BY THE OPTIMIST DAILY EDITORIAL TEAM
Cancer treatment has no shortage of big ideas, but this one has a certain dark charm: send in bacteria that thrive where healthy human cells struggle, then let them chew through a tumor’s interior.
A research team led by the University of Waterloo is working on a therapy concept that uses engineered bacteria to infiltrate solid tumors and consume them from the inside out. The organism at the center of the project is Clostridium sporogenes, a soil bacterium that only grows in environments with absolutely no oxygen. Conveniently (for the bacteria, less so for us), the core of many solid, cancerous tumors contains dead cells and becomes oxygen-free, creating an ideal pocket for C. sporogenes to multiply.
“Bacteria spores enter the tumor, finding an environment where there are lots of nutrients and no oxygen, which this organism prefers, and so it starts eating those nutrients and growing in size,” said Dr. Marc Aucoin, a chemical engineering professor at Waterloo. “So, we are now colonizing that central space, and the bacterium is essentially ridding the body of the tumor.”
Why tumors make a good hideout for these microbes
Solid tumors often develop a harsh internal geography: the center gets starved of oxygen, while the outer rim sits closer to blood supply and retains some. That matters because Clostridium sporogenes does well in the oxygen-free middle, then runs into trouble as it reaches the edges.
That’s the problem the Waterloo team is working to solve. When these cancer-eating microbes push toward the tumor’s outer boundary, they encounter low levels of oxygen and die before they can finish the job. They can occupy the oxygen-free zone effectively, but they need help surviving long enough to make a bigger dent near the perimeter.
The engineering fix: oxygen tolerance, but only when it’s safe
To keep the bacteria alive longer near the tumor’s edges, researchers added a gene from a related bacterium that can better tolerate oxygen. That alone isn’t enough, though, because oxygen tolerance comes with risk: you don’t want bacteria turning into overachievers in oxygen-rich places like the bloodstream. So the team tackled the timing.
They used a natural bacterial communication method called quorum sensing, chemical signaling that builds as bacteria multiply. The oxygen-resistant gene stays off while only a few bacteria are present, then switches on only after a large enough population has established itself inside the tumor. The microbes don’t get their “oxygen upgrade” until they’ve proven they’re in the right place.
Synthetic biology, built like a circuit board
The group has already shown that pieces of this approach can work. In one study, researchers demonstrated that Clostridium sporogenes can be modified to tolerate oxygen. In a follow-up, they tested whether their quorum sensing system could reliably flip a genetic “switch,” using bacteria programmed to produce a green fluorescent protein when the signal was strong enough.
“Using synthetic biology, we built something like an electrical circuit, but instead of wires we used pieces of DNA,” said Dr. Brian Ingalls, a professor of applied mathematics at Waterloo. “Each piece has its job. When assembled correctly, they form a system that works in a predictable way.”
That controllability is what makes the concept medically viable. A biological system that behaves predictably is far more useful in a clinical setting than one that doesn’t.
What comes next
Researchers now plan to combine the oxygen-resistant gene and the quorum-sensing mechanism into one bacterium, then test it against tumors in preclinical trials. The project grew out of work by Ph.D. student Bahram Zargar, supervised by Ingalls and Dr. Pu Chen, a retired professor of chemical engineering at Waterloo, with Dr. Sara Sadr, a former Waterloo doctoral student, playing a leading role in the research. The team has partnered with CREM Co Labs, a Toronto environmental microbiology company co-founded by Dr. Zargar.
The approach is still in early stages, and preclinical results don’t always translate to human trials. But the underlying idea is sound: the tumor’s low-oxygen core, long treated as an obstacle by conventional therapies, is exactly what makes it a viable target for bacteria that can’t function anywhere else.
Did this solution stand out? Share it with a friend or support our mission by becoming an Emissary.
