This happens even with the most effective siRNA delivery materials, suggesting that there is a lot of room to improve the delivery rate, Anderson says.
"We believe that these particles can be made more efficient. They're already very efficient, to the point where micrograms of drug per kilogram of animal can work, but these types of studies give us clues as to how to improve performance," Anderson says.
Molecular traffic jam
The researchers found that once cells absorb the lipid-RNA nanoparticles, they are broken down within about an hour and excreted from the cells.
They also identified a protein called Niemann Pick type C1 (NPC1) as one of the major factors in the nanoparticle-recycling process. Without this protein, the particles could not be excreted from the cells, giving the siRNA more time to reach its targets. "In the absence of the NPC1, there's a traffic jam, and siRNA gets more time to escape from that traffic jam because there is a backlog," says Gaurav Sahay, an MIT postdoc and lead author of the Nature Biotechnology paper.
In studies of cells grown in the lab without NPC1, the researchers found that the level of gene silencing achieved with RNA interference was 10 to 15 times greater than that in normal cells.
Lack of NPC1 also causes a rare lysosomal storage disorder that is usually fatal in childhood. The findings suggest that patients with this disorder might benefit greatly from potential RNA interference therapy delivered by this type of nanoparticle, the researchers say. They are now planning to study the effects of knocking out the NPC1 gene on siRNA delivery in animals, with an eye toward testing possible si
|Contact: Sarah McDonnell|
Massachusetts Institute of Technology