IN-VIVO FATE OF PHOSPHOROTHIOATE ANTISENSE OLIGODEOXYNUCLEOTIDES - PREDOMINANT UPTAKE BY SCAVENGER RECEPTORS ON ENDOTHELIAL LIVER-CELLS

Systemically administered phosphorothioate antisense oligodeoxynucleot ides can specifically affect the expression of their target genes, whi ch affords an exciting new strategy for therapeutic intervention. Earl ier studies point to a major role of the liver in the disposition of t hese oligonucleotides. The aim of the present study was to identify th e cell type(s) responsible for the liver uptake of phosphorothioate ol igo-deoxynucleotides and to examine the mechanisms involved. In our st udy we used ISIS-3082, a phosphorothioate antisense oligodeoxynucleoti de specific for murine ICAM-1. Intravenously injected [H-3]ISIS-3082 ( dose: 1 mg/kg) was cleared from the circulation of rats with a half-li fe of 23.3 +/- 3.8 min. At 90 min after injection (>90% of [H-3]ISIS-3 082 cleared), the liver contained the most radioactivity, whereas the second-highest amount was recovered in the kidneys (40.5 +/- 1.4% and 17.9 +/- 1.3% of the dose, respectively). Of the remaining tissues, on ly spleen and bone marrow actively accumulated [H-3]ISIS-3082. By inje cting different doses of [H-3]ISIS-3082, it was found that uptake by l iver, spleen, bone marrow, and kidneys is saturable, which points to a receptor-mediated process. Subcellular fractionation of the liver ind icates that ISIS-3082 is internalized and delivered to the lysosomes. Liver uptake occurs mainly (for 56.1 +/- 3.0%) by endothelial cells, w hereas parenchymal and Kupffer cells account for 39.6 +/- 4.5 and 4.3 +/- 1.7% of the total liver uptake, respectively. Preinjection of poly inosinic acid substantially reduced uptake by liver and bone marrow, w hereas polyadenylic acid was ineffective, which indicates that in thes e tissues scavenger receptors are involved in uptake. Polyadenylic aci d, but not polyinosinic acid, reduced uptake by kidneys, which suggest s renal uptake by scavenger receptors different from those in the live r. We conclude that scavenger receptors on rat liver endothelial cells play a predominant role in the plasma clearance of ISIS-3082. As scav enger receptors are also expressed on human endothelial liver cells, o ur findings are probably highly relevant for the therapeutic applicati on of phosphorothioate oligodeoxynucleotides in humans. If the target gene is not localized in endothelial liver cells, the therapeutic effe ctiveness might be improved by developing delivery strategies that red irect the oligonucleotides to the actual target cells.