title: Inhibition of respiratory syncytial virus in vitro and in vivo by the immunosuppressive agent leflunomide.
abstract: BACKGROUND
  Respiratory syncytial virus (RSV) is the primary cause of bronchiolitis and pneumonia in infants and young children worldwide and is often the cause of infections in bone marrow, solid organ transplant, cystic fibrosis and congenital heart disease patients, as well as respiratory tract disease in elderly adults. Treatment options are limited to ribavirin, which is only marginally effective, and passive immunoprophylaxis, which is very expensive. The immunosuppressive agent leflunomide has been shown to exert potent antiviral activity against several herpesviruses and polyomavirus BK. In the current study we have tested the hypothesis that leflunomide exerts antiviral activity against RSV.
  
  
  METHODS
  Human Hep-2 or small airway epithelial cells were inoculated with RSV and treated with A77 1726, the active metabolite of leflunomide. Syncytia formation was assessed by immunohistochemical staining, and virus yield was measured by plaque assay. Cotton rats were intranasally inoculated with RSV, treated with leflunomide by gavage, and pulmonary viral loads were measured by plaque assay of lung homogenates.
  
  
  RESULTS
  Phase contrast microscopy and immunohistochemical staining demonstrated profound attenuation of RSV-induced syncytia formation in infected cultures treated with A77 1726, the active metabolite of leflunomide. Plaque assays of virus yield in RSV-inoculated cell cultures demonstrated potent, dose-dependent A77-mediated antiviral activity. Likewise, pulmonary viral loads in RSV-inoculated cotton rats were reduced by >3 log by leflunomide compared with vehicle-treated controls, even when leflunomide treatment was delayed until day 3 post-inoculation.
  
  
  CONCLUSIONS
  These findings suggest promise for leflunomide as a convenient, orally administered addition to the growing arsenal of antiviral therapeutics. While specific antiviral mechanisms remain to be elucidated, leflunomide shows unique bifunctional potential to both reduce viral load and, by virtue of its well-documented anti-inflammatory activity, attenuate the destructive inflammation associated with RSV disease.
authors.affiliation: Integrated Biomedical Sciences, Ohio State University, Columbus, USA.
authors.forename: Melinda C Cox
authors.initials: MC
authors.lastname: Dunn
authors.forename: Deborah A
authors.initials: DA
authors.lastname: Knight
authors.forename: W James
authors.initials: WJ
authors.lastname: Waldman
mesh_terms: D000818:Animals; D000998:Antiviral Agents / Q000008:administration & dosage / Q000494:pharmacology* / Q000627:therapeutic use; D001980:Bronchi / Q000166:cytology / Q000821:virology; D045744:Cell Line, Tumor; D003588:Cytopathogenic Effect, Viral / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004847:Epithelial Cells / Q000821:virology; D006801:Humans; D007166:Immunosuppressive Agents / Q000008:administration & dosage / Q000494:pharmacology* / Q000627:therapeutic use; D007555:Isoxazoles / Q000008:administration & dosage / Q000494:pharmacology* / Q000627:therapeutic use; D000077339:Leflunomide; D018357:Respiratory Syncytial Virus Infections / Q000188:drug therapy* / Q000821:virology; D018113:Respiratory Syncytial Virus, Human / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D016205:Sigmodontinae; D016896:Treatment Outcome; D019562:Viral Load / Q000187:drug effects
chemical_list: D000998:Antiviral Agents; D007166:Immunosuppressive Agents; D007555:Isoxazoles; D000077339:Leflunomide