Abstract B55: Epigenetic reprogramming of mesenchymal stem cells by ovarian carcinoma to facilitate metastasis
Authors: Frisbie Leonard , Fan HuiHui , Pisanic Thomas , Shen Hui , Coffman Lan 
Published: September 2020

Abstract
Ovarian cancer, the most deadly gynecologic cancer, resides within a complex tumor microenvironment that supports cancer growth, survival, and spread. Carcinoma-associated mesenchymal stem cells (CA-MSCs) are stromal stem cells within the ovarian TME that strongly support tumor growth promoting cancer initiation, increasing the cancer stem cell pool and enhancing chemotherapy resistance. We recently demonstrated that ovarian cancer stimulation converts normal tissue-derived MSCs into CA-MSCs. The goal of this work is to investigate the mechanism of cancer-mediated CA-MSC formation. We hypothesize that ovarian cancer stimulation induces the epigenetic reprogramming of MSCs creating CA-MSCs. EPIC array DNA methylation analysis, histone mass spectrometry, and Assay for Transposase-Accessible Chromatin using sequencing (ATACseq) were performed on CA-MSCs derived from ovarian cancer patient samples and normal MSCs derived from benign fallopian tube and omentum. We demonstrate that CA-MSCs have large-scale DNA methylation differences vs. normal tissue MSCs. This DNA methylation pattern is distinct from cancer cells; however, the CA-MSC methylation pattern is represented in the DNA methylation pattern of bulk tumor from clear-cell, endometrioid, and high-grade serous cancers, indicating the importance of stromal contribution to bulk tumor analysis. DNA methylation changes were acquired during the conversion of a normal MSC into a CA-MSC and retained after CA-MSC adipocyte and fibroblast differentiation. Histone mass spectrometry and ATACseq demonstrated enrichment in repressive histone marks and overall decreased ATACseq peaks consistent with altered chromosome accessibility. Integration of DNA methylation, ATACseq, and RNAseq data demonstrates strong correlation between epigenetic changes and transcriptomic changes. Interestingly, cell:cell adhesion pathways were consistently upregulated consistent with a partial mesenchymal-to-epithelial transition (MET). This partial MET engenders CA-MSCs with enhanced tumor cell-binding capacity. Direct tumor cell:CA-MSC binding enhanced ovarian cancer migration, extravasation, and nonadherent survival in vitro and increased ovarian cancer metastasis in vivo. This partial MET may be mediated via WT1, a mediator of MET during development, as knockdown of WT1 prevented the formation of a CA-MSCs while overexpression of WT1 enhances the formation of a CA-MSC. Collectively, we demonstrate ovarian cancer stimulates the epigenetic reprogramming of normal MSCs into CA-MSCs, thus enhancing direct tumor cell binding, which facilitates ovarian cancer metastasis. Further investigation is needed to identify the molecular drivers of this reprogramming to allow the disruption of the protumorigenic TME, which may represent a powerful approach to the treatment of ovarian cancer.
Citation Format: Leonard Frisbie, HuiHui Fan, Thomas Pisanic, Hui Shen, Lan Coffman. Epigenetic reprogramming of mesenchymal stem cells by ovarian carcinoma to facilitate metastasis [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research; 2019 Sep 13-16, 2019; Atlanta, GA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(13_Suppl):Abstract nr B55.