Radioimmunoscintigraphy and radioimmunotherapy of renal cell carcinoma xenografts.

From a panel of monoclonal antibodies (MAb) reactive with human renal cell carcinoma generated by this laboratory, three (designated A6H, C5H, and D5D) were selected for in vivo studies with a nude mouse xenograft model. These studies included 131I- and 111In-labeled MAb radioimmunoscintigraphy and 131I-labeled MAb radioimmunotherapy. In the imaging studies, these radiolabeled MAb allowed visualization of subcutaneous xenografts larger than 40 mg and subrenal capsule xenografts smaller than 20 mg. Comparisons of tumor to non-tumor tissue radiolabel distribution yielded unusually high ratios and depended on the MAb-xenograft combination. The 111In-radiolabeled A6H showed increased accumulation in the liver compared with 131I-A6H, but this still did not necessitate background subtraction for good visualization of small, subrenal capsule renal cell carcinoma xenografts. Radioimmunotherapy studies with 131I-A6H in BALB/c nu/nu mice bearing established renal cell carcinoma xenografts showed a prolonged (greater than 90 days) regression in tumor burden and possible "cures," whereas three sets of control mice showed progressive and rapid increases in tumor size. These studies indicated that MAb, which show good tissue biodistribution and high imaging sensitivity, could also be capable of delivering effective radiotherapy to the tumor when "human equivalent" radiolabeled-MAb doses are used.