Localization of G(D2)-specific monoclonal antibody 3F8 in human osteosarcoma

3F8 is a murine IgG3 monoclonal antibody specific for the antigen disialoganglioside G(D2). Immunofluorescence staining showed strong binding of 3F8 to 15 of 17 human osteosarcomas, including primary and metastatic tumors. The targeting potentials of the native monoclonal antibody (3F8) and the F(ab')₂ fragment (p-3F8) were tested in BALB/c athymic nude mice xenografted with human osteosarcomas. After radiolabeling with iodine using the chloramine T method, both 3F8 and p-3F8 retained immunoreactivities. The irrelevant IgG3 antibody TIB114 and its F(ab')₂ fragment were used as negative controls. A Ewing's sarcoma xenograft, which was low in G(D2) antigen, was also studied for comparison. Mice were sacrificed 1 day and 4 days after i.v. antibody injection. 3F8 and p-3F8 showed preferential accumulation in osteosarcoma over normal tissues with tumor:nontumor ratios of 2.7-58:1 and 1.4-82:1, respectively, on Day 1. These ratios improved to 10-163:1 and 6.0-75:1 on Day 4. The intact antibody 3F8 showed selective tumor uptake with a much higher percentage of injected dose per g than the fragment p-3F8 and exhibited a longer tissue half-life than p-3F8. These data indicate that anti-G(D2) monoclonal antibodies may be useful for imaging and targeted therapy of human osteogenic sarcoma. The F(ab')₂ fragment has the advantage of achieving favorable tumor:nontumor ratios sooner after antibody injection while the intact antibody shows better retention by tumor tissues.