Evaluation of 2,7-Naphthyridines as Targeted Anti-Staphylococcal Candidates with Microbiota-Sparing Properties

The rising resistance of bacterial and fungal strains, particularly in biofilm form, is diminishing the efficacy of available therapies and poses a major threat to human health. This highlights the need for new antimicrobial agents. A review of biological studies has shown that 2,7-naphthyridine derivatives exhibit a wide spectrum of pharmacological properties, including antimicrobial activity, which has contributed to the development of new compounds containing this scaffold. In this work, the obtained compounds were tested to assess their ability to eradicate biofilm formed by selected reference strains of opportunistic pathogens: Staphylococcus aureus, Pseudomonas aeruginosa and Candida albicans as well as towards normal microbiota representative, referred to as the Lactobacillus crispatus. The tested 2,7-naphthyridine derivatives showed selective antimicrobial activity, exclusively against S. aureus. 10j demonstrated the highest, among tested compounds, activity on this pathogen (MIC = 8 mg/L), while compound 10f exhibited ~100-fold stronger activity (MIC = 31 mg/L) than the majority of the library compounds. The in vitro assessment on fibroblast cell lines demonstrated low cytotoxicity of both compounds 10f and 10j, which was subsequently confirmed in vivo using the Galleria mellonella larval model, where no signs of systemic toxicity were observed during the 5-day observation period. Due to the structural similarity of the compounds 10f and 10j to typical gyrase/topoisomerase IV inhibitors, molecular dynamics simulations were performed on a ternary complex containing protein, DNAds, and a 1,5-naphthyridine inhibitor (PDB ID: 6Z1A). Molecular dynamics of the gyrase-DNA ternary complex supported stable binding of both hydrazone derivatives, with 10j showing slightly more favorable MM/GBSA energetics driven by electrostatics and halogen bonding, consistent with its ~4-fold lower MIC versus 10f. Taken together, our data highlight compound 10j as a promising microbiota-sparing antibacterial candidate, particularly suitable for selective interventions against S. aureus, for instance in vaginal infections, where targeted eradication of the pathogen without disturbing protective commensals is highly desirable.