Repurposed chemotherapy drug boosts fosfomycin activity against MRSA

A research paper published in Engineering, introduces a repurposing strategy that uses the FDA-approved anticancer agent 5-fluorouracil (5-FU) as an antibiotic adjuvant to strengthen fosfomycin (FOS) against methicillin-resistant Staphylococcus aureus (MRSA), a major global public health hazard.

MRSA has maintained an infection rate above 30% in China over five years tracked by the China Antimicrobial Surveillance Network, while nearly 150,000 MRSA infections occur annually across the European Union, accompanied by over 7,000 recorded deaths. Fosfomycin acts by inhibiting peptidoglycan synthesis at an earlier stage than β-lactam antibiotics, yet its performance as a single therapeutic agent remains limited. The research team from Yangzhou University identified consistent synergistic antibacterial effects between 5-FU and FOS across multiple MRSA clinical isolates via checkerboard analysis, with fractional inhibitory concentration index (FICI) values falling below 0.5, the standard threshold defining drug synergy. Parallel testing on vancomycin-resistant Enterococcus faecium A4 detected no synergistic response, indicating strain-specific activity of this pairing.

In vitro characterizations verified that the two-agent combination suppresses both nascent biofilm formation and eradicates mature biofilm-embedded MRSA cells, a critical advantage given biofilms enable persistent, recurrent bacterial infections. Genomic, transcriptomic and metabolomic assays clarified the molecular target of 5-FU: cytidine triphosphate (CTP) synthase encoded by the pyrG gene, a rate-limiting enzyme converting uridine triphosphate to CTP during pyrimidine metabolism. Molecular docking confirmed direct binding interactions between 5-FU and key amino acid residues of CTP synthase, while pyrG gene knockout eliminated nearly all synergistic effects between 5-FU and FOS. Exogenous supplementation of pyrimidine metabolites including cytosine, uracil and thymine weakened the drug combination’s potency, further validating pyrimidine pathway disruption as the core driver of synergy.

Transcriptome profiling revealed widespread disturbance of pyrimidine metabolism, mismatch repair and energy metabolism pathways following combined treatment. Disrupted pyrimidine biosynthesis lowered dihydroorotate dehydrogenase levels and raised intracellular 8-hydroxy-2′-deoxyguanosine concentrations, a marker of severe bacterial DNA damage. Metabolic cascades triggered by pyrimidine imbalance sequentially damaged bacterial cytoplasmic membranes, dissipated proton motive force, boosted intracellular ATP production and accumulated reactive oxygen species (ROS). Supplementation with the ROS scavenger N-acetylcysteine neutralized the synergistic bactericidal effect, confirming oxidative stress as a necessary mediator of bacterial cell death.

Two in vivo infection models supported the translational value of the pairing. In Galleria mellonella larvae challenged with MRSA, the combination treatment achieved full survival of infected subjects, while monotherapy groups recorded low survival rates over the observation window. In murine peritonitis sepsis models, co-administration of 5-FU and FOS improved animal survival and reduced bacterial burdens across heart, liver, spleen, lung and kidney tissues relative to single-drug regimens. Safety assessments confirmed the tested 40 mg·kg⁻¹ dose of 5-FU produced no detectable toxicity in larval and mammalian hosts, with normal weight gain, unaltered serum biochemical parameters and intact liver and kidney histology observed after sustained exposure.

The study notes that combined administration of 5-FU and FOS also slows the emergence of bacterial resistance, addressing a key barrier to long-term antibiotic utility. The authors conclude that targeting pyrimidine metabolic pathways with repurposed non-antibiotic agents offers a viable framework to restore susceptibility to older broad-spectrum antibiotics such as fosfomycin for treating MRSA-related invasive and biofilm-associated infections.

The paper “Boosting Fosfomycin Efficacy Against Methicillin-Resistant Staphylococcus aureus Infections by Targeting Pyrimidine Metabolism,” is authored by Jianya Luo, Qingyan Lv, Mengping He, Zhiqiang Wang, Yuan Liu. Full text of the open access paper: https://doi.org/10.1016/j.eng.2026.01.025. For more information about Engineering, visit the website at https://www.sciencedirect.com/journal/engineering.