Preclinical Therapy High-Throughput Screening Identifies Two Classes of Antibiotics as Radioprotectors: Tetracyclines and Fluoroquinolones

Purpose: Discovery of agents that protect or mitigate normal tissue from radiation injury during radiotherapy, accidents, or terrorist attacks is of importance. Specifically, bone marrow insufficiency, with possible infection due to immunosuppression, can occur after total body irradiation (TBI) or regional irradiation and is a major component of the acute radiation syndrome. The purpose of this study was to identify novel radioprotectors and mitigators of the hematopoietic system. Experimental Design: High-throughput screening of small-molecule libraries was done using viability of a murine lymphocyte line as a readout with further validation in human lymphoblastoid cells. The selected compounds were then tested for their ability to counter TBI lethality in mice. Results: All of two major classes of antibiotics, tetracyclines and fluoroquinolones, which share a common planar ring moiety, were radioprotective. Furthermore, tetracycline protected murine hematopoietic stem/progenitor cell populations from radiation damage and allowed 87.5% of mice to survive when given before and 35% when given 24 h after lethal TBI. Interestingly, tetracycline did not alter the radiosensitivity of Lewis lung cancer cells. Tetracycline and ciprofloxacine also protected human lymphoblastoid cells, reducing radiation-induced DNA double-strand breaks by 33% and 21%, respectively. The effects of these agents on radiation lethality are not due to the classic mechanism of free radical scavenging but potentially through activation of the Tip60 histone acetyltransferase and altered chromatin structure. Conclusions: Tetracyclines and fluoroquinolones can be robust radioprotectors and mitigators of the hematopoietic system with potential utility in anticancer radiotherapy and radiation emergencies. (Clin Cancer Res 2009;15(23):OF1–8) Total body irradiation (TBI) with 5 to 10 Gy doses results in an acute radiation syndrome with possible lethality due primarily to hematopoietic failure and/or infection caused by immune impairment (1). Indeed, immunohematopoietic cells are very sensitive to radiation, dying mainly in interphase by apoptosis (2). The peaceful and military use of atomic power after World War II spurred efforts to find agents for the prophylaxis, mitigation, or treatment of radiation injury, efforts that have been reintensified recently by an increased threat of terrorist use of radiation sources. Numerous compounds have radioprotective effects (3, 4). Examples are tempol, antioxidant vitamins, and melatonin, with the best studied being the thiol Amifostine (WR2721). Most are free radical scavengers that reduce initial radiation-induced DNA damage and work best if added just before or at the time of irradiation. Because of this, and their poor toxicity profile, amifostine and similar compounds are not practical countermeasures in a radiation incident (5). More recently, targeting superoxide dismutase (3, 4) and activation of Toll-like receptor 5/NF-κB pathway by flagellin suggest that alternative approaches may be of value (6). Furthermore, certain cytokines such as granulocyte colony-stimulating factor, stem Authors' Affiliations: Departments of Radiation Oncology and Pathology and Laboratory Medicine, and Public Health-Biostatistics/Radiology, The Pasarow Mass Spectrometry Laboratory, and Molecular Screening Shared Resource, David Geffen School of Medicine at University of California at Los Angeles, Los Angeles, California; and Department of Radiation Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts Received 7/24/09; revised 9/1/09; accepted 9/8/09; published OnlineFirst 11/17/09. Grant support: University of California at Los Angeles Center for Biological Radioprotectors grant U19 AI067769/NIAID and Dana-Farber/Harvard Center for Medical Counter Measures Against Radiation grant U19 AI067751. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. Note: Supplementary data for this article are available at Clinical Cancer Research Online (http://clincancerres.aacrjournals.org/). Requests for reprints: William H. McBride, Department of Radiation Oncology, Roy E. Coats Research Laboratories, Room B3-109, David Geffen School of Medicine at University of California at Los Angeles, 10833 Le Conte Avenue, Los Angeles, CA 90095-1714. Phone: 310-794-7051; Fax: 310-206-1249; E-mail: [email protected]. F 2009 American Association for Cancer Research. doi:10.1158/1078-0432.CCR-09-1964 OF1 Clin Cancer Res 2009;15(23) December 1, 2009 www.aacrjournals.org Published Online First on November 17, 2009 as 10.1158/1078-0432.CCR-09-1964 Research. on April 10, 2017. © 2009 American Association for Cancer clincancerres.aacrjournals.org Downloaded from Published OnlineFirst November 17, 2009; DOI: 10.1158/1078-0432.CCR-09-1964