"Anti-cancer" in the Japanese paradise frog: how a bacterium from its intestines destroyed 100% of tumors in mice

When oncologists talk about "breakthrough" discoveries, they usually mean a new molecule or a modified antibody drug. This time, the source of a potential anti-cancer agent was found where medicine usually doesn't look for drugs - in the gut of a tiny Japanese paradise frog, whose microbiome gave science a bacterium that can completely eliminate colorectal tumors in mice after a single injection and trigger immune "memory" against cancer.

What exactly was discovered in the Japanese paradise frog

ScienceAlert reports: a team from the Japan Advanced Institute of Science and Technology (JAIST) has discovered that one of the strains of bacteria from the intestines of the Japanese paradise frog (Dryophytes japonicus) has extremely potent anticancer activity against colorectal tumors in mice.¹ It's not about a "magic pill," but about a living microorganism — Ewingella americana, which was isolated, purified and administered intravenously to laboratory animals.^{1 4}

Researchers deliberately turned to amphibians and reptiles, because these classes of animals extremely rarely get cancer, even though they live in harsh conditions and are constantly in contact with pathogens.^{1 4} The hypothesis was bold: if their microbiome helps them suppress tumor processes, perhaps part of this ability could be “borrowed” for therapy in mammals.

How they searched for an "anti-cancer" bacterium: 45 strains and 9 contenders

A team led by Professor Eijiro Miyako from JAIST selected 45 bacterial strains from the intestines of three species: the Japanese paradise frog, the Japanese red-bellied newt (Cynops pyrrhogaster) and the lizard Takydromus tachydromoides.^{4 8} All of these animals belong to the so-called "lower vertebrates" and exhibit a surprisingly low incidence of cancer in nature.

After a series of tests in test tubes and on mouse models of colorectal cancer, the researchers narrowed the list down to nine strains that showed notable anti-tumor activity.^{4 9} Among them, one candidate turned out to be absolutely exceptional - Ewingella americana, a bacterium that was previously known to microbiologists as a conditionally pathogenic but was never considered a drug.

Ewingella americana: a double blow to the tumor

Key feature Ewingella americana — the ability to act by two mechanisms at once, ScienceAlert and News-Medical emphasize.^{1 6} First, the bacterium directly attacks tumor tissue in conditions of low oxygen (hypoxia) typical of solid tumors, and there it multiplies rapidly, destroying cancer cells.

Secondly, it "revitalizes" the host's immune system: in mice, the activity of T-lymphocytes, B-cells, and neutrophils increases, which join the attack, creating a combined effect of direct bacterial action and immune response.^{1 6} Authors of the journal article Gut Microbes describe this as the formation of a powerful antitumor microenvironment that changes the “rules of the game” at the very site of the disease.

Results in mice: 100% disappearance of tumors after one injection

The most impressive part of the work is the experiments in a mouse model of colorectal cancer. According to Ponderwall and LinkedIn reviews of the study results, a single intravenous injection E. americana led to the complete disappearance of tumors in all animals in the experimental group.^{4 5} Unlike standard chemotherapy, which often results in partial regression, a 100 percent "complete response" was observed here — the tumors didn't just shrink, they completely disappeared.

Another striking effect was the “vaccine-like” effect: when the researchers re-injected the mice with cancer cells after 30 days, tumors did not develop over the next month.^{1 4} This indicates that the immune system "remembered" the tumor antigen and was ready to respond immediately, effectively forming anti-cancer immunity.

Comparison with chemotherapy and immunotherapy

To assess the real power of the new approach, the researchers set E. americana in direct comparison with classical chemotherapy (doxorubicin) and modern immunotherapies, in particular anti-PD-L1 therapy.^{4 6} In the groups receiving doxorubicin or anti-PD-L1, only a slowdown in tumor growth was observed, but not their complete disappearance.

Instead, one dose E. americana gave a 100% complete response without the systemic toxicity typical of doxorubicin: the mice maintained their weight and showed no signs of damage to the liver, kidneys, or other organs.^{4 6} Against this background, the bacterium looks like a potentially more powerful and at the same time gentler tool for anti-cancer therapy - at least within the framework of this model.

Safety: a drug-producing bacterium that leaves the body on its own

One reason for caution with bacterial therapies is the risk of infections. Ewingella americana is known as an opportunistic pathogen that sometimes causes infections in people with weakened immune systems, so the issue of safety was key from the very beginning.^{1 6}

According to ScienceAlert and News-Medical, in mice, the bacterium was quickly cleared from the blood, did not cause prolonged bacteremia, and did not accumulate in healthy organs, and histological analysis revealed no tissue damage after therapy.^{1 6} This allowed the authors to cautiously speak of an “acceptable safety profile” at the preclinical level, although they themselves emphasize that the path to clinical trials in humans is still far and requires additional engineering and testing.

According to E. americana survives in the tumor and why it matters

One of the mysteries that the study uncovered is why this particular bacterium is so effective in tumor conditions. The fact is that many solid tumors have areas of hypoxia — low oxygen levels — where classical immune cells work worse and the effectiveness of chemotherapy drugs decreases.^{1 4}

Ewingella americana has evolved to survive in environments with low oxygen content, which allows it to actively reproduce precisely where other agents "suffocate."^{1 4} According to the researchers, this makes it a natural "Trojan horse" that penetrates the least accessible areas of the tumor, destroys them from the inside, and at the same time changes the local environment so that immune cells can enter and work effectively.

Amphibians as a “drug storehouse”: a broader context

Although the current study focuses on bacteria from the gut of the Japanese frog, it fits into a broader trend: amphibians have long been known as a source of bioactive molecules with antimicrobial and antitumor activity.^{9 10} Magazine review Gut Microbes and previous work with natural peptides shows that skin and tissue secretions of frogs and newts contain dozens of peptides capable of selectively killing cancer cells.

For example, the peptides gaegurin-5 and gaegurin-6 from the skin of the Korean frog showed activity against colorectal and mammary carcinoma cells, and dermazeptin-PP from a South American amphibian demonstrated a stronger antitumor effect than cisplatin with less toxicity in a mouse model of lung cancer.^{9 10} Against this background, the discovery E. americana logically continues the story: now the source of therapy is not a peptide from the skin, but a bacterium from the intestines.

From mice to humans: what else needs to be proven

Despite the headlines about "a powerful cancer cure inside a frog," the authors themselves emphasize that all we have is success in mice, and the path to humans consists of many stages.^{1 6} It remains to be seen whether the effect will persist in other cancer models, such as breast, lung, and pancreatic tumors, as well as in animals with immune systems closer to humans.

A separate line of work is the modification of the E. americana or creating safer "daughter" strains based on it that will not cause infections but will retain antitumor activity.^{4 6} A possible way to isolate key molecules produced by the bacterium is also possible - then the therapy will no longer look like a live injection of a microorganism, but as a targeted drug that reproduces its effect.

The place of bacteria in the future of oncology

The idea of ​​using bacteria against cancer is not new: for example, weakened strains BCG has been used for decades to treat bladder cancer by stimulating a local immune response.^{1 6} The novelty of the approach with E. americana in that it involves the systemic introduction of a bacterium that directly colonizes the tumor, rather than just “teasing” the immune system on the surface of the mucosa.

This opens up the prospect of creating a whole class of "living" anticancer drugs, each of which will be tailored to a specific type of microenvironment - hypoxic tumors, metastatic foci, microscopic residual cells after surgery.^{1 4} However, experts caution that any such approaches will require rigorous safety monitoring and will likely be combined with, rather than replacing, conventional chemotherapy or immunotherapy.

Why is this discovery important for Ukraine?

For Ukrainian oncologists and researchers, this story is a reminder that the fight against cancer has long gone beyond "the search for another pill molecule."^{3 6} World science is actively entering the "dark forests" of the microbiome, biodiversity, amphibians, and reptiles, where solutions inaccessible to traditional pharmacology may be hidden.

Ukraine has its own unique ecosystems, rich in amphibians and reptiles, and powerful schools of microbiology and oncology.³ Collaboration with international teams like JAIST or participation in joint projects studying natural microbiomes and peptides can be a chance not only to apply other people's discoveries, but also to add your own findings to the world's arsenal.

Key message of the study: the value of biodiversity

The authors of the work about E. americana conclude their article with an emphasis that goes far beyond oncology: “Our results demonstrate the enormous untapped potential that lies within diverse microbial ecosystems and underscore the critical importance of conserving biodiversity for the advancement of medical science and therapeutic innovation.”^{1 6}

In other words, every frog, newt, or lizard that humanity loses to deforestation, climate change, or pollution may not only be “another species in the Red Book,” but also a lost chance for a cure for a disease that is currently considered incurable.^{1 6} The Japanese paradise frog has turned out to be a lucky exception for science this time — but its story is more of an argument in favor of such exceptions not becoming an unaffordable luxury.

Sources

1. ScienceAlert: “Powerful Anti-Cancer Drug Discovered Inside Japanese Tree Frog” — a popular review of JAIST research on the bacterium Ewingella americana from the intestines of the Japanese paradise frog and its anticancer effects in mice.
2. News-Medical: “Frog-derived bacteria offer dual-action anticancer effects and high safety” — details of preclinical trials E. americana, mechanism of action, safety profile and comparison with doxorubicin and immunotherapy.
3. Ponderwall: "The Science of Ewingella americana Cancer Treatment" — analytical analysis of JAIST experiments, rates of 100% complete tumor response and "vaccine-like" effect.
4. LinkedIn / Scientific Digests (JAIST): Brief summary of the study, highlighting the complete disappearance of colorectal tumors in mice after a single injection E. americana and preventing relapses.
5. Economic Times / The New York Post (retail): promotional materials about the potential of "frog bacteria", which in experiments outperformed chemotherapy and immunotherapy without pronounced toxicity.
6. Gut Microbes: a scientific publication by Prof. Eijiro Miyako's team describing the selection of 45 strains, nine candidates, and unique efficacy Ewingella americana in hypoxic tumors.
7. Reviews in Gut Microbes and on PubMed: review articles on antiulcer and anticancer peptides derived from amphibians and their lower toxicity compared to traditional chemotherapy.