Gene Therapy for CF using Canonic Liposome Mediated Gene Transfer: Phase 1 Trial 
domain deletions in recombinant CFTR lead to alterations in single chloride channel currents 
compatible with the notion that CFTR directly functions as a chloride channel (23,24). Mice 
obtained after inactivation of the murine CFTR exhibit defects in c AMP-stimulated chloride 
transport and correction of these abnormalities has been reported following transfer of the 
normal human CFTR in vivo (11,25). In addition to its role as a chloride channel, other CFTR 
functions have been defined, including a role in regulating epithelial amiloride- sensitive sodium 
transport (16-18), calcium dependent chloride transport (26), and trafficking of epithelial 
endocytic and exocytic vesicles (27). 
I.B.3. Pathophysiology of CF. 
Over 300 mutations in CFTR have been described which are associated with clinical CF, 
and evidence suggests heterogenieity in the molecular pathogenesis of the disease. For example, 
the most common CFTR mutation, deletion of a phenylalanine residue at CFTR position 508 
(i.e., Delta F508), appears to cause biosynthetic arrest of the full-length CFTR, with premature 
degradation of CFTR in the endoplasmic reticulum and failure to properly insert the protein in 
the apical membrane (28,29). The second most common CFTR mutation (a glycine -* aspartic 
acid replacement at CFTR position 551, i.e., G551D) is associated with normal cellular 
processing, but may cause disease by interfering with nucleotide binding and activation of CFTR 
(30). Other mutations cause premature stop codons within the protein (31,32). 
The fluid and electrolyte content of normal respiratory mucous is dependent upon CFTR 
chloride channel activity, and it has been suggested that failure to secrete chloride by CF 
epithelial cells results in diminished hydration of mucous, sputum hyperviscosity, and the 
pulmonary sequelae of the disease. This model for disease pathogenesis, together with an 
improved understanding of the molecular physiology of CF, has lead to several novel therapeutic 
approaches. Drugs designed to activate chloride secretion into the airways despite defective 
CFTR (e.g. , extracellular nucleotides [18]), and methods to allow normal biosynthetic processing 
or activation of the Delta F508 CFTR (e.g. , methylxanthines, temperature modulation) (21 ,33,34) 
are currently undergoing in vitro or in vivo evaluation. Associated functions of CFTR, such as 
the regulation of amiloride sensitive sodium transport, may also contribute to clinical disease. 
For example, potential difference measurements across the airway epithelium (see below) 
indicate excessive airway sodium reabsorption through an amiloride inhibitable pathway. Because 
excess sodium uptake from the airways could result in excessive removal of airway water and 
dessication of respiratory mucous, mechanisms for blocking airway sodium uptake in CF are 
currently under investigation. The use of aerosolized amiloride to treat CF pulmonary disease 
is currently undergoing Phase n/III multi-center human trials. 
I.B.4. Gene Transfer-Based Therapy of CF Lung Disease 
The findings of gene transfer mediated correction of the CF defect in cultured cells and 
in CF mice, together with the failure of all current therapies to allow CF patients to live beyond 
young adulthood, indicates the need for new approaches to CF therapy and the possibility of 
gene transfer-based protocols in the disease. Five protocols using recombinant El deleted 
adenovirus to deliver wild type CFTR to the nasal and lower airway epithelium of CF patients 
have already been approved by the Recombinant DNA Advisory Committee of the NIH (12). 
Recombinant adenovirus has been shown to efficiently deliver reporter genes to respiratory 
epithelium of cotton rats, to human airway epithelium grown in vitro or in a reconstituted 
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Recombinant DNA Research, Volume 18 
