[Preparation, quality control and biodistribution of 131I-herceptin in New Zealand rabbits].

ABSTRACT

OBJECTIVE: To study the immunoactivity,biodistribution and metabolic pattern of (131)I-Herceptin in rabbits. METHODS: Herceptin was radiolabelled with (131)I and its radiochemicalpurity (RCP) measured by size-exclusion high-pressure liquid chromatography (HPLC). The binding rate to BT-474 cells was measured to evaluate the immunoactivity of (131)I-Herceptin. (131)I-herceptin (2.0 mCi/kg) was injected intravenously into New Zealand rabbits. Scintigraphy on emission computed tomography was performed at 3 h, 1, 3 and 5 days after injection, and the radiocounts of the heart, liver and kidney etc. were compared with that of the muscle to calculate the organ-to-muscle activity ratio (O/M). On the fifth day,the rabbits were killed and the blood, myocardium, lung and other organs were obtained for measuring the radiocounts on gamma-counter to calculate the uptake percentage per gram tissue (ID%/g). RESULTS: The labeling rate of (131)I-herceptin was 93% with RCP of 95% and binding rate to BT-474 cells of 36.9%. After injection of (131)I-herceptin, the heart, lung and liver displayed dense radioactive regions but not the muscles and intestines. Three hours after injection, the O/M ratio of the heart was significantly higher than that of the lung, kidney and intestine (P<0.05), but decreased significantly one day after injection (t=10.817, P<0.001) with further decrement on days 3 and 5 (P<0.05). The O/M ratio of liver on day 1, 3, and 5 reduced significantly in comparison with that at 3 h (P<0.05). The uptake percentage was higher in the blood (11.3 ID/g%) than in the liver (2.8 ID/g%) and the myocardium (1.8 ID/g%). CONCLUSIONS: (131)I-herceptin possesses high immunoactivity which distributes mainly in the blood, liver and kidney, but with low uptake in the myocardium.