Scientists introduced Clostridium novyi, a bacteria that causes mild illnesses in humans that typically lurks inside the soil and feces, in cancer tumors and found that these shrank and some cases were destroyed completely. The research suggests that bacteria, when engineered to reduce toxicity, can be a viable fighting tool against cancer, one with less destructive side effects than chemotherapy.

Killing cancer with bacteria

Image: Spore Coat Architecture of Clostridium novyi NT Spores. Source: Journal of Bacteriology

Dr. Shibin Zhou and colleagues at  Johns Hopkins University first became interested in bacteria as a potential cancer treatment some ten years ago after reading the archaic works of New York doctor William Coley, who 100 year ago reported patients sometimes went into remission after they contracted a serious bacterial infection. Coley then isolated bacteria and inserted it into patients in hope that he might replicate what he observed. The challenges he come across were numerous, like making patients more ill than they were before treatment. Then,  chemotherapy and radiation therapy started to become popular and scientists lost interested in anti-cancer bacteria.

The researchers first made sure they genetically modified the bacteria to make it less toxic, then used it to infect tumors (direct injection) that were growing in live patients: 16 pet dogs and one human. The human patient’s tumor that was treated with bacteria shrank, while other tumors in the patient’s body continued to grow. Three of the dogs were cured of cancer completely, and three others saw their tumors shrink by at least 30 percent.

One important caveat about C. novyi is that it only operates in oxygen-free (anerobic) environments. This held true when researchers found some of the tumors who supported oxygen didn’t show any sign of shrinking. Some drugs work by cutting off the tumor’s blood supply — and, with it, oxygen. Complementing these drugs with engineered bacteria might render some extremely promising results, yet more tests are required before any dramatic claim is voiced. Also, there’s a concern that some bacterial infections can cause cancer, though there’s no evidence that C. novyi itself is involved.

C. novyi isn’t the first bacteria to offer promising anti-cancer prospects. Dartmouth-Hitchcock Medical Center researchers used a genetically modified strain of a parasite that dwells in cat feces to treat cancer in mice. Considering the parasite in question also causes toxoplasmosis, a condition thought to cause humans to go insane, some people might show reluctance for opting this treatment. Some viruses, like measles, have also been shown to shrink tumors.

The findings appeared in the journal Science Translational Medicine.