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Optic nerve head astrocytes are the specialized glia cells that provide structural and trophic support to the optic nerve head. In response to cellular injury, optic nerve head astrocytes undergo reactive astrocytosis, the process of cellular activation associated with cytoskeletal remodeling, increases in the rate of proliferation and motility, and the generation of Reactive Oxygen Species. Antioxidant intervention has previously been proposed as a therapeutic approach for glaucomatous optic neuropathy, however, little is known regarding the response of optic nerve head astrocytes to antioxidants under physiological versus pathological conditions. The goal of this study was to determine the effects of three different antioxidants, manganese (III) tetrakis (1-methyl-4-pyridyl) porphyrin (Mn-TM-2-PyP), resveratrol and xanthohumol in primary optic nerve head astrocytes. Effects on the expression of the master regulator nuclear factor erythroid 2-related factor 2 (Nrf2), the antioxidant enzyme, manganese-dependent superoxide dismutase 2 (SOD2), and the pro-oxidant enzyme, nicotinamide adenine dinucleotide phosphate oxidase 4 (NOX4), were determined by quantitative immunoblotting. Furthermore, efficacy in preventing chemically and reactive astrocytosis-induced increases in cellular oxidative stress was quantified using cell viability assays. The results were compared to the effects of the prototypic antioxidant, Trolox. Antioxidants elicited highly differential changes in the expression levels of Nrf2, SOD2, and NOX4. Notably, Mn-TM-2-PyP increased SOD2 expression eight-fold, while resveratrol increased Nrf2 expression three-fold. In contrast, xanthohumol exerted no statistically significant changes in expression levels. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) uptake and lactate dehydrogenase (LDH) release assays were performed to assess cell viability after chemically and reactive astrocytosis-induced oxidative stress. Mn-TM-2-PyP exerted the most potent glioprotection by fully preventing the loss of cell viability, whereas resveratrol and xanthohumol partially restored cell viability. Our data provide the first evidence for a well-developed antioxidant defense system in optic nerve head astrocytes, which can be pharmacologically targeted by different classes of antioxidants.

SELENOF expression is significantly lower in aggressive breast tumors compared to normal tissue, indicating that its reduction or loss may drive breast tumorigenesis. Deletion of SELENOF in non-tumorigenic immortalized breast epithelial MCF-10A cells resulted in enhanced proliferation, both in adherent culture and matrix-assisted three-dimmensional (3D) growth. Modulation of SELENOF in vitro through deletion or overexpression corresponded to changes in the cell-cycle regulators p21 and p27, which is consistent with breast tumor expression data from the METABRIC patient database. Together, these findings indicate that SELENOF affects both proliferation and cell death in normal epithelial and breast cancer cells, largely through the regulation of p21 and p27. In glandular cancers like breast cancer, the filling of luminal space is one of the hallmarks of early tumorigenesis. Loss of SELENOF abrogated apoptosis and autophagy, which are required for the formation of hollow acini in MCF-10A cells in matrix-assisted 3D growth, resulting in luminal filling. Conversely, overexpression of SELENOF induced cell death via apoptosis and autophagy. In conclusion, these findings are consistent with the notion that SELENOF is a breast tumor suppressor, and its loss contributes to breast cancer etiology.

African American women die of breast cancer at a much higher rate than Caucasian women. While the reasons behind this racial disparity are multifactorial, recent findings point to biological components that remain to be fully elucidated. We have recently identified SELENOF as a new tumor suppressor in breast cancer. Consequently, its reduction or loss may drive disease progression and poor outcome. Conversely, we have shown that restoring SELENOF expression elicited anti-tumor activity. Therefore, therapeutic strategies to mitigate the loss of SELENOF may be exploited to improve outcome for patients affected by the loss of SELENOF. Based on two different Chicago-based cohorts, we reported that the breast tumors from African Americans exhibited a 5-10-fold higher frequency of SELENOF single nucleotide polymorphisms (SNPs) compared to Caucasians; these genetic variations result in attenuated translation of SELENOF and thus reduced SELENOF levels. This is supported by preliminary data showing that SELENOF expression is significantly lower in breast tumors from African American patients compared to Caucasians, and lower SELENOF expression predicts shorter survival in these patients. Our goal is to elucidate the role of SELENOF in breast cancer and determine its impact on breast tumorigenesis. We hypothesize that either enhancing SELENOF levels or mimicking its downstream signaling can be exploited to mitigate the loss of SELENOF and elicit anti-tumor activity. Targeting tumor suppressors remains challenging. We identified the eukaryotic initiation factor 4a3 (eIF4a3) as a putative translational repressor of SELENOF, and our preliminary data shows that pharmacologic inhibition of eIF4a3 results in increased SELENOF protein levels. We also found that SELENOF overexpression induces cell death by engaging the inositol-requiring enzyme 1 (IRE1) to determine cell fate. The therapeutic strategies under investigation are likely to result in novel and more effective personalized medicine, and may help close the breast cancer racial disparity gap. Citation Format: Roudy C. Ekyalongo, Alexandra Zigrossi, Brenna Flowers, Alan M. Diamond, Irida Kastrati. SELENOF is a novel tumor suppressor and a new target to overcome breast cancer racial disparity [abstract]. In: Proceedings of the 15th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2022 Sep 16-19; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2022;31(1 Suppl):Abstract nr C059.

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