Illustration of bacteria of different shapes, including cocci and rod-shaped bacteria.

Innovation

These tiny magnetic robots can infiltrate tumors — and maybe destroy cancer

Bacterial cancer treatments are coming back into fashion (with some futuristic upgrades).

KATERYNA KON/SCIENCE PHOTO LIBRARY/Science Photo Library/Getty Images

Doctors aren’t always able to remove hard-to-reach cancerous tumors with surgery, so some patients must receive aggressive chemotherapy and/or radiation therapy — a combination that can prove ineffective.

But a new cancer treatment may offer a way to take down inoperable tumors with pinpoint accuracy, no radiation required.

Researchers have figured out how to deliver cancer-killing compounds (called enterotoxins) to tumors using bionic bacteria that are steered by a magnetic field. These “micro-robots” can hunt down and converge on a specific tumor, then shrink it by releasing the bacteria's own naturally produced anti-cancer chemicals. The results were recently published in the journal Science.

This high-tech cancer treatment could allow magnetic bacteria (grey) to squeeze through narrow spaces between cells and attack tumors.Yimo Yan / ETH Zurich

“Cancer is such a complex disease, it’s hard to combat it with one weapon,” says Simone Schürle-Finke, a micro-roboticist at the Swiss Federal Institute of Technology in Zürich, Switzerland, and one of the authors of the new study.

She and her lab hope that these magnetic, bacteria-riding little robots will offer a precise and powerful addition to the cancer treatment toolbox.

Here’s the background — The idea of curing cancerous tumors with bacteria is surprisingly old. American oncologist William Coley first started injecting his patients with a mixture of dead bacteria and bacterial proteins in the 1890s. After he reported successfully treating people with otherwise inoperable tumors, his work garnered equal parts enthusiasm and skepticism from the medical community.

Despite Coley’s vocal critics (including members of the American Medical Association), his formula, dubbed “Coley’s toxins,” would go on to be sold as a cancer treatment for the next seventy years. By the 1960s, though, Coley’s toxins had all but fallen by the wayside in favor of promising new treatments, like radiation and chemotherapy.

William Coley used bacteria like Streptococcus pyogenes to treat cancer.Shutterstock

Significant interest in bacteria as a cancer treatment didn’t re-emerge until the dawn of CRISPR, a revolutionary bioengineering technology, in the early 2010s. And today, labs are realizing the limits of today’s standard cancer interventions, such as their imprecise nature and harmful side effects.

Today, researchers like Schürle-Finke and her team are putting micro-robots inside genetically engineered bacteria to target cancerous growths like never before. Once these microbes reach a tumor, “you basically have a little nano-factory that continues to release molecules that can be toxic to cancer cells,” she says. The only issue? Figuring out how to get the bacteria bots in place.

What’s new — Many inoperable tumors can’t be addressed by surgery simply because of their location — they may be too hard to reach with a knife, let alone inject with a syringe full of bacterial cyborgs. This means that researchers have had to brainstorm some creative ways to navigate therapeutic bacteria toward cancer cells.

Schürle-Finke was pondering this conundrum when inspiration struck. “Maybe I could help with magnetic guidance,” she recalled thinking. Most bacteria can’t be pushed around with magnets, but as luck would have it, one special group of aquatic bacteria does: magnetotactic bacteria, which use the tiny iron crystals produced in their bodies like an internal compass.

Scientists were able to direct the bacteria with a magnetic field.Boris SV/Moment/Getty Images

So she took the next logical step — ordering some magnetotactic bacteria online. “I was surprised,” Schürle-Finke says, “You can just buy them.”

Back in the lab, her team got to work equipping the bacteria with fluorescent tags and nanoparticles filled with drugs. In these genetically engineered bacteria, the nanoparticles propel them to release cancer-fighting compounds on demand.

Then, they injected the bacteria bots into tumor-ridden mice. Using an externally generated magnetic field, scientists were able to successfully direct the bacteria and park them on the mice’s tumors with more than three times the precision of the control group (which wasn’t subjected to a magnetic field.)

What’s next — Though this study offers a solid proof-of-concept, micro-robotic bacteria technology still needs to be refined before it becomes a mainstream cancer treatment.

For one thing, “these bacteria that we tested, they’re quite foreign to the human body,” Schürle-Finke says, and they don’t naturally produce cancer-fighting compounds.

In the future, bioengineers may try to identify the cluster of genes responsible for producing magnetotactic bacteria's magnetic iron pellets and transfer it to a more familiar model organism, like a harmless strain of E. coli, Salmonella, or Clostridium.

Still, Schürle-Finke is excited about the possibility that bacterial therapy holds. And she’s ready to continue bridging the gap across scientific disciplines, from oncology to microbiology to robotics. “I think it’s beautiful that we’re experiencing this convergence of sciences,” she says.

On November 9, 2022, this post was updated with clarifications from Simone Schürle-Finke.

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