Radioimmunoimaging in Malignant Melanoma with ¹¹¹ln-labeled Monoclonal Antibody 96.5

A radiolabeled monoclonal antibody (96.5) reactive with an M_r97,000 antigen found on over 80% of melanoma cell lines and tissue extracts was examined for its ability to detect malignant melanoma metastases in vivo. For imaging purposes, it was conjugated with diethyltriaminepentaacetic acid and subsequently labeled with ¹¹¹ln by chelation. Thirty-one patients with metastatic melanoma received single injections of monoclonal antibody 96.5 at concentrations ranging from 0.5 to 20 mg and at specific activities of ¹¹¹ln ranging from 0.125 to 4 mCi/mg. Total-body scans were performed at various time intervals following administration. No serious side effects were observed. Of a total of 100 previously documented metastatic sites, 50 imaged for a specificity of 50%. The number of sites imaged increased significantly as the amount of antibody administered increased relative to the average radiation dose. Considerable background uptake of isotope was observed in blood pool and other organs with gradual acquisition of label in tumor sites by 48 to 72 h. Hence, tumor imaging of melanoma using¹¹¹ In-labeled monoclonal antibody 96.5 appeared feasible, especially at antibody doses above 2 mg.