Synthesis and evaluation of new iodine-125 radiopharmaceuticals as potential tracers for malignant melanoma

The synthesis, labeling, and biodistribution of four 125I radiopharmaceuticals designed to localize in melanoma were tested. Uptake in tumors was demonstrated by autoradiography of whole-body sections and quantitated by measurement of radioactivity of selected tissues and tumors using melanoma-bearing mice. N-(2-diethylaminoethyl)-4-iodobenzamide was selected for its highest melanoma uptake: 60 min after IV injection of 6.5% and 4% ID/g, respectively for murine B16 and human melanotic melanoma. Tumor uptake showed the highest values of all analyzed tissues from 6 to 24 hr after injection. High uptake in melanotic tumor tissue with relatively low uptake in blood, muscle, brain, lung, and liver tissue resulted in high tumor/nontumor ratios (at 24 hr for B16, tumor/blood = 37, tumor/brain = 147, tumor/muscle = 95). This agent was compared with iodoamphetamine. Scintigraphic images of the tumor confirmed that external detection of melanoma is possible with this new radiopharmaceutical.