Neutrophils exposed to a cholesterol metabolite secrete extracellular vesicles that promote epithelial-mesenchymal transition and stemness in breast cancer cells.

Breast cancer is very prevalent. Although detection and treatment of primary disease has improved significantly, 20-30 % of patients will develop recurrent metastatic disease; this stage being associated with poor survival. Small extracellular vesicles (sEVs) are emerging as critical mediators of intercellular communication in the tumor microenvironment (TME). Here, we investigate the mechanisms by which sEVs derived from neutrophils treated with the cholesterol metabolite, 27-hydroxycholesterol (27HC), influence breast cancer progression. Interestingly, sEVs released from 27HC treated neutrophils enhanced epithelial-mesenchymal transition (EMT) and stem-like properties in breast cancer cells. This resulted in a striking loss of adherence, increased migratory capacity and resistance to cytotoxic chemotherapy. When exploring the potential mechanism, we found that EVs from 27HC-treated neutrophils had altered microRNAs (miR) expression. Decreased miRs within 27HC-sEVs, particularly of the let-7 family, resulted in activation of the WNT/β-catenin signaling pathway in recipient cancer cells, suggesting that this may be a predominant pathway for adopting stem-like properties. Our findings underscore a novel mechanism by which a cholesterol metabolite can modulate neutrophils and thereby contribute to breast cancer pathophysiology through EV-mediated intercellular communication. This work represents the first steps in developing this axis for potential therapeutic interventions.