If a drug can be guided to the right place in the body, the treatment is more effective and there are fewer side-effects. Researchers at Lund University in Sweden have now developed magnetic nanoparticles that can be directed to metallic implants such as artificial knee joints, hip joints and stents in the coronary arteries.
Associate Professor Maria Kempe, her brother and colleague Dr Henrik Kempe and members of staff at Skεne University Hospital have shown that the principle works in animal experiments. They have succeeded in attaching a clot-dissolving drug to the nanoparticles and, with the help of magnets, have directed the particles to a blood clot in a stent in the heart to dissolve it. Thus the nanoparticles have been able to stop an incipient heart attack.
A stent is a tube-shaped metal net used to treat narrowing of the coronary arteries. First the artery is expanded using a balloon catheter, then a stent is inserted to keep the artery open. However, the method is not without problems: depending on the type of stent inserted, the cells of the artery wall can grow and again obstruct the artery or a blood clot can develop in the stent.
In the Lund researchers' experiments, the nanoparticles were coated with a drug used to treat blood clots. The particles could also carry other drugs, e.g. drugs to stop the cell growth that makes an artery become narrower.
"They could also carry antibiotics to treat an infection developed after insertion of an implant. We have developed polymer materials that can be loaded with antibiotics -- these could produce interesting results in this context," says Maria Kempe.
Guiding drug-loaded magnetic particles using a magnet outside the body is not a new idea. However, previous attempts have failed for various reasons: it has only been possible to reach the body's superficial tissue and the particles have often obstructed the smallest blood vessels.
The Lund researchers' attempt has succeeded partly because nanotechnology has made the particles tiny enough to pass through the smallest arteries and partly because the target has been a metallic stent. When the stent is placed in a magnetic field, the magnetic force becomes sufficiently strong to attract the magnetic nanoparticles. For the method to work the patient therefore has to have an implant containing a magnetic metal.
"It takes many years to develop a treatment method that can be used on patients. But the good initial results make us hopeful," says Maria Kempe.
- Kempe et al. The use of magnetite nanoparticles for implant-assisted magnetic drug targeting in thrombolytic therapy. Biomaterials, 2010; DOI: 10.1016/j.biomaterials.2010.07.107
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