Researchers Develop Tumor-Eating Bacteria for Targeted Cancer Therapy

Scientists at the University of Waterloo are developing an innovative cancer therapy that uses genetically engineered bacteria to attack tumors from the inside. The approach targets one of cancer's key weaknesses: the oxygen-starved core found in many solid tumors.

At the heart of the strategy is Clostridium sporogenes, a microbe that thrives only in completely oxygen-free environments. The inner regions of solid tumors—often filled with dead cells and lacking oxygen—provide ideal conditions for this bacterium to grow. Once bacterial spores enter the tumor, they detect the nutrient-rich, oxygen-poor environment and begin multiplying, effectively consuming tumor tissue from within.

However, a major challenge arises as the bacteria spread outward. The outer edges of tumors contain small amounts of oxygen, which can kill the microbes before they finish destroying the cancer. To overcome this, researchers inserted a gene from a related, more oxygen-tolerant bacterium. This modification allows the engineered bacteria to survive longer in areas with limited oxygen.

Safety was a critical concern. Activating oxygen tolerance too early could enable the bacteria to grow in healthy, oxygen-rich tissues like the bloodstream. To prevent this, the team used quorum sensing—a natural bacterial communication system. As bacteria multiply inside the tumor, they release chemical signals. When the population reaches a specific threshold, the signal triggers activation of the oxygen-resistance gene, ensuring the feature turns on only within the tumor environment.

Using synthetic biology, researchers designed DNA “circuits” to control this process precisely. Their next step is to combine these engineered features into a single strain and test its effectiveness in pre-clinical tumor models.

REFERENCE: Sara Sadr, Bahram Zargar, Marc G. Aucoin, Brian Ingalls. Construction and Functional Characterization of a Heterologous Quorum Sensing Circuit in Clostridium sporogenes. ACS Synthetic Biology, 2025; 14 (12): 4857 DOI: 10.1021/acssynbio.5c00628