Directly radiolabeled phage with spleen-targeting specificity

Phage display technique is a powerful approach for discovering new tumor- and organ-targeting ligands, and radiolabeled phage has a potential to analyze the phage-binding sensitivity and specific imaging. In this study, phage II (the spleen-targeting phage) in mice was isolated after three rounds biopanning, and labeled by (99m)Tc using mercaptoacetyltriglycine (MAG(3)) as chelator to evaluate their binding properties in vivo. The amount of phage II eluted from spleen was enriched by plague assay each round. (99m)Tc-MAG(3)-phage II showed the less retention in blood at any time point than half that of (99m)Tc-MAG(3)-phage I (the radiolabeled original Ph.D-12 phage as control). The accumulation in spleen between (99m)Tc-MAG(3)-phage I and II was of different tendency. The highest uptake of (99m)Tc-MAG(3)-phage II in spleen was 24.80 %ID/g at 30 min; and of (99m)Tc-MAG(3)-phage I, 30.93% ID/g at 5 min. After circulating (99m)Tc-MAG(3)-phage II for 120 min, its accumulation in spleen decreased though higher than that of (99m)Tc-MAG(3)-phage I. In other organs, the (99m)Tc-MAG(3)-phage II showed low retention and high spleen-to-organ or tissue ratios. In conclusion, the radiolabeled phage II is convenient for studying the binding and specificity of spleen-targeting peptides found via phage display in vivo.