Abstract LB156: Identified the ISG15 mediated extracellular vesicles drives ovarian cancer progression and metastasis: extracellular vesicular ISG15 is a potential biomarker and therapeutic target
Authors: Dorayappan Kalpana Deepa Priya , Wagner Vincent , Park Dongju , Newcomer Meghan M. , Lightfoot Michelle DS , Kalaiyarasan Deepika , Sakaue Takahiko , Khadraoui Wafa , Cosgrove Casey , Maxwell Larry J. , Wang Qi-En Wang , O’Malley David , Pollock Raphael E. , Cohn David E. , Karuppaiyah Selvendiran 
Published: April 2023

Abstract
Background & Objective: High-grade serous ovarian cancer (HGSOC) accounts for over 80% of all epithelial ovarian cancer (OC) diagnoses, and the majority of patients with HGSOC are diagnosed with advanced metastatic disease. Aberrant expression of interferon stimulated gene 15 (ISG15) has been demonstrated in human malignancies, and we have identified that ISG15 is highly expressed in HGSOC tumors and peritoneal ascites. This study seeks to determine whether ISG15 contributes to HGSOC progression and metastasis through extracellular vesicle (EVs) secretion.
Method: ISG15 expression was analyzed in ascites samples and primary ovarian cancer cells (POCC) from different patients by ELISA and WB. Cell surface biotinylation assay was done to show the modulation of endo and exocytosis by ISG15 and STAT3. Immunoprecipitation pull down assay was done to demonstrate the interaction of ISG15 with activated STAT3. Confocal microscopy showed the co-localization of STAT3 with the endosome marker TSG101. In-vivo studies were done using bio-luminescence imaging in orthotopic ovarian tumor mouse models to measure tumor progression and metastasis.
Results: ISG15 was found to be significantly elevated in HGSOC metastases (pelvic, mesenteric and diaphragmatic samples) as compared to primary ovarian tumors or benign samples. We observed that ISGylation was increased in POCC cells derived from ascites with increased USP18 expression. Our results confirmed a significant decrease in EV’s secretion in ISG15 KD POCC cells. Mice injected with ISG15 OE -POCC cells showed increased tumor burden when compared to the ISG15Kd cells in mice. Furthermore, we observed a significant reduction of ovarian tumor growth and metastasis in an orthotopic mouse model treated with a small molecule inhibitor-DAP5 that targeted ISG15 or exosome blocker (Amiloride) compared to untreated mice. In addition, we found the expression of ISG15 within the EVs represents a promising development in elucidating prognostic markers for HGSOC patients.
Conclusion: Based on our results, ISG15 expression is elevated in HGSOC patient ascites and metastatic disease sites. The aberrant expression of ISG15 in patient ascites plays a key role in the secretion of EVs carrying ISG15, which contributes to HGSOC progression and metastases. Our study provides the pre-clinical evidence regarding new molecular targets, novel prognostic markers, and innovative therapeutic strategies for HGSOC, aiming to ultimately improve the survival of patients suffering from this disease.
Citation Format: Kalpana Deepa Priya Dorayappan, Vincent Wagner, Dongju Park, Meghan M. Newcomer, Michelle DS Lightfoot, Deepika Kalaiyarasan, Takahiko Sakaue, Wafa Khadraoui, Casey Cosgrove, Larry J. Maxwell, Qi-En Wang Wang, David O’Malley, Raphael E. Pollock, David E. Cohn, Selvendiran Karuppaiyah. Identified the ISG15 mediated extracellular vesicles drives ovarian cancer progression and metastasis: extracellular vesicular ISG15 is a potential biomarker and therapeutic target [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB156.