Human sarcoma-associated murine monoclonal antibody labeled with indium-111, gallium-67, and iodine-125

Monoclonal antibody (MAb) 23H7 is a hybridoma-derived IgG that is generated following fusion of mouse myeloma cell line P3U1 and spleen cells from BALB/c mice hyperimmunized with a human fibrosarcoma. It detects a mesenchymal antigen of 23KD expressed on human sarcoma tissues and other neoplasms, including myeloid leukemias, but it rarely binds to normal tissues. The MAb 23H7 was labeled with 67Ga and 111In using the bifunctional ligand method. The 67Ga was chelated to the MAb via desferrioxamine B, while 111In was chelated via the cyclic anhydride of diethylenetriamine pentaacetic acid. Higher specific activity was obtained with 67Ga than with 111In (4.5 and 2 muCi/microgram, respectively); both gave stable complexes. When 23H7 was labeled with 125I, considerable breakdown was observed. This, together with the physical shortcomings of this isotope, emphasizes the advantages of labeling with 111In and 67Ga. The rapid blood clearance of the labeled sarcoma-associated MAb may be beneficial for early tumor uptake and for imaging shortly after injection.