Characterization of insoluble macromolecular Sn(II) complex and its application to the 99mTc labeling of human serum albumin-bearing mercapto groups.

A chelating ion exchange resin containing aminophosphonic acid groups was used as a polymer matrix for the preparation of an insoluble macromolecular Sn(II)(R-Sn) complex. Sn(II), which strongly bound to the surface of the polymer matrix by chelation, retained the ability to reduce 99mTc in the R-Sn complex. Human serum albumin-bearing-mercapto groups (HMA) was labeled with 99mTc at pH 2-3 using the R-Sn complex or SnCl2 as reducing agent. The 99mTc-HMA labeled with the R-Sn complex resulted in a higher sustained level of radioactivity in the blood of mice than the 99mTc-HMA labeled with SnCl2. These results suggest that the use of the R-Sn complex minimized Sn(II) contamination of the 99mTc labeling solution and can be used effectively as a reducing agent for 99mTc labeling of proteins containing sulfhydryl groups.