Abstract 2524: MiR-29b may suppress peritoneal metastasis via the effects on peritoneal mesothelial cells as well as on tumor cells

Abstract

Abstract Background: Peritoneal metastasis (PM) frequently occur in patients with gastric cancer with poor prognosis. Peritoneal cavity is lined with monolayer of mesothelial cells (MC) and contains various types of cells and exosomes. MC play an important role in the development of PM through mesothelial-mesenchymal transition (MMT). MiR-29 family is well known as tumor suppressor. However, the role of miR-29s in PM is not well characterized. We have previously reported that miR-29 family in exosome derived from peritoneal fluid was downregulated in patients with peritoneal metastasis of gastric cancer. In this study, we investigated the functions of miR-29s in the process of peritoneal metastasis. Methods: Exosomes were purified from peritoneal fluids of 85 patients with gastric cancer and miR-29 levels in peritoneal exosomes were quantified with RT-PCR using TaqMan Advanced miRNA Assays. Proliferation and migration of human gastric cancer cell lines, MKN45 and NUGC, were examined with MTT and transwell assays, respectively. Human peritoneal mesothelial cells (HPMCs) were isolated by trypsinization of omental tissues obtained from patients undergoing bariatric surgery and cultured in DMEM supplemented with 20% fetal bovine serum. MiR-29b mimic and negative control were transfected by lipofection method using RNAiMAX. MMT was induced by the culture of HPMCs with 10 ng/ml TGF-β. Expressions of cytokeratin and vimentin were evaluated with flow cytometry. Results: The expressions of miR-29a, miR-29b and miR-29c in peritoneal exosomes were all downregulated in 33 patients with PM as compared to those without PM. Transfection of miR-29b mimic significantly decreased the proliferation of MKN45 and NUGC-4 by 22~58% as compared with negative control miRNA (p<0.01). Migration was inhibited more strongly by 84~90% (p<0.01). After 48 hour-culture with TGF-β, HPMCs apparently changed the morphology from round to spindle shape. The expression level of cytokeratin in HPMCs was decreased while vimentin tended to be upregulated by TGF-β. However, transfection of miR-29b, but not control miRNA, significantly suppressed the morphological changes and reduced the expression levels of vimentin with restored expression of cytokeratin, suggesting the inhibition of MMT in HPMCs. Conclusion: MiR-29b suppresses mesenchymal transition of MC as well as of tumor cells. Replacement of miR-29b to peritoneal cavity might be used for the treatment for peritoneal metastasis. Citation Format: Yuki Kimura, Hideyuki Ohzawa, Akira Saito, Naohiro Sata, Joji Kitayama. MiR-29b may suppress peritoneal metastasis via the effects on peritoneal mesothelial cells as well as on tumor cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2524.