Cancer associated fibroblasts-derived exosomes contribute to radioresistance through promoting colorectal cancer stem cells phenotype.

Radioresistance observed in patients with colorectal cancer (CRC) may be related to the presence of cancer stem cells (CSCs), but the underlying mechanism(s) remain unclear. Cancer-associated fibroblasts (CAFs) can regulate the stemness of cancer cells and tumor radiosensitivity. In addition, exosomes have been reported to modify treatment response by mediating cell-cell communication. In this study, we aimed to investigate whether exosomes derived from CAFs (CAF-exosomes) are involved in mediating resistance to radiotherapy in colorectal cancer and to explore the underlying mechanism. We found that CSCs were inherently resistant to cell death induced by radiotherapy. CAF-derived CM promoted clonogenicity and radioresistance of CRC cells. Further investigations revealed that exosomes isolated from CM induced the above effects whereas exosome-depleted CM (solution) was not able to induce clonogenicity and radioresistance. Finally, exosomes could activate transforming growth factor-β (TGF-β) signaling pathway and TGFβ1-neutralizing antibody inhibit this effect and decrease clonogenicity and expression levels of stemness genes. In conclusion,our findings suggest CAFs promote stemness of CRC cells and thus increase radiation resistance. Exosomes derived from CAFs play a crucial role through activating TGF-β signaling pathway in this process.