Different activities of unscheduled DNA synthesis in human melanoma and bone marrow cells

Unscheduled DNA synthesis (UDS) indicated by melphalan was studied in freshly collected tumor cells from human melanoma metastases. Comparative studies were done on human bone marrow blast cells. Significant levels of UDS comparable with those in myeloblasts were found in only two of eight melanoma cell populations. This difference between melanoma and blast cells was not related to different cellular uptake of melphalan. When UDS was induced by ultraviolet irradiation, significant levels of UDS were found in all melanoma and blast cell populations studied. Also, in a human melanoma cell line, high levels of UDS were found after exposure to ultraviolet irradiation, while treatment with melphalan did not result in detectable levels of UDS. Possible explanations for the divergent results of UDS in melphalan-exposed melanoma cells are discussed.