Nucleic acid carriers for lung gene therapy : overcoming the mucus barrier in lung diseases – LuTher

Lung diseases such as asthma and chronic obstructive pulmonary disease (COPD) are major causes of morbidity and death worldwide for which therapies with efficient and prolonged local activity are much needed. Though it is considered as a promising approach to treat lung diseases, gene therapy still is reliant on the development of efficient and safe nucleic acid carriers. Poor gene transfer into the lungs has been attributed to numerous causes (limited cellular uptake, unproductive intracellular trafficking, carrier toxicity and immunogenicity…). A less elucidated bottleneck however is the adhesive and hyper viscoelastic airway mucus that prevents transfection particles from freely reaching the epithelium, thereby limiting gene transfer to the lungs.

The LuTher research program aims at the development of nucleic acid carriers for administration to the airways. Sulfur-containing carriers will be designed so they display intrinsic mucolytic properties allowing transfection particles to overcome the mucus barrier in chronic inflammatory airway diseases associated with mucus hypersecretion such as asthma and COPD. They will be engineered to display biodegradability under various stimuli so as to liberate thiols in situ. These thiols are likely to disrupt disulfide bridges in the mucus biopolymer and reduce its viscoelasticity, allowing better penetration of the nucleic acid containing nanoparticles towards the targeted lung epithelium. The deeper and quicker the particles penetrate the mucus layer, the less they are subjected to elimination by mucociliary clearance and coughing. This in fine improves delivery of the therapeutic nucleic acid to the airway epithelial cells, which is mandatory for high transfection efficiency. Structure-activity relationship analysis is central to the project and will be conducted via biophysical and biological evaluations of the mucolytic carriers so as to determine the key parameters for efficiency and safety, and for improving the compounds through a feedback loop. Evaluations of the mucolytic carriers will include rating of transport and stability of transfection particles in mucus in vitro and ex vivo, and assessment of their efficiency in delivering pDNA and siRNA in both in vitro and in vivo models for asthma and COPD. Gene transfer efficiency will be determined using pDNA coding for the Luciferase protein whereas gene silencing experiments will be performed with p65 and MMP-12 targeting siRNAs, two potential targets for the treatment of asthma and COPD.

The dual-function nucleic acid carriers proposed herein have no counterpart to date. Combining mucolytic activity and transfection properties in a single drug delivery system constitutes a strategy that has not yet been investigated for improving airway transfection. The intimate collocation of the transfection particles and in situ generated mucolytic agents is expected to boost the diffusion of transfection particles through the mucus towards the lung epithelial cells, provoking only local mucus alteration and thus keeping microviscosity of the latter to a minimum.

A large number of nucleic acid delivery platforms, including viral and non-viral systems, have been developed to treat lung diseases. Poor gene transfer has been attributed to numerous biological barriers, including limited cellular uptake across the apical membrane, unproductive intracellular trafficking, carrier toxicity and immunogenicity. A less elucidated bottleneck however is the adhesive and hyperviscoelastic mucus that prevents gene carriers from freely reaching the epithelium, thereby limiting nucleic acid transfer. Consequently, overcoming the mucus barrier should be considered as an essential design criterion in developing a delivery platform capable of achieving clinical end points for lung gene therapy. This is the very purpose of the LuTher proposal.