Extracellular vesicles secreted by triple-negative breast cancer stem cells trigger premetastatic niche remodeling and metastatic growth in the lungs

Tumor secreted extracellular vesicles (EVs) are potent intercellular signaling platforms. They are responsible for the accommodation of the premetastatic niche (PMN) to support cancer cell engraftment and metastatic growth. However, complex cancer cell composition within the tumor increases also the heterogeneity among cancer secreted EVs subsets, a functional diversity that has been poorly explored. This phenomenon is particularly relevant in highly plastic and heterogenous triple-negative breast cancer (TNBC), in which a significant representation of malignant cancer stem cells (CSCs) is displayed. Herein, we selectively isolated and characterized EVs from CSC or differentiated cancer cells (DCC; EVs(CSC) and EVs(DCC), respectively) from the MDA-MB-231 TNBC cell line. Our results showed that EVs(CSC) and EVs(DCC) contain distinct bioactive cargos and therefore elicit a differential effect on stromal cells in the TME. Specifically, EVs(DCC) activated secretory cancer associated fibroblasts (CAFs), triggering IL-6/IL-8 signaling and sustaining CSC phenotype maintenance. Complementarily, EVs(CSC) promoted the activation of alpha-SMA+ myofibroblastic CAFs subpopulations and increased the endothelial remodeling, enhancing the invasive potential of TNBC cells in vitro and in vivo. In addition, solely the EVs(CSC) mediated signaling prompted the transformation of healthy lungs into receptive niches able to support metastatic growth of breast cancer cells.