A novel immunoscintigraphy technique using metabolizable linker with angiotensin II treatment

Immunoscintigraphy is a tumour imaging technique that can have specificity, but high background radioactivity makes it difficult to obtain tumour imag ing soon after the injection of radioconjugate. The aim of this study is to see whether clear tumour images can be obtained soon after injection of a radiolabelled reagent using a new linker with antibody fragments (Fab), in conditions of induced hypertension in mice. Fab fragments of a murine monoc lonal antibody against human osteosarcoma were labelled with radioiodinated 3'-iodohippuryl N-epsilon-maleoyl-L-lysine (HML) and were injected intrave nously to tumour-bearing mice. Angiotensin II was administered for 4 h befo re and for 1 h after the injection of radiolabelled Fab. Kidney uptake of I -125-labelled-HML-Fab was much lower than that of I-125-labelled-Fab radioi odinated by the chloramine-T method, and the radioactivity of tumour was in creased approximately two-fold by angiotensin II treatment at 3 h after inj ection, indicating high tumour-to-normal tissue ratios, A clear tumour imag e was obtained with I-131-labelled-HML-Fab at 3 h post-injection. The use o f HML as a radiolabelling reagent, combined with angiotensin II treatment, efficiently improved tumour targeting and enabled the imaging of tumours. T hese results suggest the feasibility of PET scan using antibody fragment la belled with F-18-fluorine substitute for radioiodine.