Scientists in Japan have made a breakthrough in oncology, discovering that a bacterium living in the gut of the Japanese tree frog is capable of completely destroying colon tumors in mice with just a single intravenous injection. The study, conducted by a team led by Professor Eiichiro Miyako from the Japan Advanced Institute of Science and Technology (JAIST), was published in the journal Gut Microbes.
An unexpected source of medicine
The discovery is based on a strain of the bacterium Ewingella americana. The choice of donors for the study was dictated by a unique biological feature of amphibians and reptiles: these animals rarely suffer from spontaneous tumors, despite living in an environment saturated with pathogens and enduring significant cellular stress. Scientists hypothesized that their gut microbiota might harbor powerful anti-cancer properties.
The team collected 45 bacterial strains from Japanese tree frogs, fire-bellied newts, and grass lizards. After selecting the nine most promising candidates, it was E. americana that showed phenomenal results.
100% effectiveness against cancer
In experiments using a colon cancer model, a single dose of the bacterium led to the complete disappearance of tumors in all animals. For comparison, standard treatment methods, including immune checkpoint inhibitors (anti-PD-L1 antibody) and the chemotherapy drug liposomal doxorubicin, showed significantly lower effectiveness even when administered four times.
The results were dramatic: all mice that received the bacterium survived until the end of the observation period, whereas the entire control group died within a month. Furthermore, when cancer cells were reintroduced into the surviving animals, the tumor did not develop, indicating the formation of a robust anti-cancer immunity.
Dual mechanism of attack
Scientists found that the bacterium acts through two pathways simultaneously. First, as a facultative anaerobe, it is capable of growing both in the presence and absence of oxygen. This allows it to multiply easily in oxygen-poor tumor zones. Within 24 hours of administration, the bacterial population inside the tumor increased by approximately 3000 times, directly damaging cancer cells.
Second, the presence of the bacterium triggers a powerful immune response. It attracts T-cells, B-cells, and neutrophils to the tumor, which release inflammatory signaling molecules such as TNF-α and IFN-γ. This enhances the immune response and accelerates the death of cancer cells.
Safety and selectivity
One of the key findings was the high selectivity of the bacterium. E. americana accumulated almost exclusively in the tumor and did not colonize healthy organs. This is explained by the characteristics of tumor tissue: tumor blood vessels are unusually permeable, facilitating the entry of bacteria from the bloodstream into the neoplasm.
The safety of the method was tested separately. The bacteria were rapidly cleared from the bloodstream (half-life of about 1.2 hours) and were undetectable in the body within 24 hours. They were not found at all in the liver, spleen, lungs, kidneys, or heart. The observed mild, temporary inflammation resolved within 72 hours, and no signs of chronic toxicity were detected over the 60-day observation period.
Future plans
Researchers emphasize that all results so far have been obtained only in mice and serve as early proof of concept. The team's future work is directed toward testing the approach on other types of solid tumors, including breast cancer, pancreatic cancer, and melanoma. They also plan to study dose fractionation, direct injection of the bacterium into the tumor, and combining this method with existing chemo- and immunotherapy.