Malignant melanoma is known as a highly aggressive cancer showing exceptional abilities to metastasize and resist existing therapies. Its incidence worldwide is increasing, having a prognosis of which is hardly to predict. Currently there are no effective treatments against malignant melanoma. Therefore, it is important to increase the understanding on how these aggressive proporties of melanoma are regulated. Melanoma is composed of not only the malignant cells, but also the supporting stroma, including fibroblasts, endothelial cells, immune cells, soluble molecules and the extracellular matrix (ECM), which together is called the tumor microenvironment (TME). Recently evidences implicating TME factors in cancer metastasis and modulation of drug-responses have been compelling. In the present work we investigated the influence of one of the TME factors S100A4 protein on the two melanoma cell lines Melmet 1 and Melmet 5, and how this affects the cell responses to the BRAF inhibitor vemurafenib. This study was based on in vitro cultures of melanoma cells stimulated with S100A4 and subsequently treated with vemurafenib before the cell proliferation and the cell viability were measured by the MTS assay. In addition, the levels of the tumorigenesis- and resistance-associated cytokine IL-8, secreted from melanoma cells in response to S100A4 and/or vemurafenib, was evaluated by the ELISA-method.
It was observed that extracellular S100A4 protein reduced the proliferation of melanoma cells in vitro. The melanoma cell sensitivity to the drug vemurafenib was also reduced in the presence of S100A4 leading to slightly higher cell survival. The S100A4-dependent effect on proliferation and the drug-sensitivity was observed in the proliferative phenotype cells Melmet 5, and not in the invasive phenotype cells Melmet 1. It was also observed that exposure to S100A4 stimulated the melanoma cells to secrete high levels of IL-8. Treatment with vemurafenib reduced the IL-8 secretion from both the non-stimulated controls and the S100A4-stimulated Melmet 1 and Melmet 5.