Key points:
- A new type of nanoparticle can be delivered to the lungs of mice to perform gene editing.
- The lipid nanoparticles deliver mRNA encoding CRISPR/Cas9 components designed to snip out and replace disease-causing genes.
- In tests with mice, after three doses, about 60 percent of lung epithelial cells were transfected.
In a first, engineers at MIT and the University of Massachusetts Medical School have demonstrated highly efficient delivery of RNA to the lungs of mice. The researchers developed nanoparticles to deliver mRNA encoding the machinery needed for CRISPR/Cas9 gene editing. This could open the door to designing therapeutic nanoparticles that can snip out and replace disease-causing genes.
For the study, published in Nature Biotechnology, the researchers developed lung-targeting lipid nanoparticles made up of molecules that contain two parts: a positively charged headgroup and a long lipid tail. The positive charge of the headgroup helps the particles to interact with negatively charged mRNA, and it also helps mRNA to escape from the cellular structures that engulf the particles once they enter cells. The lipid tail structure, meanwhile, helps the particles pass through the cell membrane.
The researchers came up with 10 different chemical structures for the lipid tails, along with 72 different headgroups. By screening different combinations of these structures in mice, the team was able to identify those that were most likely to reach the lungs.
In further tests, the researchers showed they could use the nanoparticles to deliver mRNA encoding CRISPR/Cas9 components designed to cut out a stop signal that was genetically encoded into the animals’ lung cells.
According to the study, after one dose of mRNA, about 40 percent of lung epithelial cells were transfected. Two doses brought the level to more than 50 percent, and three doses up to 60 percent. The most important targets for treating lung disease are two types of epithelial cells—club cells and ciliated cells, and each of these was transfected at about 15 percent.
The new nanoparticles break down quickly, allowing them to be cleared from the lung within a few days, reducing the risk of inflammation. The particles can also be delivered multiple times to the same patient if needed.
Next, the researchers plan to use a mouse model of cystic fibrosis to see if the particles can successfully deliver mRNA that would correct the genetic mutation that causes the disease. They also hope to develop treatments for other lung diseases, such as idiopathic pulmonary fibrosis.