Inhibitory effects of UM-C162 on Staphylococcus aureus alpha-toxin-induced toxicity

Abstract Staphylococcus aureus is a leading cause of nosocomial and community-acquired infections. The increasing prevalence of methicillin-resistant S. aureus (MRSA) and vancomycin-resistant S. aureus (VRSA) strains underscores the urgent need for novel anti-virulence agents. UM-C162, a recently identified small molecule, has been shown to suppress S. aureus biofilm formation and virulence in a Caenorhabditis elegans infection model. Transcriptomic and biochemical analyses revealed that UM-C162 disrupts the production of S. aureus haemolysins, proteases, and clumping factors. In this study, UM-C162 inhibited alpha-toxin (hla)-induced toxicity. Molecular docking and interaction analyses suggest that UM-C162 may bind directly to alpha-toxin. Its inhibitory activity was validated using a rabbit red blood cell haemolysis assay, yielding an IC50 of 36.97 µM. Co-incubation with recombinant alpha-toxin significantly reduced toxin-mediated injury to human alveolar epithelial (A549) cells, as observed by confocal microscopy, without causing cytotoxicity or cytolysis, as confirmed by MTS and LDH assays. This protective effect did not result from inhibition of alpha-toxin oligomerisation, as UM-C162 failed to prevent deoxycholate-induced heptamer formation. Furthermore, RT-qPCR analysis revealed that UM-C162 downregulates hla gene expression at the mRNA level. Collectively, these findings demonstrate that UM-C162 impairs S. aureus alpha-toxin activity and support its further development as a promising anti-virulence agent.