A Bacterium from the Gut of This Tiny Frog Can Clear out Aggressive Colon Tumors in Mice

With this little frog's bacterium, researchers achieved a 100% cure rate in mice for colon cancer.

The Japanese tree frog (Dryophytes japonicus) spends most of its time dodging herons and catching flies. But unbeknownst to this small, green amphibian, it has a biological weapon that might just become a valuable tool in our fight against cancer.

Researchers have shown that a bacterium plucked from the gut of this frog can successfully eradicate aggressive colon tumors in mice. With this bacterium, researchers achieved a 100% cure rate, outperforming standard chemotherapy and even modern immunotherapy.

Fighting Cancer with Bacteria

We often hear that sharks don’t get cancer (they do, but rarely). But researchers at the Japan Advanced Institute of Science and Technology (JAIST) turned their gaze elsewhere. They looked at amphibians and reptiles, hypothesizing that the gut microbiomes of these resilient creatures might harbor protective secrets.

They zoomed in on a promising strain of a microbe called Ewingella americana.

E. americana is promising because of its lifestyle. It is a facultative anaerobe, meaning it can survive in oxygen but thrives where oxygen is scarce. This is promising because solid tumors typically create a low-oxygen environment. For many drugs, this creates a hard-to-breach fortress. But E. americana loves it.

The study showed that once injected, the bacteria cleared out of healthy, oxygen-rich organs like the liver and lungs within 24 hours. However, inside the suffocating environment of the tumor, the bacterial population exploded, increasing 3,000-fold. This selective targeting allows the treatment to deliver a concentrated strike exactly where it is needed, sparing healthy tissue from collateral damage.

But colonization is only half the battle. Once entrenched, E. americana launches a direct cytotoxic attack, killing cancer cells through its own metabolic processes and secreted factors. Then, it alerted the immune system, prompting it to attack the tumor. Tumors often survive by hiding themselves from the immune system, and the bacterium blows their cover.

Does It Actually Work?

To validate these findings, the researchers pitted E. americana against two major types of oncology treatment: standard chemotherapy and an anti-PD-L1 antibody (a checkpoint inhibitor used in immunotherapy).

The mice treated with chemotherapy saw their tumor growth delayed, but not stopped. The immunotherapy group fared only slightly better, with one out of five mice achieving a complete cure. Meanwhile, all the mice treated with the bacteria saw their tumors completely disappear. Even more impressive was the durability of the cure. When researchers tried to re-implant cancer cells into the cured mice 30 days later, the tumors failed to grow. The treatment had effectively vaccinated the mice, generating an immunological memory that rejected the cancer upon recurrence.

Plenty of things can kill cancer, but many of them aren’t safe to use for patients, and “injecting bacteria in cancer patients” naturally raises alarms. But the study suggests E. americana is surprisingly safe.

Because the bacteria aren’t that fond of well-oxygenated environments, they don’t linger in the blood or healthy tissues. They clear out of the bloodstream within 24 hours. In mouse patients, the bacteria don’t seem to affect any healthy organs. Moreover, E. americana is just a regular microbe that can be killed easily with standard antibiotics in case something goes wrong.

RelatedPosts

In a remarkable first, woman’s advanced breast cancer is eradicated
Immigrating drastically changes people’s microbiome
A Popular Artificial Sweetener Could Be Making Cancer Treatments Less Effective
Tiny “Water Bear” Protein Could Help Shield Cancer Patients From Radiation

Of course, this is still a small study and conducted entirely in mice, who aren’t exactly like humans. The researchers utilized tumors implanted under the skin rather than in organs, a simplified model that doesn’t fully capture the complexity of human metastasis or the specific environment of the gut. Furthermore, the dosing requires extreme precision and much work remains to figure out the best approach. Yet, even with these caveats, E. americana serves as a powerful proof-of-concept, cracking open a door to a future where the unmapped biodiversity of nature helps us fight our deadliest diseases.

The study was published in Gut Microbes.