Abstract B013: STEAP1 facilitates iron transport in ewing sarcoma to support mitochondrial activity

Abstract

Abstract Ewing sarcoma (EwS) is a highly aggressive bone-associated tumor of children and young adults with strong propensity to progress and dismal outcome for patients with advanced stages of the disease. EwS is defined by a pathognomonic recurrent potent transcription factor, in 85-90% of cases EWSR1-FLI1. One of the previously described transcriptional targets of EWSR1-FLI1 is six-transmembrane epithelial antigen of the prostate 1 (STEAP1). STEAP1 is a member of the STEAP membrane-bound protein family involved in reduction of iron and copper which is a crucial step for metal transport and overexpressed in various malignancies. However, a precise functional role of STEAP1 in cancers including EwS remains elusive. EwS cell lines with knockout (KO) or knockdown (KD) of STEAP1 were created to perform functional studies for elucidating the functions of STEAP1 in EwS, including transient metal measurements. Additionally, the measurement of functional mitochondrial activity was performed by an extracellular flux analyzer. The activity of the mitochondrial electron transport chain complexes was measured by blue native PAGE. We showed that STEAP1 functions as a metalloreductase and STEAP1 KO cells have lower intracellular iron levels. Furthermore, we discovered that STEAP1 KO cells have significantly lower levels of the mitochondrial labile iron pool. Consequently, EwS cells with STEAP1 KO demonstrated impaired mitochondrial respiration and increased glycolysis rates. Additionally, the functional activity of iron-sulfur containing proteins and the the assembly of subunits of the mitochondrial electron transport chain complexes were decreased. This study is the first to demonstrate in vitro involvement of STEAP1 in transitional metal homeostasis and mitochondrial activity. These discoveries unveil alternative therapeutic strategies for EwS patients such as using compounds that promote an iron-dependent form of cell death, ferroptosis, or drugs that decrease metabolic adaptability. Citation Format: Taras Shyp, Rouhollah Mousavizadeh, Gian Luca Negri, Hai-Feng Zhang, Michael Lizardo, Poul Sorensen. STEAP1 facilitates iron transport in ewing sarcoma to support mitochondrial activity [abstract]. In: Proceedings of the AACR Special Conference: Sarcomas; 2022 May 9-12; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(18_Suppl):Abstract nr B013.