Abstract 3095: Targeting ALDH1A1 and regulatory networks that support stemness in ovarian cancer cells

Abstract

Abstract Epithelial ovarian cancer (OC) is the deadliest amongst gynecologic cancers with the majority of deaths caused by cancer recurrence. A new paradigm explaining tumor relapse involves the persistence of cancer stem cells after chemotherapy. OC stem cells (OCSCs) are hypothesized to be largely responsible for the emergence of chemoresistant tumors, and we have previously shown that OCSCs contribute to recurrent, drug resistant high-grade serous OC (HGSOC) using ALDH (aldehyde dehydrogenase) activity as a robust functional marker to identify OCSCs. Of the ALDH isoforms, ALDH1A1 is an intracellular enzyme that oxidizes toxic aldehydes to carboxylic acids and plays a role in controlling cell differentiation pathways. High levels of ALDH1A1 expression have been associated with poor outcome in OC patients. Our group and others have demonstrated that OCSCs with high expression of ALDH1A1 have a greater ability to initiate ovarian tumors in vivo. However, the mechanism by which ALDH1A1 maintains stemness phenotype remains poorly understood. In the current study, we hypothesized that ALDH1A1 upregulation in OCSCs was associated with genetic changes that mediate the cellular signals needed for survival. To test this hypothesis, we used a novel ALDH1A1-specific small molecule inhibitor named compound 974. Treatment of HGSOC cell lines with compound 974 reduced ALDH enzyme activity (p<0.01) and inhibited stem-like properties including spheroid formation (p<0.01) and clonogenic survival (p<0.05). To further examine the effect of compound 974 to inhibit ALDH1A1 and consequently tumor initiation, mice were injected with 106, 105 and 104 OVCAR3 cells treated in vitro with compound 974 (5µM for 48h). Tumor initiation was delayed by 974 treatment compared to vehicle-treated group. Extreme limiting dilution analysis revealed that compound 974 reduced CSC frequency compared to control. Transcriptomic sequencing of ovarian cancer cells treated with compound 974 revealed significant inhibition of genes and pathways associated with stemness (NF-κB, KLF4, FZD7), chemoresistance (ABCB1) and senescence pathway genes (p15, p21). Furthermore, key genes associated with senescence associated secretory phenotype (SASP) such as IL6, IL8 and IL1α were significantly inhibited. Taken together, these data warrant further investigation into the mechanism of ALDH1A1 inhibition and loss of stemness in HGSOC. Citation Format: Vaishnavi Muralikrishnan, Kenneth P. Nephew, Thomas D. Hurley. Targeting ALDH1A1 and regulatory networks that support stemness in ovarian cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3095.