A new radioactive drug selectively accumulating in melanoma cells

The biological effects brought about by the selective accumulation of 35S-labelled methylthionine bromide (MTB) in pigmented hamster melanoma cells were examined in vitro and in vivo. In vitro incubation of melanoma cells in 35S-carrier-containing medium was found to suppress mitotic activity within 150 h whereas the same concentration of an inactive carrier did not affect normal proliferation. If the cells were in contact for 3 h with 35S-carrier in non-toxic concentration before reimplantation into the skin, a clear-cut correlation between 35S radioactivity and the capacity of growth initiation could be found. The growth of melanoma in situ could also be delayed by injecting the 35S-carrier to tumour-bearing animals. (orig.)