Liver uptake of phosphodiester oligodeoxynucleotides is mediated by scavenger receptors

The therapeutic activity of antisense oligodeoxynucleotides (ODNs) often is impaired due to premature degradation and poor ability to reach the (intra)cellular target. In this study, we addressed the in vivo fate of ODNs and characterized the major sites responsible for the clearance of intravenously injected phosphodiester ODN. On injection into rats, P-32-ODNs (miscellaneous sequences and GT-containing ODNs with variable G content) are rapidly cleared from the bloodstream (t(1/2) = 0.6-0.7 min), with the liver being the main site of elimination. The contribution of the liver to ODN clearance depended on its sequence and varied considerably. Hepatic uptake tended to be lower for G-rich ODNs as a result of increased bone marrow uptake. Within the liver, both Kupffer cells (KC) and endothelial cells (EC) were responsible for P-32-ODN uptake. To elucidate the mechanism of liver uptake, P-32-ODN binding studies using isolated EC and KC were performed. Binding to both cell types seemed to be saturable, of moderate affinity, and mediated by a membrane-bound protein. The inhibition profiles of P-32-ODN binding to EC and KC by various (poly)anions were essentially equal and corresponded closely to those of (125)l-acetylated low-density lipoprotein. In summary, the results indicate that scavenger receptors on nonparenchymal liver and bone marrow cells contribute to the elimination of ODNs from the bloodstream. Minor changes in ODN sequence markedly affect receptor recognition, resulting in considerable shifts in the biodistribution of antisense ODNs.