A novel inhalable nanoparticle system decorated with the cell-penetrating TAT peptide successfully delivered siRNA through lung mucus and into bronchial cells, reducing inflammatory IL-8 gene expression.
IL-8 gene knockdownTAT-decorated polyplexes penetrated bronchial epithelial cells and reduced expression of the inflammatory IL-8 gene after LPS stimulation
What the researchers found
The researchers created polyplexes (polymer-siRNA complexes) using a newly designed copolymer (PHEA-bAPAE-PEG-MLB) and decorated their surface with thiolated TAT peptide via thiol-ene chemistry. The TAT-decorated polyplexes demonstrated several key properties:
They maintained siRNA binding during mucus diffusion, passed through the mucin layer efficiently despite only forming weak bonds with mucin chains, and were highly cytocompatible (non-toxic to cells). In cellular uptake studies, the polyplexes effectively penetrated into the cytoplasm of bronchial epithelial cells and reduced IL-8 gene expression after LPS-induced inflammation. The final formulation was converted into an inhalable dry powder by encapsulating the polyplexes in mannitol-based microparticles via spray freeze drying, producing highly porous particles with suitable aerodynamic properties for lung delivery.
Why it matters
Current asthma treatments primarily manage symptoms rather than targeting the underlying inflammatory gene expression. Inhaled siRNA therapy could silence specific genes driving inflammation, but the lung's mucus barrier makes delivery extremely challenging. Using TAT peptide as a cell-penetrating agent to overcome this barrier represents a creative approach that could open the door to gene-level asthma treatments delivered conveniently as dry powder inhalers.
How the study worked
The study involved multi-step polymer synthesis: first creating a protonable copolymer from PHEA backbone with amine and PEG modifications, then complexing it with siRNA to form nanosized polyplexes, and finally decorating them with thiolated TAT peptide. Testing included mucus diffusion assays, cytocompatibility studies, cellular uptake imaging in bronchial epithelial cells, IL-8 gene expression measurement after LPS stimulation, and spray freeze drying to create inhalable microparticles. All experiments were conducted in vitro.
What this study cannot tell us
All experiments were conducted in vitro — no animal studies or human testing was performed. Mucus diffusion was tested with purified mucin rather than native airway mucus, which is more complex. IL-8 knockdown was demonstrated after artificial LPS stimulation, which may not fully replicate asthma pathophysiology. The aerodynamic performance of the microparticles was characterized technically but not tested in an actual inhalation model.
How to read the evidence
This is an early-stage in vitro drug delivery study demonstrating proof-of-concept for a novel formulation. While the results are promising across multiple characterization and functional assays, no animal or human data exist yet. This represents the earliest phase of therapeutic development.
When this study was published
Published in 2023, this is a recent formulation study. As an in vitro proof-of-concept, it would require animal studies and eventual clinical trials before any therapeutic application.
The bigger picture
Cell-penetrating peptides like TAT are gaining traction as delivery tools across many therapeutic areas. This work applies them to the challenging problem of inhaled gene therapy, where the mucus barrier, immune clearance, and need for precise lung deposition all complicate delivery. If inhalable siRNA formulations can be made practical, they could transform treatment of asthma and other respiratory inflammatory diseases by targeting root causes rather than just symptoms.
Questions still open
- Will the TAT-decorated polyplexes maintain their mucus-penetrating and cell-penetrating properties in the complex environment of an asthmatic airway in vivo?
- How durable is the IL-8 gene silencing effect, and would repeated dosing be needed for sustained asthma control?
- Could this TAT peptide-siRNA delivery platform be adapted to target other inflammatory genes beyond IL-8 in respiratory diseases?
Common questions
What is TAT peptide and why is it useful for drug delivery?
How could silencing a gene help treat asthma?
Read the original research
TAT decorated siRNA polyplexes for inhalation delivery in anti-asthma therapy.
European journal of pharmaceutical sciences : official journal of the European Federation for Pharmaceutical Sciences, 190, 106580
Citation
Drago, Salvatore Emanuele; Cabibbo, Marta; Craparo, Emanuela Fabiola; Cavallaro, Gennara. (2023). TAT decorated siRNA polyplexes for inhalation delivery in anti-asthma therapy.. European journal of pharmaceutical sciences : official journal of the European Federation for Pharmaceutical Sciences, 190, 106580. https://doi.org/10.1016/j.ejps.2023.106580