Abstract B066: Elucidating the impact of ascites on high grade serous ovarian cancer through in vitro multi-model characterization

Abstract High grade serous ovarian cancer (HGSOC) is one of the most lethal gynecological neoplasia worldwide, due to late diagnosis, high relapse rate and drug resistance. At the time of the diagnosis, HGSOC patients frequently present ascites with intraperitoneal tumor dissemination. Metastasis occurs through the shedding of cells from the primary tumor and movement to the peritoneal cavity, with the generation of ascites, where cells can grow in the absence of adhesion and eventually adhere to distant tissues. In this context, malignant ascites acts as a source of soluble factors which provide a pro-inflammatory, immunosuppressive and tumour-promoting microenvironment for tumoral cells in the peritoneum, contributing to tumor progression. Thus, understanding the influence of ascitic factors on tumoral cells would allow to identify pathogenetic mechanisms associated to metastasis, cancer stemness and chemoresistance, and be crucial for target discovery and drugs development. Our approach is based on the use of 2D and 3D patient-derived in vitro culturing models obtained from ascites of HGSOC patients, cultured in parallel in the standard conditions and with the supplementation of ascitic fluid. Specifically, we compared freshly isolated ascites tumor cells (i. e. never put in culture), 2D primary cells and two types of 3D spheroids, as models that enrich for ovarian cancer stem cells (CSCs), namely bulk spheroids and single-cell Metastatic Ovarian Cancer Spheroids (sMOCS) (Velletri, Villa, Cilli, Barzaghi et al. 2021). First, we investigated the role of ascitic fluid in supporting the growth of our models, recreating the peculiar tumor microenvironment of peritoneal ascites: we showed an increase in proliferation rate, propagability, sphere forming efficiency and dimension in the presence of ascitic fluid. Also, we performed bulk RNAseq analysis showing that ascitic fluid supplementation allows to preserve the metabolic status of fresh samples, typically lost in standard culturing conditions. In parallel, 2D cells and 3D spheroids showed a model-specific effect of ascites’ supplementation. In 2D primary cells it caused the downregulation of genes involved in the biosynthesis of cholesterol and in inflammatory response, while in 3D spheroids it induced upregulation of pathways involved in proliferation and glycolysis, suggesting a phenotype specific for CSCs. Moreover, our data allowed the scoring of CSC-related genes, upregulated in our 3D models compared to fresh ascites and 2D cells, and ascites-dependent genes, as they are up/downregulated in 2D cells and/or spheroids in the presence of ascitic fluid. These results shed light on the specific effects of ascites acting as microenvironment on tumor cells, highlighting its relevance for in vitro patient-derived models to better capture tumor features and to improve culturing conditions. Also, they pave the way to the identification of new disease-relevant pathways and targets to be exploited for more refined care of patients. Citation Format: Bianca Barzaghi, Pietro Lo Riso, Marta Rosa Sallese, Carlo Emanuele Villa, Giulia Picco, Alessia Gatto, Ugo Cavallaro, Giuseppe Testa. Elucidating the impact of ascites on high grade serous ovarian cancer through in vitro multi-model characterization abstract. In: Proceedings of the AACR Special Conference on Ovarian Cancer; 2023 Oct 5-7; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84 (5 Suppl₂): Abstract nr B066.