Abstract 6517: Extracellular vesicles derived from vaginal bacteria initiate the progression of early phase ovarian carcinoma at fallopian tubes

Abstract [Objective] Microbiota contributes to cancer hallmarks, but the relationship vaginal bacteria and ovarian cancer are entirely unclear. Extracellular vesicles (EVs), including exosomes, play a crucial role in cancer biology, and bacteria secrete EVs, named bacterial EVs (bEV). Recent understanding revealed that high-grade serous carcinoma (HGSC) has raised from fallopian tube epithelial cells (FT cells) but the detailed mechanism how FT cells acquired malignant potential is largely unknown. This study aimed to elucidate the mechanism of initiation of early-phase ovarian carcinoma at fallopian tubes via vaginal bEV. [Methods] For selecting promising bacteria, vaginal bacterial 16s sequencing data were referred to, and the data from 181 patients with ovarian tumors were analyzed. bEVs were directly collected from patients’ fallopian tubes using cellulose nanofiber-based EV sheets (Yokoi A et al. Nat Commun. 2023), and bEV-RNA was extracted. Selected bacteria were cultured with monitoring OD values, and bEVs were isolated using the optimal serial centrifugation method. bEV-RNA were analyzed by small RNA sequencing and validated by qRT-PCR. Functional analyses were performed in vitro and in vivo, and the effect of bEVs on FT cells was investigated. [Results] Based on vaginal bacterial 16s rRNA sequencing, four indigenous common vaginal bacteria were selected. Those bacteria were successfully cultured and cryo-electron microscopy confirmed isolated bEV. Cell viability analysis showed that none of the bEVs affected the proliferation of FT cells. On the other hand, specific Lactobacillus species promoted cell motility (p <0.05), especially in p53 gain-of-function (GOF) cells. Furthermore, treatment of bEV resulted the sloughed-off features of p53-GOF-FT cells on basement membrane components (p <0.05). These phenotypes mimic the actual progression of FT cells implant to ovaries. In in vivo experiments, although vaginal treatment of bacterial bodies did not reach FT, bEVs were incorporated by FT cells, which were confirmed by confocal microscopy imaging. We collected bEVs on FT from 15 ovarian cancer patients using cellulose nanofiber-based EV sheets, and small RNA sequencing for bEV-RNA revealed that the profiles between HGSC and benign patients were different, and specific sequences of Lactobacillus species were detected. mRNA sequencing for FT cells treated with bEV from specific Lactobacillus species showed that gene expression was significantly altered, and IPA/GSEA analyses identified several cancer-related pathways. Target functional genes in FT cells were identified and validated by qRT-PCR. [Conclusions] These results demonstrated the unknown early mechanism of ovarian cancer development by pathogenic bEV exposure, and the new target gene alternation was identified in FT cells as the new therapeutic target. Citation Format: Akira Yokoi, Eri Asano-Inami, Kosuke Yoshida, Yukari Nagao, Masami Kitagawa, Hiroaki Kajiyama. Extracellular vesicles derived from vaginal bacteria initiate the progression of early phase ovarian carcinoma at fallopian tubes [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 6517.