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

Abstract

Vascular immunotargeting, the adminis tration of drugs conjugated with antibodies to endothe lial surface antigens, has the potential for drug delivery to the endothelium. Our previous cell culture studies showed that biotinylated antibodies to PECAM-1 (a highly expressed endothelial surface antigen) coupled with streptavidin (SA, a cross-linking protein that facil itates anti-PECAM internalization and targeting) may provide a carrier for the intracellular delivery of ther apeutic enzymes. This paper describes the PECAM directed vascular immunotargeting of a reporter en zyme (b-galactosidase, b-Gal) in intact animals. Intravenous injection of [125I]SA-b-Gal conjugated with either anti-PECAM or IgG led to a high 125I uptake in liver and spleen, yet b-Gal activity in these organs rapidly declined to the background levels, suggesting rapid degradation of the conjugates. In contrast, anti PECAM/[125I]SA-b-Gal, but not IgG/[125I]SA-b-Gal, accumulated in the lungs (36.061.3 vs. 3.960.6% in jected dose/g) and induced a marked elevation of b-Gal activity in the lung tissue persisting for up to 8 h after injection (10-fold elevation 4 h postinjection). Using histochemical detection, the b-Gal activity in the lungs was detected in the endothelial cells of capillaries and large vessels. The anti-PECAM carrier also pro vided 125I uptake and b-Gal activity in the renal glomer uli. Predominant intracellular localization of anti-PE CAM/SA-b-Gal was documented in the PECAM expressing cells in culture by confocal microscopy and in the pulmonary endothelium by electron microscopy. Therefore, vascular immunotargeting is a feasible strat egy for cell-selective, intracellular delivery of an active foreign enzyme to endothelial cells in vivo, and thus may be potentially useful for the treatment of acute pulmonary or vascular diseases