To build their targeted particles, the researchers used a technique called "layer-by-layer assembly." This means each layer can be tailored to perform a specific function.
When the outer layer (made of polyethylene glycol, or PEG) breaks down in the tumor's acidic environment, a positively charged middle layer is revealed. That positive charge helps to overcome another obstacle to nanoparticle drug delivery: Once the particles reach a tumor, it's difficult to get them to enter the cells. Particles with a positive charge can penetrate the negatively charged cell membrane, but such particles can't be injected into the body without a "cloak" of some kind because they would also destroy healthy tissues.
The nanoparticles' innermost layer can be a polymer that carries a cancer drug, or a quantum dot that could be used for imaging, or virtually anything else that the designer might want to deliver, says Hammond, who is the Bayer Professor of Chemical Engineering at MIT.
Other researchers have tried to design nanoparticles that take advantage of tumors' acidity, but Hammond's particles are the first that have been successfully tested in living animals.
The researchers are planning to further develop these particles and test their ability to deliver drugs in animals. Hammond says she expects it could take five to 10 years of development before human clinical trials could begin.
Hammond's team is also working on nanoparticles that can carry multiple payloads. For example, the outer PEG layer might carry a drug or a gene that would "prime" the tumor cells to be susceptible to another drug carried in the particle's core.
|Contact: Caroline McCall|
Massachusetts Institute of Technology