Optimization of antibody labeling with rhenium-188 using a prelabeled MAG3 chelate.

We report the optimization of polyclonal IgG labeling by 188Re using S-benzoyl-MAG(3) as a model for labeling monoclonal antibodies (MoAb). We examined the in vitro stability of the labeled protein and its localization and excretion in mice with induced focal inflammation. Stability in serum was greater than 85.5% after 24 h. Biodistribution and imaging studies following administration to mice showed mainly renal and hepatic excretion and high IT/NT ratios (4.5 and 4.6) at 24 and 48 h, respectively. This indirect method of labeling antibodies using a 188Re-labeled active ester of MAG(3) produced 188Re-MAG(3)-IgG of high in vitro stability and favorable uptake at sites of focal inflammation.