Identification of the melanoma stem cell in long-term cultures and SOX6 - as specific biomarker

Background: Melanoma is the most aggressive skin cancer and its resistance to existing therapies in advanced stages is already known. This resistance can be directly related to the presence of cancer stem cells. We developed an experimental model that involved study of isolates of melanoma lineages (TM1 and TM5), cells that had some “stem” characteristics, in order to better characterize them. Materials and Methods: We used a specific culture medium containing: RPMI, basic fibroblast growth factor, epidermal growth factor, leukemia inhibitory factor and retinoic acid. Three lineages were used: melan-a, TM1 and TM5. Both melanoma lineages remained viable for 8 consecutive months in culture, melan-a lineage did not survive the changes within the microenvironment and selection with greater adaptive capacity was achieved. These cells presented some characteristics of stem cells and relationship with malignancy. Results: These cells presented certain characteristics, including the formation of adherent or non-adherent spheres, quiescence, survival, expression of stem cells molecules and transdifferentiation in other cellular types. We called these TM1 dif and TM5 dif cells “fibroblasto-like, melanocyte-like, and neural-like.” We observed that SOX6 is a specific biomarker for these cells as its expression was totally lost during the growth of long-term cultures. In vivo , tumors formed by TM5 dif had higher malignancy with greater growth of the lesion and ulceration than control tumors (TM5ctr). Conclusion: Our findings show that melanoma lineages, grown with specific media, in long-term culture, present a good protocol for the isolation of a subpopulation with some characteristics and behavior of stem cells. This can contribute to a better understanding of the role these cells play in melanomagenesis.