INCREASED STREPTAVIDIN UPTAKE IN TUMORS PRETARGETED WITH BIOTINYLATEDANTIBODY USING A CONJUGATE OF STREPTAVIDIN-FAB FRAGMENT

Radiolabeled streptavidin accumulated in tumors pretargeted with bioti nylated antibody. However, the absolute delivery of radioactivity was limited. To increase the tumor uptake of radioactivity further, we con jugated streptavidin with a mouse monoclonal antibody (MAb) fragment, OST6Fab, which recognizes antigen on human osteosarcoma. Another mouse MAb, OST7, which also reacts with the same tumor but recognizes an ep itope different from the OST6 epitope, was biotinylated. The radioiodi nated strepravidin-OST6Fab conjugate was administered to tumor-bearing mice after the biotinylated OST7 pretargeting. The uptake of the conj ugate in tumors pretargeted with the biotinylated antibody was signifi cantly higher than that of streptavidin and that of the conjugate of s treptavidin and irrelevant Fab fragment. Renal uptake of radioactivity was decreased markedly, and the blood clearance was retarded by the c onjugation with Fab fragment. In conclusion, the conjugate of streptav idin with specific Fab fragment increased the accumulation of radioact ivity in tumors pretargeted with biotinylated antibody. NUCL MED BIOL 25;6:557-560, 1998. (C) 1998 Elsevier Science Inc.