Delivery of gene therapy vectors via pulmonary routes
A host of respiratory diseases could benefit from pulmonary gene transfer, including cystic fibrosis, and potentially more common chronic conditions such as asthma and emphysema. In addition, the surface epithelial cells of the lung may be used to produce and transfer to the circulation therapeutic gene products such as hormones and enzymes, e.g. insulin. Although non-viral gene vectors are capable of mediating gene transfer both in vitro and in vivo following nebulisation, the delivery efficiency of conventional nebuliser systems is greatly reduced due to the restrictions of the device and the physico-chemical characteristics of the particles at elevated concentrations in the nebuliser reservoir. These limitations are particularly important to expensive gene transfer pharmaceuticals. While newer nebuliser technologies are under development, pressurised metered-dose inhalers (pMDIs) and dry powder inhalers (DPIs) may provide more viable alternatives for delivering therapeutically active macromolecules, particularly genes, to the lung.
Aims of Project
My research group has gained unique expertise in preparing and characterising spray-dried gene vector powders amenable to dispersion throughout the airways through particle modification (Figure 2A,B) (Li et al., 2003; Li et al., 2005a; Li et al., 2005b; Seville et al., 2002, Li & Birchall, 2006). For example, a novel dry powder inhaler formulation comprising trehalose, as thermoprotectant, dimethyl-b-cyclodextrin (DMC), as a dispersibility enhancer, and a synthetic lipid:polycation:pDNA (LPD) gene therapy vector was found to comprise small (Figure 2A; mean diameter 3-4 mm) spherical particles of altered surface morphology (Figure 1B) with a low tendency to aggregate (Li et al., 2005a). Gene expression efficiency of these spray-dried powders, following 6 months storage at room temperature, was shown to be at least comparable to that of freshly prepared aqueous systems, with the LPD dry powders also retaining functionality in the presence of respiratory mucus (Figure 2B). Following confirmation of efficient lung deposition in vitro, current collaborative studies are assessing the in vivo pulmonary gene delivery efficiency for potential clinical testing of our systems. Our discoveries using novel dry powder dispersibility enhancers have recently been patented and have been supported by funding from The Wellcome Trust and Wales Office of Research & Development.
My group is currently developing a further patented technology for producing drug and DNA nanoparticles for dispersion in hydrofluoroalkane (HFA) propellant. Initially, drug/DNA is loaded into the aqueous pool of the reverse micelles that form when a water-in-oil microemulsion is formed between water, organic solvent and surfactant. We have discovered that following removal of the water and organic solvent the dimensions of the surfactant-coated particles and their ability to disperse in HFA propellants allows for the production of stable medicinal aerosols capable of efficient pulmonary delivery by pMDI (fine particle fraction <5.8mm: 55.4, 55.8, 50.7 and 58.7 % for salbutamol, ipratropium, formoterol and insulin respectively). Importantly, this formulation process has also demonstrated utility for systemic pulmonary delivery using both in vitro and in vivo models. Our pMDI research has been supported by EPSRC, Cardiff Partnership Fund and the pharmaceutical industry.