Melatonin blunts the tumor-promoting effect of cancer-associated fibroblasts by reducing IL-8 expression and reversing epithelial-mesenchymal transition

Most studies on melatonin have focused on tumor cells but have ignored the tumor microenvironment (TME), especially one of its important components, the cancer-associated fibroblasts (CAFs). Therefore, we attempted to explore the role of melatonin in TME.We investigated the regulatory role of melatonin in the tumor-promoting effect of CAFs and its underlying mechanism by using cell and animal models.CAFs promoted tumor progression, but melatonin weakened the tumor-promoting effect of CAFs. Compared with tumor cells, IL-8 was mainly expressed in CAFs. CAFs-overexpressing IL-8 induced the epithelial-mesenchymal transition (EMT) of tumor cells, and a positive crosstalk was observed between CAFs and tumor cells undergoing EMT, thereby further promoting the IL-8 expression. Melatonin suppressed this crosstalk by inhibiting the NF-κB pathway, thereby impeding the IL-8 expression from CAFs. Importantly, melatonin reversed CAFs-derived IL-8-mediated EMT by inhibiting the AKT pathway. Melatonin was found to directly and indirectly inhibit tumor progression.Our research reveals the potential action mechanism of melatonin in regulating the CAF-tumor cell interaction and suggests the potential of melatonin as an adjuvant of tumor therapy.