|Budget Amount *help
¥5,200,000 (Direct Cost : ¥5,200,000)
Fiscal Year 1997 : ¥2,100,000 (Direct Cost : ¥2,100,000)
Fiscal Year 1996 : ¥3,100,000 (Direct Cost : ¥3,100,000)
To identify the sites and rates of catabolism of proteins of interest in vivo, the radiolabeling reagents should satisfy the following criteria : (1)the reagents should not induce intra-or inter-molecular cross-linking during the conjugation reactions with proteins, (2)the chelator-protein conjygates should form complexes of high plasma stability with high specific activities with metallic radionuclides such as indium-111, and (3)the radiolabeled proteins should generate fadiometabolites of long residence times at the sites of accumulation after lysosomal proteolysis.
Our prior studies indicated that indium-111-labeled peptides and proteins using DTPA as the chelating agent generate lysine-or phenylalanine-adduct of DTPA-Indium chelate after lysosomal proteolysis at the sites of accumulation, and the radiometabolites exhibit long residence times of the radioactivity in the lysosomal compartment These. findings stimulated us to design residualizing reagents using DTPA as the basic struct
ure. In this project, one terminal carboxylate of DTPA was attached with phenylalanine, phenylethylamine, ethylamine and aniline, and the complexation reactions of the conjugates with indium and the stabilities of the resulting indium-labeled compounds in freshly prepared plasma were estimated. When phanylalanine and phenylethylamine were attached to DTPA,the indium chelates showed higher stabilities than those of unmodified DTPA without impairing the complexation yields. However, both ethylamine and aniline conjugated DTPA decreased the stabilities of the resulting indium chelates. These findings suggested that stabilities of the indium-DTPA chelate can be increased by incorporating bulky substitution groups at a suitable distance, probably because of the restriction of C-C bonds in DTPA skeleton as well as the direct interaction of benzene group with the metal, indium-111. Our previous studies also demonstrated that use of galactosyl-neoglycoalbumin (NGA) provide reliable estimation of the fate of radiometabolites after lysosomal proteolysis in hepatic parenchymal cells. To better estimate the disappearance rates of the radiometabolites quantitatively, we constructed new pharmacokinetic models. These models allow quantitative estimation of radiometabolites derived from various chelating reagents used for radiolabeling. The gathered findings in this project should provide a good basis for future design of residualizing labels suitable to pursue the sites and rates catabolism of proteins of interest.