AT-211-METHYLENE BLUE IN TARGETED RADIOTHERAPY OF DISSEMINATED MELANOMA

Targeted radiotherapy with At-211-methylene blue (At-211-MTB) is a sys temic treatment selectively directed at melanoma due to a high affinit y of MTB to melanin synthesized in the tumor cells. Since MTB forms a strong complex with melanin, it is an effective carrier for a number o f radioisotopes to be addressed to the tumor deposits of any size incl uding individually dispersed melanoma cells. Thus, appropriately radio labeled MTB can be used for either diagnosis or therapy of the neoplas m. As predicted and found in animal experiments, At-211-MTB is most ef fective therapeutically Histopathological investigations showed that t he highly pigmented At-211-MTB-treated tumors were characterized initi ally by perivascular oedema and hydropic degeneration of tumor cells f ollowed by gradual development of extensive areas of coagulative necro sis. The necrotic tumor areas contained microvessels occluded by throm bi and tended to undergo microfocal calcification. Although melanoma-b earing animals successfully treated with At-211-MTB did not reveal any adverse effects of the therapy, detailed toxicological studies were u ndertaken. No serious macro- or microscopic lesions were observed in n ormal organs of At-211-MTB treated mice. Only the relative number of s mall lymphocytes in the groin lymph nodes in a minority of animals was variably reduced, most often in conjunction with the treatment of hig hly, but not poorly, pigmented tumors.