title: Rhesus θ-defensin-1 (RTD-1) exhibits in vitro and in vivo activity against cystic fibrosis strains of Pseudomonas aeruginosa.
abstract: OBJECTIVE
  Chronic endobronchial infections with Pseudomonas aeruginosa contribute to bronchiectasis and progressive loss of lung function in patients with cystic fibrosis. This study aimed to evaluate the therapeutic potential of a novel macrocyclic peptide, rhesus θ-defensin-1 (RTD-1), by characterizing its in vitro antipseudomonal activity and in vivo efficacy in a murine model of chronic Pseudomonas lung infection.
  
  
  METHODS
  Antibacterial testing of RTD-1 was performed on 41 clinical isolates of P. aeruginosa obtained from cystic fibrosis patients. MIC, MBC, time-kill and post-antibiotic effects were evaluated following CLSI-recommended methodology, but using anion-depleted Mueller-Hinton broth. RTD-1 was nebulized daily for 7 days to cystic fibrosis transmembrane conductance regulator (CFTR) F508del-homozygous mice infected using the agar bead model of chronic P. aeruginosa lung infection. In vivo activity was evaluated by change in lung bacterial burden, airway leucocytes and body weight.
  
  
  RESULTS
  RTD-1 exhibited potent in vitro bactericidal activity against mucoid and non-mucoid strains of P. aeruginosa (MIC90 = 8 mg/L). Cross-resistance was not observed when tested against MDR and colistin-resistant isolates. Time-kill studies indicated very rapid, concentration-dependent bactericidal activity of RTD-1 with ≥3 log10 cfu/mL reductions at concentrations ≥4× MIC. No post-antibiotic effect was observed. In vivo, nebulized treatment with RTD-1 significantly decreased lung P. aeruginosa burden (mean difference of -1.30 log10 cfu; P = 0.0061), airway leucocytes (mean difference of -0.37 log10; P = 0.0012) and weight loss (mean difference of -12.62% at day 7; P < 0.05) when compared with controls.
  
  
  CONCLUSIONS
  This study suggests that RTD-1 is a promising potential therapeutic agent for cystic fibrosis airway disease.
authors.affiliation: School of Pharmacy, University of Southern California, 1985 Zonal Avenue, Los Angeles, CA 90033, USA beringer@usc.edu.
authors.forename: Paul M
authors.initials: PM
authors.lastname: Beringer
authors.affiliation: School of Pharmacy, University of Southern California, 1985 Zonal Avenue, Los Angeles, CA 90033, USA.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Bensman
authors.affiliation: School of Pharmacy, University of Southern California, 1985 Zonal Avenue, Los Angeles, CA 90033, USA.
authors.forename: Henry
authors.initials: H
authors.lastname: Ho
authors.affiliation: School of Pharmacy, University of Southern California, 1985 Zonal Avenue, Los Angeles, CA 90033, USA.
authors.forename: Melissa
authors.initials: M
authors.lastname: Agnello
authors.affiliation: School of Pharmacy, University of Southern California, 1985 Zonal Avenue, Los Angeles, CA 90033, USA.
authors.forename: Nicole
authors.initials: N
authors.lastname: Denovel
authors.affiliation: School of Pharmacy, University of Southern California, 1985 Zonal Avenue, Los Angeles, CA 90033, USA.
authors.forename: Albert
authors.initials: A
authors.lastname: Nguyen
authors.affiliation: School of Pharmacy, University of Southern California, 1985 Zonal Avenue, Los Angeles, CA 90033, USA.
authors.forename: Annie
authors.initials: A
authors.lastname: Wong-Beringer
authors.affiliation: Department of Pathology & Laboratory Medicine, Keck School of Medicine, University of Southern California, 2011 Zonal Avenue, Los Angeles, CA 90033, USA.
authors.forename: Rosemary
authors.initials: R
authors.lastname: She
authors.affiliation: Department of Pathology & Laboratory Medicine, Keck School of Medicine, University of Southern California, 2011 Zonal Avenue, Los Angeles, CA 90033, USA.
authors.forename: Dat Q
authors.initials: DQ
authors.lastname: Tran
authors.affiliation: Department of Pediatrics, Massachusetts General Hospital and Harvard Medical School, 275 Cambridge Street, Boston, MA, USA.
authors.forename: Samuel M
authors.initials: SM
authors.lastname: Moskowitz
authors.affiliation: Department of Pathology & Laboratory Medicine, Keck School of Medicine, University of Southern California, 2011 Zonal Avenue, Los Angeles, CA 90033, USA USC Norris Comprehensive Cancer Center, 1441 Eastlake Avenue, Los Angeles, CA, USA.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Selsted
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000008:administration & dosage* / Q000494:pharmacology; D058491:Bacterial Load; D001835:Body Weight; D003550:Cystic Fibrosis / Q000150:complications; D023082:Defensins / Q000008:administration & dosage* / Q000494:pharmacology; D004195:Disease Models, Animal; D006801:Humans; D007958:Leukocyte Count; D008168:Lung / Q000382:microbiology / Q000473:pathology; D008253:Macaca mulatta; D008297:Male; D008810:Mice, Inbred C57BL; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability / Q000187:drug effects; D011552:Pseudomonas Infections / Q000188:drug therapy* / Q000382:microbiology; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000302:isolation & purification; D016896:Treatment Outcome
chemical_list: D000900:Anti-Bacterial Agents; D023082:Defensins; C450142:theta-defensin