Digitoxin for Airway Inflammation in Cystic Fibrosis: Preliminary Assessment of Safety, Pharmacokinetics, and Dose Finding.

RATIONALE

Cystic fibrosis (CF) lung disease progresses by a combination of airway inflammation, bacterial colonization, and infection. Airway inflammation is predominantly neutrophilic and complicates airway clearance therapies through cellular debris; excessive DNA; excessive and viscous mucus; and high concentrations of neutrophils, IL-8, and related cytokines liberated along the nuclear factor-κB signaling pathway.

OBJECTIVES

We conducted a preliminary, single-site, randomized, double-blind, placebo-controlled study to evaluate the effects over 28 days of two dose levels (0.05 mg and 0.1 mg daily) of an older cardiac glycoside, digitoxin, as compared with placebo, on safety, pharmacokinetics, and inflammatory markers in induced sputum obtained from 24 subjects with mild to moderate CF lung disease.

METHODS

Patients with CF 18-45 years old with any genotype combination were eligible. The primary objective was to measure the effects of digitoxin on IL-8 and neutrophil counts in induced sputum. Secondary objectives were to measure (1) the pharmacokinetics of digitoxin in sera of patients with stable CF; (2) safety indices, including ECG changes and sputum microbiology; (3) the effect of digitoxin on gene expression in nasal epithelial cells of patients with stable CF; and (4) quality-of-life scores using the Cystic Fibrosis Questionnaire-Revised.

MEASUREMENTS AND MAIN RESULTS

It took several weeks to achieve a therapeutic serum level of digitoxin in subjects with CF. No safety concerns emerged during the study. Digitoxin treatment showed a trend toward reduction in sputum free neutrophil elastase and neutrophil counts, but not a reduction in sputum IL-8. Digitoxin treatment did not reach statistical significance for the primary or secondary outcome measures over the 28-day study period. However, the nasal mRNA from the group receiving 0.1 mg of digitoxin daily had a distinct distribution of global gene expression levels as compared with either the 0.05-mg dose or placebo treatment. The mRNAs encoding chemokine/cytokine or cell surface receptors in immune cells were decreased in nasal epithelial cells at the higher dose, leading to pathway-mediated reductions in IL-8, IL-6, lung epithelial inflammation, neutrophil recruitment, and mucus hypersecretion.

CONCLUSIONS

At a dose of 0.1 mg daily for 28 days, digitoxin was safe for adults with CF lung disease, but it did not achieve a significant decrease in sputum inflammatory markers. Clinical trial registered with www.clinicaltrials.gov (NCT00782288).