Four permanent strains of human malignant melanoma, derived from a single melanoma nodule in one patient, exhibited different survival responses to the S-phase-specific drug, arabinosylcytosine. In one strain, survival was reduced by a fraction equivalent to the proportion of cells in S phase. The other three stains were much more resistant to drug doses as high as 100 µg/ml treated for 1 hr; however, treatments of longer duration (up to 8 hr) did cause a reduction in the surviving fraction of one resistant strain tested. Different mechanisms of cell killing by arabinosylcytosine may be responsible for the differential responses observed in these four melanoma strains.

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Supported by Damon Runyon Memorial Cancer Fund 1059 and Contract PH 43-66-1156, Chemotherapy, National Cancer Institute, NIH, USPHS.

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