Evaluation of 1, 4, 7-Triazacyclononane (TACN) as a potential Metallo-B-Lactamase inhibitor in Enterobacteriaceae: Restoring the Activity of B-lactams

Metallo-B-lactamase (MBL)-producing Enterobacteriaceae are of grave clinical concern particularly as there are no MBL inhibitors approved for clinical use. The discovery and development of MBL inhibitors to restore the efficacy of available B-lactams is thus imperative. We investigated a zinc-chelating moiety, 1, 4, 7-triazacyclononane (TACN) for its inhibitory activity against clinical carbapenem-resistant Enterobacteriaceae (CRE). Minimum inhibitory concentrations, minimum bactericidal concentrations, serum effect, fractional inhibitory concentrations index and time-kill kinetics were performed using broth micro-dilution techniques according to the CLSI guidelines. Enzyme kinetic parameters and cytotoxicity effects of TACN were determined using spectrophotometric assays. The interactions of the enzyme-TACN complex were investigated by computational studies. Meropenem (MEM) regained its activity against carbapenemase-producing Enterobacteriaceae, with the MIC decreasing to 0.03 mg/L in the presence of TACN. TACN-MEM combinations showed bactericidal effect with MIC/MBC ratio of less than or equal to 4 and synergistic activity was observed. Human serum effects on the MICs were insignificant and TACN was found to be non-cytotoxic at concentrations above the MIC values. Computational studies predicted that TACN inhibit MBLs by targeting their catalytic active site pockets. This was supported by its inhibition constant Ki = 0.044 uM and inactivation constant kinact = 0.0406 (min -1 ) demonstrating that TACN inhibits MBLs efficiently and holds promise as a potential inhibitor. Importance of study: Carbapenem-resistant Enterobacteriaceae (CRE)-mediated infections remain a huge public health concern and have been reported as critical in the World Health Organization Priority Pathogens List for the Research and Development of New Antibiotics. CRE produce enzymes such as Metallo-B-lactamases (MBLs), which inactivate B-lactam antibiotics. Combination therapies involving a B-lactam antibiotic and a B-lactamase inhibitor remain a major treatment option for infections caused by B-lactamase-producing organisms. Currently, no MBL inhibitor-B-lactam combination therapy is clinically available for MBL-positive bacterial infections. Hence, developing efficient molecules capable of inhibiting these enzymes remain a way forward to overcome this phenomenon. TACN played a significant role in the inhibitory activity of the tested molecules against CREs by potentiating the carbapenem. This study demonstrated that TACN inhibits MBLs efficiently and holds promise as a potential MBLs inhibitor to help curb the global health threat posed by MBL-producing CREs.