Recent Progress in Nucleic Acid Pulmonary Delivery toward Overcoming Physiological Barriers and Improving Transfection Efficiency

Abstract

Pulmonary delivery of therapeutic agents has been considered the desirable administration route for local lung disease treatment. As the latest generation of therapeutic agents, nucleic acid has been gradually developed as gene therapy for local diseases such as asthma, chronic obstructive pulmonary diseases, and lung fibrosis. The features of nucleic acid, specific physiological structure, and pathophysiological barriers of the respiratory tract have strongly affected the delivery efficiency and pulmonary bioavailability of nucleic acid, directly related to the treatment outcomes. The development of pharmaceutics and material science provides the potential for highly effective pulmonary medicine delivery. In this review, the key factors and barriers are first introduced that affect the pulmonary delivery and bioavailability of nucleic acids. The advanced inhaled materials for nucleic acid delivery are further summarized. The recent progress of platform designs for improving the pulmonary delivery efficiency of nucleic acids and their therapeutic outcomes have been systematically analyzed, with the application and the perspectives of advanced vectors for pulmonary gene delivery.

Keywords: delivery vectors; inhaled materials; nucleic acids; pulmonary bioavailability; pulmonary delivery.

Figure 1

Factors influencing the pulmonary bioavailability of the inhaled nucleic acid. Created with BioRender.com.

Figure 2

The macromolecular structure of airway mucins and the fate of pulmonary deposited particles. A) The mucin backbone has various glycosylation modifications. B) The mucin monomer contains serine‐, threonine‐, and proline‐rich amino acids in the backbone. C) The mucin monomer assembles into multimer states that exist as linear, branched, or side‐linked structures via disulfide bonds. D) The fate of aerosol drugs after deposition in the bronchus or alveolus via mucociliary clearance, macrophage phagocytosis, or uptake into epithelial cells or systemic circulation. Created with BioRender.com.

Figure 3

Chemical structures of commonly used polymeric materials as nanocarriers for pulmonary gene delivery.

Figure 4

Chemical structures of commonly used lipid materials as nanocarriers for pulmonary gene delivery.

Figure 5

Improve effective pulmonary deposition and reduce macrophage clearance. A) Schematic representation of the respiratory tract and aerodynamic size‐dependent pulmonary deposition. Created with BioRender.com. B) Results of the simulation with computational fluid dynamics (CFD) of particle behavior at different sizes (1 µm, 5 µm, and 50 µm), which are dragged by flows of 6, 24, and 95 L min⁻¹. The red areas indicate a high density of trapped particles. Reproduced with permission.^{[ 125 ]} Copyright 2012, Sociedad Española de Neumología y Cirugía Torácica (SEPAR). C) Strategies avoid alveolar macrophage phagocytosis of deposited particles: particles with size in microscales, unmodified hydrophobic surface, or decorated with active targeting ligands could be effectively swallowed by alveolar macrophage, while the particles with reduced nanoscale size or surface modified by hydrophilic layer could effectively reduce macrophage phagocytosis. Created with BioRender.com. Note: There is a text error in the cited image (Figure B), which we get the copyright to use but have no right to edit, which the Center should be Flow 24 L min⁻¹, Size 5 µm, while the Right‐bottom should be Flow 95 L min⁻¹, Size 50 µm.

Figure 6

Strategies to overcome the mucosal barrier and improve mucus penetration: A) The deposited particles with size not larger than low‐viscosity channels or pores within the mucus could rapidly penetrate the respiratory mucus layer; B) Particles with neutral or negative surface charges could avoid the mucus traction due to the electrostatic repulsion; C) Particle surface modification with a fluorinated layer or hydrophilic layer (PEGylation) could be isolated from the interaction with the mucus layer; D) Nucleic acid delivery using virus‐based carrier or co‐delivery with mucin degradation agents could achieve mucus penetration effectively. Created with BioRender.com.

Figure 7

Endosomal escape mechanism of lipid and polymer‐based gene delivery vector. A) Schematic diagram of the proton sponge effect for cationic polymer‐based nanoparticle endosomal escape. B) Schematic diagram of the fusion pore mechanism and transient pore mechanism for cationic lipid‐mediated endosomal escape. Created with BioRender.com.

Figure 8

Strategies to improve extracellular stability of therapeutic nucleic acid. A) Chemical modifications of the nucleoside bases to enhance the stability of RNA therapeutics. B) Gene‐encapsulated formulations are designed to improve the stability of RNA therapeutics. C) Improving mRNA stability via chemical modification, complementary RNA/Oligo RNA hybridization, or hydrophobic moieties combination. Created with BioRender.com.

Figure 9

Schematic illustration of CA‐O and ssRNA nano‐formulation to improve their intracellular stability. CA‐O could bind with ssRNA by coordination between the Zn/DPA head and phosphate in the RNA backbone, then encapsulated nucleic acid inside the particles to protect from enzyme‐based degradation. Created with BioRender.com.