Emerione A, a novel fungal metabolite as an inhibitor of New Delhi metallo-β-lactamase-1, restores carbapenem susceptibility in carbapenem-resistant isolates

New Delhi Metallo-Beta-Lactamase Inhibitors: A Systematic Scoping Review

Background/Objectives: Among various carbapenemases, New Delhi metallo-beta-lactamases (NDMs) are recognized as the most powerful type capable of hydrolyzing all beta-lactam antibiotics, often conferring multi-drug resistance to the microorganism. The objective of this review is to synthesize current scientific data on NDM inhibitors to facilitate the development of future therapeutics for challenging-to-treat pathogens. Methods: Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) Extension for Scoping Reviews, we conducted a MEDLINE search for articles with relevant keywords from the beginning of 2009 to December 2022. We employed various generic terms to encompass all the literature ever published on potential NDM inhibitors. Results: Out of the 1760 articles identified through the database search, 91 met the eligibility criteria and were included in our analysis. The fractional inhibitory concentration index was assessed using the checkerboard assay for 47 compounds in 37 articles, which included 8 compounds already approved by the Food and Drug Administration (FDA) of the United States. Time-killing curve assays (14 studies, 25%), kinetic assays (15 studies, 40.5%), molecular investigations (25 studies, 67.6%), in vivo studies (14 studies, 37.8%), and toxicity assays (13 studies, 35.1%) were also conducted to strengthen the laboratory-level evidence of the potential inhibitors. None of them appeared to have been applied to human infections. Conclusions: Ongoing research efforts have identified several potential NDM inhibitors; however, there are currently no clinically applicable drugs. To address this, we must foster interdisciplinary and multifaceted collaborations by broadening our own horizons.

Novel partially reversible NDM-1 inhibitors based on the naturally occurring houttuynin

Discovering novel NDM-1 inhibitors is an urgent task for treatment of 'superbug' infectious diseases. In this study, we found that naturally occurring houttuynin and its sulfonate derivatives might be effective NDM-1 inhibitors with novel mechanism, i.e. the attribute of partially covalent inhibition of sulfonate derivatives of houttuynin against NDM-1. Primary structure-activity relationship study showed that both the long aliphatic side chain and the warhead of aldehyde group are vital for the efficiency against NDM-1. The homologs with longer chains (SNH-2 to SNH-5) displayed stronger inhibitory activities with IC50 range of 1.1-1.5 μM, while the shorter chain the weaker inhibition. Further synergistic experiments in cell level confirmed that all these 4 compounds (at 32 μg/mL) recovered the antibacterial activity of meropenem (MER) against E. coli BL21/pET15b-blaNDM-1.

Endophytes: a uniquely tailored source of potential antibiotic adjuvants

Multidrug microbial resistance is risking an annual loss of more than 10 million people' lives by 2050. Solutions include the rational use of antibiotics and the use of drugs that reduce resistance or completely obliterate them. Here endophytes come to play due to their high-yield production and inherent nature to produce antimicrobial molecules. Around 40%, 45% and 17% of antibacterial agents were obtained from fungi, actinomycetes, and bacteria, respectively, whose secondary metabolites revealed effectiveness against resistant microbes such as MRSA, MRSE, and Shigella flexneri. Endophyte's role was not confined to bactericidal effect but extended to other mechanisms against MDR microbes, among which was the adjuvant role or the "magic bullets". Scarce focus was given to antibiotic adjuvants, and many laboratories today just screen for the antimicrobial activity without considering combinations with traditional antibiotics, which means real loss of promising resistance combating molecules. While some examples of synthetic adjuvants were introduced in the last decade, the number is still far from covering the disused antibiotics and restoring them back to clinical use. The data compiled in this article demonstrated the significance of quorum sensing as a foreseen mechanism for adjuvants from endophytes secondary metabolites, which call for urgent in-depth studies of their molecular mechanisms. This review, comprehensively and for the first time, sheds light on the significance of endophytes secondary metabolites in solving AMR problem as AB adjuvants.

Hydroxyhexylitaconic acids as potent IMP-type metallo-β-lactamase inhibitors for controlling carbapenem resistance in Enterobacterales

Metallo-β-lactamases (MBLs) represent one of the main causes of carbapenem resistance in the order Enterobacterales. To combat MBL-producing carbapenem-resistant Enterobacterales, the development of MBL inhibitors can restore carbapenem efficacy for such resistant bacteria. Microbial natural products are a promising source of attractive seed compounds for the development of antimicrobial agents. Here, we report that hydroxyhexylitaconic acids (HHIAs) produced by a member of the genus Aspergillus can suppress carbapenem resistance conferred by MBLs, particularly IMP (imipenemase)-type MBLs. HHIAs were found to be competitive inhibitors with micromolar orders of magnitude against IMP-1 and showed weak inhibitory activity toward VIM-2, while no inhibitory activity against NDM-1 was observed despite the high dosage. The elongated methylene chains of HHIAs seem to play a crucial role in exerting inhibitory activity because itaconic acid, a structural analog without long methylene chains, did not show inhibitory activity against IMP-1. The addition of HHIAs restored meropenem and imipenem efficacy to satisfactory clinical levels against IMP-type MBL-producing Escherichia coli and Klebsiella pneumoniae clinical isolates. Unlike EDTA and Aspergillomarasmine A, HHIAs did not cause the loss of zinc ions from the active site, resulting in the structural instability of MBLs. X-ray crystallography and in silico docking simulation analyses revealed that two neighboring carboxylates of HHIAs coordinated with two zinc ions in the active sites of VIM-2 and IMP-1, which formed a key interaction observed in MBL inhibitors. Our results indicated that HHIAs are promising for initiating the design of potent inhibitors of IMP-type MBLs.IMPORTANCEThe number and type of metallo-β-lactamase (MΒL) are increasing over time. Carbapenem resistance conferred by MΒL is a significant threat to our antibiotic regimen, and the development of MΒL inhibitors is urgently required to restore carbapenem efficacy. Microbial natural products have served as important sources for developing antimicrobial agents targeting pathogenic bacteria since the discovery of antibiotics in the mid-20th century. MΒL inhibitors derived from microbial natural products are still rare compared to those derived from chemical compound libraries. Hydroxyhexylitaconic acids (HHIAs) produced by members of the genus Aspergillus have potent inhibitory activity against clinically relevant IMP-type MBL. HHIAs may be good lead compounds for the development of MBL inhibitors applicable for controlling carbapenem resistance in IMP-type MBL-producing Enterobacterales.

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.

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.

Drug development concerning metallo-β-lactamases in gram-negative bacteria

β-Lactams have been a clinical focus since their emergence and indeed act as a powerful tool to combat severe bacterial infections, but their effectiveness is threatened by drug resistance in bacteria, primarily by the production of serine- and metallo-β-lactamases. Although once of less clinical relevance, metallo-β-lactamases are now increasingly threatening. The rapid dissemination of resistance mediated by metallo-β-lactamases poses an increasing challenge to public health worldwide and comprises most existing antibacterial chemotherapies. Regrettably, there have been no clinically available inhibitors of metallo-β-lactamases until now. To cope with this unique challenge, researchers are exploring multidimensional strategies to combat metallo-β-lactamases. Several studies have been conducted to develop new drug candidates or calibrate already available drugs against metallo-β-lactamases. To provide an overview of this field and inspire more researchers to explore it further, we outline some promising candidates targeting metallo-β-lactamase producers, with a focus on Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter baumannii. Promising candidates in this review are composed of new antibacterial drugs, non-antibacterial drugs, antimicrobial peptides, natural products, and zinc chelators, as well as their combinations with existing antibiotics. This review may provide ideas and insight for others to explore candidate metallo-β-lactamases as well as promote the improvement of existing data to obtain further convincing evidence.

Bioinspired Asymmetric Total Synthesis of Emeriones A–C**

We report asymmetric bioinspired total syntheses of the fungal metabolites emeriones A–C via stereoselective oxidations of two bicyclo[4.2.0]octadiene diastereomers. The central bicyclic scaffolds are prepared in an 8π/6π electrocyclization cascade of a stereodefined pentaene, which contains the fully assembled side chains of the emeriones. The anti‐aldol side chain is made using a Paterson‐aldol addition, and the epoxide of the dioxabicyclo[3.1.0]hexane side chain via ring‐closure onto an oxidized acetal. Our work has enabled the structural revision of emerione C, and resulted in the synthesis of a “missing” family member, which we call emerione D. DFT calculations identified two methyl groups that govern torquoselectivity in the 8π/6π cascade.