Gut bacteria metabolize Flutamide into inactive metabolites (FLU-6, FLU-9, and FLU-5) that show no anticancer activity, thereby attenuating its therapeutic efficacy against prostate cancer, with substantial interpatient variability in this metabolic capability.
Key Findings
Results
Gut bacteria metabolize Flutamide into two primary microbial metabolites: FLU-6 (a nitroreduction product) and FLU-9 (an acetylation product), with Escherichia coli among the key species involved.
FLU-6 is produced via nitroreduction of Flutamide by gut bacteria.
FLU-9 is produced via acetylation of Flutamide by gut bacteria.
Escherichia coli was specifically identified as one of the species capable of performing these biotransformations.
FLU-6 is further metabolized by the host into a third metabolite, FLU-5.
Results
E. coli genes nfsA and nfsB were identified as essential for the nitroreduction of Flutamide into FLU-6.
Gene knockout experiments in E. coli were used to identify the responsible enzymes.
Knockout of nfsA and nfsB abolished or significantly reduced Flutamide nitroreduction.
Acetyltransferases were confirmed via heterologous expression to mediate the production of the acetylated metabolite FLU-9.
Results
Antibiotic intervention in mouse models significantly reduced microbial metabolites of Flutamide.
An antibiotic-treated mouse model was used to deplete the gut microbiota.
Antibiotic treatment significantly reduced the levels of FLU-6 and FLU-9 in these animals.
This finding confirms that the production of these metabolites is dependent on gut microbial activity rather than host metabolism alone.
Results
Synthesized FLU-6, FLU-9, and FLU-5 showed no anticancer activity in prostate cancer cell lines.
The three metabolites (FLU-6, FLU-9, FLU-5) were chemically synthesized for testing.
In vitro testing in prostate cancer cell lines demonstrated absence of anticancer activity for all three metabolites.
This contrasts with the parent compound Flutamide, which has established antiandrogen and anticancer activity.
Results
Oral administration of E. coli in a xenograft mouse model diminished Flutamide's therapeutic efficacy by altering its metabolic profile.
A xenograft model of prostate cancer was used to assess in vivo therapeutic outcomes.
Mice administered oral E. coli showed altered Flutamide metabolism with increased conversion to inactive metabolites.
The presence of E. coli resulted in measurably reduced anticancer efficacy of Flutamide compared to controls.
Results
Clinical sample analysis revealed substantial interpatient variability in gut microbial metabolism of Flutamide, allowing patients to be categorized into subgroups with high or low metabolic capability.
Clinical samples from prostate cancer patients were analyzed for Flutamide metabolite profiles.
Significant interpatient variability in the production of FLU-6 and FLU-9 was observed.
Patients could be stratified into 'high' and 'low' metabolic capability subgroups based on this variability.
The authors indicate these findings provide new insights into personalized prostate cancer therapy.
What This Means
This research suggests that bacteria living in the gut can break down Flutamide — a drug used to treat prostate cancer — into different chemical forms that no longer work against cancer. The study identified that gut bacteria, including common species like Escherichia coli, convert Flutamide into at least two inactive byproducts through two distinct chemical processes (reduction and acetylation), and the body then further converts one of those byproducts into yet another inactive form. When researchers tested these byproducts in laboratory cancer cell experiments and in mice with prostate tumors, none of the byproducts showed any ability to fight cancer, while the original Flutamide drug does.
When mice were given antibiotics to reduce their gut bacteria, the conversion of Flutamide into these inactive forms was significantly reduced, suggesting that the bacteria are directly responsible for this drug breakdown. In a mouse tumor model, introducing E. coli by mouth caused Flutamide to be metabolized into these inactive forms more extensively, and the drug became measurably less effective at controlling tumor growth. This provides a plausible biological mechanism by which gut bacteria could contribute to drug resistance in prostate cancer patients.
Importantly, when the researchers analyzed samples from actual prostate cancer patients, they found that different patients had very different levels of this microbial drug breakdown — some patients had gut bacteria that converted much more of the Flutamide into inactive forms than others. This research suggests that differences in each patient's gut microbiome could help explain why some patients respond well to Flutamide while others do not, and points toward potential strategies such as modifying the gut microbiome or adjusting drug dosing to improve treatment outcomes for prostate cancer patients.
Li S, Ding H, Wang J, Yuan L, Zhou Y, Xu W, et al.. (2026). Gut microbial metabolism of Flutamide attenuates its therapeutic efficacy against prostate cancer.. Gut microbes. https://doi.org/10.1080/19490976.2026.2682803