A new approach toward a pancreas-seeking zinc radiopharmaceutical. I. Accumulation of 65Zn-amino acid and aminopolycarboxylic acid complexes in pancreatic tissue slices.

There have been many attempts to develop zinc-containing radiopharmaceuticals for use as pancreas-seeking agents, but little consideration has been given to Zn-complex structure as being a factor that contributes to Zn utilization by the pancreas. In the present study, various ligands having N-O donor groups (amino acids and aminopolycarboxylic acids) with variable numbers of coordination sites (2-6) were investigated with regard to the coordination of the radiometal Zn. As an experimental model, freshly prepared slices of rat pancreas were studied, and Sephadex-column chromatography analysis was also performed. The structure and stability of Zn complexes were found to affect the accumulation of Zn in pancreas slices. In particular, the administration of tetradentate ligand complexes of 65Zn-ethylenediamine-N,N'-diacetic acid (EDDA) and 65Zn-nitrilotriacetic acid (NTA) resulted in high Zn utilization in the pancreas. Also, Zn complexes of intermediate stability (as demonstrated by elution behavior at Sephadex-column chromatography) produced the best results.