Engineered bacteria could target solid tumors from the inside out.

Researchers at the University of Waterloo modified Clostridium sporogenes to tolerate oxygen and paired that change with a quorum-sensing switch so the trait activates only after bacteria accumulate inside a tumor; they plan pre-clinical tests to combine both features.

Researchers at the University of Waterloo report laboratory work on bacteria designed to grow inside the oxygen-poor cores of many solid tumors. The team focuses on Clostridium sporogenes, a soil bacterium that normally survives only in environments without oxygen. They modified the organism to better tolerate oxygen and used a bacterial communication system to limit when that change becomes active. The work builds on earlier experiments and is intended for further pre-clinical testing. Key findings: - Clostridium sporogenes naturally thrives in oxygen-free tumor cores and can multiply there. - The researchers introduced a gene from a related bacterium to improve oxygen tolerance so bacteria might survive closer to tumor edges. - To reduce the risk of unintended growth in oxygenated parts of the body, the team linked the oxygen-tolerance gene to a quorum-sensing switch that activates only after a large bacterial population forms. - Earlier tests showed the engineered oxygen tolerance and separately confirmed the quorum-sensing switch using a green fluorescent protein as a marker. - The next planned step is to combine the oxygen-tolerance modification and the quorum-sensing control into one strain and test it in pre-clinical tumor models. Summary: If combined successfully and validated in further tests, the engineered bacteria are reported as a possible way to act within the low-oxygen center of solid tumors. The immediate next step is pre-clinical testing of a single engineered strain that contains both the oxygen-tolerance gene and the quorum-sensing control system.