Selective Incorporation of i_-3,4-Dihydroxyphenylalanme by S-91 Cloudman Melanoma in Wfro1

The incorporation of precursors of the biopigment mela nin into melanotic and amelanotic S-91 Cloudman mela noma, mouse fibroblast L-929, and Chinese hamster ovary cells was studied. Tyrosine did not selectively accumulate in pigmented cells compared to that in nonpigmented con trol cells. Inhibition of protein synthesis with cycloheximide provided an estimate of the partition of tyrosine between protein (95%) and pigment biosynthesis (5%). L-3,4-Dihydroxyphenylalanine, a more proximal precursor of melanin, was selectively incorporated into pigmented cells up to 60 times that of control lines. a-Melanocytestimulating hormone and theophylline, agents that en hance pigmentation, further increased the incorporation of L-3,4-dihydroxyphenylalanine into melanocytic cells. A unique property of melanoma cells thereby has been de fined that may permit a selective chemotherapeutic and diagnostic approach.