Inhibiting Mycobacterium abscessus Cell Wall Synthesis: Using a Novel Diazabicyclooctane β-Lactamase Inhibitor To Augment β-Lactam Action.

Mycobacterium abscessus () infections are a growing menace to the health of many patients, especially those suffering from structural lung disease and cystic fibrosis. With multidrug resistance a common feature and a growing understanding of peptidoglycan synthesis in , it is advantageous to identify potent β-lactam and β-lactamase inhibitor combinations that can effectively disrupt cell wall synthesis. To improve existing therapeutic regimens to address serious infections, we evaluated the ability of durlobactam (DUR), a novel diazobicyclooctane β-lactamase inhibitor to restore susceptibilities in combination with β-lactams and provide a biochemical rationale for the activity of this compound. In cell-based assays, susceptibility of subsp. isolates to amoxicillin (AMOX), imipenem (IMI), and cefuroxime (CXM) was significantly enhanced with the addition of DUR. The triple drug combinations of CXM-DUR-AMOX and IMI-DUR-AMOX were most potent, with MIC ranges of ≤0.06 to 1 μg/mL and an MIC/MIC of ≤0.06/0.25 μg/mL, respectively. We propose a model by which this enhancement may occur, DUR potently inhibited the β-lactamase Bla with a relative Michaelis constant ( ) of 4 × 10 ± 0.8 × 10μM and acylation rate (/) of 1 × 10 M s. Timed mass spectrometry captured stable formation of carbamoyl-enzyme complexes between DUR and Ldt and d,d-carboxypeptidase, potentially contributing to the intrinsic activity of DUR. Molecular modeling showed unique and favorable interactions of DUR as a Bla inhibitor. Similarly, modeling showed how DUR might form stable Michaelis-Menten complexes with Ldt and d,d-carboxypeptidase. The ability of DUR combined with amoxicillin or cefuroxime and imipenem to inactivate multiple targets such as d,d-carboxypeptidase and Ldt supports new therapeutic approaches using β-lactams in eradicating . Durlobactam (DUR) is a potent inhibitor of Bla and provides protection of amoxicillin and imipenem against hydrolysis. DUR has intrinsic activity and forms stable acyl-enzyme complexes with Ldt and Ldt. The ability of DUR to protect amoxicillin and imipenem against Bla and its intrinsic activity along with the dual β-lactam target redundancy can explain the rationale behind the potent activity of this combination.