Molecular changes induced in melanoma cells by stromal cells and anti-BRAF therapy.

Tumor-associated stromal cells can enable cancer cells to become insensitive to therapy. They can promote aggressive phenotype in cancer cells, which become less responsive to drugs such as BRAF inhibitors (BRAFi) used to treat melanomas. To clarify potential mechanism behind stromal influence on melanoma, we analyzed gene expression in Melmet 5 melanoma cells grown as mono-cultures or co-cultures with lung fibroblasts with/without BRAFi. We have shown that Melmet 5 growing as co-cultures gained a de-differentiated, invasive transcriptional state, which is known to be linked to BRAFi-resistance. The transcriptional changes induced by BRAFi were much larger in Melmet 5 mono-cultures compared to co-cultures, indicating a much dampened transcriptional response to BRAFi in melanoma under the influence of fibroblasts. We conclude that interaction with the stromal cells stimulate melanoma cell transition to the invasive de-differentiated phenotype, leading to a worse response to BRAF inhibitors. Total RNA was isolated from Melmet 5 cell line growing as mono- or co-cultures with fibroblasts for 72 hours and treated with BRAFi for the last 24 hours.