Metallo-β-Lactamases:A Major Threat to Human Health

Antibiotic resistance is one of the most significant challenges facing global healthcare. Since the 1940s, antibiotics have been used to fight infections, initially with penicillin and subsequently with various derivatives including cephalosporins, carbapenams and monobactams. A common characteristic of these antibiotics is the four-memberedβ-lactam ring. Alarmingly, in recent years an increasing number of bacteria have become resistant to these antibiotics. A major strategy employed by these pathogens is to use Zn(II)-dependent enzymes, the metallo-β-lactamases (MBLs), which hydrolyse theβ-lactam ring. Clinically useful MBL inhibitors are not yet available. Consequently, MBLs remain a major threat to human health. In this review biochemical properties of MBLs are discussed, focusing in particular on the interactions between the enzymes and the functionally essential metal ions. The precise role(s) of these metal ions is still debated and may differ between different MBLs. However, since they are required for catalysis, their binding site may present an alternative target for inhibitor design.

Unusual metallo-β-lactamases may constitute a new subgroup in this family of enzymes

Metallo-β-lactamases (MBLs) are a family of Zn2+-dependent enzymes that have contributed strongly to the emergence and spread of antibiotic resistance. Novel members as well as variants of existing members of this family are discovered continuously, compounding their threat to global health care. MBLs are divided into three subgroups, i.e. B1, B2 and B3. The recent discovery of an unusual MBL from Serratia proteamaculans (SPR-1) suggests the presence of an additional subgroup, i.e. B4. A database search reveals that SPR-1 has only one homologue from Cronobacter sakazakii, CSA-1.These two MBLs have a unique active site and may employ a mechanism distinct from other MBLs, but reminiscent of some organophosphate-degrading hydrolases.

Identification and preliminary characterization of novel B3-type metallo-β-lactamases

Antibiotic resistance has emerged as a major global threat to human health. Among the strategies employed by pathogens to acquire resistance the use of metallo-β-lactamases (MBLs), a family of dinuclear metalloenzymes, is among the most potent. MBLs are subdivided into three groups (i.e. B1, B2 and B3) with most of the virulence factors belonging to the B1 group. The recent discovery of AIM-1, a B3-type MBL, however, has illustrated the potential health threat of this group of MBLs. Here, we employed a bioinformatics approach to identify and characterize novel B3-type MBLs from Novosphingobium pentaromativorans and Simiduia agarivorans. These enzymes may not yet pose a direct risk to human health, but their structures and function may provide important insight into the design and synthesis of a still elusive universal MBL inhibitor.

IMB-XH1 identified as a novel inhibitor of New Delhi metallo-β-lactamase-1

The problem of drug resistance of Gram-negative bacteria has become increasingly serious and has aroused widespread public concern.The "super bacteria" producing New Delhi metallo-beta-lactamase(NDM-1) are resistant to almost all β-lactam antibiotics.However, clinically existing β-lactamase inhibitors are ineffective against metallo-β-lactamases(MBLs) including NDM-1.Therefore, effective NDM-1 inhibitors are urgently needed.In this study, a high-throughput screening model for NDM-1 inhibitors was optimized and used to screen NDM-1 inhibitors.As a result, IMB-XH1 was screened out as a novel NDM-1 inhibitor from 52 100 compounds of different sources.The combined use of IMB-XH1 can increase the sensitivity of E.coli BL21(DE3)(pET-30 a(+)-NDM-1) to β-lactam antibiotics.Enzymatic kinetic studies indicate that IMB-XH1 is a non-competitive inhibitor of NDM-1 and also has inhibitory activity against other MBLs such as IMP-4, ImiS and L1.As a novel NDM-1 inhibitor, its activity and mechanism of action need to be further explored.

An integrated microfluidic chip-mass spectrometry system for rapid antimicrobial resistance analysis of bacteria producingβ-lactamases

Bacteria producingβ-lactamases have become a major issue in the global public health field.To restrain the development of drug resistance and reduce the abuse of antibiotics,it is very important to rapidly identify bacteria producingβ-lactamases and put forward a reasonable treatment plan.Here,an integrated microfluidic chip-mass spectrometry system was proposed for rapid screening ofβ-lactamaseproducing bacteria and optimization ofβ-lactamase inhibitor dosing concentration.The concentration gradient generator followed by an array of bacterial culture chambers,as well as micro-solid-phase extraction columns was designed for sample pretreatment before mass analysis.By using the combination system,the process of the hydrolysis of antibiotics byβ-lactamase-producing bacteria could be analyzed.To validate the feasibility,four antibiotics and two antibiotic inhibitors were investigated using three strains including negative control,SHV-1 and TEM-1 strains.SHV-1 and TEM-1 strains were successfully distinguished as theβ-lactamase producing strains.And the acquired optimal concentrations ofβ-lactamase inhibitors were in accordance with the results by that obtained from the traditional microdilution broth method.The total analysis time only needed around 2 h,which was faster than conventional methods that require a few days.The technique presented herein provides an easy and rapid protocol forβ-lactamase resistance related studies,which is important for the inhibition of antimicrobial resistance development and the reduction of antibiotics abuse.

Design,synthesis and biological evaluation of sulfenimine cephalosporin sulfoxides as β-lactamase inhibitors

A series of sulfenimine cephalosporin sulfoxide derivatives （Ta-v） were designed, synthesized and evaluated for their inhibitory activity against TEM-1 and cephalosporinase in cell-free systems. Some of the tested compounds showed enhanced inhibitory activity against class C β-lactamase cephalospor- inase compared with the tazobactam. The most promising compounds 7c and 7n （IC50 ~ 7.6 and 8.6 μmol/L, respectively） were further investigated in combination with cefradine against a variety of clinical isolated fi-lactamase-producing bacterial strains.

Insights on the structural characteristics of NDM-1: The journey so far

New Delhi metallo-β-lactamase (NDM-1) has created a medical storm ever since it was first reported;as it is active on virtually all clinically used β-lactam antibiotics. NDM-1 rampancy worldwide is now considered a nightmare scenario, particularly due to its rapid dissemination. An underlying theme in the majority of recent studies is structural characterization as knowledge of the three-dimensional structure of NDM-1 shall help find connections between its structure and function. Moreover, structural details are even critical in order to reveal the resistance mecha- nism to β-lactam antibiotics. In this perspective, we review structural characteristics of NDM-1 that have been delineated since its first report. We anticipate that these structure-function connections made by its characterization shall further serve as future guidelines for elucidating pathways towards de novo design of functional inhibitors.

Strategic design of lysine-targeted irreversible covalent NDM-1 inhibitors

New Delhi metallo-β-lactamase 1(NDM-1) can hydrolyze most β-lactam antibiotics, which is the major factor for drug resistance of Gram-negative bacteria. The binding of most reversible inhibitors to NDM-1 is relatively weak due to the shallow active pocket of NDM-1. Alternatively, irreversible covalent inhibitors can prevent their dissociation from the target, leading to permanent inactivation of the protein.Herein, we report a series of irreversible covalent inhibitors of NDM-1 targeting the conserved Lys211 in the active pocket. Several methods, including mass spectrometry, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, fluorescent labeling, and coumarin probe were used to demonstrate that pentafluorophenyl ester formed a covalent bond with Lys211. Moreover, our target inhibitor, in combination with meropenem, achieved an antibacterial effect on drug-resistant bacteria, along with an excellent safety profile. Our new strategy in designing lysine-targeted irreversible covalent NDM-1 inhibitors provides a potential option for the clinical treatment of Gram-negative bacteria.