Growth and pigmentation in genetically related Cloudman S91 melanoma cell lines treated with 3-isobutyl-1-methyl-xanthine and beta-melanocyte-stimulating hormone.

4 clonal sublines of Cloudman S91 melanoma cells, S91/mel, S91/I3, S91/6 and S91/amel, were evaluated for changes in growth, pigment content and plating efficiency during and after treatment with a cyclic-AMP phosphodiesterase inhibitor-melanin-stimulating agent, 3-isobutyl-1-methyl-xanthine (IBMX) plus beta-melanocyte stimulating hormone (beta-MSH) or IBMX alone. After combined treatment, increases in melanin content on day 3 were 48, 27, 11, and 2 pg/cell in the four cell lines respectively. In each case IBMX alone was less effective than IBMX plus beta-MSH. Doubling time increased and plating efficiency decreased with increased melanization. The increases in doubling time and decreases in plating efficiency were cell line dependent. The greatest rate of increase in doubling time and decrease in plating efficiency as a function of melanin content were seen in S91/amel, which produced the least pigment. The lowest rates of increase/decrease were seen in S91/mel, which produced the most pigment. Melanin pigment induced in the cells was classified as eumelanin by EPR determination. The differential response to induction of pigmentation makes these cell lines suitable models for comparative studies on the role of melanin in pigment cell biology.

Is there a cell-to-cell contact effect on the X-ray dose-survival response of mammalian cells?

While a cell-to-cell contact effect has been reported for a Chinese hamster subline V79-171B, this was not observed for another subline V79 171-S. Therefore, we tested whether the cell-to-cell contact effect on cell survival depended on the cell line or the experimental conditions used. We have cultured and compared both sublines under identical conditions. Both sublines, cultured in Eagle's minimal essential medium (MEM) with 15% serum, had nearly identical cell doubling times and radiosensitivities. For both sublines, the survival of spheroid and monolayer cells subcultured immediately after irradiation were nearly the same, i.e., a radio-protective contact effect for spheroid cells was absent. Under conditions favorable for the repair of radiation induced damage, cell survival was higher for cells in monolayers than for cells in spheroids. Potentially lethal damage (PLD) repair and sublethal damage (SLD) repair were present in both sublines. However, the magnitude of expression of PLD by hypertonic saline was higher for monolayer than for spheroid cells. We conclude that: 1) the reported differences between V79 sublines (contact effect on survival) appear to be dependent on differences between experimental conditions rather than on cell type; 2) delayed plating technique does not detect PLD repair in round spheroid cells; and 3) detection of repair by split dose is independent of cell shape and/or two- or three-dimensional culture conditions.