Avibactam and Class C β-Lactamases: Mechanism of Inhibition, Conservation of the Binding Pocket, and Implications for Resistance

Abstract

bAvibactam is a novel non-␤-lactam ␤-lactamase inhibitor that inhibits a wide range of ␤-lactamases. These include class A, class C, and some class D enzymes, which erode the activity of ␤-lactam drugs in multidrug-resistant pathogens like Pseudomonas aeruginosa and Enterobacteriaceae spp. Avibactam is currently in clinical development in combination with the ␤-lactam antibiotics ceftazidime, ceftaroline fosamil, and aztreonam. Avibactam has the potential to be the first ␤-lactamase inhibitor that might provide activity against class C-mediated resistance, which represents a growing concern in both hospital-and community-acquired infections. Avibactam has an unusual mechanism of action: it is a covalent inhibitor that acts via ring opening, but in contrast to other currently used ␤-lactamase inhibitors, this reaction is reversible. Here, we present a high-resolution structure of avibactam bound to a class C ␤-lactamase, AmpC, from P. aeruginosa that provided insight into the mechanism of both acylation and recyclization in this enzyme class and highlighted the differences observed between class A and class C inhibition. Furthermore, variants resistant to avibactam that identified the residues important for inhibition were isolated. Finally, the structural information was used to predict effective inhibition by sequence analysis and functional studies of class C ␤-lactamases from a large and diverse set of contemporary clinical isolates (P. aeruginosa and several Enterobacteriaceae spp.) obtained from recent infections to understand any preexisting variability in the binding pocket that might affect inhibition by avibactam.

Unexpected Challenges in Treating Multidrug-Resistant Gram-Negative Bacteria: Resistance to Ceftazidime-Avibactam in Archived Isolates of Pseudomonas aeruginosa

“…Therefore, our analysis suggested that amino acid substitutions in the AmpC enzyme are unlikely to be the main mechanism conferring resistance to ceftazidime or ceftazidime-avibactam since there was no correlation between the PDC enzyme and the MIC. These results are consistent with previous investigations that analyzed the activity of ceftazidime-avibactam against P. aeruginosa isolates containing 57 different AmpC enzymes (37).…”

In Vitro Activity of Aztreonam-Avibactam against Enterobacteriaceae and Pseudomonas aeruginosa Isolated by Clinical Laboratories in 40 Countries from 2012 to 2015

“…It is possible that some of the isolates may harbor mutations in PBP3, such as the 4-amino-acid insertion shown to reduce the activity of aztreonam-avibactam (28). Resistance may also arise from single amino acid substitutions or ⍀-loop mutations in coresident class A and C serine ␤-lactamases that can lead to a reduced affinity of avibactam for the ␤-lactamase binding site, resulting in poor inhibition of ␤-lactamase activity (13,29,30). Porin deficits and overexpression of efflux pumps may also be contributory.…”

“…Avibactam protects ␤-lactams from hydrolysis by class A enzymes (including TEM, CTX-M ESBLs, and KPCs), class C enzymes (e.g., CMY, ACT, FOX), and some class D enzymes (e.g., OXA-48, OXA-139) (2,(10)(11)(12)(13). When combined with avibactam, aztreonam is able to inhibit cell wall synthesis in MBL-producing bacteria, despite the presence of cocarried serine ␤-lactamases (2,9,14).…”

Targeting Antibiotic Resistance

“…It is a covalent, reversible inhibitor that has been shown to have a very fast “on” rate, as well as a very slow “off” rate for deacylation, with a half‐life measured in days 173. X‐ray crystal structures of avibactam in complex with three different β‐lactamases have provided important insight into the mode of action 174, 175, 176. Avibactam interacts with conserved key residues in a fairly rigid conformation, and the highly polar sulfate group (which mimics the β‐lactam carboxylic acid, Figure 37) engages in strong polar interactions with Arg261 (Figure 38).…”