Tc-99m-HYNIC-derivatized ternary ligand complexes for Tc-99m-labeled polypeptides with low in vivo protein binding

6-Hydrazinopyridine-3-carboxylic acid (HYNIC) is a representative agent use d to prepare technetium-99m (Tc-99m)-labeled polypeptides with tricine as a coligand. However, Tc-99m-HYNIC-labeled polypeptides show delayed eliminat ion rates of the radioactivity not only from the blood but also from nontar get tissues such as the liver and kidney. In this study, a preformed chelat e of tetrafluorophenol (TFP) active ester of [Tc-99m](HYNIC)(tricine)(benzo ylpyridine: BP) ternary complex was synthesized to prepare Tc-99m-labeled p olypeptides with higher stability against exchange reactions with proteins in plasma and lysosomes using the Fab fragment of a monoclonal antibody and galactosyl-neoglycoalbumin (NGA) as model polypeptides. When incubated in plasma, [Tc-99m] (HYNIC-Fab)(tricine)(BP) showed significant reduction of t he radioactivity in high molecular weight fractions compared with [Tc-99m] (HYNIC-Fab)(tricine)(2). When injected into mice, [Tc-99m] (HYNIC-NGA)(tric ine) (BP) was metabolized to [Tc-99m] (HYNIC-lysine) (tricine)(BP) in the l iver with no radioactivity detected in protein-bound fractions in contrast to the observations with [Tc-99m](HYNIC-NGA)(tricine)(2). In addition, [Tc- 99m](HYNIC- NGA)(tricine)(BP) showed significantly faster elimination rates of the radioactivity from the liver as compared with [Tc-99m](HYNIC-NGA)(t ricine)(2). Similar results were observed with Tc-99m-labeled Fab fragments where [Tc-99m] (HYNIC-Fab)(tricine)(BP) exhibited significantly faster eli mination rates of the radioactivity not only from the blood but also from t he kidney. These findings indicated that conjugation of [Tc-99m](HYNIC)(tri cine)(BP) ternary ligand complex to polypeptides accelerated elimination ra tes of the radioactivity from the blood and nontarget tissues due to low bi nding of the [Tc-99m](HYNIC)(tricine)(BP) complex with proteins in the bloo d and in the lysosomes. Such characteristics would render the TFP active es ter of [Tc-99m](HYNIC)(tricine)(BP) complex attractive as a radiolabeling r eagent for targeted imaging. (C) 2001 Elsevier Science Inc. All rights rese rved.