Triple-negative breast cancer-derived extracellular vesicles promote a hepatic pre-metastatic niche via a cascade of microenvironment remodeling.

Triple negative breast cancer (TNBC) patients often develop metastases in visceral organs including the liver but the detailed molecular mechanisms of TNBC liver metastasis is not clearly understood. In this study, we tried to dissect the process of pre-metastatic niche formation in liver by using patient-derived xenograft (PDX) models of TNBC with different metastatic propensity. RNA sequencing of TNBC PDX models that successfully metastasized to liver showed up-regulation of Cx3cr1 gene in the liver microenvironment. In syngeneic breast cancer models, the Cx3cr1 up-regulation in liver preceded the development of cancer cell metastasis and was the results of recruitment of CX3CR1-expressing macrophages. The recruitment was induced by the CX3CL1 production from the liver endothelial cells and this CX3CL1-CX3CR1 signaling in the pre-metastatic niche resulted in up-regulation of MMP9 that promoted macrophage migration and cancer cell invasion. Additionally, our data suggest that the extra-cellular vesicles derived from the breast cancer cells induced the TNF-alpha expression in liver which leads to the CX3CL1 up-regulation. Lastly, the plasma CX3CL1 levels in 155 breast cancer patients were significantly associated with development of liver metastasis. Implications: Our data provides previously unknown cascades regarding the molecular education of pre-metastatic niche in liver for TNBC.