Extracellular Vesicles From a Model of Melanoma Cancer-Associated Fibroblasts Induce Changes in Brain Microvascular Cells Consistent With Pre-Metastatic Niche Priming.

Malignant melanoma has one of the lowest 5-year survival rates of any cancer and is characterised by its high invasiveness and metastatic potential, with especially poor outcomes in patients who develop brain metastases. Crosstalk between melanoma cells and cells of the tumour microenvironment (TME), including cancer-associated fibroblasts (CAFs), is a central driver of disease progression. While the role of melanoma-derived small extracellular vesicles (sEVs) in reprogramming stromal cells has been well documented, the reciprocal effects of CAF-derived sEVs remain less clear. Here, using an in vitro model of melanoma CAFs, we show that CAF sEVs alter melanoma cells and fibroblasts to promote oncogenic traits and remodel endothelial cells, including brain microvascular cells, in ways consistent with early pre-metastatic niche (PMN) changes. Multi-omics cargo profiling revealed significant differential expression of proteins and RNAs linked to extracellular matrix organisation, vascular remodelling, and patient outcomes, with functional validation identifying THBS1 as an EV cargo that restrains endothelial sprouting while potentially promoting barrier destabilisation. Together, these findings suggest that CAF-derived sEVs contribute to local and distal PMN remodelling, highlight their potential as therapeutic targets, and identify EV cargoes with promise as circulating biomarkers in melanoma.