The direct labelling of serum transferrin (sTf) with Tc-99m on high-affinity binding sites, producing a complex of excellent stability, is described. The high-affinity binding sites were prepared by pre-treating sTf with 2-mercaptoethanol. For the radiolabelling step, thiourea was used as an exchange ligand and a filtration procedure used to remove Tc-99m that had not complexed with the protein. RT112 bladder tumour cells incubated in the presence of labelled sTf showed a rapid initial uptake of Tc-99m, reaching a plateau after about 20 min. Radiolabelling was also carried out without a pre-reduction step in an attempt to form a co-ordination complex between Tc-99m and the Fe3+-binding site of sTf, analogous to that formed by Fe. The tumour cell uptake of sTf labelled without pre-reduction was then examined. In contrast to Fe-59(3+) and other radio-metals co-ordinated with the Fe3+-binding site which show a continuous increase in incorporation with time, the uptake of Tc-99m rapidly reached a plateau. ((C) 2002 Lippincott Williams Wilkins).
- RECEPTOR EXPRESSION