Pulmonary RNA interference against acute lung injury mediated by mucus- and cell-penetrating nanocomplexes

Trans-mucosal delivery of anti-inflammatory siRNA into alveolar macrophages represents a promising modality for the treatment of acute lung injury (ALI). However, its therapeutic efficacy is often hurdled by the lack of effective carriers that can simultaneously overcome the mucosal barrier and cell membrane barrier. Herein, we developed mucus/cell membrane dual-penetrating, macrophage-targeting polyplexes which enabled efficient intratracheal delivery of TNF-α siRNA (siTNF-α) to attenuate pulmonary inflammation against lipopolysaccharide (LPS)-induced ALI. P-G@Zn, a cationic helical polypeptide bearing both guanidine and zinc dipicolylamine (Zn-DPA) side charged groups, was designed to condense siTNF-α and promote macrophage internalization due to its helicity-dependent membrane activity. Coating of the polyplexes with charge-neutralizing carboxylated mannan (Man-COOH) greatly enhanced the mucus penetration potency due to shielding of the electrostatic adhesive interactions with the mucus, and it cooperatively enabled active targeting to alveolar macrophages to potentiate the intracellular delivery efficiency of siTNF-α. As such, intratracheally administered Man-COOH/P-G@Zn/siTNF-α polyplexes provoked notable TNF-α silencing by ∼75 % in inflamed lung tissues at 500 μg siRNA/kg, and demonstrated potent anti-inflammatory performance to treat ALI. This study provides an effective tool for the synchronized trans-mucosal delivery of siRNA into macrophages, and the unique properties of the polyplexes render remarkable potentials for anti-inflammatory therapy against ALI. STATEMENT OF SIGNIFICANCE: siRNA-mediated anti-inflammatory management of acute lung injury (ALI) is greatly challenged by the insufficient delivery across the mucus layer and cell membrane. To address such critical issue, mucus/cell membrane dual-penetrating, macrophage-targeting polyplexes are herein developed, which are comprised of an outer shell of carboxylated mannan (Man-COOH) and an inner nanocore formed by TNF-α siRNA (siTNF-α) and a cationic helical polypeptide P-G@Zn. Man-COOH coating endowed the polyplexes with high mucus-penetrating capability and macrophage-targeting ability, while P-G@Zn bearing both guanidine and zinc dipicolylamine afforded potent siTNF-α condensation capacity and high intracellular delivery efficiency with reduced cytotoxicity. Intratracheally administered polyplexes solicit pronounced TNF-α silencing and anti-inflammatory efficiencies in ALI mice. This study renders an effective example for overcoming the multiple barriers against trans-mucosal delivery of siRNA into macrophages, and holds profound potentials for gene therapy against ALI.