Aerosolized Recombinant Human DNase I for the Treatment of Cystic Fibrosis

¹ From Pulmonary Research, Genentech Inc, South San Francisco

Respiratory symptoms, recurrent infectious exacerbations, and progressive lung destruction in cystic fibrosis can be attributed to bacterial persistence and the accumulation of viscous purulent secretions in the airways. Purulent secretions contain high concentrations of extracellular DNA, a viscous material released by leukocytes. To evaluate the potential clinical utility of recombinant human DNase I (rhDNase or Pulmozyme), the human enzyme was cloned, sequenced, and expressed. In in vitro studies, rhDNase has been shown to reduce the viscoelasticity, reduce the adhesiveness, and improve the mucociliary transportability of cystic fibrosis sputum. In short-term phase 1 and phase 2 clinical trials, rhDNase has been shown to be safely tolerated and to improve the FEV₁, FVC, and symptoms of dyspnea. A long-term placebo-controlled phase 3 study was performed in 968 adults and children (5 years) with cystic fibrosis to determine the effect of rhDNase on the risk of respiratory exacerbations requiring parenteral antibiotics and on the FEV₁. Compared with placebotreated patients, patients treated with rhDNase once daily or twice daily experienced a reduced risk of respiratory exacerbations by 28% (p=0.04) and 37% (p=0.01), respectively, and had a mean improvement in FEV₁ of 5.8% (p<0.01) and 5.6% (p<0.01), respectively. Compared with placebo-treated patients, patients treated with rhDNase spent 2.7 fewer days receiving parenteral antibiotics (p=0.04) and spent 1.3 fewer days in the hospital (p=0.06) over the 6-month treatment period. Inhalation of rhDNase did not cause anaphylaxis but was associated with upper airway symptoms (ie, voice alteration, hoarseness, pharyngitis) that were generally mild and transient. In conclusion, aerosol administration of rhDNase was safely tolerated, reduced the risk of infectious exacerbations requiring parenteral antibiotics, and improved pulmonary function and patient well-being.

Key Words: airway obstruction • cystic fibrosis • DNase • sputum