Written by Charlotte Harrison, Science Writer
Delivering gene therapies to the lung is challenging because of its specialized cell types and defence mechanisms that protect it from foreign particles. A study in Nature Biotechnology describes a more efficient way of delivering gene editing tools to mouse lungs, enabling the authors to show the likely first description of CRISPR editing in the lung.
Better lipid nanoparticles
The study focused on lipid nanoparticles as a CRISPR–Cas9 delivery system. The authors first synthesized over 700 biodegradable lipids that contained combinations of different head and tail groups connected by a linker molecule. Head groups enable nanoparticles to interact with mRNA and escape cellular defence mechanisms, and tail groups enable the nanoparticles to pass through the cell membrane.
The lipids were incorporated into standard lipid nanoparticle formulations, and then screened in cells and mice to determine which lipids had the best RNA transfection efficiency in lung cells. A lipid called RCB-4-8 was identified as the most promising molecule for intratracheal delivery, especially as it was much more effective than a clinically approved lipid.
Notably, RCB-4-8 could deliver an RNA system to the two main types of lung airway epithelial cells, ciliated and club epithelial cells. This finding suggests RCB-4-8 has potential for use in disorders such as cystic fibrosis.
“This lipid can enable us to deliver mRNA to the lung much more efficiently than any other delivery system that has been reported so far,” said first author Bowen Li in a news release.
CRISPR edits in the lung
Next, the researchers studied the gene-editing properties of RCB-4-8 in mouse lungs. Intratracheal administration of lipid nanoparticles loaded with a CRISPR-Cas9-based fluorescent reporter system showed that gene editing was indeed feasible in the lung.
The researchers also tested a hybrid delivery approach. This involved Cas9 mRNA packaged in lipid nanoparticles and guide RNAs delivered by a viral vector. Such an approach might be useful for tissue-specific genome editing (enabled by the the viral-vector component) while the lipid nanoparticle component limits the duration of Cas9 expression to avoid potential safety issues.
The authors note that their next step on the journey to possible clinical application of RCB-4-8 is to test whether it can transduce airway epithelial stem cells in mice and nonhuman primates. In addition, they plan to test RCB-4-8’s ability to deliver mRNA to correct a mouse model of cystic fibrosis. They also hope to make the nanoparticles more stable so they could be aerosolized for use in a nebulizer.