Prevention of melanoma brain colonization by inhibition of cytokines secretion from activated astrocytes

Introduction

The brain microenvironment (BM) consisting of astrocytes, microglia, neurons and brain endothelial cells sustains the normal brain functions and the structures of the cerebral capillaries that form the blood brain barrier (BBB). During tumor progression, malignant cells release vascular endothelial growth factor (VEGF) and other cytokines that increase the permeability of blood vessels allowing them to intravasate into the circulation. In addition, the cells can take advantage of the patho-physiology of the tumor angiogenenic leaky blood vessels at distant organs and extravasate from them at inflamed sites. Such activated site can be the brain parenchyma which may become a pro-inflammatory metastatic niche [1-3]. Although little is known about the mechanisms and the factors that contribute to the metastatic process, in such conditions, astrocytes mediating a neuroinflammatory response release pro-inflammatory cytokines that disturb the integrity of the BBB, enhancing the permeability of the capillary endothelium and preparing a metastatic niche for melanoma colonization[4].

Material and methods

We hypothesize that melanoma cells may regulate the BM by altering the astrocytes secretome. Consequently, we established three melanoma brain metastasis mouse models that present a pro-inflammatory microenvironment and a pro-metastatic niche preceding the colonization of melanoma to the brain. siRNA targeting specific chemokine, neutralizating antibody and the CRISPR/Cas9 system were used to downregulate the expression and secretion of chemokines for the further in vitro studies.

Results and discussion

We identified MCP-1, a pro-inflammatory chemokine, implicated in the paracrine interaction between melanoma cells and the brain. The positive staining for GFAP and MCP-1 in the tumor area suggests a cooperation between melanoma and the tumor microenvironment, in which MCP-1 plays a pro-tumorigenic role during cell migration. Astrocytes-secreted MCP-1 expression increases when co-cultured with melanoma cells or their conditioned media (CM). Downregulation of MCP-1 using siRNA, neutralizing antibody or CRISPR/Cas9 system leads to decreased migration of melanoma cells in vitro.Moreover, neutralizing antibody -targeting MCP-1 reduces melanoma invasion in matrigel towards sprouting aortas.

Conclusion

Consequently, investigating the changes in melanoma and astrocytes gene-expression could be the key for interfering and preventing melanoma colonization to the brain