Biological evaluation and comparison of three different procedures for labelling of amino acids tyrosine and lysine with technetium-99m

The Tc-99m-labelling of the amino acids tyrosine (Tyr) and lysine (Lys), fundamental building blocks of proteins and peptides, as well as biological properties of the labelled compounds are investigated. Three different approaches for the labelling with Tc-99m have been investigated: direct reduction with stannous tin in the presence of the amino acids, the preformed chelate approach through polydentate chelates DTPA and GH, and the 'organometallic approach' using [Tc-99m(CO)(3)(H2O)(3)](+) precursor. The direct labelling approach was not successful and the yield was poor. In the presence of DTPA and GH, the labelling efficiency was between 43.6 and 97.8%, depending on the amino acid and the polydentate chelate. The use of [Tc-99m(CO)(3)(H2O)(3)](+) precursor point at the formation of Tc-99m(l) co-ordinated complexes with high yield. In this approach, pH and heating influenced the yields. The results of organ distribution study for [Tc-99m(Tyr)(H2O)(CO)(3)] and [Tc-99m(Lys)(H2O)(CO)(3)] show accumulation in liver, kidneys and intestine., Copyright (C) 2007 John Wiley & Sons, Ltd.