For many breast cancer patients receiving neoadjuvant chemotherapy, a frustrating clinical puzzle persists: despite no detectable drug-resistance mutations in their tumors, the treatment response remains disappointingly poor. Could the answer lie outside the tumor itself — perhaps in the trillions of microbes residing in the patient's gut?
A multidisciplinary research team from Foshan, China has now provided compelling evidence that the answer may indeed be yes. In a study published online in Science Bulletin , Dr. Zhou Dan (Chief Physician, Breast Medicine Center, Foshan Second People's Hospital) as first author and Dr. Yuhua Deng (Institute of Translational Medicine, The First People's Hospital of Foshan / Southern University of Science and Technology) as corresponding author report the complete characterization of a novel "gut microbiota → metabolite → host post-translational modification → breast cancer progression" pathogenic circuit.
From Clinical Puzzle to Microbial Suspect
The team began by integrating three layers of 'omics data from treatment-naïve breast cancer patients: fecal metagenomics (gut microbiome), serum untargeted metabolomics, and tumor transcriptomics. This multi-omic approach led them to a specific gut commensal bacterium — Ruminococcus lactaris — which was significantly enriched in patients who showed poor response to neoadjuvant chemotherapy.
The researchers discovered that R. lactaris can synthesize uridine diphosphate N-acetylglucosamine (UDP-GlcNAc), a metabolite that enters systemic circulation. In breast cancer patients, serum UDP-GlcNAc levels were elevated before treatment and correlated with treatment outcomes, suggesting its potential as a circulating biomarker.
Hijacking the Host's "Sugar Switch"
Once in the bloodstream, microbial-derived UDP-GlcNAc is taken up by breast cancer cells, where it systemically activates OGT (O-GlcNAc transferase), the sole enzyme responsible for O-GlcNAcylation — a widespread sugar-based protein modification that regulates protein stability, activity, and localization.
The team elucidated the core molecular mechanism: UDP-GlcNAc-activated OGT modifies the transcription factor NFIB via O-GlcNAcylation, enhancing NFIB protein stability. Stabilized NFIB then binds to the promoters of both OGT and the proto-oncogene KIT, upregulating their expression. This creates a self-amplifying positive-feedback loop: more OGT produces more O-GlcNAcylation, which further stabilizes NFIB, which in turn drives even more OGT and KIT — continuously fueling tumor proliferation, invasion, migration, and chemoresistance.
Notably, this pro-tumor effect was observed even though the host hexosamine biosynthetic pathway contributes the majority of circulating UDP-GlcNAc; the microbial-derived portion acts as a critical "tipping point" that pushes the system into a pathological state.
Blunting Chemotherapy — and How to Stop It
The functional consequences are clinically significant. In both cell culture and mouse models, the presence of UDP-GlcNAc significantly attenuated the anti-tumor efficacy of paclitaxel, a first-line chemotherapeutic agent for breast cancer. Cancer cells treated with paclitaxel plus UDP-GlcNAc showed markedly higher viability than those treated with paclitaxel alone.
The good news? The team demonstrated across multiple experimental systems — cell lines, SPF mice, germ-free mice, and patient-derived breast cancer organoids — that genetic or pharmacological inhibition of OGT (using the inhibitor OSMI-1) effectively breaks this pro-tumor axis. Tumor growth was significantly suppressed even when R. lactaris and its UDP-GlcNAc output remained present. In patient-derived organoids, OGT inhibition reduced proliferation (EdU staining) and increased cell death (Calcein-AM/PI staining), offering a clear translational proof-of-concept.
An Antibiotic Warning
The study also uncovered an unexpected ecological twist: Streptomyces kanamyceticus , another gut microbe, can convert UDP-GlcNAc into aminoglycoside antibiotics. These aminoglycosides selectively inhibit Gram-negative bacteria, thereby reshaping the gut microbial community to create an environment favoring R. lactaris overgrowth — a vicious cycle that further amplifies the pro-tumor effect.
This finding carries a practical clinical message: the use of aminoglycoside antibiotics in breast cancer patients should be carefully evaluated to avoid inadvertently promoting a tumor-favorable gut microbiota composition.
A Model of Clinical-Basic Collaboration
This work represents a close collaboration between clinical and basic research teams. Dr. Zhou Dan's clinical team at the Breast Medicine Center identified the real-world clinical question and collected well-characterized patient samples, while Dr. Yuhua Deng's translational research team leveraged multi-omics platforms and mechanistic experimental systems to unravel the underlying biology. Together, they transformed a bedside observation into a mechanistic understanding with direct therapeutic implications.
What's Next?
The team plans to expand the clinical cohort for validation and further explore the diagnostic and therapeutic potential of gut microbial metabolites in breast cancer screening and adjuvant treatment, aiming to translate these laboratory findings into clinically actionable solutions.
About the Institutions
The Breast Medicine Center, Foshan Second People's Hospital is a specialized center for breast disease diagnosis and treatment, focusing on locally advanced breast cancer neoadjuvant therapy, complex breast-conserving surgery, breast reconstruction, and minimally invasive breast treatments.
The Institute of Translational Medicine, The First People's Hospital of Foshan / Southern University of Science and Technology (Foshan) hosts a 3,000-square-meter central laboratory equipped with six core technical platforms (sample preparation, molecular biology, cell culture, histopathology, animal models, and microscopy/imaging) and over 700 instruments valued at more than RMB 45 million, providing comprehensive support for basic and translational research.
Science Bulletin
Experimental study