Exserohilum Rostratum Using High Throughput Drug Repurposing Screens
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Rapid Identification of Antifungal Compounds against Exserohilum rostratum Using High Throughput Drug Repurposing Screens Wei Sun1., Yoon-Dong Park2., Janyce A. Sugui2, Annette Fothergill3, Noel Southall1, Paul Shinn1, John C. McKew1, Kyung J. Kwon-Chung2, Wei Zheng1*, Peter R. Williamson2,4* 1 National Center for Advancing Translational Sciences, National Institutes of Health, Bethesda, Maryland, United States of America, 2 Laboratory of Clinical Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, United States of America, 3 University of Texas Health Science Center, San Antonio, Texas, United States of America, 4 Section of Infectious Diseases, Immunology and International Medicine, University of Illinois College of Medicine, Chicago, Illinois, United States of America Abstract A recent large outbreak of fungal infections by Exserohilum rostratum from contaminated compounding solutions has highlighted the need to rapidly screen available pharmaceuticals that could be useful in therapy. The present study utilized two newly-developed high throughput assays to screen approved drugs and pharmaceutically active compounds for identification of potential antifungal agents. Several known drugs were found that have potent effects against E. rostratum including the triazole antifungal posaconazole. Posaconazole is likely to be effective against infections involving septic joints and may provide an alternative for refractory central nervous system infections. The anti-E. rostratum activities of several other drugs including bithionol (an anti-parasitic drug), tacrolimus (an immunosuppressive agent) and floxuridine (an antimetabolite) were also identified from the drug repurposing screens. In addition, activities of other potential antifungal agents against E. rostratum were excluded, which may avoid unnecessary therapeutic trials and reveals the limited therapeutic alternatives for this outbreak. In summary, this study has demonstrated that drug repurposing screens can be quickly conducted within a useful time-frame. This would allow clinical implementation of identified alternative therapeutics and should be considered as part of the initial public health response to new outbreaks or rapidly-emerging microbial pathogens. Citation: Sun W, Park Y-D, Sugui JA, Fothergill A, Southall N, et al. (2013) Rapid Identification of Antifungal Compounds against Exserohilum rostratum Using High Throughput Drug Repurposing Screens. PLoS ONE 8(8): e70506. doi:10.1371/journal.pone.0070506 Editor: Ping Wang, Research Institute for Children and the Louisiana State University Health Sciences Center, United States of America Received April 16, 2013; Accepted June 18, 2013; Published August 21, 2013 This is an open-access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication. Funding: This work was supported by the Intramural Research Programs of the National Center for Advancing Translational Sciences and National Institute of Allergy and Infectious Diseases, National Institutes of Health. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: [email protected] (PRW); [email protected] (WZ) . These authors contributed equally to this work. Introduction more disseminated infections in immunocompromised populations have been reported [6,7,8]. Unusual or highly antibiotic resistant organisms may subject E. rostratum is sensitive to amphotericin B, a commonly used large numbers of individuals to unexpected infectious diseases due antifungal agent, but the severe and potentially lethal side-effects to greater globalization that brings more widespread distribution of this drug have limited its use in certain patients. While networks and potential threats such as bioterrorism. Limited traditional antibiotic susceptibility testing has provided initial therapeutic options or failures in conventional therapy during recommendations of using amphotericin B for treatment, the these outbreaks can be encountered because of either intolerable advanced age (median 69) of the patient population in this drug toxicities or lack of efficacious drugs. Recently, a large outbreak has limited the therapeutic efficacy in many patients, outbreak of fungal infections has been caused by the widespread mainly due to drug toxicity. There are few alternative drugs that distribution of contaminated preservative-free methylprednisolone are known for the treatment of infections caused by E. rostratum. acetate prepared by a single compounding pharmacy [1,2,3,4]. It The conventional process for drug discovery and development has currently resulted in 741 infections with 55 deaths [5]. cannot accommodate such a sudden outbreak as it requires 10–12 Exserohilum rostratum, a dermatiaceous fungus commonly found on years in average to develop a drug. Recently, a drug repurposing plants, in soil and in households, has been identified as one of the screen with approved drugs and pharmacologically active agents predominant pathogens in the current multistate outbreak of [9] has emerged as an alternative approach to rapidly identify new fungal meningitis and other infections associated with contami- therapeutic indications that have been successfully applied to nated steroid injections. Although it rarely causes infections in several diseases [10,11,12,13,14,15]. This unique approach may healthy people, infections of skin and corneal tissues as well as also help to quickly identify alternative therapeutics for the PLOS ONE | www.plosone.org 1 August 2013 | Volume 8 | Issue 8 | e70506 Repurposing Screen of E. rostratum Table 1. Assay protocol for the measurements of fungicidal compounds. Step Parameter Value Description 1 PBS/Medium 2.5 ml/well PBS or RPMI Medium 2 Compound 0.023 ml/well Compound in DMSO solution 3 Hyphae/Conidia 2.5 ml/well Hyphae in PBS or Conidia in RPMI Medium 4 Incubation 24 hr 37uC, 5% CO2 5 Detection reagent 4 ml/well ATP content assay reagent 6 Incubation 15 min Room temperature 7 Plate reading Luminescence mode ViewLux plate reader Note: PBS was dispensed in the hyphae assay following by transferring of compound and addition of hyphae cell suspension. RPMI Medium, compound and conidia cells in RPMI Medium were sequentially added in the conidia assays. doi:10.1371/journal.pone.0070506.t001 treatment of infections caused by outbreaks such as that by E. rostratum. Here we report the development and optimization of two assays using E. rostratum hyphae and conidia in an ATP content assay format for high throughput screening. Both assays were screened in parallel against two known compound libraries including 4096 approved drugs and 1280 compounds with pharmacologically known activities. Within seven weeks, the activities of 20 known antifungals, 8 other anti-infectious agents and 10 other drugs against E. rostratum were identified from the screens. While some of these drugs may be considered as alternative therapeutics to treat E. rostratum infections, others could serve as tools for identification of new molecular targets for future drug development. Materials and Methods Materials Amphotericin B (catalog # A9528) was purchased from Sigma- Aldrich (St. Louis, MO). The ATP content kit (ATPlite, catalog No. 6016941) was purchased from PerkinElmer (Waltham, MA). PBS (Catalog No. 10010049) was purchased from Life technolo- gies. The 1536-well white sterile tissue culture treated polystyrene plates (Catalog No. 789092-F) were purchased from Greiner Bio- One (Monroe, NC). Preparation of Exserohilum rostratum conidia and hyphal fragments Conidia and hyphae of E. rostratum were obtained as described by Richard et al. [16], with the following modifications. Briefly, Figure 1. Scheme of hyphae and conidia assay methodology. conidia were harvested from Potato Dextrose Agar (PDA) cultured Conidia harvested from colonies grown on potato dextrose agar (PDA) were incubated in nutrient-rich RPMI media with compounds to identify media with 0.05% Tween 80, and the conidial suspension was inhibitors of E. rostratum growth. Alternatively, hyphal fragments, filtered using a Cell Strainer (100 mm, BD Falcon REF 352340). obtained by growth on Yeast Extract Peptone Dextrose agar (YPD) and After centrifugation at 700g for 10 min, the suspension was size-reduced by sonication, were incubated with compounds under decanted and conidia were resuspended at 16105 per ml in RPMI nutrient-deprived conditions to identify fungicidal compounds. and counted in a hemocytometer. Hyphae were harvested from doi:10.1371/journal.pone.0070506.g001 yeast extract peptone dextrose (YPD) culture media with 0.05% Tween 80. Hyphal fragments were sized by vortexing 15 sec twice Mammalian cell culture with 0.4 mm glassbeads, and the hyphae suspension was filtered Human neuroblastoma SH-SY5Y cell line (Catalog No. CRL- by cheese cloth twice. Microscopy was used to determine the size 2266) was purchased from ATCC (Manassas, VA). SH-SY5Y cell of hyphal fragments, which ranged between 10–50 mm. To line was cultured in 175-cm2 tissue culture flasks (Costar, normalize concentrations of hyphal fragments for batch to batch Cambridge, MA) with 30 ml of growth medium at 37uCina consistency, carbohydrate