Abstract A76: Role of frizzled-7 in platinum tolerance ovarian cancer

Abstract

Abstract While ovarian cancer (OC) is considered as a highly chemoresponsive tumor, 75% women experience tumor relapse associated with chemoresistance. It has been hypothesized that ovarian cancer stem cells (OCSCs) are responsible for developing chemoresistant recurrent tumors and sharing characteristics with normal SCs. Measuring aldehyde dehydrogenase 1 (ALDH1) enzymatic activity has been demonstrated as an established method for OCSC identification and isolation. Our previous studies indicated that while chemotherapy initially “debulks” the mass of OC, residual tumors are enriched in OCSCs. Here, we aimed to identify new markers for CSC enriched platinum-resistant OCs using in vitro and in vivo models. We found that the surviving cells after repeated treatment with platinum were enriched in ALDH(+) cells, formed more spheroids and contained cells expressing CSC-related transcription factors (Sox 2) compared to parental cells, supporting that repeated platinum treatment selects cells with stem-like properties. Next, CSC RT-PCR based platform was used to compare wild-type and chemoresistant OCs and to rule out candidate genes that may drive stemness and chemoresistance. CSC array showed that Frizzled 7 receptor (FZD7), a transmembrane receptor involved in canonical Wnt/β-catenin, emerged as a top highly expressed marker in platinum-resistant compared to parental cells and was next studied as a putative new marker for CSC-enriched chemoresistant OCs. FZD7 expression was increased in platinum-resistant cells compared to parental cells at mRNA and protein levels. FZD7(+) cells were detectable and represent ~2-15% on OC cell lines and cells dissociated from human tumors. FZD7(+) population enriched in the platinum-resistant OCs and xenografts. In addition, KD FZD7 in chemoresistant OC cells restored chemosensitivity of OCs, decreased spheroid formation, and delayed tumor initiation, suggesting the role of FZD7 in regulating chemoresistance and stemness of OCs. RNA sequencing results of FZD7(+)/FZD7(-) OCs revealed that FZD7(+) cells downregulated genes associated to DNA damage response, and upregulated “persister cells” related genes, including EMT and stemness-associated genes. Importantly, mitochondrial dysfunction and oxidative phosphorylation were enriched in FZD7(-) OCs compared with FZD7(+) cells. As “persister cells” have been demonstrated to be dependent on antioxidant protein, glutathione peroxidase 4 (GPX4), for cell survival and maintaining mitochondrial oxidative phosphorylation in other cancer models, we checked GPX4 expression in FZD7(+) OCs and platinum-resistant OCs; the expression of GPX4 is correlated with FZD7 expression associated with chemoresistance. Platinum-resistant cells are more sensitive to GPX4 inhibitor treatment and KD FZD7 decreased GPX4 expression and blunt sensitivity of OCs to GPX4 inhibitor treatment, further supporting that platinum-resistant OCs are “persister like cells,” which are protected by GPX4 from lipid peroxidation stress and ferroptosis. Citation Format: Yinu Wang, Guanyuan Zhao, Hao Huang, Salvatore Condello, Jianjun Wei, Daniela Matei. Role of frizzled-7 in platinum tolerance ovarian cancer [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 A76.