The primary pharmacology of ceftazidime/avibactam: resistance in vitro

Drug Discovery in the Field of β-Lactams: An Academic Perspective

β-Lactams are the most widely prescribed class of antibiotics that inhibit penicillin-binding proteins (PBPs), particularly transpeptidases that function in peptidoglycan synthesis. A major mechanism of antibiotic resistance is the production of β-lactamase enzymes, which are capable of hydrolyzing β-lactam antibiotics. There have been many efforts to counter increasing bacterial resistance against β-lactams. These studies have mainly focused on three areas: discovering novel inhibitors against β-lactamases, developing new β-lactams less susceptible to existing resistance mechanisms, and identifying non-β-lactam inhibitors against cell wall transpeptidases. Drug discovery in the β-lactam field has afforded a range of research opportunities for academia. In this review, we summarize the recent new findings on both β-lactamases and cell wall transpeptidases because these two groups of enzymes are evolutionarily and functionally connected. Many efforts to develop new β-lactams have aimed to inhibit both transpeptidases and β-lactamases, while several promising novel β-lactamase inhibitors have shown the potential to be further developed into transpeptidase inhibitors. In addition, the drug discovery progress against each group of enzymes is presented in three aspects: understanding the targets, screening methodology, and new inhibitor chemotypes. This is to offer insights into not only the advancement in this field but also the challenges, opportunities, and resources for future research. In particular, cyclic boronate compounds are now capable of inhibiting all classes of β-lactamases, while the diazabicyclooctane (DBO) series of small molecules has led to not only new β-lactamase inhibitors but potentially a new class of antibiotics by directly targeting PBPs. With the cautiously optimistic successes of a number of new β-lactamase inhibitor chemotypes and many questions remaining to be answered about the structure and function of cell wall transpeptidases, non-β-lactam transpeptidase inhibitors may usher in the next exciting phase of drug discovery in this field.

The Effectiveness of Imipenem-Relebactam against Ceftazidime-Avibactam Resistant Variants of the KPC-2 β-Lactamase

BACKGROUND

Ceftazidime-avibactam was approved by the FDA to treat infections caused by Enterobacterales carrying bla_KPC-2. However, variants of KPC-2 with amino acid substitutions at position 179 have emerged and confer resistance to ceftazidime-avibactam.

METHODS

The activity of imipenem-relebactam was assessed against a panel of 19 KPC-2 D179 variants. KPC-2 and the D179N and D179Y variants were purified for biochemical analyses. Molecular models were constructed with imipenem to assess differences in kinetic profiles.

RESULTS

All strains were susceptible to imipenem-relebactam, but resistant to ceftazidime (19/19) and ceftazidime-avibactam (18/19). KPC-2 and the D179N variant hydrolyzed imipenem, but the D179N variant's rate was much slower. The D179Y variant was unable to turnover imipenem. All three β-lactamases hydrolyzed ceftazidime at varying rates. The acylation rate of relebactam for the D179N variant was ~2.5× lower than KPC-2. Poor catalytic turnover by the D179Y variant precluded the determination of inhibitory kinetic parameters. Acyl-complexes with imipenem and ceftazidime were less prevalent with the D179N variant compared to the D179Y variant, supporting the kinetic observations that the D179Y variant was not as active as the D179N variant. Relebactam was slower to form an acyl-complex with the D179Y variant compared to avibactam. The D179Y model with imipenem revealed that the catalytic water molecule was shifted, and the carbonyl of imipenem was not within the oxyanion hole. Conversely in the D179N model, imipenem was oriented favorably for deacylation.

CONCLUSIONS

Imipenem-relebactam overcame the resistance of the D179 variants, suggesting that this combination will be active against clinical isolates harboring these derivatives of KPC-2.