Recent advances in nanoparticle-based therapeutics have led to new delivery systems that can deliver siRNAs, exogenous DNA, and mRNA to cells. Liposomes combined with plasmids have been used to enhance the internalization of the genetic material into the cytosol via endocytosis. Nanoparticles consist of a nucleic acid complex with other materials, such as lipid, polymers, peptides, and polysaccharides
[38]. Solid lipid nanoparticles that can remain solid at physiological temperatures have been employed because they stay protected from nucleic acid degradation caused by the nuclease. Despite the risk of cytotoxicity, synthetic polymers, such as polyethyleneimine (PEI) or polyethylene glycol (PEG), are commonly used for gene transfer, given their higher efficiency. Another approach relies on molecular conjugates, consisting of a polylysine-DNA complex and a macromolecule receptor ligand that can be internalized by the target cells
[39]. Lipid nanoparticles (LNPs) are formulated by combining lipid-based components and siRNA or modRNA; the combination of the organic and aqueous components induces hydrophobic/hydrophilic interactions, resulting in the formation of nanoparticles
[40]. The lipidoid components can be optimized through combinatorial chemistry approaches to achieve higher stability of the LNPs at 4 °C after synthesis, without requiring freezing temperatures for their transport and storage, thus facilitating their distribution to clinical settings
[41]. A study assessing the efficacy of formulated LNPs showed that LNPs remained stable for 15 days in storage at 4 °C after synthesis; although there was a reduction in activity within the first 24 h, the ability to transfect cells in vitro successfully was retained and remained unchanged for the remaining days
[42]. This study also demonstrated rapid and highly efficient transfection of cells in vivo in rats and pigs, with peak expression within 20 h of delivery. The expression decreased to an almost negligible level by week 2 after administration, which renders this approach applicable for indications where transient expression is preferred or when repeated administration is feasible
[42]. Non-viral vectors are less used for lung delivery. This is a path that remains to be further explored. Another advantage of using nanoparticles for the delivery of RNA-based gene therapy includes the enhancement of cellular uptake, endosomal escape, and protection from nuclease degradation; furthermore, targeted delivery can be achieved by enhancing nanoparticle compatibility through surface modifications. A study tested two polymers to deliver miRNA mimics into CF airway epithelial cells, including PEI and chitosan
[43]. While PEI-based nanoparticles were more effective in facilitating miRNA uptake into the epithelial cells than chitosan, both nanoparticles appeared to be nontoxic
[43]. Another study used an experimental PAH rat model to assess the therapeutic effects of the intravenous delivery of antisense oligonucleotide against miR-145 (anti-miRNA-145) with loaded LNPs injected three times over 5 weeks. The authors found that anti-miRNA-145 was distributed mainly in the lungs, liver, kidney, and spleen, and no major off-target effects were observed in rats
[44]. A recent review summarized the delivery of miRNA by employing various types of nanoparticle-based therapeutics in respiratory diseases, including the common nanoparticles mentioned above and some novel nanoparticle delivery systems
[45]. Apart from RNA-based therapies, decoy oligodeoxynucleotides (ODNs) were recently found to be another promising gene therapy agent, especially nuclear factor KB (NFKB) decoy ODNs, which have shown great potential in the treatment of respiratory diseases by reducing the NF
kB-mediated inflammatory signaling pathway
[46]. Various nanoparticles have been tested to deliver NF
kB decoy ODNs both in vitro and in vivo with impressive outcomes. In an in vitro model of CF induced by interleukin-1β or
Pseudomonas aeruginosa lipopolysaccharide-stimulated bronchial epithelial cell lines, NFkB decoy ODNs coated with polysialic acid-N-trimethyl chitosan or poly(D,L-lactide-co-glycolide), large porous particles efficiently reduced the secretion of multiple pro-inflammatory mediators of CF
[47][48]. Moreover, in a PAH rat model, a single intratracheal instillation of polymeric nanoparticle (NP)-mediated NF-kB decoy resulted in the delivery of NPs into lungs and attenuated the setting of PAH by reducing vascular remodeling and inflammation
[49]. More details about NFKB decoy ODN-based gene therapies in respiratory diseases were summarized in a recent review
[46].