The transcription factor Nrf2 is an important modulator of antioxidant and drug metabolism, carbohydrate and lipid metabolism, as well as heme and iron metabolism. Regulation of Nrf2 expression occurs transcriptionally and post-transcriptionally. Post-transcriptional regulation entails ubiquitination followed by proteasome-dependent degradation. Additionally, Nrf2-mediated gene expression is subject to negative regulation by ATF3, Bach1 and cMyc. Nrf2-mediated gene expression is an important regulator of a cell’s response to radiation. Although a majority of studies have shown that Nrf2 deficient cells are radiosensitized and Nrf2 over expression confers radioresistance, Nrf2’s role in mediating the radiation response of crypt cells is controversial. The Nrf2 activator CDDO attenuates radiation-mediated crypt injury, whereas intestinal crypts in Nrf2 null mice are radiation resistant. Further investigation is needed in order to define the relationship between Nrf2 and radiation sensitivity in Lgr5+ and Bmi1+ cells that regulate regeneration of crypt stem cells. In hematopoietic compartments Nrf2 promotes the survival of irradiated osteoblasts that support long-term hematopoietic stem cell (LT-HSC) niches. Loss of Nrf2 in LT-HSCs increases stem cell intrinsic radiosensitivity, with the consequence of lowering the LD5030. An Nrf2 deficiency drives LT-HSCs from a quiescent to a proliferative state. This results in hematopoietic exhaustion and reduced engraftment after myoablative irradiation. The question of whether induction of Nrf2 in LT-HSC enhances hematopoietic reconstitution after bone marrow transplantation is not yet resolved. Irradiation of the lung induces pulmonary pneumonitis and fibrosis. Loss of Nrf2 promotes TGF-β/Smad signaling that induces ATF3 suppression of Nrf2-mediated target gene expression. This, in turn, results in elevated reactive oxygen species (ROS) and isolevuglandin adduction of protein that impairs collagen degradation, and may contribute to radiation-induced chronic cell injury. Loss of Nrf2 impairs ΔNp63 stem/progenitor cell mobilization after irradiation, while promoting alveolar type 2 cell epithelial-mesenchymal transitions into myofibroblasts. These studies identify Nrf2 as an important factor in the radiation response of normal tissue.

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Ewing sarcoma is a rare cancer found in children and young adults. Long term survival rates are approximately 70% for patients who present without clinically overt metastases. However, 5 year survival is less than 20% for patients with recurrent tumors or metastasis. Thus, there is a need to improve local tumor control and to treat metastatic disease. Eighty five percent of these cancers are driven by the reciprocal chromosomal translocation t (11;22) (q24;q12), a consequence of a fusion between the 5' portion of Ewing sarcoma breakpoint region 1 on EWSR1 (chromosome 22) and the 3' portion of Friend leukemia virus integration site 1 on FLI1 (chromosome 11). Nucleophosmin1 (NPM1) is a chaperone protein involved in many cellular functions, including DNA repair. NPM1 has been shown to be a novel prognostic biomarker for patients with localized Ewing's sarcoma. Overall survival is significantly lower for patients whose tumors express high levels of NPM1. Besides promoting repair of DNA double strand breaks NPM1 directly interacts with and induces c-Myc-induced hyperproliferation and transformation. Consistent with this knowledge is the observation that relapsed Ewing's patients exhibit high levels of c-Myc expression compared to disease-free patients. Therefore, we wanted to ascertain whether NPM1 represented a molecular target for controlling growth of Ewing's sarcoma. CRISPR/Cas9-mediated targeting of NPM1 exons 3 and 4, as well as lentivirus-mediated shRNA targeting of NPM1 mRNA revealed that targeting of NPM1 expression reduced survival (colony formation) of TC32 and A673 cells (P<0.05). NPM shRNA also reduced TC32 sphere formation under non-adherent conditions. YTR107 and NSC348884 are small molecule inhibitors of NPM1 oligomerization, which is required for NPM1 activity. Both drugs reduced survival of TC32 and A673 Ewing's sarcoma cells in a dose-dependent fashion (P<0.05). We interpret these data to indicate that NPM1 represents a potential molecular target for controlling growth of Ewing's sarcoma. Supported in part by RO1CA140409. Citation Format: Geri Traver, Konjeti R. Sekhar, Narsimha R. Renthala, Peter A. Crooks, Maxwell Ofori, Michael L. Freeman. Targeting NPM1 for controlling growth of Ewing sarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3189.