivery of a foreign enzyme to endothelium in vivo using vascular immunotargeting

Vascular immunotargeting, the administration of drugs conjugated with antib odies to endothelial surface antigens, has the potential for drug delivery to the endothelium. Our previous cell culture studies showed that biotinyla ted antibodies to PECAM-1 (a highly expressed endothelial surface antigen) coupled with streptavidin (SA, a cross-linking protein that facilitates ant i-PECAM internalization and targeting) may provide a carrier for the intrac ellular delivery of therapeutic enzymes. This paper describes the PECAM-dir ected vascular immunotargeting of a reporter enzyme (beta -galactosidase, b eta -Gal) in intact animals. Intravenous injection of [I-125]SA-beta -Gal c onjugated with either anti-PECAM or IgG led to a high I-125 uptake in liver and spleen, yet beta -Gal activity in these organs rapidly declined to the background levels, suggesting rapid degradation of the conjugates. In cont rast, anti-PECAM/[I-125]SA-B-Gal, but not IgG/[I-125]SA-beta -Gal, accumula ted in the lungs (36.0+/-1.3 vs. 3.9+/-0.6% injected dose/g) and induced a marked elevation of beta -Gal activity in the lung tissue persisting for up to 8 h after injection (10-fold elevation 4 h postinjection). Using histoc hemical detection, the beta -Gal activity in the lungs was detected in the endothelial cells of capillaries and large vessels. The anti-PECAM carrier also provided I-125 uptake and beta -Gal activity in the renal glomeruli. P redominant intracellular localization of anti-PECAM/SA-beta -Gal was docume nted in the PECAM-expressing cells in culture by confocal microscopy and in the pulmonary endothelium by electron microscopy. Therefore, vascular immu notargeting is a feasible strategy for cell-selective, intracellular delive ry of an active foreign enzyme to endothelial cells in vivo, and thus may b e potentially useful for the treatment of acute pulmonary or vascular disea ses.