Exogenous Surfactant Enhances the Delivery of Recombinant Adenoviral Vectors to the Lung

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Abstract
Somatic gene therapy for pulmonary diseases must be accomplished in vivo, requiring the spread of a gene transfer vector across a vast expanse of respiratory epithelium. Surfactant, a naturally occurring protein and lipid mixture used to treat the respiratory distress syndrome of prematurity, disperses rapidly and evenly throughout the lung. We employed exogenous bovine surfactant (Survanta beractant) as a carrier vehicle for pulmonary delivery of a recombinant adenovirus expressing β-galactosidase (β-Gal). Rats treated with an adenovirus-beractant mixture demonstrated more uniform lobar distribution of transgene expression than rats treated with the same amount of virus in saline. Tissue homogenates were examined for quantitative β-Gal expression by reaction with o-nitrophenol β-d-galactopyranoside (ONPG). The degree of β-Gal activity was affected by both the volume and type of carrier used to deliver the virus. At low volumes (0.5 ml, 1.3 ml/kg), beractant-treated animals demonstrated significantly greater pulmonary β-Gal activity than saline-treated animals (p < 0.002) and untreated controls. At high volume (1.2 ml, 4 ml/kg), average β-Gal activity was similar between groups treated with beractant or saline, but was more variable within the saline treated group. Higher volumes of delivery medium were associated with increased levels of β-Gal expression regardless of the carrier used. Survanta was well tolerated by the animals and did not affect the duration of transgene expression. Exogenous beractant provides a useful medium for delivering recombinant adenoviruses to the lung when diffuse distribution of transgene expression is desired. Adult Sprague-Dawley rats were treated by direct intratracheal instillation with 1–3 ×1010 infectious units per kilogram (iu/kg) of a recombinant type 5 adenoviral vector expressing β-galactosidase (β-Gal). Virus was delivered in saline or Survanta beractant at a low volume of 0.5 ml (1.3 ml/kg) or a high volume of 1.2 ml (4 ml/kg). The distribution of transgene expression was more uniform in the beractant-treated group. β-Gal activity was quantitated by spectrophotometry following reaction with β-d-galactopyranoside (ONPG). At low volume, beractant/virus-treated animals had higher pulmonary β-Gal activities than saline/virus-treated animals, which did not differ significantly from untreated controls. At high volume, beractant-treated rats demonstrated less variability in β-Gal activity than saline-treated animals. Beractant provides a safe carrier for delivering recombinant adenoviral vectors to the lung in a volume sufficient to ensure optimal tissue delivery and subsequent transgene expression.