Reactivity of ^99mTc(V) "3+1" mixed-ligand complexes towards glutathione

The stability and reactivity of mixed-ligand ^99mTc complexes of the general formula [^99mTcOL¹L², where L¹H₂ is either an N-substituted bis-(2-mercaptoethyl]amine [SNMeS] or 3-thiapentane-1,5-dithiol [SSS] and L²H is a monodentate thiol [RS], were investigated. The complexes undergo transchelation reactions with glutathione and other SH-group containing blood constituents. The reactions are reversible and can be inhibited by addition of diethylmaleate. Challenge experiments were performed with a broad set of ^99mTc mixed-ligand complexes to investigate the influence of both tridentate ligand and the monodentate ligand on the stability of this type of complex. The occurence of ligand exchange reactions with glutathione depends on the donor set of the tridentate ligands as well as the structure of the monodentate ligands.Especially the stability of complexes containing a monodentate ligand with an amine nitrogen in the side chain can be increased by lengthening the carbon chain between the sulfhydryl group and the nitrogen. Thus, it might be possible to improve their in vivo performance.