Therapeutics , Targets , and Chemical Biology Aurano fi n Induces Lethal Oxidative and Endoplasmic Reticulum Stress and Exerts Potent Preclinical Activity against Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) exhibits high remission rates after initial chemoimmunotherapy, butwith relapses with treatment, refractory disease is the most common outcome, especially in CLL with the deletion of chromosome 11q or 17p. In addressing the need of treatments for relapsed disease, we report the identification of an existing U.S. Food and Drug Administration-approved small-molecule drug to repurpose for CLL treatment. Auranofin (Ridaura) is approved for use in treating rheumatoid arthritis, but it exhibited preclinical efficacy in CLL cells. By inhibiting thioredoxin reductase activity and increasing intracellular reactive oxygen species levels, auranofin induced a lethal endoplasmic reticulum stress response in cultured and primary CLL cells. In addition, auranofin displayed synergistic lethality with heme oxygenase-1 and glutamate-cysteine ligase inhibitors against CLL cells. Auranofin overcame apoptosis resistance mediated by protective stromal cells, and it also killed primary CLL cells with deletion of chromosome 11q or 17p. In TCL-1 transgenic mice, an in vivo model of CLL, auranofin treatment markedly reduced tumor cell burden and improved mouse survival. Our results provide a rationale to reposition the approved drug auranofin for clinical evaluation in the therapy of CLL.Cancer Res; 74(9); 2520–32. 2014 AACR. Introduction Accelerated expansion of chronic lymphocytic leukemia (CLL) cells with bulky lymphadenopathy and organomegaly, with or without compromised hematopoiesis, is treated with myelotoxic chemoimmunotherapy (1, 2). In CLL, the unmutated immunoglobulin heavy chain variable region genes (IGHV), acquired chromosomal abnormalities including deletion 17p13 and deletion 11q22, as well as increased expression of ZAP70 (zeta-associated protein) or CD38 are features associated with poor outcome (3). Notwithstanding high remission rates due to initial chemoimmunotherapy, eventual relapse with treatment-refractory disease is the typical outcome, except in a minority of patients who successfully receive allogeneic stem cell transplantation (2, 3). Therefore, novel effective and safe treatments need to be tested and developed. To this end, repurposing of an existing and U.S. Food and Drug Administration (FDA)-approved small-molecule drug in the treatment of CLL is a worthy goal (4). Compared with normal lymphocytes, CLL cells have intrinsically higher levels of reactive oxygen species (ROS) and are under oxidative stress due to an imbalanced redox status (5–8). ROS-mediated oxidation of the sulfur-containing amino acids in proteins such as phosphatases and transcription factors, for example, NF-kB, p53, hypoxia-inducible factor-1a, and nuclear factor erythroid 2-related factor 2 (Nrf2), regulates their function and role in modifying cellular growth and survival (9). Elevated ROS levels also render CLL cells more sensitive to agents that further increase ROS and oxidative stress (6). Nrf2 activates genes involved in the response to oxidative stress, including heme oxygenase-1 (HMOX-1) and glutamate cysteine ligase modifier (GCLM), which are involved in glutathione (GSH) synthesis (10, 11). Elevated levels of ROS may overcome antioxidant mechanisms and induce protein oxidation, which leads to intracellular accumulation of potentially toxic, misfolded, and polyubiquitylated (poly-Ub) proteins (12). This accumulation triggers an HDAC6-mediated, adaptive and protective heat shock and proteotoxic stress response (13, 14). During this, HDAC6 binds to the poly-Ub–misfolded proteins Authors' Affiliations: Houston Methodist Research Institute; The University of Texas M.D. Anderson Cancer Center, Houston, Texas; Hematology Branch, National Heart Lung and Blood Institute (NHLBI); National Center for Advancing Translational Sciences, NIH, Bethesda, Maryland; The University of KansasMedical Center; Institute for AdvancingMedical Innovation, Kansas University, Kansas City, Kansas; Division of Hematology, Department of Internal Medicine, The Comprehensive Cancer Center at the Ohio State University, Columbus, Ohio; and Weill Cornell Medical College, New York, New York Note: Supplementary data for this article are available at Cancer Research Online (http://cancerres.aacrjournals.org/). W. Fiskus and N. Saba contributed equally to this work. Corresponding Author: Kapil N. Bhalla, Houston Methodist Research Institute, 6670 Bertner Avenue, R9-113, Houston, TX 77030. Phone: 713-441-9113; Fax: 713-441-5349; E-mail: knbhalla@tmhs.org doi: 10.1158/0008-5472.CAN-13-2033 2014 American Association for Cancer Research. Cancer Research Cancer Res; 74(9) May 1, 2014 2520 on April 30, 2017. © 2014 American Association for Cancer Research. cancerres.aacrjournals. org Downloaded from Published OnlineFirst March 5, 2014; DOI: 10.1158/0008-5472.CAN-13-2033