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  • Title: (99m)Tc-HYNIC-derivatized ternary ligand complexes for (99m)Tc-labeled polypeptides with low in vivo protein binding.
    Author: Ono M, Arano Y, Mukai T, Fujioka Y, Ogawa K, Uehara T, Saga T, Konishi J, Saji H.
    Journal: Nucl Med Biol; 2001 Apr; 28(3):215-24. PubMed ID: 11323230.
    Abstract:
    6-Hydrazinopyridine-3-carboxylic acid (HYNIC) is a representative agent used to prepare technetium-99m ((99m)Tc)-labeled polypeptides with tricine as a coligand. However, (99m)Tc-HYNIC-labeled polypeptides show delayed elimination rates of the radioactivity not only from the blood but also from nontarget tissues such as the liver and kidney. In this study, a preformed chelate of tetrafluorophenol (TFP) active ester of [(99m)Tc](HYNIC)(tricine)(benzoylpyridine: BP) ternary complex was synthesized to prepare (99m)Tc-labeled polypeptides 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, [(99m)Tc](HYNIC-Fab)(tricine)(BP) showed significant reduction of the radioactivity in high molecular weight fractions compared with [(99m)Tc](HYNIC-Fab)(tricine)(2.) When injected into mice, [(99m)Tc](HYNIC-NGA)(tricine)(BP) was metabolized to [(99m)Tc](HYNIC-lysine)(tricine)(BP) in the liver with no radioactivity detected in protein-bound fractions in contrast to the observations with [(99m)Tc](HYNIC-NGA)(tricine)(2.) In addition, [(99m)Tc](HYNIC-NGA)(tricine)(BP) showed significantly faster elimination rates of the radioactivity from the liver as compared with [(99m)Tc](HYNIC-NGA)(tricine)(2.) Similar results were observed with (99m)Tc-labeled Fab fragments where [(99m)Tc](HYNIC-Fab)(tricine)(BP) exhibited significantly faster elimination rates of the radioactivity not only from the blood but also from the kidney. These findings indicated that conjugation of [(99m)Tc](HYNIC)(tricine)(BP) ternary ligand complex to polypeptides accelerated elimination rates of the radioactivity from the blood and nontarget tissues due to low binding of the [(99m)Tc](HYNIC)(tricine)(BP) complex with proteins in the blood and in the lysosomes. Such characteristics would render the TFP active ester of [(99m)Tc](HYNIC)(tricine)(BP) complex attractive as a radiolabeling reagent for targeted imaging.
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