A Poly-Functional Gene Delivery System for Cystic Fibrosis.

Montier T, Mottais A, Berchel M, Le Gall T, Sibril Y, Laurent V, Davies L, Gill DR Hyde SC, Jaffres P

Molecular Therapy, Vol 25 S1, Abstract 479

The American Society of Gene and Cell Therapy Annual Conference, Washington, DC, 2017

Objective: Cystic Fibrosis (CF) gene therapy is the only therapeutic strategy independent of mutations. Today, it is based on a safe and efficient delivery of cftr gene copy into pulmonary epithelial cells. Nevertheless, many extracellular obstacles such as the presence of bacteria can impair the efficiency of the gene transfer. Therefore, it is relevant to develop multi-functional systems combining a transfecting capacity and an antibacterial activity in order to eliminate the bacteria and thus facilitate the entry of the transgene into the target cells. A previous study has enabled us to identify a combination of a cationic lipid and a N-heterocyclic carbene-silver complexes that can be delivered by aerosol which has a transfecting capacity as well as a broad spectrum of antibacterial activity. The aim of this work was to develop new combinations of original silver salt and cationic lipids to increase the antibacterial effect and maintain the transfection efficiency while reducing the quantities of silver salt used.

Methods: Firstly, the antibacterial activity against Gram + (Staphylococcus aureus) and Gram - (Escherichia coli and Pseudomonas aeruginosa) bacterial strains of each compound alone was evaluated in order to demonstrate a structure/activity relationship. Secondly, in contrast to the combination previously used (1/1molar ratio), the neo-synthesized N-heterocyclic carbene-silver complexes were combined with a cationic lipid in a 0.5/1 molar proportion of respectively. Thirdly, the transfecting activity and the cytotoxicity were then evaluated by direct deposition on bronchial epithelial cells.

Results: All newly synthesized N-heterocyclic carbene-silver complexes showed antibacterial activity against Gram + and Gram - bacteria strains with minimal inhibitory concentrations (MIC) in the same scale (μM) of that of antibiotics. The antibacterial activities obtained with the neo-synthetic compounds were better against Gram + than those of the carbene-silver complexes previously used. When associated to a cationic lipid, the antibacterial activity was still obtained. The cytotoxicity induced from the new combinations was higher than the cytotoxicity observed with the previous carbene-silver complexes. The transfection efficiency by direct deposition of the new combinations was better than with the cationic lipid alone.

Discussion and Conclusion: The addition of aliphatic chain on the silver salt was beneficial for the antibacterial activity. These new molecules have a very interesting antibacterial potential and could represent an alternative to antibiotics. In fact, preliminary tests allowed us to observe, with this type of compounds, the absence of resistance emergences of bacteria which are frequently isolated in CF patients. Moreover, under infectious conditions (bacteria in the environment of epithelial cells), the combination of a cationic lipid with a carbene-silver complexes enables the transfer of the transgene into the target cells. For future research, it may be relevant to test new molar proportions in order to decrease the cytotoxicity and to evaluate these combinations following aerosolization.