Malignant melanoma is a heterogeneous tumor, originated from the transformation of melanocytes, which are cells that normally produce melanin in the skin and distribute to neighboring cells. However, unlike melanocytes, melanoma cells do not secrete the pigment, which is stored in the cytoplasm in organelles called melanosomes, conferring the hyperpigmentation characteristic of melanomas.
The heterogeneity is a characteristic of melanomas, due to genetic and epigenetic mutations that modify cell proliferation, differentiation, and cell death. Indeed, it is postulated that melanomagenesis comprises processes of de-differentiation of transformed and mature melanocytes that undergo anaplasia.
Melanoma is the most deadly and most aggressive among all skin tumors accounting for 90% of skin cancer deaths. Characterized by two phases, the radial growth phase (RGP), in which there is no metastasis, and then leads to the vertical growth phase (VGP), where metastases occur. Increasing evidence suggests that tumor progression is critically associated with the acquisition of an epithelial-mesenchymal transition (EMT) phenotype, which allows tumor cells to acquire the ability to migrate and to invade adjacent tissues and thereby license these cells for metastasis in distant locations.
Some studies have demonstrated the reversal of the phenotype of human metastatic melanoma cells by the embryonic microenvironment, through a cellular reprogramming. The use of reprogramming is a good starting point, which may contribute significantly to the understanding of the main molecular mechanism underlying the pathogenesis of this aggressive tumor and to develop new biological strategies based on anticancer therapies. Recently, it has been demonstrated that tumor cells can be reprogrammed into an induced pluripotent state (iPS) by transfection with specific transcription factors. A study initiated by Takahashi et al. 2006 and 2007, which demonstrated that it is possible to transdifferent (murine and human) fibroblasts into induced pluripotent cells (iPS) by viral transfection of transcription factors such as Oct4, SOX2, c-Myc, and Klf-4, after which cells were able to take on characteristics of pluripotent stem cells.
The objective of this work was to establish a model to study the possible cellular mechanisms of loss of malignancy through the reprogramming of tumor cells into“normal” induced pluripotent stem cells (iPS). We used non-viral DNA minicircles containing the four factors of reprogramming Oct4, Sox2, Lin28, Nanog (OSLN) and the green fluorescent protein (GFP) reporter gene to reprogram B16F10 murine melanoma cells. This technique is advantageous because it allows us to verify the response of tumor cells after reprogramming in the absence of genomic modification, viral sequences, effectively mitigating safety concerns.
Our data imply that, as a result of reprogramming the B16F10 cells, less aggressive murine melanoma reprogrammed cancer cells can be obtained which we called the “Murine Melanoma Reprogrammed Cancer Cells” (MMRCC). These cells represent an interesting model for studying the mechanism of cell malignancy, as well as providing a new tool for screening cancer drugs. However, neither the morphology nor the expressions of pluripotent stem cell markers are reliable to conclude whether the cells have actually been reprogrammed. Therefore, the three isolated clones, as well as the B16F10 line cells, were injected subcutaneously into the dorsal flanks of mice.
We did not observe the formation of teratomas, which is a proof of the concept of complete reprogramming. But in contrast, tumors formed by MMRCC showed significantly smaller tumors when compared to tumors formed by the parental B16F10 cell line. As well as the analysis showed less necrosis and less phenotypic heterogeneity of tumor cells in the tumors generated by the MMRCC than the B16F10 lineage. Therefore, although reprogramming is incomplete, this leads to the formation of less aggressive tumors. Thus, our data open new perspectives to study heterogeneity and the asymmetric division of tumor cells, which was widely observed in culture.
They suggest a new intermediate point in the reprogramming process, which may serve as the basis for future studies on cancer biology, the association between pluripotency and tumor cells and tumor stem cells.
The study, Murine melanoma cells incomplete reprogramming using non-viral vector was recently published in the journal Cell Proliferation.