Abstract AP29: A SINGLE CELL RNA-SEQUENCING APPROACH TO UNCOVERING HUMAN OVARIAN TUMOR AND IMMUNE CELL HETEROGENEITY, AND THEIR RESPONSE TO MULLERIAN INHIBITING SUBSTANCE USING PATIENT ASCITES SAMPLES
Authors: Mohan Raghav , Kano Motohiro , Saatcioglu Hatice , Takahashi Nobuhiro , Zhang LiHua , Nagykery Nicholas , Poulo Joy , Donahoe Patricia K , Pepin David 
Published: June 2021

Abstract
Mullerian inhibiting substance (MIS) has been shown to inhibit the growth of a stem-like population of ovarian cancer cells both in vivo and in vitro. We have previously shown that its receptor, MISRII, is expressed in a majority of ovarian serous adenocarcinomas. However the determinants of response and the pathways elicited by MIS treatment have been difficult to elucidate due the heterogeneity of tumors both across the patient population and within each sample. To address this complexity we have developed an assay in which patient cancer cells and immune cells are isolated from ascites of recurrent chemoresistant ovarian cancer and incubated in cleared supernatant from autologous ascites for 24h in presence of drug (MIS 10ug/ml) or vehicle control (N=3). This protocol allows for short-term culture in conditions nearly identical to the peritoneal environment. A parallel experiment was conducted using matching pure primary cancer cell lines (derived from the ascites samples) treated in media (MIS 10ug/ml or vehicle for 24h), but lacking immune cells and soluble factors otherwise present in ascites. The effect of treatment on cell sates, and the interaction between immune cells and cancer cells was interrogated by clustering analysis of single cell RNA sequencing (inDROP). We uncovered a high degree of heterogeneity of expression of known and novel markers related to epithelial-mesenchymal states and stemness markers, both across patients and within patient samples, suggesting dynamically coexisting cancer cell states and hierarchies that are patient-specific. These markers were validated in vitro across a larger cohort of primary patient cells lines (N=12) grown as tumor spheroids (with and without MIS 10ug/ml for 24h). Additionally, we have identified a varying abundance of immune cell types (Macrophages, dendritic cells, NK cells, T cells, B cells), and an unexpected effect of MIS on gene expression in both macrophage and cancer cells. The knowledge gained on the response rate in patients, and the biomarkers identified in this study will be fundamental for the successful translation of MIS to the clinic, and further our understanding of the role of non-cell autonomous inhibition of cancer cells by immune components and patient heterogeneity.
Citation Format: Raghav Mohan, Motohiro Kano, Hatice Saatcioglu, Nobuhiro Takahashi, LiHua Zhang, Nicholas Nagykery, Joy Poulo, Patricia K Donahoe, David Pepin. A SINGLE CELL RNA-SEQUENCING APPROACH TO UNCOVERING HUMAN OVARIAN TUMOR AND IMMUNE CELL HETEROGENEITY, AND THEIR RESPONSE TO MULLERIAN INHIBITING SUBSTANCE USING PATIENT ASCITES SAMPLES [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr AP29.