Scientists have discovered a promising new approach to fighting cancer in the gut bacteria of a Japanese tree frog, with one strain completely shrinking tumors in mice, with no severe side effects.
The Japanese tree frog (Dryophytes japonicus) wasn't a lucky find. We know amphibians and reptiles rarely develop cancer, and researchers from the Japan Advanced Institute of Science and Technology wanted to see whether transferring gut bacteria from frogs to mice might have any anti-cancer effects.
A total of 45 different bacterial strains from frogs, newts, and lizards were shortlisted for testing, with 9 strains showing notable tumor-fighting capabilities.
The most impressive of the bunch was the frog bacteria, Ewingella americana.
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"These findings suggest that gut microbiomes of lower vertebrates harbor numerous uncharacterized bacterial species with exceptional therapeutic potential," the researchers write in their published paper.
While other strains showed short-lived anti-tumor effects, a single dose of E. americana didn't just shrink tumors in treated mice – their tumors disappeared completely.
What's more, when cancer cells were reintroduced 30 days later to mice treated with E. americana, tumors didn't develop in the following month.
Further analysis revealed that E. americana works in two ways: It attacks tumor tissue while also amping up the body's immune response, enlisting extra help from T cells, B cells, and neutrophils – key fighters in the immune system.
The researchers think E. americana's effectiveness lies in the way it has evolved to survive in low-oxygen environments (such as cancer tumors) that typically suppress immune cells and reduce the effectiveness of chemotherapy drugs.
Based on these preliminary animal studies, E. americana seems fairly safe, too. The bacteria were cleared quickly from the bloodstream of mice, didn't cause any long-lasting toxicity, and didn't appear to affect healthy organs.
Injections of E. americana were also more effective at shrinking tumors in mice than several current treatments, including doxorubicin, a chemotherapy drug.
"These results suggest that E. americana represents a promising therapeutic candidate with an acceptable safety profile suitable for potential clinical development," the researchers write.
It's still early days, and much more testing is needed to see whether the findings of these animal studies could translate into humans.
The researchers also want to test E. americana against other types of cancers in animal models, see how it works in combination with other treatments, and experiment with drug-delivery methods.
Safety will be paramount if bacterial treatment is to progress to clinical trials. E. americana are bacteria after all, and can cause infections in humans. Figuring out if they can be used in people without any harmful effects will be a challenge.
In the meantime, scientists are exploring other ways of co-opting bacteria to kill cancer cells, with at least one bacterial therapy already used to treat some cases of bladder cancer.
Frogs and other reptiles may add to that arsenal in time by providing another source of potential cancer therapeutics.
"Our findings demonstrate the vast untapped potential residing within diverse microbial ecosystems and highlight the critical importance of biodiversity conservation efforts in advancing medical science and therapeutic innovation," the researchers conclude.
The research has been published in Gut Microbes.