A potential new radiopharmaceutical for parathyroid imaging: radiolabeled parathyroid-specific monoclonal antibody--II. Comparison of 125I- and 111In-labeled antibodies.

The biodistributions of 111In-BB5-G1 and 111In-F(ab')2 were compared with the biodistributions of the corresponding 125I-labeled molecules. For BB5-G1 intact antibody, the relative uptake of the 111In- and 125I-labeled molecules in human parathyroid tissue implants was similar at 24 h, but by 96 h the uptake of the 111In-BB5-G1 %ID/g was four times greater than that observed with the 125I-labeled antibody. For the F(ab')2 fragments, the relative parathyroid uptake of the two preparations was similar at all times tested. The uptake by the clearance organs was significantly higher when the 111In-labeled molecules were used. Imaging results suggest that 111In-BB5-G1 or 111In-F(ab')2 may be a useful radiopharmaceutical for parathyroid radioimmunodetection.