Study reveals how nitroxoline antibiotic works through iron deprivation and pathogen-driven metabolite reactivation
Researchers have identified the primary antibacterial mechanism of nitroxoline (NTX) as iron deprivation via metal chelation, and found that urinary pathogens themselves convert inactive metabolites back into the active drug. The study also showed that the body's detoxification products — NTX-sulphate and NTX-glucuronide — lack antibacterial activity on their own. This mechanistic framework helps explain why nitroxoline remains effective as a urinary tract antibiotic despite being metabolized by the host.
A new preprint on bioRxiv systematically investigates the mode of action of nitroxoline (NTX), an older antibiotic experiencing renewed interest amid rising antimicrobial resistance. The researchers determined that NTX's principal antibacterial activity stems from its ability to chelate iron — acting as a metallophore — thereby depriving bacterial cells of this essential nutrient, as evidenced by induction of iron acquisition pathways and loss of protein-bound iron in treated bacteria. The two main human metabolites of NTX, NTX-sulphate and NTX-glucuronide, were found to be biologically inactive and incapable of metal chelation. Critically, ex vivo experiments showed that clinically relevant uropathogens such as Escherichia coli and Klebsiella pneumoniae can enzymatically reconvert these inactive metabolites back into active NTX within human urine. This pathogen-driven reactivation provides a molecular explanation for why NTX retains therapeutic efficacy in urinary tract infections despite extensive first-pass metabolism. The findings also offer a rationale for the drug's favorable safety profile, since systemic exposure to the active compound is limited by host detoxification. The work positions nitroxoline as a mechanistically well-understood candidate for combating drug-resistant urinary pathogens.
What's missing
As a preprint, this study has not yet undergone formal peer review. The ex vivo reactivation experiments were conducted in human urine samples, and it is unclear how broadly the findings generalize across patient populations, urine compositions, or other uropathogens beyond E. coli and K. pneumoniae. The study does not address whether bacterial resistance to NTX's iron-deprivation mechanism exists or could readily emerge, nor does it provide clinical outcome data linking the reactivation mechanism to patient-level efficacy.
What different sources said
- bioRxivCenter
Pathogen-driven reactivation of metabolite prodrugs defines nitroxoline's iron-deprivation antibiotic activity
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