When Betty Kim and her colleagues at MD Anderson Cancer Center in Houston started studying gut bacteria, they were looking for a new way to help cancer drugs work better. What they found surprised them: tiny organisms living in the gut may hold the key to making chemotherapy more effective.
The researchers discovered that reshaping gut bacteria with a short course of antibiotics helped chemotherapy reach tumors more easily. In experiments with animals, this approach roughly doubled how long cancer-fighting nanoparticles stayed in the bloodstream, allowing more of the drug to reach the actual tumor. Animals with colon, breast, melanoma, and pancreatic cancers all survived longer with this treatment.
The study, published in the journal Nature Materials, was led by three researchers: Betty Kim, a professor of neurosurgery; Wen Jiang, an associate professor of radiation oncology; and Jennifer Wargo, a professor of surgical oncology. All three work at The University of Texas MD Anderson Cancer Center in Houston.
So how does this work? Nanoparticle-based chemotherapy packages cancer drugs inside microscopic carriers, like tiny bubbles or particles. This type of treatment is used for several cancers, including breast, ovarian, and pancreatic cancer. The problem is that most of the drug never reaches the tumor. Liver cells called Kupffer cells act like security guards, clearing these drug particles from the body before they can do their job.
Here is where gut bacteria come in. These tiny organisms produce chemical signals called bile acids, which travel to the liver and tell Kupffer cells to stay alert. When the researchers gave mice a commonly used antibiotic called metronidazole, it selectively reduced certain gut bacteria. With fewer bacteria producing bile acids, the Kupffer cells went into a "quiet" state and stopped clearing the drug particles so aggressively. The result: more chemotherapy reached the tumor.
To confirm the microbiome was really driving this effect and not just leftover antibiotic, the team performed fecal microbiota transplantation, moving gut bacteria from treated animals into germ-free recipients. Even without any antibiotic in their systems, these recipients still showed improved drug delivery to tumors. The benefit came from the bacteria themselves.
"For decades, scientists have tried to address how aggressively the liver filters nanomedicine by redesigning the drugs themselves," Jiang said. "Our research shows that the host's biology, specifically the gut microbiome, is just as important as the particle design."
The findings open a new avenue for cancer treatment. Because metronidazole is already approved by the Food and Drug Administration and has a well-established safety record, testing it alongside nanoparticle-based chemotherapy in human patients could happen relatively soon. The researchers are not proposing fecal transplantation as a cancer treatment itself, but rather using antibiotics as a simple way to reshape the gut microbiome and help existing chemotherapy work better.
This builds on earlier work from Wargo's laboratory showing that gut bacteria can also boost immunotherapy, another type of cancer treatment that helps the immune system fight tumors. Together, these findings suggest that the tiny universe living inside our guts may be a powerful tool in the fight against cancer.