SCINTIGRAPHY AND BIODISTRIBUTION OF MONOCLONAL ADRENOCORTICAL ANTIBODY IN MICE GRAFTED WITH HUMAN ADRENOCORTICAL CARCINOMA

Background. A murine monoclonal antibody recognizing normal and neopla stic human adrenocortical cells has been evaluated for scintigraphic l ocalization and biodistribution In 53 nude mice grafted subcutaneously with human adrenocortical cell lines SW-13 and T-CAR 1. Methods. The immunoglobulin GI antibody and its Fab'(2) fragment were purified and labeled with I-125. The tumor grafts exhibited diameters of 5 to 15 mm at 4 to 6 weeks after transplantation, when mice received a single su bcutaneous or intraperitoneal injection of 50 mu g iodinated intact or fragmented antibody, respectively. Results. Examination up to 8 days after immunoglobulin G administration showed mean radioactivity ratios less than 1.0 for tumor to blood and corresponding ratios in tumor lu ng, liver, spleen, and kidney from 0.6 to 5.3 at the time of peak tumo r to blood ratio. A high background activity tons noted on scintigraph ic tumor visualization with the iodinated immunoglobulin G. In contras t, the radiolabeled Fab'(2) fragment displayed gradually rising tumor to blood ratios, which, 4 days after injection, averaged 10.5 for T-CA R 1 and 5.3 for SW-13. Tumor transplants were scintigraphically visual ized without substantial background activity 3 days after Fab'(2) inje ction, when the ratio of radioactivity in the tumor to the investigate d murine organs was 0.5 to 7.3. Conclusions. The findings substantiate that immunoscintigraphy with the Fab'(2) fragment of the antiadrenoco rtical Ac5 antibody may become a tool to localize human adrenocortical carcinoma.