[Recent advances in tumor-seeking agents--radioimmunoimaging of cancers using monoclonal antibodies]

Abstract

Development of biotechnology has made it possible to produce monoclonal antibodies (MoAbs) which associate with tumors. Injected RN-labeled MoAbs would be expected to accumulate in specific tumors. This concept can be evaluated not only from the point of diagnosis but also the therapy of cancers. Before applying RN-labeled MoAbs to patients with cancers, certain factors influencing radioimmunodetection should be investigated, such as (1) Labeling nuclides:RN should be selected by considering its physical properties. Biodistributions of RN-labeled MoAbs differ from one RN to another. (2) Labeling method: labeling techniques and optimum conditions should be established for each MoAb, in order to retain the immunoreactivity and stability of RN-labeled MoAb in vivo. (3) Circulating antigen:RN-labeled MoAb, once injected, may be challenged by the circulating antigen in the blood. We found that uptake of MoAbs against tumor markers (AFP, DU-PAN II) into tumors (hepatoma or pancreatic tumor) was decreased, and that the background activity was increased when the concentration of AFP or DU-PAN II in the blood was high. In addition to this fundamental information with respect to each MoAb, some clinical considerations are necessary for the application of RN-MoAbs to humans, mainly possible side effects. Clinical applications of immunoscintigraphy have not been well developed in Japan, although more than 2,000 cases utilizing this technique have been reported in Europe. In Europe and the U.S.A., tumors were detected with about 70% positivity without any serious side effects. General concerns regarding MoAb products, which have been proposed by the FDA, are also discussed in this paper.