A comparison of iodine and indium labelled anti CEA intact antibody, F(ab)2 and Fab fragments by imaging tumour xenografts.

An intact anti CEA monoclonal antibody (C198) and its F(ab)2 and Fab fragments have been radiolabelled with 131I and 111In and their biodistributions and tumour imaging capabilities examined in mice with human tumour xenografts. 131I labelled F(ab)2 and Fab fragments showed improved tumour visualization compared with intact antibody, principally because of the more rapid whole body elimination of the radiolabel. Studies using 111In labelled fragments demonstrated that a major proportion (greater than 60%) of the administered radioactivity was retained in the kidneys and this was detrimental to tumour imaging in the mouse xenograft model. The present study emphasizes the importance of selecting the most appropriate combination of antibody preparation and radiolabel, and that the choice of radionuclide is influenced by both its physical and subsequent pharmacological characteristics.