Extracellular vesicles of carcinoma-associated fibroblasts creates a pre-metastatic niche in the lung through activating fibroblasts

Objectives: Carcinoma-associated fibroblasts (CAFs) have been known to promote cancer progression by modifying the primary tumor microenvironment. We aimed to elucidate the intercellular communication between CAFs and secondary organs in salivary adenoid cystic carcinoma (SACC) metastasis. Methods: Pre-metastatic and metastatic animal models of SACC were established using extracellular vesicles (EVs) from CAFs and SACC cells. Lung fibroblasts (LFs) were treated with EVs and their transcriptomic alterations were identified by RNA sequencing. ITRAQ were performed to analyze EV cargos. TC I-15 was used to inhibit EV uptake by LFs and SACC lung metastasis in vivo. Results: Here, we show that CAF EVs induced lung pre-metastatic niche formation in mice and consequently increased SACC lung metastasis. The pre-metastatic niche induced by CAF EVs was different from that induced by SACC EVs. CAF EVs presented a great ability for matrix remodeling and periostin is a potential biomarker characterizing the CAF EV-induced pre-metastatic niche. We found that lung fibroblast activation promoted by CAF EVs was a critical event at the pre-metastatic niche. Integrin alpha 2 beta 1 mediated CAF EV uptake by lung fibroblasts, and its blockage by TC I-15 prevented lung pre-metastatic niche formation and subsequent metastasis. Plasma EV integrin beta 1 was considerably upregulated in the mice bearing xenografts with high risk of lung metastasis. Conclusions: We demonstrated that CAF EVs participated in the pre-metastatic niche formation in the lung. Plasma EV integrin beta 1 might be a promising biomarker to predict SACC metastasis at an early stage. An integrated strategy targeting both tumor and stromal cells is necessary to prevent SACC metastasis.