Lipophilic Trimethoprim Analogues and Their Potent Antibacterial Activity Against Trimethoprim-Resistant MRSA

Abstract

The alarming emergence of methicillin-resistant Staphylococcus aureus (S. aureus) or MRSA has posed a severe threat worldwide. In addition to β-lactam antibiotics, MRSA has also been reported resistance towards other antibiotics, including trimethoprim. The rise of multi-drug resistance has called for new antibacterial strategies. In this study, we revisited trimethoprim and its binding to dihydrofolate reductase (DHFR) in trimethoprim-resistant strains. S. aureus DHFR has a shallow surface cavity that is electron-rich. Therefore, incorporating lipophilic groups into trimethoprim could improve its binding to S. aureus DHFR and potentially enhance antibacterial activity. We synthesized lipophilic trimethoprim derivatives and subjected to susceptibility testing against methicillin-susceptible S. aureus, global predominant MRSA USA300 strain, and trimethoprim-resistant MRSA strain COL. (E)-5-(3,4-dimethoxy-5-(4-methoxystyryl)benzyl) pyrimidine-2,4-diamine or TMP-sytrene-OMe (6) was the most potent growth inhibitory activity with minimum inhibitory concentration (MIC) of 4 µg/mL and minimum bactericidal concentration (MBC) of 8 µg/mL against trimethoprim-resistant strain COL. The modification led to a significant improvement over TMP. DHFR kinetic assay indicated that compound 6 inhibited DHFR-catalyzed reaction in concentration-dependent manner. Molecular docking studies suggested the increase of binding interactions to S. aureus DHFR and trimethoprim-resistant S1DHFR when compared to trimethoprim. These findings underscore the promise of lipophilic-incorporated trimethoprim derivatives as effective antibiotics against MRSA infections.