Scientists around the world are researching how anti-cancer drugs can most efficiently reach the tumours they target. One possibility is to use modified bacteria as “ferries” to carry the drugs through the bloodstream to the tumours. Researchers at ETH Zurich have now succeeded in controlling certain bacteria so that they can effectively cross the blood vessel wall and infiltrate tumour tissue.
Led by Simone Schürle, Professor of Responsive Biomedical Systems, the ETH Zurich researchers chose to work with bacteria that are naturally magnetic due to iron oxide particles they contain. These bacteria of the genus Magnetospirillum respond to magnetic fields and can be controlled by magnets from outside the body.
Exploiting temporary gaps
In cell cultures and in mice, Schürle and her team have now shown that a rotating magnetic field applied at the tumour improves the bacteria’s ability to cross the vascular wall near the cancerous growth. At the vascular wall, the rotating magnetic field propels the bacteria forward in a circular motion.
To better understand the mechanism to cross the vessel wall works, a detailed look is necessary: The blood vessel wall consists of a layer of cells and serves as a barrier between the bloodstream and the tumour tissue, which is permeated by many small blood vessels. Narrow spaces between these cells allow certain molecules from the to pass through the vessel wall. How large these intercellular spaces are is regulated by the cells of the vessel wall, and they can be temporarily wide enough to allow even bacteria to pass through the vessel wall.
Strong propulsion and high probability
With the help of experiments and computer simulations, the ETH Zurich researchers were able to show that propelling the bacteria using a rotating magnetic field is effective for three reasons. First, propulsion via a rotating magnetic field is ten times more powerful than propulsion via a static magnetic field. The latter merely sets the direction and the bacteria have to move under their own power.
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