As cancer cells proliferate, they consume large amounts of oxygen. This results in oxygen-poor regions in a tumour. It is notoriously difficult to treat these hypoxic regions using conventional pharmaceutical nanocarriers, such as liposomes, micelles and polymeric nanoparticles.
Now, a team led by Sylvain Martel of the NanoRobotics Laboratory at the Polytechnique Montréal has developed a method that exploits the magnetotactic bacteria Magnetoccus marinus (MC-1) to overcome this problem.

MC-1 seeks out low oxygen levels

“In their natural environment, MC-1 bacteria (which have a chain of magnetic nanoparticles in their cells, acting like a microscopic magnetic compass needle) use the geomagnetic field (the one oriented towards the magnetic north pole in the Northern hemisphere) to search and swim deeper towards low oxygen concentrations (about 0.5% oxygen) in their environment,” explains Martel. “These organisms seek out such low oxygen levels because they are microaerophilic (meaning that they survive in low oxygen environments). Interesting is the fact that this oxygen concentration is the same as the one found in hypoxic regions of tumours.”
The researchers created an artificial environment to allow these bacteria to migrate towards the hypoxic regions in mice with colorectal cancers. “We first produce a weak magnetic field pointing towards the tumour to guide drug-loaded bacteria and make them swim towards the tumour (a process called magnetotaxis),” says Martel. “Once inside the tumour and sufficiently close to the hypoxic zones, we remove the magnetic field to allow the bacteria to use their internal oxygen sensors (aerotaxis) and follow the decreasing oxygen gradient in the tumour until they reach the 0.5% oxygen level.”

Enhancing cancer treatment

These bacteria are general transport vehicles that can transport a huge variety of therapeutic agents, such as various drug molecules, radiotherapeutic agents, stem cells and immunotherapeutics,” he tells nanotechweb.org. “In the short term, we will be using our technique to study how it can enhance cancer treatment. The possibilities are vast since all therapeutic agents for treating solid tumours share a common problem – the effective delivery to the site of treatment.”
In the more long term, the researchers say they would like to look into the effects of various therapeutic agents using its technique. They then hope to collaborate with other research groups around the world.
“In the next few months, we will begin developing medical protocols with interventional platforms at the human scale to facilitate the potential translation of this technology to clinics,” adds Martel. Finally, we will integrate mathematical models to modulate the guiding magnetic field to further improve the targeting ratio of these bacteria to tumours and continue safety studies, which are encouraging so far, to prove without a shadow of a doubt that these bacteria are safe to use.”