Intraperitoneal transfer of miR-29b-containing small extracellular vesicles can suppress peritoneal metastases of gastric cancer.

Small extracellular vesicles (sEV) contain various microRNAs (miRNAs) and play crucial roles in the tumor metastatic process. Although miR-29b levels in peritoneal exosomes was markedly reduced in patients with peritoneal metastases (PM), their role has not been fully clarified. In this study, we asked if the replacement of miR-29b can affect the development of PM in murine model. UE6E7T-12, a human bone marrow derived mesenchymal stem cells (BMSCs), were transfected with miR-29b-integrating recombinant lenti-viral vector and sEV isolated from culture supernatants using ultracentrifugation. The sEV contained markedly increased amounts of miR-29b compared with negative controls. Treatment with TGF-β1 decreased the expression of E-cadherin and calretinin with increased expression of vimentin and fibronectin on human peritoneal mesothelial cells (HPMCs). However, the effects were totally abrogated by the adding miR-29b-rich sEV. The sEV inhibited proliferation and migration of HPMCs by 15% (p< 0.005, n=6), 70% (p< 0.005, n=6), and inhibited adhesion of NUGC-4 and MKN45 to HPMCs by 90 % (p< 0.0001, n=5) and 77% (p< 0.0001, n=5), respectively. MiR-29b-rich murine sEV were similarly obtained using mouse BMSCs and examined for in vivo effects with a syngeneic murine model using YTN16P, a highly metastatic clone of gastric cancer cell. Intraperitoneal (IP) transfer of the sEV for every 3 days markedly reduced the number of PM from YTN16P in the mesentery (p< 0.05, n=6) and the omentum (p< 0.05, n=6). BMSC-derived sEV are a useful carrier for IP administration of miR-29b which can suppress the development of PM of gastric cancer.