Ιdentification of SQ109 analogs with enhanced antimicrobial activity against methicillin-resistant <i>Staphylococcus aureus</i>

The rise of antimicrobial resistance necessitates the development of novel or repurposed molecules with potent antibacterial properties. In this study, we evaluated the lipid-based antimicrobial candidate, SQ109, and 14 of its analogs for their efficacy against methicillin-resistant <i>Staphylococcus aureus</i> (MRSA). Analogs AK126 and AK127, featuring a bulky benzyl- or phenyl-substituent at the adamantyl C-2 position, respectively, exhibited the most potent antimicrobial activity with no detectable resistance development. To elucidate their mechanisms of action, we combined molecular dynamics simulations, fluorescence-based assays, and scanning electron microscopy. Our results showed that SQ109, AK126, and AK127 target the <i>S. aureus</i> membrane by disrupting the proton motive force and inducing membrane damage in a dose-dependent manner. Additionally, AK126 and AK127 showed activity against <i>S. aureus</i> persister cells and synergized with gentamicin to facilitate its uptake. Lastly, both analogs exhibited higher selectivity for negatively charged membranes over the largely zwitterionic epithelial membrane. While further optimization is needed, these findings highlight two new scaffolds as a basis for the development of new agents capable of combating difficult-to-treat MRSA infections.