Comparative studies using 125I- and 111In-labeled monoclonal antibodies

HDP-1 monoclonal antibody was labeled with 111In using deferoxamine, diethylenetriaminepentaacetic acid or 1-(para-bromoacetamidobenzyl)-EDTA as chelating agents or with 125I. The in vitro binding capacity and stability of the labeled molecules were evaluated using affinity chromatography. The biodistribution and imaging capabilities were compared using an animal model system that does not involve the use of tumors. Similar studies were done using the corresponding labeled F(ab')2 and Fab' fragments. All labeled molecules, except those treated with deferoxamine, were stable in vitro. When tested in vivo, all retained their capacity to localize in the target tissue (lung). The lung %ID/g levels for the 111In-labeled molecules were, however, slightly lower than those observed for the corresponding 125I-labeled molecules. High uptake was also observed in the liver or kidneys when the 111In-labeled molecules were used; no such results were obtained with the 125I-labeled molecules. More work appears to be necessary before the use of bifunctional chelates becomes the optimal method for radiolabeling monoclonal antibodies for use in tumor imaging.