Gut Fungus Drives Liver Cancer Progression by Producing a Toxic Metabolite
A common gut fungus accelerates fatty liver-associated liver cancer by flooding the liver with kynurenic acid, activating a cancer-promoting pathway.
Summary
Researchers at the Chinese University of Hong Kong discovered that a gut fungus called Rhizopus arrhizus is significantly elevated in patients progressing from metabolic liver disease to liver cancer. The fungus produces kynurenic acid, a metabolite that binds to a protein called IQGAP1 inside tumor cells, switching on the MAPK signaling pathway that drives uncontrolled cell growth. In mouse models, introducing R. arrhizus or kynurenic acid alone was enough to accelerate tumor development. This research reveals an unexpected fungal-metabolic axis in liver cancer and suggests that targeting this host-fungus interaction — whether through antifungal strategies or blocking the kynurenic acid-IQGAP1 binding — could open new avenues for preventing or treating metabolic dysfunction-associated liver cancer.
Detailed Summary
Liver cancer linked to metabolic dysfunction-associated steatotic liver disease (MASLD) is a growing global threat, yet the biological drivers pushing fatty liver disease toward malignancy remain incompletely understood. A new study published in Cell Metabolism identifies a surprising culprit: a common environmental and gut fungus, Rhizopus arrhizus, that produces a metabolite capable of directly fueling tumor growth.
Researchers performed mycobiome profiling across human samples spanning the full spectrum from healthy liver to MASLD to MASLD-associated hepatocellular carcinoma (HCC). R. arrhizus emerged as the most consistently enriched fungal species as disease severity increased. To confirm causality, the team tested the fungus in multiple mouse models of MASLD-HCC, demonstrating that it reliably accelerated tumorigenesis.
The key mechanism centers on kynurenic acid (KYNA), a metabolite generated by R. arrhizus and already known from tryptophan metabolism. KYNA levels were elevated in portal vein blood, liver tissue, and stool samples from fungus-treated mice. In human MASLD-HCC cell lines, KYNA stimulated proliferation, suppressed cell cycle arrest, and reduced apoptosis. Critically, KYNA was found to directly bind IQGAP1, a scaffolding protein in tumor cells, triggering activation of the MAPK/ERK oncogenic signaling cascade.
These findings position gut fungi as active contributors to liver cancer biology, not merely bystanders. For patients with fatty liver disease — a condition affecting hundreds of millions worldwide — the fungal composition of their gut microbiome may influence cancer risk in ways that bacterial microbiome research has previously overlooked.
The authors propose that blocking the R. arrhizus–KYNA–IQGAP1 axis represents a viable therapeutic strategy. Antifungal interventions or small-molecule inhibitors disrupting KYNA-IQGAP1 binding could complement existing approaches. Importantly, this summary is based on the abstract only, and full mechanistic and clinical details await open-access publication.
Key Findings
- R. arrhizus was the top enriched gut fungus across progression from fatty liver disease to liver cancer in human samples.
- Kynurenic acid produced by R. arrhizus directly promoted tumor cell proliferation and suppressed apoptosis in human HCC cells.
- KYNA binds IQGAP1 protein in tumor cells, activating the oncogenic MAPK signaling pathway.
- R. arrhizus accelerated liver tumor growth in multiple mouse models, confirming a causal role.
- Blocking the fungus-kynurenic acid-IQGAP1 interaction is proposed as a new therapeutic target for MASLD-associated liver cancer.
Methodology
The study combined human mycobiome profiling across MASLD disease stages with in vitro experiments in human MASLD-HCC cell lines and in vivo tumorigenesis assays in multiple mouse models. Mechanistic work identified KYNA as the active fungal metabolite and mapped its binding to IQGAP1 with downstream MAPK pathway activation. This summary is based on the abstract only; full methodological detail is not available.
Study Limitations
This summary is based on the abstract only, as the full paper is not open access; complete methods, data, and supplementary findings are unavailable for review. The causal mouse model data are compelling, but human interventional evidence is lacking. Whether R. arrhizus abundance reflects modifiable lifestyle or dietary factors, and whether reducing it alters clinical cancer outcomes, remains to be established.
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