Magnets made by soil bacteria offer hope for breast and prostate cancer

Scientists are developing magnetically guided microscopic projectiles that can be injected into patients’ blood to attack breast, prostate and other tumours.

The project – led by researchers at Sheffield University – builds on progress in two key medical fields. The first involves viruses that specifically attack tumours. The second focuses on soil bacteria that manufacture magnets which they use to align themselves in the Earth’s magnetic field.

“The essence of this approach is straightforward: we are using bugs as drugs,” said Dr Munitta Muthana, one of the project’s leaders. “We are taking a class of viruses that naturally target tumours and are developing ways to help them reach internal tumours by exploiting bacteria that make magnets. It’s a twin approach and it has a lot of promise, we believe.”

The anti-cancer viruses that are being exploited by the Sheffield group – who have been funded by Cancer Research UK – are known as oncolytic viruses. They occur naturally but can also be modified to improve their efficacy and to limit the chances of them infecting healthy cells.

After infection with an oncolytic virus, a cancer cell will burst open and die. The US Food and Drug Administration has already approved the use of T-Vec, a modified herpes simplex virus that infects and kills tumour cells and is now being used to treat people with certain types of melanoma, a skin cancer.

However, the Sheffield team – whose work has just been awarded the Roger Griffin prize for cancer drug discovery – want to expand the range of tumours that can be tackled this way. In particular, they want to target breast and prostate cancers as priorities.

Dr Munitta Muthana, a senior lecturer at the University of Sheffield, is one of the project’s leaders.
‘We are simply using bugs as drugs,’ says Dr Munitta Muthana, one of the project’s leaders.

“The problem is that oncolytic viruses attract the attention of the body’s immune defences and only skin-deep tumours can be tackled this way before the viruses are blocked fairly quickly by our cell defences,” said Dr Faith Howard, another project leader.

A solution, the scientists say, is to coat the viruses in magnetic particles. Injected into the blood, these microscopic projectiles could then be directed quickly to a tumour – by using magnets placed over a patient’s body – before their progress can be blocked by immune defences.

“It’s like having a coat of armour or a shield,” added Muthana. “The magnets help protect the virus but crucially they also help them to target a tumour. We place a magnet over a tumour and it will draw the virus speedily and directly to it.”

An oncolytic virus had a diameter of about 180 nanometres while the magnets needed to be about 50 nanometres in size, added Howard. (A nanometre is a billionth of a metre.) “These tiny magnets could be made in the laboratory but we have found bacteria do a better job of manufacturing them than we could,” she added.

Some species of soil bacteria synthesise iron oxide nanoparticles that are called magnetosomes. These are used as compasses that allow the microbes to navigate in Earth’s magnetic field and help them find optimum conditions for their growth and survival. “These microscopic magnets they make are perfectly shaped and ideally suited to the microscopic packages we need to target deep cancers,” Howard said.

Having developed the technology, the Sheffield team is now working to ensure they can manufacture sufficient supplies so that clinical trials on humans can begin soon. To date, trials have focused on animal models. “These early tests have been very encouraging and we now need to take the next steps to bring this technique to a state where it can be administered to humans – hopefully in a few years’ time,” she said.