Hydrogels releasing polymeric nanoparticles for local delivery of nucleic acids

With the continuous progress in research and clinical success, nucleic acid-based therapeutics are expected to take a more substantial place for the medical treatment of a great variety of chronic and life-threatening diseases in the future. However, nucleic acids have unfavorable biopharmaceutical properties making the delivery of these molecules in the target cells very difficult. Polymeric vectors have been extensively studied to function as gene delivery systems. The variation in the chemical composition of the polymers and the availability of a broad range of chemical tools to add functionalities, allow that the properties of the polymeric systems to be adjusted and tailor made for the desired application. In the search for new delivery strategies, one emerging approach is the use of hydrogels for local administration of nucleic acids. By avoiding some of the target transport challenges, the in vivo efficacy can potentially be improved while simultaneously limiting off-target effects. The aim of the work described in this thesis was to design and synthesize polyplex-containing injectable hydrogel formulations for sustained and local release of nucleic acids. In order prepare the hydrogels, complexes are formed between nucleic acids and cationic poly(2-dimethylaminoethyl methacrylate) (PDMAEMA)-based polymers (referred to as polyplexes), followed by the loading of the polyplexes in a thermosensitive hydrogel consisting of poly(N-isopropylacrylamide)-poly(ethylene glycol)-poly(N-isopropylacrylamide) (PNIPAM-PEG-PNIPAM) block copolymers. Because PNIPAM-based polymers display a phase transition in water (i.e. cloud point) around 32 °C, they are very attractive materials for biomedical and pharmaceutical applications because they can be administered as liquid formulation at room temperature and subsequently rapidly solidify at body temperature. The designed triblock copolymer (PNIPAM-PEG-PDMAEMA, NPD) used for polyplex formation combines multiple functionalities, including cationic properties, needed for complexation with nucleic acids, and thermosensitive properties to anchor the polyplexes in the thermosensitive hydrogel. In-depth mechanistic studies were performed to evaluate the physicochemical properties of polyplexes formed between nucleic acids (pDNA and siRNA) and the multiresponsive polymer, and their capability to delivery their cargo in vitro. Furthermore, loading of siRNA-polyplexes in a thermosensitive hydrogel resulted in a sustained release of siRNA in the form of intact polyplexes. Local and sustained nucleic acid delivery using hydrogels is therefore a promising approach, and additional optimizations of the polymeric carrier and in vivo evaluation will hopefully further underscore the clinical potential of the polyplex-hydrogel system.