Abstract 4320: Ovarian cancer persister cells are characterized by enhanced ER stress gene expression correlating with poor survival
Authors: Böpple Kathrin , Dong Meng , Kleih Markus , Gaißler Andrea , Oren Yaara , Henry Whitney S. , Oren Moshe , Aylon Yael , Winkler Bernd , Regev Aviv , Weinberg Robert A. , Kopp Hans-Georg , Aulitzky Walter E. , Essmann Frank 
Published: September 2020

Abstract
75% of women suffering from ovarian cancer are diagnosed at late stage of the disease often associated with cancer cell infiltration into the peritoneal cavity. Standard therapy is tumor resection and subsequent platin-based chemotherapy. Relapse is frequently observed caused by persisting cancer cells. Persister cells comprise a therapy-tolerant subpopulation of cancer cells and repeated therapies presumably select for increased tolerance. The present project aims to find molecular markers for the identification and targeted eradication of persister ovarian cancer cells.
Persister cells of the cisplatin-sensitive high-grade serous ovarian cancer cell line, OVCAR-3, were selected after cisplatin incubation with clinically relevant doses. Individual clones were isolated from control or cisplatin challenged OVCAR-3 cells. A subpopulation of the resulting clonal persister cells showed a distinct morphological phenotype characterized by increased migration and high viability in short- and long-term survival after cisplatin treatment. A significant upregulation (p&lt;0.001) of the endoplasmic reticulum (ER) stress marker, ATF3, was identified by RNA sequencing and this ER stress phenotype is maintained for more than 20 passages.
Additionally, the ovarian cancer OVCAR-8 luciferase reporter cell line was transduced with the “Watermelon” (WM) library [1]. The WM library is a complex barcode library that enables simultaneous tracing of cell lineage and the cellular transcriptional and proliferative states. To study cancer relapse in a CDX model, WM-labelled OVCAR-8-Luc cells were injected into mice and pulse-treated with carboplatin. Single cell RNA sequencing of 900 cells isolated from solid metastases, ascites and treatment-naïve mice revealed an increase in multiple ER stress markers including ATF3, ATF4, JUN and XBP1 in the most abundant solid relapse lineages.
Furthermore, analysis of clinical data from GEO, EGA and TCGA showed that low ATF3 expression is associated with increased 5-year-survival of patients with high-grade serous ovarian cancer (Logrank p=6.3e-6).
We found that increased ER stress correlates with survival of cancer persister cells and incidence of metastases. This phenomenon was observed in cell lines, a CDX model and clinical data from human ovarian cancer samples. We propose ER stress response, exemplified by ATF3, as a molecular marker to identify and therapeutic targeting of ovarian cancer persister cells.
[1] Metabolic switching underlies the ability of cancer persister cells to cycle under drug treatment, Oren Y et al., unpublished
Citation Format: Kathrin Böpple, Meng Dong, Markus Kleih, Andrea Gaißler, Yaara Oren, Whitney S. Henry, Moshe Oren, Yael Aylon, Bernd Winkler, Aviv Regev, Robert A. Weinberg, Hans-Georg Kopp, Walter E. Aulitzky, Frank Essmann. Ovarian cancer persister cells are characterized by enhanced ER stress gene expression correlating with poor survival [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4320.