Nebulization of RNA-Loaded Micelle-Embedded Polyplexes as a Potential Treatment of Idiopathic Pulmonary Fibrosis

Biodegradable poly(β-amino) esters (PBAEs) have been a focus of interest for delivering therapeutic siRNA for several years. While no approved therapies are on the market yet, our study aims to advance PBAE-based treatments for currently "undruggable" diseases. The PBAEs used in this study are based on a recently reported step-growth copolymerization, which results in polymers with a unique balance of lipophilicity and positive charge, thereby showcasing diverse properties. Upon incubation with siRNA, these PBAEs form a unique structure and topology, which we classify as a subtype of classical polyplex, termed "micelle-embedded polyplexes" (mPolyplexes). The impact of different nebulizers on the physicochemical performance of these nanoparticles was investigated, and it was found that various mPolyplexes can be nebulized using vibrating-mesh nebulizers without the loss of gene silencing activity nor a change in physicochemical properties, setting them apart from other nanoparticles such as marketed LNPs. Finally, their therapeutic application was tested <i>ex vivo</i> in human precision-cut lung slices from patients with lung fibrosis. mPolyplexes mediated 52% gene silencing of matrix metalloprotease 7 (MMP7) and a downstream effect on collagen I (Col I) with 33% downregulation as determined via qPCR.