Researchers at Johns Hopkins University School of Medicine have developed a novel nanoparticle system based on engineered biodegradable poly(beta-amino ester) (PBAE) polymers for efficient systemic delivery of mRNA to lung cells. This approach offers a potential breakthrough in gene therapies for genetic lung diseases, including cystic fibrosis (CF), by overcoming the limitations of traditional delivery methods.
Overcoming Delivery Challenges in Genetic Lung Diseases
Genetic lung diseases, particularly CF, pose significant treatment challenges due to the difficulty of delivering therapeutic genetic material to affected lung cells. Current methods often involve direct delivery via inhalation or intratracheal administration, which are impractical and may not reach all affected cells. Erin W. Kavanagh, the study's first author, noted that lipid nanoparticles, a common delivery method, tend to traffic towards the liver rather than the lungs, prompting the exploration of alternative polymer-based nanoparticles.
Engineering PBAE Nanoparticles for Targeted Delivery
The researchers synthesized a library of PBAE polymers with varying chemical structures, fine-tuning their properties to enhance delivery capabilities. These polymers, composed of amine groups for nucleic acid binding and hydrolytically degradable ester groups for biodegradability, offer a safer and more effective alternative to lipid nanoparticles. The team screened these polymers for their ability to transfect human bronchial epithelial cells, including cells from patients with CF, focusing on transfection efficiency, cell viability, and target gene expression levels.
High Transfection Rates in Human Cells
The optimized PBAE nanoparticles, particularly those with the E63 end cap (PBAE-E63), demonstrated high transfection efficiency in both immortalized and primary human airway epithelial cells. Transfection rates reached up to 90% in primary human nasal and bronchial epithelial cells from both healthy individuals and patients with CF. Cell viability remained high, typically between 75% and 100%, across various polymer types and doses. Kavanagh emphasized that even a 10% recovery of wild-type function in CF patients could lead to significant improvements in their disease symptoms and quality of life.
Successful Genetic Material Delivery in Mice
In vivo studies involved intravenous administration of PBAE nanoparticles to mice, revealing a strong preference for lung tissue. Bioluminescence imaging showed high luciferase levels in the lungs and minimal expression in other organs, demonstrating the system's ability to target the lungs effectively via systemic administration. Kavanagh explained that the nanoparticles' protein coating likely contributes to their affinity for lung tissue. The systemic approach is particularly relevant for CF, a multi-system disease requiring treatment beyond the lungs.
DNA Editing in Lung Cells with Repeated Administration
Using a genetic mouse model (Ai9), the researchers assessed cell-specific targeting and gene-editing efficiency in lung tissues. Repeated systemic administration of PBAE-E63 nanoparticles encapsulating Cre mRNA led to DNA editing in up to 50% of certain lung cell populations. The nanoparticles targeted and transfected various lung cell types, including endothelial, epithelial, bronchial, and alveolar cells. Kavanagh highlighted the potential of this approach for treating genetic surfactant disorders affecting alveolar cells, which currently lack effective treatments.
Safety and Tolerability of PBAE Nanoparticles
Multiple administrations of the nanoparticles, up to nine times, showed no significant toxicity. Body weight monitoring, blood tests, and histological examination of lung tissues revealed no adverse effects on body weight, liver and kidney function, or lung histology. Kavanagh noted that the biodegradability and PEGylation of PBAE nanoparticles contribute to their tolerability and reduced immunogenicity, allowing for repeated dosing, a key advantage over AAV delivery methods.
Future Directions
Researchers are currently exploring the use of this delivery system in CRISPR-based therapies, specifically encapsulating adenine base editors to correct a rare CF variant. Preliminary results show clinically significant recovery of protein function in cells carrying this CF variant. Plans are underway to move into a mouse disease model to further validate the targeting of the lungs. Kavanagh expressed optimism about large-scale production and clinical translation, citing the cost-effectiveness and ease of manufacturing PBAEs compared to AAVs.
