Delivering drugs by magnet

Medication molecules aboard nanoparticles can be released using magnetic fields. Joel F Hooper reports.

Magnetic fields can trigger targeted nano-scale drug delivery.
Magnetic fields can trigger targeted nano-scale drug delivery.
Cordelia Molloy / Science Photo Library

Targeting drugs to a particular site in the body is a topic of major interest in medicine. If drugs can be localised to where they are needed – for example, targeting chemotherapy drugs to the site of a tumour – then side-effects can be significantly reduced.

Publishing in Nature Catalysis, Sergiy Minko and a team of researchers from the University of Georgia and Clarkson University in the US report a method to release drugs from a carrier nanoparticle using a magnetic field.

Nanoparticles in magnetic fields have been used in drug delivery before, but an alternating magnetic field is usually used to heat them up, causing their thermo-responsive coating to dissolve and release their cargo. This can be a problem when the cargo is heat sensitive, or when heating of the particle causes damage to surrounding tissue. Now, Minko’s team have devised a way to release drugs from nanoparticles with magnets, without any heat necessary.

To achieve this, the team uses two types of nanoparticles, each with a magnetic iron oxide core coated with a polymer. The nanoparticles are then loaded up with two different proteins, which are attached to the polymer coating.

The first type of nanoparticle is loaded with a carrier protein attached to a drug molecule. The second type is loaded with an enzyme that acts like a pair of scissors and snips the drug molecule free from the protein.

In the absence of a magnetic field, the two types of nanoparticles don’t interact, and the drug molecule remains safely bound. But when a moderate magnetic field is applied, a dipole is generated in the magnetic cores of the nanoparticles.

This causes them to cluster together, like a pile of bar magnets thrown into a desk drawer.

As the nanoparticles gather, their polymer coatings begin to merge. This brings the carrier protein with its drug cargo into contact with the enzyme that is able to digest it. When the protein is digested, the drug molecule is released into the surrounding area, allowing it to interact with its target.

So far, Minko’s team have demonstrated this technique on cancer cells in a petri dish, but they hope to apply it to patients in the future. It is hoped that the nanoparticles can be injected into the blood stream, and a targeted magnetic field can be applied to the site of the tumour, causing drug release without harming the rest of the body.

Joel Hooper is a senior research fellow at Monash University, in Melbourne, Australia.
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