Biodistribution of (99m)Tc Tricarbonyl Glycine Oligomers

(99m)Tc tricarbonyl glycine monomers, trimers, and pentamers were synthesized and evaluated for their radiolabeling and in vivo distribution characteristics. We synthesized a (99m)Tc-tricarbonyl precursor with a low oxidation state (I). (99m)Tc(CO)(3)(H(2)O)(3) (+) was then made to react with monomeric and oligomeric glycine for the development of bifunctional chelating sequences for biomolecules. Labeling yields of (99m)Tc-tricarbonyl glycine monomers and oligomers were checked by high-performance liquid chromatography. The labeling yields of (99m)Tc-tricarbonyl glycine and glycine oligomers were more than 95%. We evaluated the characteristics of (99m)Tc-tricarbonyl glycine oligomers by carrying out a lipophilicity test and an imaging study. The octanol-water partition coefficient of (99m)Tc tricarbonyl glycine oligomers indicated hydrophilic properties. Single-photon emission computed tomography imaging of (99m)Tc-tricarbonyl glycine oligomers showed rapid renal excretion through the kidneys with a low uptake in the liver, especially of (99m)Tc tricarbonyl triglycine. Furthermore, we verified that the addition of triglycine to prototype biomolecules (AGRGDS and RRPYIL) results in the improvement of radiolabeling yield. From these results, we conclude that triglycine has good characteristics for use as a bifunctional chelating sequence for a (99m)Tc-tricarbonyl- based biomolecular imaging probe.