The use of electroimmunoassay for the determination of the in vivo stability of labelled proteins.

: The in vivo stability of 125I, 99Tcm and 67Ga labelled HSA was measured by electroimmunoassay (EIA). Radiolabelled HSA compounds were intravenously injected into rabbits, and blood samples were taken 2, 5, 10, 30 and 60 min after injection. The activity and HSA content of rabbit sera were measured simultaneously. The results showed that HSA had been eliminated from the bloodstream at the same rate in all three cases (95-97% of HSA were in the circulation). Significant differences in the activity of serum samples are unequivocally due to differences in labelling and type of binding. Metal isotope detachment values were: 99Tcm-HSA, 47.3%; 67Ga-DF-HSA, 20.8% and 125I-HSA, 11.4% The data demonstrate that EIA may be a suitable method for the determination of the serum stability of protein-based radiopharmaceuticals.