Human melanomas can become progressively resistant to the growth-inhibitory effects of a broad family of structurally diverse cytokines which includes interleukin 6 (IL-6). Uncovering this multicytokine resistance was made possible by the availability of cell lines established from early-stage radial growth phase or vertical growth phase primary melanomas as well as more advanced primary lesions and distant metastases. Because Oncostatin M (OSM) is also a member of the IL-6 family we evaluated the effects of this cytokine on the growth of human melanoma cell lines obtained from different stages of disease progression. The results showed that three different cell lines derived from early-stage melanomas were strongly growth inhibited by OSM, as they are by IL-6. Three cell lines, established from advanced-stage melanomas, were growth inhibited by OSM, but much higher concentrations (in the range of 10-fold) were required to obtain 50% growth inhibition; these cell lines were not inhibited by IL-6. Three other cell lines that were IL-6 resistant (two of which were advanced stage) were also found to be OSM resistant. Only one advanced-stage IL-6-resistant cell line was found to be highly sensitive to OSM-mediated growth inhibition. In addition, we found that variants isolated from early-stage WM35 melanoma cells that possess a much more aggressive tumorigenic phenotype in nude mice were significantly more resistant to both OSM- and IL-6-mediated growth inhibition. The results demonstrate that OSM can function as a growth inhibitor of human melanoma cells but that its ability to do so is progressively diminished or lost with disease progression. This finding is consistent with the concept of acquired “multicytokine resistance” during melanoma progression.

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Supported by grants from the NIH (CA41233), the National Cancer Institute of Canada, and the Share Foundation (R. S. K.). R. S. K. is a Terry Fox Career Scientist of the National Cancer Institute of Canada. C. L. and H. K. are research fellows of the Medical Research Council of Canada.

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