Different growth responses to agents which elevate cAMP in human melanoma cell lines of high and low experimental metastatic capacity

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Abstract
Human melanoma variants of low and high experimental metastatic activity, which had been derived from the same parental line, showed markedly different growth responses to agents which elevated intracellular cAMP. The high metastatic line had a significant decrease inin vitro proliferation following treatment with cholera toxin (10−9 M) and forskolin (100μM), with both agents causing virtual cessation of cell growth after 3–5 days incubation. Pre-treatment with 10−9 M cholera toxin reduced colony forming ability to 11–15 per cent of control values, saturation densities were decreased to 10–25 per cent of controls and these cytostatic responses were accompanied by changes in cellular morphology. Lung colonising capacity of this cell line after i.v. injection into athymic mice was reduced significantly by prior exposure to cholera toxin (a median of 2 lung nodules versus 26 lung nodules for untreated, control cells). In contrast, low metastatic cell lines showed no significant growth inhibition in the presence of these agents. Cholera toxin (10−9 M) reduced colony forming ability of these cells to only 74 per cent of control values and there were no significant decreases in growth rate nor any morphological changes in response to either cholera toxin or forskolin. The variable response obtained in the cell lines appeared neither to be a consequence of variation in induced levels of intracellular cAMP nor in differences between the cell lines in response to the same agent; forskolin (100μM) induced a maximal 25-fold elevation and cholera toxin (10−9 M) a 2·5-fold elevation increase in cAMP. These data show that highly metastatic variants of a human melanoma cell line differ from their less metastatic counterparts in the way they respond to agents which elevate the second messenger molecule cAMP.