Abstract 2418: Copy number variation status of DNA in extracellular vesicles as novel biomarkers of high-grade serous ovarian carcinoma

Abstract Objective: Ovarian cancer is a gynecologic malignancy with a dismal prognosis due to the lack of accurate methods for early diagnosis methods and effective therapies. High-grade serous ovarian carcinoma (HGSOC) is the most common subtype and copy number variations (CNVs) are the dominant genomic events in HGSOC. Extracellular vesicles (EVs) circulate in body fluids and carry pathological genomic information positively. In this study, we evaluated the significance of EV-DNA as novel biomarkers for HGSOC patients. Methods: A total of 124 samples from HGSOC patients and cell lines were analyzed. EVs were isolated using the ultracentrifuge method. Comprehensive CNV statuses were analyzed by whole genome sequencing (WGS) and SNP array. In reference to the Ovarian Cancer Moon Shot database, 30 dominant CNVs in HGSOC were selected as dominant targets for analysis by droplet digital PCR (ddPCR). For predicting the response to PARP inhibitors, HGSOC patients who were treated with olaparib were collected, and DNA was extracted from FFPE tissue at the time of surgery. Results: NTA assays and cryo-electron microscopic analyses showed that the EVs were successfully isolated from all samples. Both WGS and SNP arrays detected correlating CNVs in cell-DNA and EV-DNA for cell lines, and in tissue-DNA and EV-DNA in ascites for patients. The CNV status was also accurately measured by ddPCR. Copy numbers of RAD51, BRCA1, AKT2, CCNE1, and MSH6 were significantly higher in malignant tissue than in benign tissue (p<0.0001, p<0.0001, p=0.0012, p=0.002. p=0.0328, respectively), and were detectable in EV-DNA from ascites. Additionally, the amount of DNA in malignant ascites was significantly higher than in benign ascites (p=0.016), and increased DNA in ascites itself suggested the presence of malignancy. Furthermore, EV-DNA more accurately reflected the CNV status of tumor DNA than cell-free DNA in ascites. Regarding the prediction of PARP inhibitor response, the CNV status in EV-DNA from patients who were treated with olaparib, a PARP inhibitor, demonstrated a marked difference between responders and non-responders. The equation calculated based on the combination of six genes (RB1, GABRA6, CTNNB1, MYC, RAD51, BARD1) could predict the response to olaparib (AUC: 1.0). The selected genes were validated in vitro using EV-DNA, and responders could be identified using the prediction equation calculated from CNV status of the selected genes in EV-DNA from ascites. Conclusion: CNV status of EV-DNA was correctly evaluated and can serve as novel diagnostic and prognostic biomarkers for HGSOC. Citation Format: Ryosuke Uekusa, Akira Yokoi, Kosuke Yoshida, Juntaro Matsuazki, Yusuke Yamamoto, Hiroaki Kajiyama. Copy number variation status of DNA in extracellular vesicles as novel biomarkers of high-grade serous ovarian carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2418.