Radiolabeled antibody: iodine versus radiometal chelates

The use of monoclonal antibodies in radioimmunoimaging and radioimmunotherapy was investigated in the Rauscher murine erythroleukemia system. Immunoglobulins labeled with isotopes of iodine or with chelated radiometals were compared with respect to efficiency of radiolabeling, in vitro and in vivo chemical stability of incorporated isotope, catabolism, kinetics of tumor targeting, and therapeutic efficacy. Labeling was found to be efficient for all isotopes studied, including those of iodine, scandium, yttrium, indium, gadolinium, and bismuth. The use of isotopes of iodine was limited due to rapid catabolism from the tumor target within a few hours; in contrast, antibody labeled with indium or gadolinium reached maximal tumor levels within 6 to 12 hours of injection and showed a biologic half-life at the tumor of 2 to 3 days. With yttrium, tumor levels were stable up to 5 days after injection. Our findings are discussed with relevance to current and future applications of radiolabeled antibodies.