The irregular use of antibiotics has created a natural selection pressure for bacteria to adapt resistance. Bacterial resistance caused by metallo-β-lactamases (MβLs) has been the most prevalent in terms of posing a threat to human health. The New Delhi metallo-β-lactamase-1 (NDM-1) has been shown to be capable of hydrolyzing almost all β-lactams. In this work, eight aromatic Schiff bases 1-8 were prepared and identified by enzyme kinetic assays to be the potent inhibitors of NDM-1 (except 4). These molecules exhibited a more than 95 % inhibition, and an IC50 value in the range of 0.13-19 μM on the target enzyme, and 3 was found to be the most effective inhibitor (IC50 = 130 nM). Analysis of structure-activity relationship revealed that the o-hydroxy phenyl improved the inhibitory activity of Schiff bases on NDM-1. The inhibition mode assays including isothermal titration calorimetry (ITC) disclosed that both compounds 3 and 5 exhibited a reversibly mixed inhibition on NDM-1, with a Ki value of 1.9 and 10.8 μM, respectively. Antibacterial activity tests indicated that a dose of 64 μg·mL-1 Schiff bases resulted in 2-128-fold reduction in MICs of cefazolin on E. coli producing NDM-1 (except 4). Cytotoxicity assays showed that both Schiff bases 3 and 5 have low cytotoxicity on the mouse fibroblast (L929) cells at a concentration of up to 400 μM. Docking studies suggested that the hydroxyl group interacts with Gln123 and Glu152 of NDM-1, and the amino groups interact with the backbone amide groups of Glu152 and Asp223. This study provided a novel scaffold for the development of NDM-1 inhibitors.
Keywords: Antibiotic resistance; Aromatic Schiff base; Inhibitor; Metallo-β-lactamases; Steady-state kinetic.
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