Magnetic bacteria in the fight against cancer

Let us imagine a tiny vehicle, a nanocar (with dimensions a million times less than a millimeter), endowed with a magnetic structure that allows it to be controlled and directed by means of magnetic fields. Imagine that we introduce that car into the human body and take it to the precise place where a drug needs to be released or cancer cells eliminated. Numerous scientists around the world are working on this bold idea, including the multidisciplinary group Magnetism and Magnetic Materials (GMMM) of the University of the Basque Country (UPV/EHU). This team participates in an investigation that takes a new step to materialize the idea.

Specifically, this group, led by Maria Luisa Fernández-Gubieda, professor at the Faculty of Science and Technology of the University of the Basque Country, explores the use of magnetic bacteria, known as magnetotactic bacteria, in the fight against cancer. These microorganisms have the amazing ability to form magnetic iron oxide nanoparticles within their cells.

These particles, with diameters of about 50 nanometers (100 times smaller than blood cells), are organized, within the bacterium, in the form of a chain, which acts as a magnetic compass and orients the bacterium as a whole in the direction defined by a magnetic field. The idea would be to use them to treat cancer by means of magnetic hyperthermia or drug transport: they would direct the bacteria to the place where the tumor is located, and would be heated by external fields to burn the cancer cells and/or release drugs by means of heat or another external stimulus. .

Image, captured by transmission electron microscopy, showing one of a magnetotactic bacterium, Magnetovibrio blakemorei, with the nanomagnets it synthesizes inside. (Photo: Magnetism and Magnetic Materials Group of the UPV/EHU)

Now, in collaboration with a team from the Berlin Helmholtz Center in Germany, led by Sergio Valencia, they have been able to explore the magnetic properties of these bacteria in more detail. The degree of success of all possible applications depends on the magnetic properties of these bacteria, and specifically on each of the nanomagnets that make up their chains. However, the magnetic signal of a single particle is so weak that, until now, it was necessary to study the response of averages of hundreds or thousands of nanoparticles to obtain meaningful results.

Having only those averaged values ​​restricted the design of custom nanomagnet applications. And this is what has now changed. Physicist Lourdes Marcano has developed a new method. “Now we can obtain precise information about the magnetic properties of several individual nanomagnets simultaneously,” she says.

Indeed, the new method makes it possible to measure the magnetic properties of individual magnetic nanostructures, even when they are inside biological entities. Specifically, thanks to the magnetic images obtained in the X-ray transmission microscope at the BESSY II synchrotron (Helmholtz Center in Berlin), and with the help of theoretical simulations, they have obtained precise information on the magnetic anisotropy of each nanoparticle within the magnetic field. microscope view. Magnetic anisotropy describes how a magnetic nanoparticle reacts to external magnetic fields applied in an arbitrary direction. It is therefore an important parameter to control and direct the magnetic nanoparticles.

At the moment, obtaining magnetic images of magnetic nanoparticles inside a biological cell with sufficient resolution is only possible in large synchrotron radiation facilities, such as the one at the Helmholtz Center in Berlin. “However, in the future, with the development of compact plasma X-ray sources, this method could become a standard laboratory technique,” says Sergio Valencia.

“The bacterium is an excellent magnetic model that helps us understand the behavior of magnetic nanoparticles and develop models that transcend other systems,” explains María Luisa Fernández-Gubieda. Her group is currently working on controlling the mobility of bacteria through external magnetic fields that allow them to be directed to the tumor and at that point activate them, also through magnetic fields, and that they perform the desired function.

The study is titled “Magnetic Anisotropy of Individual Nanomagnets Embedded in Biological Systems Determined by Axi-asymmetric X-ray Transmission Microscopy.” And it has been published in the academic journal ACS nano. (Source: UPV/EHU)