Life is not easy in the cold, lightless reaches of the South China Sea. To survive, microbes have evolved fiercely competitive and extremely resilient. Some build chemical weapons, complex molecules that help them fend off rivals. Now, scientists have found one of those weapons that may help humans fight a very different enemy: cancer.

In new study, researchers from the Chinese Academy of Sciences report the discovery of EPS3.9, a long-chain sugar made by Spongiibacter nanhainus and its close relatives. In lab experiments and in mice with liver cancer, EPS3.9 not only halted tumor growth but also set off a powerful immune response, showing the immune system where to strike cancer.

Like Setting Off a Flare Inside a Tumor

Researchers started looking at the bacteria in 2024, when they found that it has inhibitory effects on agricultural fungi and human pathogenic bacteria, including notorious drug-resistant pathogens. They’ve now focused on cancer, and also found it to be remarkably effective.

EPS3.9 works by triggering pyroptosis — a dramatic, “fiery” form of programmed cell death. The cell swells, bursts, and releases inflammatory molecules that act like distress signals, summoning immune cells to the site.

This is a phenomenon quite different from apoptosis, which is a form of programmed cell death that is crucial for normal development. Cancerous cells disrupt apoptosis and multiply in an unregulated fashion. But unlike apoptosis, which is orderly and quiet, pyroptosis is explosive, and that’s a good thing..

Pyroptosis is often triggered by microbial infections and is associated with inflammation. However, in recent years, it’s also emerged as a promising cancer therapy. By killing tumor cells in such a loud and messy way, it can also alert the immune system to join the attack. Cancer cells rely on evading the immune system, so this is like sounding the alarm on them.

“Our work not only provides a theoretical basis for developing more carbohydrate-based drugs but also highlights the importance of exploring marine microbial resources,” said corresponding author Chaomin Sun, PhD, of the Chinese Academy of Sciences.

Cancer Treatment from the Oceans

For now, the compound destroyed cancer cells in the lab and in mice. In tests with human leukemia cells, EPS3.9 caused widespread cell death. In mice, it significantly shrank liver tumors and sparked anti-tumor immune activity.

There’s a long way from this to ensuring this is safe and effective in clinical trials. Yet, it’s a promising avenue.

Modern cancer therapies increasingly look to the immune system for help. Immunotherapies, such as checkpoint inhibitors and CAR-T cells, have revolutionized treatment for some patients. Many tumors evade detection, but EPS3.9 offers a different approach — destroying, cancer cells in a way that makes them impossible to ignore. By causing the cells to erupt and spill danger signals, the compound could help alert the immune system to tumors that would otherwise fly under the radar.

Marine microbes like Spongiibacter are also a largely untapped resource. Life in extreme environments forces them to evolve unusual chemistry. Over the past few decades, scientists have found antibiotics, antivirals, and anticancer agents in ocean organisms, from sponges to bacteria. EPS3.9’s discovery adds to that list.

If EPS3.9 proves safe and effective in humans, it could pave the way for an entirely new class of carbohydrate-based cancer therapies — treatments that don’t just destroy tumors, but also rally the body’s own defenses to keep the fight going. For now, a humble microbe from the ocean’s depths has opened an intriguing new front in the war on cancer.

Journal Reference: Ge Liu, Yeqi Shan, Chaomin Sun. A Novel Exopolysaccharide, Highly Prevalent in Marine Spongiibacter, Triggers Pyroptosis to Exhibit Potent Anticancer Effects. The FASEB Journal, 2025; 39 (14) DOI: 10.1096/fj.202500412R