Abstract 3037: Dissecting treatment resistance in patients with ovarian cancer and PDX-models using single-cell RNA-sequencing
Authors: Izar Benjamin , Tirosh Itay , Stover Elizabeth , Rotem Asaf , Shah Parin , Cuoco Mike , Rodman Chris , Liu Joyce , Matulonis Ursula , Rozenblatt-Rosen Orit , Garraway Levi , Regev Aviv 
Published: July 2017

Abstract
Background: Ovarian cancer (OvCa) is frequently associated with malignant effusions, which are complex ecosystems with heterogeneous populations of malignant cells and non-malignant cells. Bulk RNA-seq or whole-exome sequencing (WES) only reflect average cellular behavior and thereby mask intrinsic cell diversity with potential relevance for treatment resistance.
Approach: To overcome some of these barriers, we applied single-cell RNA-sequencing (scRNA-seq) to malignant and non-malignant cells isolated from patients with platinum treatment resistant disease. Furthermore, we used patient-derived xenograft (PDX) cohorts, in which we isolated cells for scRNA-seq from vehicle tumors (VEH), treated the other models with carboplatin, and harvested cells at the time of minimal residual disease (MRD) or disease progression (PROG).
Results: To date, we have profiled ~12000 single cells from 12 patients with treatment naïve (n=3) or platinum-resistant disease (n=9), including sequential sampling in 3 patients with resistant disease. We observed significant inter- and intra-individual transcriptional heterogeneity in malignant cells. A recurrent pattern across resistant patients was the differential expression of inflammatory pathways in a subset of cells. In a patient with three consecutive specimens, we observed increasing accumulation of cells expressing a cell state characterized by tumor necrosis factor alpha (TNF-a) signaling, Importantly, these cells were genetically identical to the entire population, supporting the hypothesis that non-encoded mechanisms conferred treatment resistance. In a BRCA-mutant patient, unbiased analysis identified a stemness program in a subpopulation of cells, which was genetically identical to other cells, indicating phenotypic conversion. To systemically interrogate mechanisms of resistance to platinum therapy, sequenced single cells isolated from PDX models at three time points (VEH, MRD and PROG). In a BRCA-WT PDX model, resistant cells isolated at MRD and PROG shared a transcriptional program that was dominated by expression of a STAT3 program. Ex vivo cultures from platinum-resistant patients were exquisitely sensitivity to JAK/STAT3-inhibitor. Live cell imaging revealed that STAT3-inhibition prevented spheroid formation, attachment and clearance through a mesothelial monolayer in vitro.
Conclusion: Our results indicate that non-encoded mechanisms play an important role in the development of treatment resistance in ovarian cancer. Our initial studies indicate an important role of inflammatory pathways in treatment resistance, in particular STAT3 signaling, which can be overcome with specific inhibitors at nanomolar concentrations. These data suggests that single-cell profiling can be performed on clinical ovarian cancer specimens and may yield novel therapeutic avenues for patients with treatment-resistant ovarian cancer.
Citation Format: Benjamin Izar, Itay Tirosh, Elizabeth Stover, Asaf Rotem, Parin Shah, Mike Cuoco, Chris Rodman, Joyce Liu, Ursula Matulonis, Orit Rozenblatt-Rosen, Levi Garraway, Aviv Regev. Dissecting treatment resistance in patients with ovarian cancer and PDX-models using single-cell RNA-sequencing [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3037. doi:10.1158/1538-7445.AM2017-3037