Radiochemical and radioimmunological data of 99Tcm-anti-CEA labelled by two diverse methods

The aim of this study was to make a comparative evaluation of a direct and an indirect method for the labelling of anti-CEA with technetium-99m (99Tcm). With the direct method, disulphide bridges were cleaved by the use of 2-mercaptoethanol as reductant, whereas with the indirect method, the antibody was coupled to 2-iminothiolane. In both cases, a preformed intermediate chelate was used for 99Tcm exchange. The radiochemical and radiobiological behaviour of the 99Tcm-labelled species were studied. Furthermore, the influence of the labelling systems on the integrity of monoclonal antibodies, as well as the ability of 99Tcm-anti-CEA to tag onto human cancer cells, was investigated for the two labelling systems. Both methods showed a high labelling yield and resulted in immunoreactive and stable derivatives. However, detailed electrophoretical and radiochemical data, as well as the cysteine challenge trial, indicated relatively greater stability for the 2-mercaptoethanol reduction procedure.