A magnetic trap for cancer cells

Using the power of magnets, scientists are capturing cancer cells circulating in the blood...

One of the reasons why many forms of cancer are so deadly is that they are usually diagnosed relatively late, at a stage where treatment is less likely to be effective. This is because there are currently no techniques sensitive enough to detect early cancers reliably, because existing scans and blood tests simply aren’t good enough.

Now a team at Stanford University - armed with iron nanoparticles and a tiny magnetic wire - have a potential solution.

"We know that tumours shed different molecules that end up in the blood," says Prof. Sam Gambhir, who led the study. "The problem is that when the tumour is small and very early [in its development], these molecules are only shed in very low quantities. So, to find these rare molecules, we need a way to go into your blood and filter them out."

Rather than look for these chemical needles in a haystack, the team’s neat solution is to find a way to grab whole cancer cells using their the “MagWIRE” - a wire about the length of a fingernail and the same thickness as a paperclip - made up of small, but very powerful magnets. Placed in a vein, it can capture any magnetically-active particles that float by in the blood. “The problem then becomes that tumours do not produce particles that are magnetic. So we also put in little magnetic nanoparticles that stick to the molecules the tumour is making.”

In order to ensure that the magnetic nanoparticles stick themselves only to molecules produced by tumours, the researchers attached the nanoparticles to antibodies which selectively latch onto tumour molecules. The advantage of using antibodies for this purpose is that they can be designed so that they are very specific to a single molecule. This means that they are very unlikely to stick to something that isn’t their specified target.

The MagWIRE has been trialled in mice and pigs so far, and appears to work well in both. Gambhir is confident that this means the technique can be effective in humans. “Within about 20 minutes of putting the wire in your blood, we will be able to sample the entire blood volume in your body, pull out the wire, and then analyse everything stuck to it, so that we can get a detailed assessment if there may be a hidden tumour.”

The team are still looking into whether there are any adverse effects from using this diagnostic method. However, Prof Gambhir believes that wire itself is very likely to be completely safe if used correctly. It is still unknown whether the nanoparticles carry any risks, but similar iron nanoparticles are already used in humans in other contexts, such as treating anaemia, so they are also likely to prove safe.

The patients who stand to benefit the most from this technology, Gambhir believes, are those at an increased risk of cancer, based on their family history or due to a particular genetic disease.

The technique could also be used in the general population as a screening test for early cancer, although this is likely to be challening in practice. “It’s unlikely that we will put millions of people through a screening process where they would not just get a simple blood draw, but which would involve putting a wire in them for 20 minutes. However, for people who are at higher risk, it may make sense to use the MagWIRE to detect if they have an early cancer.”