Characterization of 99mTc(CO)3-iminodiacetic acid (IDA) and its comparison with 99mTc-(IDA)2 using compounds for hepatobiliary scintigraphy

The organometallic precursor of fac-[99mTc(CO)3(H2O)3]+ has attracted much attention because of the robustness and small size of Tc(I)-tricarbonyl complexes compared to Tc(V) complexes and the good labeling affinity with a variety of donor atoms. Among various ligand systems, an iminodiacetic acid (IDA) was proven as a good chelating group to form a Tc(III)-compelx as well as has been shown its potential as a chelating system for fac-[99mTc(CO)3] precursor. In an attempt to confirm the similarity and the difference between 99mTc(CO)3-IDA and 99mTc-(IDA)2-complex, M(CO)3-IDA (M = 99mTc, Re) complexes of disofenin, mebrofenin and N-(3-iodo-2,4,6-trimethyl phenylcarbamoylmethyl) iminodiacetic acid were prepared, and the biological evaluation of 99mTc(CO)3-disofenin was performed. The 99mTc(CO)3-IDA complexes were prepared with a high radiolabeling yield (>98%) in a quantitative manner and showed a negative charge. The in vivo pharmacokinetic behavior of 99mTc(CO)3-disofenin showed a similar biological activity to 99mTc-(disofenin)2 in that those complexes were quickly cleared from the blood by the hepatocytes and excreted into the gallbladder and intestine. Accordingly, the 99mTc(CO)3-IDA derivatives of disofenin and mebrofenin might be used as hepatobiliary imaging agents. Since an IDA is a promising chelator for 99mTc-based radiopharmaceutical and the biological properties of 99mTc(CO)3-IDA derivative shows similar to that of 99mTc-complex, a biomolecule containing IDA can be freely radiolabeled with fac-[99mTc(CO)3]-precursor or 99mTc. However, the radiolabeling efficiency and the biological behavior demonstrates the favorable properties of 99mTc(CO)3-IDA compound for the development of a new imaging agent.