The bacteria, which contain magnetic structures, was discovered in 1975.

Interest has grown in harnessing naturally occurring cancer treatments as microbots possessing enhanced targeting abilities. In a related study published in Science Robotics, a team of scientists from ETH Zurich uses the native magnetic properties of Magnetospirillum bacteria to decimate tumors.

Harnessing nature

Magnetospirillum magneticum is a highly evolved bacteria capable of aligning itself to swim along the earth’s magnetic fields. It does so by using organelles within its cellular structure called magnetosomes comprising magnetic mineral crystals surrounded by a fatty membrane-Acting like a compass needle to orient the magnetized or magnetotactic bacteria to regions containing high oxygen concentrations.

It is these recently discovered biological magnets that the researchers have employed as a cancer therapy in mice. They did so by applying an external magnetic field to the living microbots, enabling them to traverse the intricate web of blood vessels guarding the tumors, propelling them directly into the heart of cancerous masses, which they then attacked.

The researchers achieved this without adding any potentially toxic materials to ‘magnetize’ the bacteria – eliminating the risk of adverse events.

Lead author Simone Schürle, Professor of Responsive Biomedical Systems at ETH Zurich, says, “We make use of the bacteria’s natural and autonomous locomotion as well.” She adds, “Once the bacteria have passed through the blood vessel wall and are in the tumor, they can independently migrate deep into its interior.”

The physics

Their method relies heavily on ‘magnetic torque’ where an external magnetic field exerted on an object, in this case, bacteria, causes it to spin around its axis. The researchers also applied a rotating as opposed to a static magnetic field to propel and rotate the microbots forward in a corkscrew motion–Verifying that the propulsion speed is ten times more than that provided by a static field.

The scientists reveal that as the microbots are constantly spiraling forward, they are more likely to encounter the tiny gaps that open between the cells of the blood vessels nourishing the tumor. Multiple vessels permeate the tumor, with their walls acting as a barrier, protecting the cancerous entity against any molecules that may harm it.

These walls consist of cells with minute gaps between them that can temporarily open wide enough for large molecules such as bacteria to pass through. Thus, the constant rotational movement of the microbots means they are more likely to find and pass through these windows of chance.

Schürle says, “Once the bacteria have passed through the blood vessel wall and are in the tumor, they can independently migrate deep into its interior.” For this reason, the scientists apply the external magnetic field for just an hour—long enough for the bacteria to cross the vascular barrier into the tumor.

Functionality

The team also tested the ability of Magnetosprillium to carry cargo such as cancer-killing drugs. They did this by attaching fluorescently tagged nanospheres of fat called liposomes to the bacteria. The scientists then injected the microbots and pseudo-drugs into a three-dimensional tumor model contained within a petri-dish. Results show that the biomagnets ferried and accumulated the fluorescent material throughout the cancerous tissue.

A sound methodology; in their paper, the researchers write that the culmination of natural magnetism and external torque resulted in a fourfold increase in the volume of microbots that reach and saturate the tumors.

They add that when the bacterial agents reach their target, they should also cause an immune response, where the body’s white blood cells start killing any cancer reservoirs. These prerequisites, married with a proven anti-cancer treatment, should be potent.

But they caution that even when exploiting the inherent properties of bacteria in cancer therapy, how these bacteria can reach cancer deep within the body is still in question, with human studies a long way off.

And while they have successfully applied their new technique to tumors near the body’s surface, the observations may prove less effective when used on deep-tissue malignancies that are harder to reach. However, Professor Schürle is upbeat regarding this breakthrough and believes their new approach will improve the efficacy of microrobotic cancer therapy.