Impact of melanomic extracellular vesicles in the metastatic process of uveal melanoma

Abstract

Purpose : Uveal melanoma is the most common primary intraocular tumor in adults and arises from the transformation of melanocytes. Despite the treatment of the eye tumor, the survival of patients is greatly reduced due to the development of metastases to the liver. Extracellular vesicles (EVs) are released by cancer cells, which allow oncoproteins or genetic material to be transferred to distant cells in order to modify their microenvironment and promote the spread of cancer. Our hypothesis is that EVs from the ocular tumor prepare the hepatic stroma for metastatic cell colonization via endothelial cells and by activating hepatic stellate cells. Our study aims to characterize the melanocytic and melanomic EVs and to study their impact on the hepatic microenvironment and their interactions with liver cells.

Methods : EVs were isolated from uveal melanoma cells and melanocytes by differential centrifugation. Their concentration/size were characterized by Western immunoblotting, high-sensitivity flow cytometry and cryogenic electron microscopy using exosomal or melanomic markers. The mechanisms of internalization of EVs in hepatic stellate cells and endothelial cells have been investigated by confocal microscopy using inhibitors of endocytosis pathways. The contractility of stellate cells on more or less rigid hydrogels and the tubular organization of endothelial cells on Matrigel post-exposure to melanomic EVs were determined by traction force microscopy or time-lapse. The selective biodistribution of EVs in organs was studied by fluorescence imaging in mice.

Results : The extravesicular fraction of uveal melanoma cells and melanocytes contained exosomes and microvesicles. The stellate cells that had internalized the melanomic EVs were more contractile, while the endothelial cells developed capillary-like tubular networks faster. Melanomic EVs were mainly accumulated in the liver and lungs of mice.

Conclusions : We have demonstrated that the extravesicular signaling from uveal melanoma cells activates hepatic stellate cells, which become more contractile. Melanomic EVs also have proangiogenic potential. The discovery of melanoma-specific proteins on the surface of the EVs of metastatic patients could lead to the development of new imaging modalities for micrometastases or drug vectors for targeted delivery to liver metastases.

This is a 2021 ARVO Annual Meeting abstract.