Transition states in multicytokine responsiveness during the progression of human cutaneous malignant melanoma

grantor: University of TorontoHuman cutaneous melanoma sometimes may progress through well-defined clinical stages, from normal melanocytes, via benign nevi, early-stage radial growth phase (RGP) and "thin" radial growth phase (VGP) melanoma (metastatically-incompetent), towards "thick" VGP (metastatically-competent) and metastatic melanoma. Melanocytic cells from different clinical stages have been successfully cultured in vitro for studies on tumor progression. It has been shown that normal dermal fibroblastic cells inhibit the proliferation of early-stage RGP and thin VGP melanoma derived cell lines whereas this inhibitory effect is lost on advanced-stage metastatically competent melanomas. In this thesis, evidence has been obtained showing that one molecule that is responsible for such differential growth regulatory activity is interleukin (IL) 6, a pleiotropic cytokine. Results also indicate that the loss of responsiveness to IL-6-induced growth inhibition in advanced-stage melanomas is not due to a lack of receptors, based on northern blotting and ligand binding Scatchard analysis. Studies on IL-6 gene expression by northern analysis and on IL-6 protein production by B9 cell bioassay and ELISA of culture medium of melanoma cells revealed that about half of IL-6 resistant cell lines, and none of the sensitive cell lines, produce biologically active IL-6. Attempts to down-regulate IL-6 production by use of antisense strategy with cDNA stable transfection were undertaken. The results indicate that the endogenous IL-6 can function as a growth stimulatory factor in advanced-stage melanoma cells that have spontaneously acquired endogenously IL-6 production. A similar resistance was also found in advanced-stage melanomas with respect to the growth inhibition induced by several other cytokines, such as IL-1$\alpha$ IL-1$\beta$, tumor necrosis factor $\alpha$, and oncostatin M. This phenomenon was called "multicytokine resistance". In summary, it is shown that there is a transitional change of IL-6-regulated cellular and tumor growth in human melanoma cells during disease progression, from a cell growth inhibition, to growth resistance, and finally a tumor growth stimulation. Given the possible presence of abundant levels of host or tumor-derived IL-6 in melanomas in vivo, these effects may provide rare malignant melanoma cells with a growth advantage in the primary site allowing them to become the eventual dominant population.Ph.D