Abstract 2455: Investigating cancer stem cell plasticity in ovarian cancer

Abstract

Most women diagnosed with late-stage high grade serous ovarian cancer (HGSOC) develop recurrent, platinum-resistant tumors. Ovarian cancer stem cells (OCSCs) are hypothesized to contribute to the emergence of these resistant tumors. CSCs have been postulated to reside in a plastic state, which can allow for the conversion of non-CSC to CSC. This process of dedifferentiation continues during tumor development and chemotherapeutic agents like platinum can exaggerate CSC plasticity. We have previously demonstrated that acute platinum treatment enriched for OCSCs. However, whether platinum transforms non-OCSCs into OCSCs to contribute to this subpopulation of cells remains unclear, and the underlying mechanism remains incompletely understood. To examine OCSC plasticity, aldehyde dehydrogenase (ALDH; functional marker) and fluorescence activated cell sorting were used to isolate OCSCs (ALDH+) and non-OCSCs (ALDH-) from HGSOC cell lines, OVCAR5 and OVCAR3. To determine the stability of the non-OCSC phenotype, ALDH- cells were cultured for 3 and 5 days and ALDH activity was measured using flow cytometry. At both timepoints examined, ALDH- cells remained ALDH-, with approximately less than 1% being ALDH+ (p<0.05). To determine if platinum can induce conversion of non-OCSC to OCSC, ALDH- cells were treated with cisplatin (12µM for 16h), and the percent of ALDH+ cells was measured using flow cytometry. Treatment of ALDH- cells with cisplatin resulted in conversion of approximately 3-4% of ALDH- cells into ALDH+ cells (p<0.05). Furthermore, increased expression (p<0.05) of stemness genes BMI1, NANOG, OCT4, and SOX2, analyzed using qRT-PCR, was observed in converted OCSCs compared to parental ALDH+ and whole cell populations treated with cisplatin (12µM for 16h), suggesting that platinum induced the observed differences in the stemness phenotype. With the goal of targeting key genes and pathways to inhibit platinum-induced OCSC conversion, we are carrying out RNA-sequencing analysis of the converted OCSCs and investigating the genes and pathways driving the platinum-induced conversion on non-OCSCs to OCSCs. Understanding the mechanisms involved in OCSC plasticity is critical to developing targeted therapies to block the persistence of OCSCs and ultimately reduce mortality in patients. Citation Format: Tara X. Metcalfe, Shu Zhang, Christiane Hassel, Heather M. O'Hagan, Kenneth P. Nephew. Investigating cancer stem cell plasticity in ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2455.