Radiolabeled melanin-binding peptides are safe and effective in treatment of human pigmented melanoma in a mouse model of disease.

The incidence of melanoma is rising, and therapeutic options for metastatic melanoma are limited. We report the results of experimental melanoma therapy with 188-Rhenium-labeled melanin-binding decapeptide ((188)RE-HYNIC-4B4) and a comprehensive safety evaluation of this treatment. (188)RE-HYNIC- 4B4 bound only to nonviable eumelanotic MNT1 and pheomelanotic SK-28-MEL human melanoma cells in vitro, as determined by immunofluorescence, which is consistent with the inaccessibility of intracellular melanin in live cells, and suggests specificity for tumors with a significant amount of extracellular melanin. Administration of 1 mCi (188)RE-HYNIC-4B4 to MNT1 tumor-bearing mice significantly slowed tumor growth, with the therapeutic effect being a result of specific binding to tumor melanin, as irrelevant (188)RE-labeled decapeptide did not produce therapeutic gain. Repeated doses of (188)RE-HYNIC-4B4 had a more profound effect on tumor growth than a single dose. Treatment of tumors with 0.3-0.4 cm diameter was more effective than of larger ones (0.5-0.7 cm). There was no difference in uptake of (188)REHYNIC- 4B4 in melanized tissues of black C57BL6 mice and no histologically apparent damage to these tissues in comparison with white BALB/C mice. Treatment of C57BL6 mice with (188)RE-HYNIC-4B4 did not change their behavior, as established by SHIRPA protocol, and did not cause damage to neurons and glial cells. These results indicate that radiolabeled melanin-binding peptides are efficient and safe in treatment of melanoma and could be potentially useful against this tumor.