Nanoparticles Release Drugs on Demand

Dec. 10, 2007 -- A specially designed nanoparticle affixed with a tiny magnet and a piece of DNA will free its drug cargo on demand when zapped with an electromagnetic field.

By offering a unique method for targeting therapies to disease, the approach could reduce the quantity of drugs necessary and also reduce unwanted side effects.

"You would like them not to release drug until they get to the tumor, and then once they get there, you want them to release the drug as soon as possible," said Geoffrey von Maltzahn, a Ph.D. student at the Harvard-MIT Division of Health Sciences and Technology.

The team, lead by associate professor Sangeeta Bhatia, described their technique in a recent issue of the journal Advanced Materials.

Soon after ingestion, most drugs begin leaking their chemicals into the body's blood stream, even if they are not yet near diseased tissue, such as a cancerous tumor. That can cause side effects and also make the drugs less potent.

Biomedical researchers have been exploring different ways for encapsulating drug compounds to reduce leakage. For example, one approach is to put the drug inside a polymer bead that slowly degrades and eventually exposes the drug to the tumor. Another method involves placing a particular molecule on the surface of the bead, so that it binds to a specific molecule in the tumor and then triggers the release of the drug.

But the system is not perfect.

"There is still leakage," said Warren Chan, a professor of materials science at the University of Toronto and an expert in developing nanostructures for biomedical applications. Furthermore, he said, "a lot of particles injected into the body get trapped in the liver and spleen and don't reach the target site."