A benzoxazolyl urea inhibits VraS and enhances antimicrobials against vancomycin intermediate-resistant Staphylococcus aureus

Vancomycin intermediate-resistant Staphylococcus aureus (VISA) is a pathogen of concern. VraS, a histidine kinase, facilitates the VISA phenotype. Here, we reveal a benzoxazolyl urea (chemical 1) that directly inhibits VraS and enhances vancomycin to below the clinical breakpoint against an archetypal VISA strain, Mu50. 50 μM of 1 enhances vancomycin 16-fold to 0.25 μg/mL. The MIC of oxacillin is enhanced 32-fold to 8 μg/mL, only slightly above its clinical breakpoint. The chemical also showed promising enhancement of oxacillin against several MRSA strains. 1 shows ∼30 % inhibition of ATPase activity in VraS and reduces vra gene auto-upregulation typical upon vancomycin exposure. Therefore, 1 inhibits VraS to block normal vra operon function, leading to potent enhancement of cell wall-directed antibiotics. Interestingly, a molecular modeling approach suggests 1 does not displace ATP from the active site, but acts elsewhere. While VraS inhibitors have previously been reported to function against MRSA, to the best of our knowledge, this is the first direct VraS inhibitor ever reported that shows significant enhancement of vancomycin against VISA.