Abstract B63: Lysophosphatidic acid as a mediator of ovarian cancer cell stemness

Abstract

Abstract Epithelial ovarian cancer (OC) is the deadliest gynecologic malignancy. Recurrence of advanced, multidrug-resistant metastatic disease after initially good response to standard lines of chemotherapy occurs in the majority of OC patients. Chemoresistant, recurrent OC is essentially fatal. Disease relapse is due to survival and expansion of a small pool of chemorefractory ovarian cancer stem cells (OCSCs). OC evolution to a platinum-resistant state is associated with aberrant epigenetic modifications, including altered DNA methylation and histone modifications. In addition, OC cells residing in the peritoneal cavity are exposed to a variety of external cues arising from the ascitic microenvironment, including the bioactive molecule lysophosphatidic acid (LPA), which potentially contribute to cell stemness and chemoresistance. LPA in the intraperitoneal fluid of OC patients has been strongly implicated in ovarian carcinogenesis and metastasis through a variety of mechanisms. However, regulation of OC cells by LPA is incompletely understood, and the role of LPA in OCSC acquisition/chemoresistance remains unclear. In the current study, we tested the hypothesis that LPA is a mediator of OCSC promotion and survival. Expression of aldehyde dehydrogenase (ALDH), an accepted functional marker of cancer stem cells, was assessed in a panel of high-grade serous ovarian cancer (HGSOC) cell lines (OVSAHO, OVCAR3, OVCAR5, PEO1, and Kuramochi) using an Aldefluor assay. Treatment of HGSOC cells with increasing (0-80uM, 72h) doses of LPA enriched the ALDH+ population in a cell line-specific dose-dependent manner. In PEO1 and Kuramochi cells, intermediate LPA doses (1-10uM) resulted in a 1.5-2.5-fold increase (P<0.05) of ALDH+ cells (from ∼4% to ∼8% in PEO1 and from ∼4% up to ∼10% in Kuramochi, respectively). However, 80uM LPA treatment was necessary to increase (P<0.05) the percentage ALDH+ cells in OVCAR3 (from ∼17% to 34%) and OVSAHO cells (from ∼10% up to 29%). In accordance with the results of the flow cytometry analysis, cancer stem cell properties after LPA treatment (0-80uM, every 72hr, up to 21 days) were enhanced (P<0.05), based on clonogenic assay. In particular, moderate (10-20uM) LPA treatment increased (P<0.05) cell clonogenic survival of PEO1 and Kuramochi, while a greater (80uM) LPA dose was needed for OVCAR3 and OVSAHO. Furthermore, LPA (0-80uM, 14 days) augmented spheroid formation ability in PEO1 cells (3-4-fold increase; P<0.05). Global transcriptomic and epigenomic assessment of altered genes/pathways induced by LPA are currently being examined to assess stemness-promoting pathways and epigenetic changes, which we believe will identify new biologic insights and potential therapeutic targets to eradicate OCSC in patients. Citation Format: Yuliya Klymenko, Kenneth P. Nephew. Lysophosphatidic acid as a mediator of ovarian cancer cell stemness [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 B63.