Epigenetic reprogramming of the metastatic melanoma phenotype by the microenvironment. (2006)

CS13-02 Human metastatic melanoma cells express a dedifferentiated, plastic phenotype, which may serve as a selective advantage, because melanoma cells invade various microenvironments. Over the last three decades, there has been an increased focus on the role of the tumor microenvironment in cancer progression, with the goal of reversing the metastatic phenotype. Using an embryonic chick model, we explored the possibility of reverting the metastatic melanoma phenotype to its cell type of origin, the neural-crest-derived melanocyte. GFP-labeled adult human metastatic (amelanotic) melanoma cells were transplanted in ovo adjacent to host chick promigratory neural crest cells and analyzed 48- to 96 hours after egg reincubation. Interestingly, the transplanted melanoma cells do not form tumors. Instead, we find that transplanted melanoma cells invade surrounding chick tissues in a programmed manner, distributing along host neural-crest-cell migratory pathways. The invading melanoma cells display neural-crest-cell-like morphologies and populate host peripheral structures, including the branchial arches, dorsal root and sympathetic ganglia. Analysis of the melanocyte-specific phenotype marker (Melan-A; MART-1) and neuronal marker (Tuj1) revealed a subpopulation of melanoma cells that invade the chick periphery and express MART-1 and Tuj1. Our results demonstrate the ability of adult human metastatic melanoma cells to respond to chick embryonic environmental cues, a subset of which may undergo a reprogramming of their metastatic phenotype. This model has the potential to provide insights into the regulation of tumor cell plasticity by an embryonic milieu, which may hold significant therapeutic promise. Based on the findings demonstrating the tumor-suppressive effect of the chick embryonic microenvironment on human metastatic melanoma cells, we further hypothesized that the microenvironment of human embryonic stem cells (hESCs) might have similar potential to reprogram melanoma tumor cells to assume a melanocyte-like phenotype. Thus, as proof-of-concept, we developed a 3-D model to explore the potential epigenetic effects of the hESC microenvironment on human metastatic melanoma cells. The experimental approach involved seeding H1 or HSF-6 hESCs onto a 3-D Matrigel matrix for three to four days, removing the cells, and washing the matrix, resulting in a denuded, preconditioned 3-D matrix (CMTX Matrigel). C8161 human amelanotic metastatic cutaneous melanoma cells were seeded onto the hESC preconditioned matrices or onto unconditioned (control) Matrigel for three to four days and then examined for changes in cellular morphology and the expression of a melanocyte phenotype marker, Melan-A. In addition, invasion assays were conducted in order to measure the ability of the hESC microenvironment to modulate melanoma cell function. Using this methodology, we determined that the hESC microenvironment can reprogram the phenotype of aggressive amelanotic melanoma cells to that of less invasive, Melan-A producing cells. These findings highlight the potential utility of the 3-D matrix model as a tool for examining the ability of the hESC microenvironment to influence cell fate and possibly reprogram the metastatic phenotype.