The five year survival rate for women with ovarian cancer is 9-34%. This high mortality is due to late stage diagnosis, marginally effective treatment and frequent disease recurrence. Alterations in metabolism have been widely recognized as an important hallmark of cancer. Metabolism of the micronutrient iron is significantly altered in many cancers, including ovarian cancers. The expression of genes governing iron transport (TFR1 and FPN), iron storage (FTL and FTH) and iron regulation (IRP1 and IRP2) are significantly altered in ovarian cancer compared to normal ovarian epithelial cells, resulting in higher intratumoral iron retention. However, specific pathways of intracellular iron utilization that are altered in cancer cells, and the functional consequences of disrupting these pathways, remain poorly understood.

To identify pathways of iron utilization that are perturbed in ovarian cancer, we analyzed the expression of genes involved in iron metabolism using a publicly available microarray database of ovarian cancer and normal oviduct (GSE69428). We observed that sideroflexin4 (SFXN4), an inner mitochondrial membrane protein that is essential for mitochondrial respiratory homeostasis, was significantly upregulated (p= 0.002) in ovarian cancer patient samples. We screened several ovarian cancer cell lines and observed that SFXN4 was similarly up-regulated both at the mRNA and protein level when compared to normal human ovarian surface epithelial cells.

To test the role of SFXN4 in ovarian cancer cells we performed knockdown and overexpression studies. Knockdown of SFXN4 induced S and G2-phase cell cycle arrest and reduced the ability of MDAH2774 and SKOV3 ovarian cancer cells to form colonies. Further investigation revealed that modulation of SFXN4 alters mitochondrial respiration by affecting iron-sulfur cluster biogenesis. Thus, knock-out cells exhibited impaired respiratory activity and a phenotype similar to cells with defects in iron-sulfur cluster biogenesis, including increased IRP-IRE binding and a decrease in IRP1/ACO1 aconitase activity. Furthermore, SFXN4 knock-out decreased the activity of iron-sulfur cluster-containing enzymes such as mitochondrial aconitase and succinate dehydrogenase.

Based on these observations, we postulate that SFXN4 acts as a molecular mediator that channels the excess iron present in ovarian cancer cells to iron-sulfur cluster-dependent metabolic pathways that favor growth and metastasis. SFXN4 may be a potential druggable target in ovarian cancer.

Citation Format: Bibbin Paul, Miranda Lynch, Frank Torti, Suzy Torti. Sideroflexin4: A novel regulator of iron metabolism in ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1501. doi:10.1158/1538-7445.AM2017-1501