| Budget Amount *help |
¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 2000: ¥1,400,000 (Direct Cost: ¥1,400,000)
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| Research Abstract |
We have developed a new radioiodinated compound that liberates meta-iodohippuric acid from low molecular weight (LMW) polypeptides by the action of brush border enzymes. The radioiodinated LMW polypeptide prepared by the reagent showed low renal radioactivity levels from early postinjection times without impairing the radioactivity levels in the target tissues. These results prompted us to prepare LMW polypeptides radiolabeled with radionuclides of more clinical importance such as indium-111 (^<111>In) and technetium-99m (^<99m>Tc). In this study, we estimated chelating molecules for radiolabeling polypeptides with the radionuclides.
Since ^<111>In possesses chemical characteristics similar to those of Fe^<3+>, the chelating molecules should provide ^<111>In chelates stable against transchelation with a plasma protein, apo-transferrin. We selected 1, 4, 7, 10-tetraazadodecane-N, N', N'', N'''-tetraacetic acid (DOTA) as the chelating molecule and the chelator was conjugated to polypeptid
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e using one of the four carboxylic acid of the chelator. The ^<111>In-labeled polypeptides remained stable in plasma even after 72 h incubation. However, high polypeptide concentration was required to prepare ^<111>In-labeled polypeptides in high radiochemical yields. In addition, use of one carboxylic acid in DOTA reduced complexation kinetics, which also reduced the radiochemical yields of the ^<111>In-polypeptides. From these studies, we are synthesizing a new DOTA derivative with a polypeptide binding site without modifying the four carboxylic acid of the DOTA backbone.
For ^<99m>Tc labeling of polypeptides, we conjugated 6-hydrazinopyridine-3-carboxylic acid (HYNIC) to polypeptides. The ^<99m>Tc-HYNIC-labeled polypeptides were obtained in high radiochemical yields even at low polypeptide concentrations. However, ^<99m>Tc-HYNIC-conjugated polypeptides using tricine as colingand exhibited strong protein binding with plasma proteins due to the progression of exchange reaction. Then, a preformed chelate of tetrafluorophenol 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. This approach stabilized the ^<99m>Tc chelate against the exchange reactions and provided ^<99m>Tc-labeled polypeptides of rapid plasma clearance. In tumor bearing nude mice, the ^<99m>Tc-labeled polypeptides showed significantly higher tumor-to-blood ratios of the radioactivity when compared with ^<99m>Tc-labeled polypeptides by the previous procedure. On these bases, a new HYNIC derivative with a linkage cleaved by brush border enzymes of the kidney is now under progress to prepare ^<99m>Tc-labeled LMW polypeptides of low renal radioactivity levels. Less
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