Abstract 6568: Extracellular vesicles containing circular RNAs derived from cancer-associated fibroblasts enhance adhesion and tumor formation of gastric cancer cells in the peritoneal tissues

Abstract Purpose: The poor prognosis of gastric cancer (GC) patients is strongly associated with peritoneal recurrence. Clinically, a high level of cancer-associated fibroblast (CAF) accumulation correlates with an increased risk of peritoneal recurrence after gastric cancer resection. This observation suggested that CAFs may establish metastatic niches in peritoneal tissues, distant from the primary GC. Extracellular vesicles (EVs) have been identified as key transporter for stable communication between donor and recipient cells, even over long distances. Taken together, CAF-derived EV may play a crucial role in creating a metastatic precondition at the mesothelial cells lining the peritoneal tissue. Understanding the mechanisms underlying this process may provide new insight into therapeutic strategies for preventing peritoneal recurrence in GC patients. Methods: We collected formalin-fixed paraffin-embedded (FFPE) primary GC tissues from the patients who developed peritoneal recurrence (PR group, n=5), and patients without recurrence during follow-up (Non-PR group, n=5). CAF accumulation was assessed using Mason’s trichrome staining, and circular RNA (circRNA) arrays were performed on those tissues. The expression of candidate circRNAs in cell lysates and EVs from various GC cell lines and non-cancerous cells including CAFs using qRT-PCR. The effect of CAF-derived EVs on the adhesion between mesothelial cells and cancer cells was evaluated via adhesion assay. Furthermore, CAF culture media and cancer cells were injected into the mouse peritoneum to assess the number of tumor nodules formed. Results: We observed that CAFs are more significantly accumulate in GC tissues of the PR group compared to the Non-PR group. Six circRNAs were identified as being more abundant in the PR group based on the circRNA array. Among those, that circTSSC2, circALG1, and circALG1L2 were more abundant in CAF cell lysate and CAF-derived EVs compared to GC cells, mesothelial cells, and other immune cells. The resistance to treatments with actinomycin D and RNAse R and the Sanger’s sequencing confirmed the circular structure of those RNAs. CAF-derived EVs were shown to enhance adhesion between mesothelial cells and cancer cells in our experimental models. Additionally, CAF-conditioned media significantly increased the number of tumor nodules formed in the mouse peritoneum. Conclusions: This study suggests that the EVs including specific circRNAs, secreted by CAFs accumulated in primary GC tissues, may contribute to the formation of a pre-metastatic niche in peritoneal tissues of GC patients. Those CAFs-derived EVs could serve as predictive markers for peritoneal recurrence after GC resection and as therapeutic targets to mitigate the risk of peritoneal metastatic recurrence. Citation Format: Yulim Lee, Hoon Hur, In-Hye Ham. Extracellular vesicles containing circular RNAs derived from cancer-associated fibroblasts enhance adhesion and tumor formation of gastric cancer cells in the peritoneal tissues [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 6568.