This corresponds to ∼87% of the total amount injected. Within the first 4 hours the peptide-associated radioactivity in the liver remained constant. It slowly declined to 30.5 %ID/g at 24 hours after injection. At early points in time, minor levels were detectable in the blood (at 10 minutes: 2.8 %ID/g; at 1 hour: 2.0 %ID/g), in the kidneys (at 10 minutes: 2.7 %ID/g; at 1 hour: 2.3 %ID/g) and to a lower extend in heart, lung, and spleen (at 10 minutes:

3.8 %ID/g; at 1 hour: 2.6 %ID/g). No activity was associated with the brain, indicating no crossing of the blood-brain barrier. This confirms the results of noninvasive imaging obtained with genotype D HBVpreS/2-48myr-y-125I (Fig. 2A). Notably, the organ distribution pattern entirely changed when the N-terminal Tanespimycin in vivo fatty acids were removed. At 10 minutes p.i. >50% of the ID/g of HBVpreS/1-48-y-131I was detectable

in the kidneys (Fig. 3B). The signal declined to undetectable levels within the following 4 hours. At early timepoints higher peptide levels were detectable in the blood. No specific accumulation was observed in the liver when compared to other organs. Since a similar distribution was observed for a non-myristoylated scrambled peptide (data not shown), we conclude that myristic acid may mediate binding to a serum factor preventing the 5.4 kDa peptide from filtration in the kidney. In addition, association see more with a serum factor may enhance resistance against serum proteases. To substantiate the sequence-dependence for the hepatotropism of the peptide

we tested the point mutant HBVpreS/2-48stea(G12E)-y-131I. This mutant is defective in HBV infection inhibition.20 Remarkably, the single amino acid substitution completely changed the organ distribution of the peptide in NRMI mice (Fig. 3C). The pronounced association with the liver was lost and the peptide did not retain in the mouse for 24 hours. Thus, Carbohydrate acylated HBVpreS/2-48-peptides address a homologous target in mouse and human livers with comparable binding specificities for the HBVpreS1-sequence. Finally, we performed organ distribution studies using all peptides depicted in Fig. 3D. To quantify liver association, we calculated a liver enrichment factor and compared it with the inhibitory activity of the same peptide determined in infection inhibition assays (Fig. 3D). Mutants lacking their ability to interfere with HBV infection also lost their potential to accumulate in mouse livers. Inactive peptides (e.g., those with mutations in the essential receptor binding site 9-NPLGFFP-15) behaved like the scrambled mutant, while those with a residual inhibitory activity still retained some hepatotropism. This correlation supports the hypothesis that mice harbor an HBVpreS1-specific receptor which displays the same binding specificity as its human homolog. The unexpected finding that mice harbor an HBVpreS-specific receptor in the liver prompted us to perform in vivo distribution studies in other species.