Methicillin-resistant Staphylococcus aureus (MRSA) represents a significant global public health threat. Combination therapy, particularly the use of antibiotics in conjunction with non-antibiotic agents, has emerged as a promising strategy to address the growing crisis of antibiotic resistance. Fosfomycin (FOS), increasingly utilized in clinical practice for treating drug-resistant bacterial infections, exhibits limited efficacy as a monotherapy. Here, we find that 5-fluorouracil (5-FU), a Food and Drug Administration (FDA)-approved anticancer drug, effectively enhances the antibacterial activity of FOS against MRSA, including biofilm-embedded MRSA cells. Mechanistically, 5-FU targets cytidine triphosphate (CTP) synthase, a rate-limiting enzyme responsible for the adenosine triphosphate (ATP)-dependent conversion of uridine triphosphate (UTP) to CTP. Moreover, we demonstrate that the synergistic effect of 5-FU and FOS arises from the perturbation of pyrimidine metabolism, which induces membrane damage, dissipation of the proton motive force (PMF), enhanced ATP synthesis, and accumulation of reactive oxygen species, culminating in bacterial death. In both Galleria mellonella ( G. mellonella ) and murine infection models, the combination of 5-FU and FOS markedly improves survival and reduces bacterial burdens. Collectively, our work demonstrates the therapeutic potential of 5-FU combined with FOS for tackling MRSA infections and highlights the pivotal role of perturbing pyrimidine metabolism in restoring antibiotic susceptibility.
Luo et al. (Sun,) studied this question.