While plenty of bad bacteria — like E. coli — can get you sick, many other types are beneficial, protecting the body from harmful infections and reducing inflammation. The advent of genetic modification has greatly advanced medicine’s understanding of the microscopic organisms; modified gene-hacked bacteria can even be used to detect tumors in mice.
Now, researchers at the University of Waterloo say they’ve developed a new way to treat cancer by engineering bacteria called Clostridium sporogenes, which are commonly found in soil and don’t need oxygen to grow, to literally eat tumors from the inside out.
Solid tumors are filled with dead cells and are oxygen-free, making them a perfect place for these bacteria 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,” explained Waterloo chemical engineering professor Marc Aucoin, coauthor of a recent paper about the achievement published in the journal ACS Synthetic Biology, in a statement. “So, we are now colonizing that central space, and the bacterium is essentially ridding the body of the tumor.”
Scientists hope the approach could provide an alternative to toxic and limited cancer treatments, including chemotherapy, radiation therapy, and immunotherapy. Bacteria have also been shown to help trigger an immune response against cancer.
“Using ‘bugs as drugs’ offers a promising solution to overcome some of the challenges with traditional cancer therapies,” University of Texas genomic medicine researcher Christopher Johnston,who has studied bacteria that can invade and colonize human tumors, but was not involved in the latest research, explained in a 2024 statement. “Solid tumors, which account for the majority of adult cancers, can be notoriously treatment-resistant due to their complex microenvironment. But harnessing the unique abilities of certain microbes may give us a new way to tackle those barriers.”
A pair of studies published in 2024 showed that engineered E. coli can be used to shrink tumors in mice. Scientists have also developed genetically engineered strains of Salmonella to kill cancer cells.
While Aucoin and his colleagues made significant headway in colonizing tumors with cancer-eating bacteria, the team had some major challenges to overcome. For one, once these C. sporogenes bacteria reach the edge of the tumors, the influx of oxygen can kill them. In response, the researchers genetically modified them to make them tolerate at least some oxygen, allowing them to survive near the tumors, as detailed in a 2023 study.
Through a technique called “quorum sensing,” the researchers modified the bacteria so that the oxygen-resistant gene only turned on once it had sufficiently multiplied inside the tumor, ensuring that it had a chance to destroy it, as detailed in their more recent follow-up paper. The team made the bacteria produce a green fluorescent protein to signal that it had done its job.
“Using synthetic biology, we built something like an electrical circuit, but instead of wires we used pieces of DNA,” said coauthor and Waterloo professor of applied mathematics Brian Ingalls, in a statement. “Each piece has its job. When assembled correctly, they form a system that works in a predictable way.”
For now, however, beyond some promising proof-of-concept studies, scientists have only recently begun to thoroughly test the concept of using bacteria to treat cancer in humans.
The Waterloo team is now hoping to combine the research from its two papers — oxygen resistance through genetic modification and quorum sensing — into a single bacterium and let it loose on a tumor as part of pre-clinical trials.
More on bacteria: Scientists Printed Viruses Designed by AI and They’re Successfully Reproducing
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