3-STEP TUMOR IMAGING WITH BIOTINYLATED MONOCLONAL-ANTIBODY, STREPTAVIDIN AND IN-111-DTPA-BIOTIN

The purpose of this study was to test the three step targeting of tumo rs in mice using biotinylated antibody, streptavidin and radiolabeled biotin. Nude mice bearing subcutaneous LS180 human colon cancer xenogr afts were intravenously administered with 200 mu g of the biotinylated anti-Tn monoclonal antibody MLS128, and 2 days later they got intrave nous injection of 50 mu g of streptavidin. They were intravenously inj ected 1, 4 or 7 days later with 0.5 mu g of In-111-diethylenetriamine pentaacetic acid (DTPA)-biotin. The tumor uptake, determined 2 h later , was 1.4, 0.5 and 0.6% injected dose/gram of tissue (ID/g), respectiv ely, and the blood radioactivity was 1.0, 0.2 and 0.2% ID/g, respectiv ely, When the interval between the streptavidin and radiolabeled bioti n injections was prolonged from 1 day to 7 days, the tumor to-blood ra tio 2 h after injection of In-111 labeled biotin increased from 1.5 to 4.0, Clear tumor images were obtained as early as 2 h after injection of radiolabeled biotin. In conclusion, these preliminary data suggest ed that the three-step method using the streptavidin-biotin system wou ld be applicable in an experimental mouse tumor model and provides ima ges of tumors rapidly and clearly after injection of radiolabeled biot in, (C) 1998 Elsevier Science Inc.