Exosomes from tumor-associated neutrophils suppress ferroptosis and confer chemoresistance in gastric cancer via miR-9-3p/ACSL4 axis.

Exosomes are essential mediators of cellular communication and plays important roles in cancer. In addition to exosomes from tumor cells, the recent studies suggest that exosomes from tumor microenvironment (TME) cells are also critically involved in tumor progression. Tumor-associated neutrophils (TANs) represent a major component of TME cells and have active roles in tumor progression, while the function of their derived exosomes has not been well understood thus far. In this study, we discovered that exosomes from N2 TANs promoted the resistance of gastric cancer to chemotherapy by suppressing ferroptosis. Exosomes from N2 TANs were enriched in miR-9-3p, which could be transferred to gastric cancer cells to inhibit ACSL4 expression. Exosomes from miR-9-3p depleted N2 TANs showed a decreased effect on suppressing erastin-induced ferroptosis. Exosomes derived from N2 TANs antagonized the ferroptosis-promoting effects of ACSL4 overexpression in gastric cancer cells. Additionally, we found that exosomes from N2 TANs protected gastric cancer cells from ferroptosis induced by oxaliplatin, a commonly used drug for gastric cancer therapy, which could be rescued by targeted inhibition of miR-9-3p both in vitro and in vivo. The upregulation of miR-9-3p in N2 TANs was dependent on the activation of NF-κB pathway by gastric cancer cells-derived exosomes. Moreover, we revealed that the expression level of miR-9-3p was higher in human gastric cancer tissues than normal tissues and was negativity associated with patient survival. Conclusively, we reported a previous unclarified role of N2 TANs in chemoresistance via miR-9-3p-enriched exosomes-mediated downregulation of ASCL4 and the consequent suppression of ferroptosis, which may provide a new biomarker and therapeutic target for gastric cancer.