Distribution and elimination characteristics of 111In-DTPA-D-phe1-octreotide and 111In-DTPA-L-phe1-octreotide in rats

The present study compares distribution and elimination characteristics of 111In-DTPA-D-Phe1-octreotide and 111In-DTPA-L-Phe1-octreotide in rats and evaluated the effect of the replacement of the terminal L-phenylalanine by D-phenylalanine on pharmacokinetic profiles of the radiolabelled peptides. Both agents exhibited rapid radioactivity clearance from the blood and most organs and tissues with no systematic and significant differences in activity accumulation. The long-term retention and high radioactivity concentrations for both compounds under study were found in the kidneys and organs with a high density of somatostatin receptors, such as the pancreas and adrenals. The residence times in these organs were longer for 111In-DTPA-D-Phe1-octreotide in comparison with 111In-DTPA-L-Phe1-octreotide. The major elimination pathway for both radiolabelled peptides was relatively rapid excretion into the urine. Analysis of the renal handling by an employment of the perfused rat kidney showed that both peptides were eliminated mainly by the mechanism of glomerular filtration. Rat liver perfusion experiments confirmed a very low value of bile clearance of radioactivity for both agents under study.

Oxygen bubbling can improve the labelling of pentavalent technetium-99m dimercaptosuccinic acid

It has previously been reported that almost all of the trivalent technetium-99m dimercaptosuccinic acid (99mTc (III) DMSA) present in the labelling product of pentavalent technetium-99m DMSA (99mTc (V) DMSA) can be changed into 99mTc (V) DMSA by bubbling with pure oxygen. We therefore performed studies in animals (mice) and humans to investigate the effect of such oxygen bubbling on the labelling efficiency of and on the renal uptake of 99mTc. The method of labelling of 99mTc (V) DMSA was that of Hirano. It was found that oxygen bubbling oxidized the contaminated 99mTc (III) DMSA into 99mTc (V) DMSA in vitro and decreased the uptake of radioactivity in the kidney in both animals and humans.

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.

A new approach toward a pancreas-seeking zinc radiopharmaceutical. II. 62Zn-EDDA (ethylenediamine-N,N'-diacetic acid) for pancreas PCT imaging

The functionality of various zinc complexes of amino acid derivatives as a zinc radiopharmaceutical for pancreas PCT imaging was tested using 65Zn, which has a long half-life, and 62Zn, which has a short half-life. Because of the favorable results obtained in previous in vitro pancreas section studies, the ability of those Zn complexes to retain their integrity in the presence of blood serum or in living organisms was screened using Sephadex column chromatography and mice biodistribution studies. A relationship between the structure and stability of Zn complexes played a determining role on the in vivo availability of Zn for the pancreas or liver. Among the Zn complexes tested, the tetra-coordinated structure of the Zn-EDDA complex at an equimolar ratio showed proper accumulation in the pancreas, inducing an appropriate pancreas PCT image in the dog with the positron emitter 62Zn-EDDA administered at 1 mg Zn/kg body weight.