From the BA Festival of Science, Exeter, UK.

Magnets could pull cancer drugs towards a tumour.

Bacteria that make tiny magnetic particles could be harnessed to create drugs that home in on a specific site in the body. The particles come ready-wrapped in their own biological membrane, so molecules such as anticancer drugs could easily be attached.

Doctors could then direct the drugs to a certain area of the body using magnets, says Andrew Harrison of the University of Edinburgh, UK. Confining the medicine where it's needed could, in theory, reduce the harrowing side-effects of chemotherapy.

The bacterium Magnetospirillum magnetotacticum produces particles of magnetite (more commonly known as rust) just 30-50 nanometres across. This means that they are small enough to pass through a hypodermic needle, Harrison told the British Association Festival of Science in Exeter, UK.

M. magnetotacticum seems to use its rust particles to guide its movements. The particles are strung into chains that act like a compass needle inside the cells, allowing the bacterium to sense the Earth's magnetic field and tell up from down. "Nature is capable of making amazing biominerals," Harrison says.

Drag and drop

But if these particles can be extracted from cells in sufficient numbers, Harrison suggests, they could be used to guide expensive or poisonous drug molecules to where they are needed in the body. "Drugs usually circulate throughout the body," he says. "That's not always great news."

Patients could wear an electromagnetic device to keep the drug in its place, Harrison proposes. Besides targeting tumours, the technique could potentially also be used to treat site-specific ailments such as arthritis.

It's a good idea, comments Jon Dobson, a biophysicist at Keele University, UK. But he cautions that the suggestion is not without potential pitfalls. "Getting the particles out of the cells and making them in sufficient quantities are the major problems," he told news@nature.com.

It will also be important to ensure that the particles don't clump together, Dobson warns. When moving freely in the blood, instead of confined inside a cell, their natural magnetism might cause them to aggregate. In a worst-case scenario, this could block blood vessels and cause an embolism, he says.

Harrison has also been experimenting with ways to create particles of magnetite or pure iron by purely chemical means, rather than harvesting them from bacteria. Such particles would not have any intrinsic magnetism themselves but could be moved around by a magnet, like a microscopic version of iron filings.

The main advantage of using bacteria, however, is that they have the potential to produce particles in huge numbers, Harrison says. One drawback is that M. magnetotacticum is difficult to grow, and yields of magnetite particles are not reliably high.

But genetic modification could be used to create a more robust strain. Geneticists already have identified the suite of genes responsible for producing the particles, which could potentially be transferred to another bacterial species.

If biologists can achieve that feat, targeted drugs will be a reality, Harrison predicts. "I see huge potential for genetically modified bugs," he says. "If somebody provides enough money, someone will do it." 

University of Edinburgh

University of Edinburgh