Chapter 7. Technetium-99m labelling of an annexin fragment using the 4 + 1 mixed ligand chelate system

The tridecapeptide AQVLRGTVTDFPG - an annexin fragment - was labelled with 99mTc using the 4 + 1 mixed ligand system, in which Tc(III) is coordinated by a monodentate isocyanide and the tetradentate tripodal ligand tris(2-mercaptoethyl)- amine (NS3). The tridecapeptide was N-terminally functionalized with the isocyanides 4-isocyanomethylbenzoic acid (L1) and 4-isocyanobutyric acid (L2). Technetium-99m labelling was performed in a two-step procedure using 99mTc-EDTA/mannitol as the starting complex, followed by a ligand exchange reaction with a mixture of the isocyanide and the coligand NS3. The identity of the 99mTc labelled annexin fragments was confirmed by comparison with the high performance liquid chromatography profiles of the analogous rhenium compounds. Stability studies in rats exhibited a rapid metabolism of the labelled annexin fragment. Technetium-99m labelled annexin fragments do not exhibit affinity for apoptotic cells. (author)