Radioimmunoscintigraphy of human malignant melanoma. I. Pharmacokinetics and localization of 125I-labeled monoclonal antibody RG-12 in thymectomized mice bearing renal melanoma xenotransplants.

The novel RG-12 monoclonal antibody (MoAb) recognizing a high-molecular-weight antigen of human melanoma cells was radioiodinated and its biodistribution and tumor imaging was determined in immunosuppressed mice bearing xenografted human malignant melanoma HMB-2. Control and tumor-bearing mice were injected with 6 micrograms of 125I-labeled RG-12 IgG (8.9 MBq 125I-IgG/animal). Clearance of the MoAb from plasma had a mean half life of 20.6 hours. At day 2 after injection, radiolabeled RG-12 IgG localized in the tumor was 1.43% of the injected dose bound per gram tissue (ID/g), whereas the localization in the healthy kidney was below 0.5%. Tumor to tissue ratio of MoAb accumulation was low for hepatic tissue (1.25) but high for spleen (3.30) and kidney (3.25), respectively. Scanning with a gamma camera localized tumor mass in the right kidney and implanted peritoneal metastases.