Carbapenem Use Is Driving the Evolution of Imipenemase 1 Variants

Machine Learning Models Identify Inhibitors of New Delhi Metallo-β-lactamase

The worldwide spread of the metallo-β-lactamases (MBL), especially New Delhi metallo-β-lactamase-1 (NDM-1), is threatening the efficacy of β-lactams, which are the most potent and prescribed class of antibiotics in the clinic. Currently, FDA-approved MBL inhibitors are lacking in the clinic even though many strategies have been used in inhibitor development, including quantitative high-throughput screening (qHTS), fragment-based drug discovery (FBDD), and molecular docking. Herein, a machine learning-based prediction tool is described, which was generated using results from HTS of a large chemical library and previously published inhibition data. The prediction tool was then used for virtual screening of the NIH Genesis library, which was subsequently screened using qHTS. A novel MBL inhibitor was identified and shown to lower minimum inhibitory concentrations (MICs) of Meropenem for a panel of E. coli and K. pneumoniae clinical isolates expressing NDM-1. The mechanism of inhibition of this novel scaffold was probed utilizing equilibrium dialyses with metal analyses, native state electrospray ionization mass spectrometry, UV-vis spectrophotometry, and molecular docking. The uncovered inhibitor, compound 72922413, was shown to be 9-hydroxy-3-[(5-hydroxy-1-oxa-9-azaspiro[5.5]undec-9-yl)carbonyl]-4H-pyrido[1,2-a]pyrimidin-4-one.

Development of Inhibitory Compounds for Metallo-beta-lactamase through Computational Design and Crystallographic Analysis

Metallo-β-lactamases (MBL) deactivate β-lactam antibiotics through a catalytic reaction caused by two zinc ions at the active center. Since MBLs deteriorate a wide range of antibiotics, they are dangerous factors for bacterial multidrug resistance. In this work, organic synthesis, computational design, and crystal structure analysis were performed to obtain potent MBL inhibitors based on a previously identified hit compound. The hit compound comprised 3,4-dihydro-2(1H)-quinolinone linked with a phenyl-ether-methyl group via a thiazole ring. In the first step, the thiazole ring was replaced with a tertiary amine to avoid the planar structure. In the second step, we virtually modified the compound by keeping the quinolinone backbone. Every modified compound was bound to a kind of MBL, imipenemase-1 (IMP-1), and the binding pose was optimized by a molecular mechanics calculation. The binding scores were evaluated for the respective optimized binding poses. Given the predicted binding poses and calculated binding scores, candidate compounds were determined for organic syntheses. The inhibitory activities of the synthesized compounds were measured by an in vitro assay for two kinds of MBLs, IMP-1 and New Delhi metallo-β-lactamase (NDM-1). A quinolinone connected with an amine bound with methyl-phenyl-ether-propyl and cyclohexyl-ethyl showed a 50% inhibitory concentration of 4.8 μM. An X-ray crystal analysis clarified the binding structure of a synthesized compound to IMP-1. The δ-lactam ring of quinolinone was hydrolyzed, and the generated carboxyl group was coordinated with zinc ions. The findings on the chemical structure and binding pose are expected to be a base for developing MBL inhibitors.

The directed evolution of NDM-1

β-Lactam antibiotics are among the most frequently prescribed therapeutic agents. A common mechanism of resistance toward β-lactam antibiotics is the production of β-lactamases. These enzymes are capable of hydrolyzing the β-lactam bond, rendering the drug inactive. Among the four described classes, the metallo- β-lactamases (MBLs, class B) employ one or two zinc ions in the active site for catalysis. One of the three most clinically relevant MBLs is New Delhi Metallo- β-Lactamase (NDM-1). The current study sought to investigate the in vitro protein evolution of NDM-1 β-lactamase using error-prone polymerase chain reaction. Evaluation revealed that variants were not found to confer higher levels of resistance toward meropenem based on amino acid substitutions. Thus, we postulate that increases in transcription or changes in zinc transport may be clinically more relevant to meropenem resistance than amino acid substitutions.

Resistome and Genome Analysis of an Extensively Drug-Resistant Klebsiella michiganensis KMIB106: Characterization of a Novel KPC Plasmid pB106-1 and a Novel Cointegrate Plasmid pB106-IMP Harboring blaIMP-4 and blaSHV-12

Klebsiella michiganensis is a recently emerging human pathogen causing nosocomial infections. This study aimed to characterize the complete genome sequence of a clinical Klebsiella michiganensis strain KMIB106 which exhibited extensive drug-resistance. The whole genome of the strain was sequenced using PacBio RS III systems and Illumina Nextseq 500. Annotation, transposable elements and resistance gene identification were analyzed by RAST, prokka and Plasmid Finder, respectively. According to the results, KMIB106 was resistant to multiple antimicrobials, including carbapenems, but it remained susceptible to aztreonam. The genome of KMIB106 consisted of a single chromosome and three predicted plasmids. Importantly, a novel KPC plasmid pB106-1 was found to carry the array of resistance genes in a highly different order in its variable regions, including mphA, msrE, mphE, ARR-3, addA16, sul1, dfrA27, tetD and fosA3. Plasmid pB106-2 is a typical IncFII plasmid with no resistant gene. Plasmid pB106-IMP consists of the IncN and IncX3 backbones, and two resistance genes, blaIMP-4 and blaSHV-12, were identified. Our study for the first time reported an extensively drug-resistant Klebsiella michiganensis strain recovered from a child with a respiratory infection in Southern China, which carries three mega plasmids, with pB106-1 firstly identified to carry an array of resistance genes in a distinctive order, and pB106-IMP identified as a novel IncN-IncX3 cointegrate plasmid harboring two resistance genes blaIMP-4 and blaSHV-12.

Small-molecule inhibitors of bacterial-producing metallo-β-lactamases: insights into their resistance mechanisms and biochemical analyses of their activities

Antibiotic resistance (AR) remains one of the major threats to the global healthcare system, which is associated with alarming morbidity and mortality rates. The defence mechanisms of Enterobacteriaceae to antibiotics occur through several pathways including the production of metallo-β-lactamases (MBLs). The carbapenemases, notably, New Delhi MBL (NDM), imipenemase (IMP), and Verona integron-encoded MBL (VIM), represent the critical MBLs implicated in AR pathogenesis and are responsible for the worst AR-related clinical conditions, but there are no approved inhibitors to date, which needs to be urgently addressed. Presently, the available antibiotics including the most active β-lactam-types are subjected to deactivation and degradation by the notorious superbug-produced enzymes. Progressively, scientists have devoted their efforts to curbing this global menace, and consequently a systematic overview on this topic can aid the timely development of effective therapeutics. In this review, diagnostic strategies for MBL strains and biochemical analyses of potent small-molecule inhibitors from experimental reports (2020-date) are overviewed. Notably, N1 and N2 from natural sources, S3-S7, S9 and S10 and S13-S16 from synthetic routes displayed the most potent broad-spectrum inhibition with ideal safety profiles. Their mechanisms of action include metal sequestration from and multi-dimensional binding to the MBL active pockets. Presently, some β-lactamase (BL)/MBL inhibitors have reached the clinical trial stage. This synopsis represents a model for future translational studies towards the discovery of effective therapeutics to overcome the challenges of AR.

Optimization of 1,2,4-Triazole-3-thiones toward Broad-Spectrum Metallo-β-lactamase Inhibitors Showing Potent Synergistic Activity on VIM- and NDM-1-Producing Clinical Isolates

Metallo-β-lactamases (MBLs) contribute to the resistance of Gram-negative bacteria to carbapenems, last-resort antibiotics at hospital, and MBL inhibitors are urgently needed to preserve these important antibacterial drugs. Here, we describe a series of 1,2,4-triazole-3-thione-based inhibitors displaying an α-amino acid substituent, which amine was mono- or disubstituted by (hetero)aryl groups. Compounds disubstituted by certain nitrogen-containing heterocycles showed submicromolar activities against VIM-type enzymes and strong NDM-1 inhibition (K_i = 10-30 nM). Equilibrium dialysis, native mass spectrometry, isothermal calorimetry (ITC), and X-ray crystallography showed that the compounds inhibited both VIM-2 and NDM-1 at least partially by stripping the catalytic zinc ions. These inhibitors also displayed a very potent synergistic activity with meropenem (16- to 1000-fold minimum inhibitory concentration (MIC) reduction) against VIM-type- and NDM-1-producing ultraresistant clinical isolates, including Enterobacterales and Pseudomonas aeruginosa. Furthermore, selected compounds exhibited no or moderate toxicity toward HeLa cells, favorable absorption, distribution, metabolism, excretion (ADME) properties, and no or modest inhibition of several mammalian metalloenzymes.

Classification and molecular characteristics of tet(X)-carrying plasmids in Acinetobacter species

The rapid dissemination of plasmid-mediated tet(X) genes in Acinetobacter species has compromised the clinical effectiveness of tigecycline, one of the last-resort antibiotics. However, the classification strategy and homology group of tet(X)-positive Acinetobacter spp. plasmids remain largely unknown. In this study, we classified them by genome-based replicon typing, followed by analyses of structural characteristics, transferability and in vivo effect. A total of 34 plasmids distributed in at least nine Acinetobacter species were collected, including three tet(X3)-positive plasmids and one tet(X6)-positive plasmid from our genome sequencing results. Among them, there were 28 plasmids carrying Rep_3 superfamily replicase genes and classified into six homology groups, consisting of GR31 (82.1%), GR26 (3.6%), GR41 (3.6%), GR59 (3.6%), and novel groups GR60 (3.6%) and GR61 (3.6%). Our tet(X3)-positive plasmids pYH16040-1, pYH16056-1, and pYH12068-1 belonged to the dominant GR31 group, whereas the tet(X6)-positive plasmid pYH12068-2 was unclassified. Structurally, all tet(X)-positive GR31 plasmids shared similar plasmid replication (repB), stability (parA and parB) and accessory modules [tet(X) and sul2], and 97.6% of plasmid-mediated tet(X) genes in Acinetobacter species were adjacent to ISCR2. Conjugation and susceptibility testing revealed pYH16040-1, pYH16056-1, and pYH12068-2, carrying plasmid transfer modules, were able to mediate the mobilization of multiple antibiotic resistance. Under the treatment of tigecycline, the mortality rate of Galleria mellonella infected by pYH16040-1-mediated tet(X3)-positive Acinetobacter spp. isolate significantly increased when compared with its plasmid-cured strain (p < 0.0001). The spread of such plasmids is of great clinical concern, more effects are needed and will facilitate the future analysis of tet(X)-positive Acinetobacter spp. plasmids.

Deciphering the evolution of metallo-β-lactamases: a journey from the test tube to the bacterial periplasm

Understanding the evolution of metallo-β-lactamases (MBLs) is fundamental to deciphering the mechanistic basis of resistance to carbapenems in pathogenic and opportunistic bacteria. Presently, these MBL producing pathogens are linked to high rates of morbidity and mortality worldwide. However, the study of the biochemical and biophysical features of MBLs in vitro provides an incomplete picture of their evolutionary potential, since this limited and artificial environment disregards the physiological context where evolution and selection take place. Herein, we describe recent efforts aimed to address the evolutionary traits acquired by different clinical variants of MBLs in conditions mimicking their native environment (the bacterial periplasm) and considering whether they are soluble or membrane-bound proteins. This includes addressing the metal content of MBLs within the cell under zinc starvation conditions, and the context provided by different bacterial hosts that result in particular resistance phenotypes. Our analysis highlights recent progress bridging the gap between in vitro and in-cell studies.

Metallo-β-lactamases and a tug-of-war for the available zinc at the host-pathogen interface

Metallo-β-lactamases (MBLs) are zinc-dependent hydrolases that inactivate virtually all β-lactam antibiotics. The expression of MBLs by Gram-negative bacteria severely limits the therapeutic options to treat infections. MBLs bind the essential metal ions in the bacterial periplasm, and their activity is challenged upon the zinc starvation conditions elicited by the native immune response. Metal depletion compromises both the enzyme activity and stability in the periplasm, impacting on the resistance profile in vivo. Thus, novel inhibitory approaches involve the use of chelating agents or metal-based drugs that displace the native metal ion. However, newer MBL variants incorporate mutations that improve their metal binding abilities or stabilize the metal-depleted form, revealing that metal starvation is a driving force acting on MBL evolution. Future challenges require addressing the gap between in cell and in vitro studies, dissecting the mechanism for MBL metalation and determining the metal content in situ.

β-Lactam antibiotic targets and resistance mechanisms: from covalent inhibitors to substrates

The β-lactams are the most widely used antibacterial agents worldwide. These antibiotics, a group that includes the penicillins and cephalosporins, are covalent inhibitors that target bacterial penicillin-binding proteins and disrupt peptidoglycan synthesis. Bacteria can achieve resistance to β-lactams in several ways, including the production of serine β-lactamase enzymes. While β-lactams also covalently interact with serine β-lactamases, these enzymes are capable of deacylating this complex, treating the antibiotic as a substrate. In this tutorial-style review, we provide an overview of the β-lactam antibiotics, focusing on their covalent interactions with their target proteins and resistance mechanisms. We begin by describing the structurally diverse range of β-lactam antibiotics and β-lactamase inhibitors that are currently used as therapeutics. Then, we introduce the penicillin-binding proteins, describing their functions and structures, and highlighting their interactions with β-lactam antibiotics. We next describe the classes of serine β-lactamases, exploring some of the mechanisms by which they achieve the ability to degrade β-lactams. Finally, we introduce the l,d-transpeptidases, a group of bacterial enzymes involved in peptidoglycan synthesis which are also targeted by β-lactam antibiotics. Although resistance mechanisms are now prevalent for all antibiotics in this class, past successes in antibiotic development have at least delayed this onset of resistance. The β-lactams continue to be an essential tool for the treatment of infectious disease, and recent advances (e.g., β-lactamase inhibitor development) will continue to support their future use.

Structural Comparisons of Cefotaximase (CTX-M-ase) Sub Family 1

The cefotaximase or CTX-M, family of serine-β-lactamases represents a significant clinical concern due to the ability for these enzymes to confer resistance to a broad array of β-lactam antibiotics an inhibitors. This behavior lends CTX-M-ases to be classified as extended spectrum β-lactamases (ESBL). Across the family of CTX-M-ases most closely related to CTX-M-1, the structures of CTX-M-15 with a library of different ligands have been solved and serve as the basis of comparison within this review. Herein we focus on the structural changes apparent in structures of CTX-M-15 in complex with diazabicyclooctane (DABCO) and boronic acid transition state analog inhibitors. Interactions between a positive surface patch near the active site and complementary functional groups of the bound inhibitor play key roles in the dictating the conformations of active site residues. The insights provided by analyzing structures of CTX-M-15 in complex with DABCO and boronic acid transition state analog inhibitors and analyzing existing structures of CTX-M-64 offer opportunities to move closer to making predictions as to how CTX-M-ases may interact with potential drug candidates, setting the stage for the further development of new antibiotics and β-lactamase inhibitors.

Metallo-β-lactamases in the Age of Multidrug Resistance: From Structure and Mechanism to Evolution, Dissemination, and Inhibitor Design

Antimicrobial resistance is one of the major problems in current practical medicine. The spread of genes coding for resistance determinants among bacteria challenges the use of approved antibiotics, narrowing the options for treatment. Resistance to carbapenems, last resort antibiotics, is a major concern. Metallo-β-lactamases (MBLs) hydrolyze carbapenems, penicillins, and cephalosporins, becoming central to this problem. These enzymes diverge with respect to serine-β-lactamases by exhibiting a different fold, active site, and catalytic features. Elucidating their catalytic mechanism has been a big challenge in the field that has limited the development of useful inhibitors. This review covers exhaustively the details of the active-site chemistries, the diversity of MBL alleles, the catalytic mechanism against different substrates, and how this information has helped developing inhibitors. We also discuss here different aspects critical to understand the success of MBLs in conferring resistance: the molecular determinants of their dissemination, their cell physiology, from the biogenesis to the processing involved in the transit to the periplasm, and the uptake of the Zn(II) ions upon metal starvation conditions, such as those encountered during an infection. In this regard, the chemical, biochemical and microbiological aspects provide an integrative view of the current knowledge of MBLs.

Spectroscopic and biochemical characterization of metallo-β-lactamase IMP-1 with dicarboxylic, sulfonyl, and thiol inhibitors

In an effort to probe the biophysical mechanisms of inhibition for ten previously-reported inhibitors of metallo-β-lactamases (MBL) with MBL IMP-1, equilibrium dialysis, metal analyses coupled with atomic absorption spectroscopy (AAS), native state mass spectrometry (native MS), and ultraviolet-visible spectrophotometry (UV-VIS) were used. 6-(1H-tetrazol-5-yl) picolinic acid (1T5PA), ANT431, D/l-captopril, thiorphan, and tiopronin were shown to form IMP-1/Zn(II)/inhibitor ternary complexes, while dipicolinic acid (DPA) and 4-(3-aminophenyl)pyridine-2,6-dicarboxylic acid (3AP-DPA) stripped some metal from the active site of IMP but also formed ternary complexes. DPA and 3AP-DPA stripped less metal from IMP-1 than from VIM-2 but stripped more metal from IMP-1 than from NDM-1. In contrast to a previous report, pterostilbene does not appear to bind to IMP-1 under our conditions. These results, along with previous studies, demonstrate similar mechanisms of inhibition toward different MBLs for different MBL inhibitors.