Due to the rapid proliferation of antibiotic-resistant pathogenic bacteria, known as carbapenem-resistant enterobacteriaceae, the efficacy of β-lactam antibiotics is threatened. β-lactam antibiotics constitute over 50% of the available antibiotic arsenal. Recent efforts have been focused on developing inhibitors to these enzymes. In an effort to understand the mechanism of inhibition(s) of four FDA-approved thiol-containing drugs that were previously reported to be inhibitors of New Delhi metallo-β-lactamase (NDM-1), various biochemical and spectroscopic techniques were used. Isothermal titration calorimetry demonstrated the binding affinity to NDM-1 corresponds to the reported IC50 values of the inhibitors. Equilibrium dialyses and metal analyses demonstrated that all of these inhibitors formed ternary complexes with ZnZn-NDM-1. Spectroscopic studies on CoCo-NDM-1 revealed two distinct binding modes for the thiol-containing compounds. These findings validate the need to further investigate the mechanism of inhibition of MBL inhibitors. Further research to identify inhibition capabilities beyond reported IC50 values is necessary for understanding the binding modes of these identified compounds and to provide the necessary foundation for developing clinically relevant MBL inhibitors.
Keywords: Co(ii)-substituted enzyme; Metallo-β-lactamase; Spectroscopy; Thiorphan; Tiopronin.