Recent advances in β-lactamase inhibitor chemotypes and inhibition modes

Discovery of 3-methacylic acid substituted benzoxaboroles as dual metallo- and serine-β-lactamase inhibitors

Carbapenem resistance is an ongoing clinical problem, largely driven by production of evolved serine β-lactamases (SBLs) and metallo-β-lactamases (MBLs). We here report a series of new 3-methacrylic acid-substituted benzoxaboroles as dual MBL/SBL inhibitors. Structure-activity relationship studies showed that the new compounds manifested nanomolar inhibition to the SBLs KPC-2 and OXA-48, and single-digit micromolar inhibition to the MBLs VIM-2, NDM-1, and NDM-5. Co-crystallographic analyses revealed their binding modes with VIM-2 and OXA-48, which are similar as those of taniborbactam and xeruborbactam. Bacterial assays demonstrated that compound 10 can potentiate meropenem against multidrug-resistant Gram-negative strains. This work provides new lead compounds and structural basis for developing new drug candidates against MBL/SBL-mediated carbapenem resistance.

Repurposing tavaborole to combat resistant bacterial infections through competitive inhibition of KPC-2 and metabolic disruption

The rise of carbapenem-resistant Enterobacteriaceae (CRE) strains has emerged as an increasing threat to global public health. The development of antibiotic adjuvants presents an economical and promising approach to address this crisis. Through a high-throughput screen of the FDA-approved compound library, we identified tavaborole (AN2690) as a broad-spectrum β-lactamase inhibitor. The mechanistic study revealed that tavaborole formed a reversible binding with the active serine of KPC-2, showing effective competitive inhibition. Its electron-deficient boron atom formed a borate ester bond with hydroxyl group of the serine residue at the active site of KPC-2, transitioning to an sp3-hybridized state that mimicked the tetrahedral intermediate during KPC-2 catalytic. Moreover, transcriptomic analysis and bacterial metabolism assays further unveiled tavaborole addition can inhibit tricarboxylic acid (TCA) cycle, coupled with downregulation of intracellular ATP levels, indicating that tavaborole compromised the bacterial metabolic homeostasis and exerted synergistic antibacterial activity. Notably, the combination treatment further suppressed the development of meropenem resistance. In mouse intraperitoneal infection models, tavaborole effectively restored the efficacy of meropenem against CRE bacteria. These findings elucidate the synergistic mechanisms of tavaborole, expand its potential applications in anti-infection therapeutics, and provide a promising strategy for addressing CRE infections.

Cross-subclass metallo-β-lactamase inhibitors: From structural and catalytic commonalities guiding design

The emergence of antibiotic resistance mediated by metallo-β-lactamases (MβLs) has become a problem due to its diverse and widespread resistance characteristics. Research on broad-spectrum inhibitors has become an important issue. This review summarized the reported metallo-β-lactamases inhibitors (MβLIs) with cross-class activity, as well as four practical design strategies for developing cross-subclass MβLIs. It provides a detailed analysis of current inhibitors, covering their chemical structures, mechanisms, and cross-class activities. Four design strategies are discussed: i) substrate simulation strategy, ii) combining metal-chelating motifs strategy, iii) covalent inhibition strategy, and iv) metal ion replacement strategy. These strategies offer insights into developing effective cross-subclass MβLIs to combat the increasing prevalence of resistant pathogens.

Development of molecular Trojan horses targeting New Delhi metallo-β-lactamase-1 for the restoration of meropenem susceptibility in drug-resistant bacteria

The emergence of New Delhi metallo-β-lactamase-1 (NDM-1) poses a significant threat to the clinical application of antibiotics, as it possesses the ability to hydrolyze nearly all β-lactam antibiotics. Regrettably, there are currently no clinical drugs targeting NDM-1, making it imperative to develop highly potent and minimally toxic NDM-1 inhibitors. Herein, a series of molecular Trojan horses targeting NDM-1 were synthesized by introducing ebselen into 7-aminocephalosporanic acid derivatives via a C-Se bond. Representative compound 18b exhibited potent inhibitory activity against NDM-1, with an IC50 value of 7.03 μM, and combining with meropenem (Mem) decreased the minimum inhibitory concentration (MIC) of Mem by 4-32-fold in NDM-1 expressing bacteria. Mechanistically, 18b released the ebselen moiety at the active site of NDM-1, forming a Se-S bond with Cys208 to achieve targeted drug delivery of ebselen. Importantly, 18b demonstrated potent inhibition of resistant bacterial growth and replication in mice when administered in combination with Mem. These results suggest that 18b is a promising candidate for treating infections caused by resistant bacteria expressing NDM-1.

Antibacterials with Novel Chemical Scaffolds in Clinical Development

The rise of antimicrobial resistance represents a significant global health threat, driven by the diminishing efficacy of existing antibiotics, a lack of novel antibacterials entering the market, and an over- or misuse of existing antibiotics, which accelerates the evolution of resistant bacterial strains. This review focuses on innovative therapies by highlighting 19 novel antibacterials in clinical development as of June 2024. These selected compounds are characterized by new chemical scaffolds, novel molecular targets, and/or unique mechanisms of action, which render their potential to break antimicrobial resistance particularly high. A detailed analysis of the scientific foundations behind each of these compounds is provided, including their pharmacodynamic profiles, current development state, and potential for overcoming existing limitations in antibiotic therapy. By presenting this subset of chemically novel antibacterials, the review highlights the ability to innovate in antibiotic drug development to counteract bacterial resistance and improve treatment outcomes.

Synergistic combination of ceftazidime and avibactam with Aztreonam against MDR Klebsiella pneumoniae in ICU patients

The proliferation of multidrug-resistant, metallo-beta-lactamase-producing Klebsiella pneumoniae (MBL-producing K. pneumoniae) poses a major threat to public health resulting in increasing treatment costs, prolonged hospitalization, and mortality rate. Treating such bacteria presents substantial hurdles for clinicians. The combination of Aztreonam (ATM) and ceftazidime/avibactam (CAZ/AVI) is likely the most successful approach. The study evaluated the in vitro activity of CAZ/AVI in combination with ATM against MBL-producing K. pneumoniae clinical isolates collected from Suez Canal University Hospital patients. Carbapenem-resistant K. pneumoniae were isolated and identified from different specimens. The presence of metallo-β-lactamases was detected phenotypically by modified carbapenem inactivation method (mCIM) and EDTA-CIM (eCIM) testing, and genotypically for the three metallo-β-lactamase genes: blaNDM, blaIMP, and blaVIM by conventional PCR method. The synergistic effect of CAZ/AVI with ATM against MBL-producing K. pneumoniae was detected by ceftazidime-avibactam combination disks and E-test for antimicrobial susceptibility testing. Out of the 65 K. pneumoniae isolates recovered, 60% (39/65) were carbapenem-resistant (CRKP). According to the mCIM and eCIM tests, 89.7% (35/39) of CRKP isolates were carbapenemase-positive, and 68.6% (24/35) were metallo-β-lactamase (MBL)-positive. By using the conventional PCR, at least one of the MBL genes was present in each metallo-bata-lactamase-producing isolate: 8.3% carried the blaVIM gene, 66.7% the blaNDM, and 91.7% the blaIMP gene. After doing the disk combination method for ceftazidime-avibactam plus Aztreonam, 62.5% of the isolates shifted from resistance to sensitivity. Also, ceftazidime/avibactam plus Aztreonam resistance was reduced markedly among CRKP using the E-test. The addition of Aztreonam to ceftazidime/avibactam is an effective therapeutic option against MBL-producing K. pneumoniae.Clinical Trials Registry: Pan African Clinical Trials Registry. Trial No.: PACTR202410744344899. Trial URL: https://pactr.samrc.ac.za/TrialDisplay.aspx?TrialID=32000.

Breakthrough Advances in Beta-Lactamase Inhibitors: New Synthesized Compounds and Mechanisms of Action Against Drug-Resistant Bacteria

Beta-lactam drugs hold a central place in the antibacterial arsenal, and the production of beta-lactamases by drug-resistant bacteria has severely compromised the effectiveness of nearly all available beta-lactams. Therefore, in the face of the increasing threat of drug resistance, the combined use of beta-lactamase inhibitors (BLIs) with beta-lactam antibiotics is crucial for treating infections caused by drug-resistant bacteria. Hence, the development of BLIs has always been a hot topic in the field of medicinal chemistry. In recent years, significant progress has been made in screening active drugs by enhancing the affinity of inhibitors for enzymes and the stability of their complexes, based on the design concept of competitive inhibitors. Here, we review the effects and mechanisms of newly synthesized beta-lactamase inhibitors on various BLIs in recent years, to provide ideas for the development of subsequent beta-lactamase inhibitors.

In-Vitro Activity of Dimercaptosuccinic Acid in Combination with Carbapenems Against Carbapenem-Resistant Pseudomonas aeruginosa

Carbapenenemase producers, particularly the metallo-β-lactamase (MBL) types in Pseudomonas aeruginosa, have emerged as an urgent threat in health care settings. MBLs require zinc at their catalytic site and can be inhibited by dimercaptosuccinic acid (DMSA), a metal chelator known for the treatment of lead and mercury intoxication. Isogenic strains of wild-type and OprD-deleted P. aeruginosa PA14, were constructed, producing the MBLs VIM-2, NDM-1, SPM-1, IMP-1, and AIM-1, or the non-MBL carbapenemases, GES-5 and KPC-2. In addition, 59 previously characterized clinical isolates of P. aeruginosa producing different ß-lactamases (including carbapenemases), and with known outer-membrane porin OprD status, were utilized. Minimal inhibitory concentrations values of imipenem and meropenem, and DMSA combinations were determined, and time-kill assays were performed with PA14 expressing VIM-2. Results indicated a significant additive effect of DMSA (most effective at 3 mM) and carbapenems in recombinant and clinical strains of P. aeruginosa expressing MBLs, in particular against VIM producers, which are the most prevalent carbapenemases in P. aeruginosa. This effect was best evidenced with meropenem and in strains without OprD modification. DMSA shows promising efficacy, particularly in combination therapy with meropenem, for treating infections caused by MBL-producing P. aeruginosa.

Use of adjuvants to improve antibiotic efficacy and reduce the burden of antimicrobial resistance

INTRODUCTION

The increase in antibiotic resistance, together with the absence of novel antibiotics, makes mandatory the introduction of novel strategies to optimize the use of existing antibiotics. Among these strategies, the use of molecules that increase their activity looks promising.

AREAS COVERED

Different categories of adjuvants have been reviewed. Anti-resistance adjuvants increase the activity of antibiotics by inhibiting antibiotic resistance determinants. Anti-virulence approaches focus on the infection process itself; reducing virulence in combination with an antibiotic can improve therapeutic efficacy. Combination of phages with antibiotics can also be useful, since they present different mechanisms of action and targets. Finally, combining antibiotics with adjuvants in the same molecule may serve to improve antibiotics' efficacy and to overcome potential problems of differential pharmacokinetics/pharmacodynamics.

EXPERT OPINION

The successful combination of inhibitors of β-lactamases with β-lactams has shown that adjuvants can improve the efficacy of current antibiotics. In this sense, novel anti-resistance adjuvants able to inhibit efflux pumps are still needed, as well as anti-virulence compounds that improve the efficacy of antibiotics by interfering with the infection process. Although adjuvants may present different pharmacodynamics/pharmacokinetics than antibiotics, conjugates containing both compounds can solve this problem. Finally, already approved drugs can be a promising source of antibiotic adjuvants.

Discovery of sulfone containing metallo-β-lactamase inhibitors with reduced bacterial cell efflux and histamine release issues

The design, syntheses and antibacterial evaluation of sulfone analogues of previously disclosed metallo-β-lactamase inhibitors (MBLis) are described. The novel derivatives were overall more effective in gram-negative bacterial cell-based assays when combined with imipenem and relebactam. The major contributors to the improved anti-bacterial activity are enhanced enzyme-inhibitor interactions and reduced bacterial cell efflux monitored via an efflux assay involving isogenic Pseudomonas aeruginosa efflux + and efflux - tool strains.

Elucidation of critical chemical moieties of metallo-β-lactamase inhibitors and prioritisation of target metallo-β-lactamases

The urgent demand for effective countermeasures against metallo-β-lactamases (MBLs) necessitates development of novel metallo-β-lactamase inhibitors (MBLIs). This study is dedicated to identifying critical chemical moieties within previously developed MBLIs, and critical MBLs should serve as the target in MBLI evaluations. Using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA), a systematic literature analysis was conducted, and the NCBI RefSeq genome database was exploited to access the abundance profile and taxonomic distribution of MBLs and their variant types. Through the implementation of two distinct systematic approaches, we elucidated critical chemical moieties of MBLIs, providing pivotal information for rational drug design. We also prioritised MBLs and their variant types, highlighting the imperative need for comprehensive testing to ensure the potency and efficacy of the newly developed MBLIs. This approach contributes valuable information to advance the field of antimicrobial drug discovery.

Synergistic antimicrobial action of chlorogenic acid and ultraviolet-A (365 nm) irradiation; mechanisms and effects on DNA integrity

Chlorogenic acid (CGA) is abundant in various plants and notably in coffee beans. This study investigated the bactericidal activity of CGA combined with ultraviolet-A light (UVA, 365 nm) (CGA + UVA) against Escherichia coli DH5α, with the aim of developing novel strategies for food preservation and healthcare. CGA + UVA treatment was superiorin reducing bacterial survival than either treatment alone. At 20 J/cm2 and pH 7, CGA (0.3%) + UVA treatment resulted in only about a 3-log reduction in bacterial survival, whereas at 15 J/cm2 and pH 3, no surviving bacteria could be detected, demostrating that the treatment was more effective at acidic pH. CGA + UVA treatment was also bactericidal in green plum juice, confirming that its low pH-dependent property could be effective in acidic food products. To elucidate the bactericidal mechanism of CGA + UVA treatment, its effects on reactive oxygen species (ROS) generation, membrane integrity, and enzyme activity were measured. ROS generated via the type-1 reaction, such as hydrogen peroxide (H2O2) and hydroxyl radicals (·OH), were mainly detected. CGA + UVA disrupted the bacterial cell membrane, causing the leakage of cellular components, particularly proteins. CGA + UVA treatment also led to deoxyribonucleic acid (DNA) degradation and reduced succinate-coenzyme Q reductase activity by approximately 72 %. Furthermore, CGA + UVA treatment decreased β-lactamase activity and plasmid transforming efficacy with maximal reductions of 68 % and 98 %, respectively, highlighting its potential for increasing antibiotic susceptibility and preventing the spread of antimicrobial resistance. The results demonstrate that CGA + UVA treatment could be used to effectively combat antibiotic-resistant bacteria and prevent the spoilage of preserved foods or food poisoning.

Seven-membered N-heterocycles as approved drugs and promising leads in medicinal chemistry as well as the metal-free domino access to their scaffolds

Azepanes or azepines are structural motifs of many drugs, drug candidates and evaluated lead compounds. Even though compounds having N-heterocyclic 7-membered rings are often found in nature (e.g. alkaloids), the natural compounds of this group are rather rare as approved therapeutics. Thus, recently studied and approved azepane or azepine-congeners predominantly consist of semi-synthetically or synthetically-obtained scaffolds. In this review a comparison of approved drugs and recently investigated leads was proposed taking into regard their structural aspects (stereochemistry), biological activities, pharmacokinetic properties and confirmed molecular targets. The 7-membered N-heterocycles reveal a wide range of biological activities, not only against CNS diseases, but also as e.g. antibacterial, anticancer, antiviral, antiparasitic and against allergy agents. As most of the approved or investigated potential drugs or lead structures, belonging to 7-membered N-heterocycles, are synthetic scaffolds, this report also reveals different and efficient metal-free cascade approaches useful to synthesize both simple azepane or azepine-containing congeners and those of oligocyclic structures. Stereochemistry of azepane/azepine fused systems, in view of biological data and binding with the targets, is discussed. Apart from the approved drugs, we compare advances in SAR studies of 7-membered N-heterocycles (mainly from 2018 to 2023), whereas the related synthetic part concerning various domino strategies is focused on the last ten years.

A promising metabolite, 9-aminominocycline, restores the sensitivity of tigecycline against tet(X4)-positive Escherichia coli

The emergence and widespread of tigecycline resistance undoubtedly poses a serious threat to public health globally. The exploration of combination therapies has become preferred antibacterial strategies to alleviate this global burden. In this study, tigecycline-resistant tet(X4)-positive Escherichia coli were selected for adjuvant screening. Interestingly, 9-aminominocycline (9-AMC), one of the tigecycline metabolites, exhibits synergistic antibacterial activity with tigecycline using checkerboard assay. The efficacy in vitro and in vivo was evaluated, and the synergistic mechanism was further explored. The results suggested that 9-AMC combined with tigecycline could inhibit the growth of antibiotic resistant bacteria, efficiently retard the evolution of tet(X4) gene and narrow the drug mutant selection window. In addition, the combination of tigecycline and 9-AMC could destroy the normal membrane structure of bacteria, inhibit the formation of biofilm, remarkably reduce the level of intracellular ATP level, and accelerate the oxidative damage of bacteria. Furthermore, 9-AMC is more stable in the bind of Tet(X4) inactivating enzyme. The transcriptomics analysis revealed that the genes related to the 9-AMC and tigecycline were mainly enriched in ABC transporters. Collectively, the results reveal the potentiation effects on tigecycline and the probability of 9-AMC as a novel tigecycline adjuvant against tet(X4)-positive Escherichia coli, which provides new insights for adjuvant screening.

Structure Guided Discovery of Novel Pan Metallo-β-Lactamase Inhibitors with Improved Gram-Negative Bacterial Cell Penetration

The use of β-lactam (BL) and β-lactamase inhibitor combination to overcome BL antibiotic resistance has been validated through clinically approved drug products. However, unmet medical needs still exist for the treatment of infections caused by Gram-negative (GN) bacteria expressing metallo-β-lactamases. Previously, we reported our effort to discover pan inhibitors of three main families in this class: IMP, VIM, and NDM. Herein, we describe our work to improve the GN coverage spectrum in combination with imipenem and relebactam. This was achieved through structure- and property-based optimization to tackle the GN cell penetration and efflux challenges. A significant discovery was made that inhibition of both VIM alleles, VIM-1 and VIM-2, is essential for broad GN coverage, especially against VIM-producing P. aeruginosa. In addition, pharmacokinetics and nonclinical safety profiles were investigated for select compounds. Key findings from this drug discovery campaign laid the foundation for further lead optimization toward identification of preclinical candidates.

Experimental and Theoretical Studies on the Reactions of Aliphatic Imines with Isocyanates

In the context of a project aiming at the replacement of the 3-substituted β-lactam ring in classical β-lactam antibiotics by an N(3)-acyl-1,3-diazetidinone moiety, we have investigated the reaction of isocyanates with imines derived from allyl glycinate and differently substituted propionaldehydes. Imines of aromatic aldehydes with anilines have been reported to react with acyl isocyanates to give 1,3-diazetidinones or 2,3-dihydro-4H-1,3,5-oxadiazin-4-ones, via [2+2] or [4+2] cycloaddition, respectively. However, neither of these products was formed with imines derived from allyl glycinate and 2-(mono)methyl propionaldehydes. α,α-Dimethylation of the imine enabled the [4+2] cycloaddition pathway, but the desired 1,3-diazetidinone products were not observed. Surprisingly, the imines obtained from thioesters of 2,2-dimethyl 3-oxo propionic acid reacted with aryl isocyanates or with benzyl isocyanate to give 5,5-dimethyl-2,4-dioxo-6-(aryl-/alkylthio)tetrahydropyrimidines, via thiol displacement and re-addition to a putative six-membered iminium intermediate. These experimental results obtained for the reactions could be rationalized by DFT calculations. In addition, we have shown that N(3)-acyl-1,3-diazetidinone and 2,3-dihydro-4H-1,3,5-oxadiazin-4-one products can be distinguished based on experimental IR data in combination with theoretical reference spectra employing the IR spectra alignment (IRSA) algorithm. This discrimination was not possible by means of 1 H, 13 C, or 15 N NMR spectroscopy.

Discovery of novel deoxyvasicinone derivatives with benzenesulfonamide substituents as multifunctional agents against Alzheimer's disease

A series of deoxyvasicinone derivatives with benzenesulfonamide substituents were designed and synthesized to find a multifunctional anti-Alzheimer's disease (AD) drug. The results of the biological activity evaluation indicated that most compounds demonstrated selective inhibition of acetylcholinesterase (AChE). Among them, g17 exhibited the most potent inhibitory effect on AChE (IC50 = 0.24 ± 0.04 μM). Additionally, g17 exhibited promising properties as a metal chelator and inhibitor of amyloid β peptides self-aggregation (68.34 % ± 1.16 %). Research on oxidative stress has shown that g17 displays neuroprotective effects and effectively suppresses the intracellular accumulation of reactive oxygen species. Besides, g17 demonstrated remarkable anti-neuroinflammatory effects by significantly reducing the production of pro-inflammatory cytokines (such as NO, IL-1β, and TNF-α) and inhibiting the expression of inflammatory mediators iNOS and COX-2. In vivo studies showed that g17 significantly improved AD model mice's cognitive and memory abilities. Histological examination of mouse hippocampal tissue sections using hematoxylin and eosin staining revealed that g17 effectively mitigates neuronal damage. Considering the multifunctional properties of g17, it is regarded as a promising lead compound for treating AD.

Integrating Siderophore Substructures in Thiol-Based Metallo-β-Lactamase Inhibitors

Metallo beta lactamases (MBLs) are among the most problematic resistance mechanisms of multidrug-resistant Gram-negative pathogens due to their broad substrate spectrum and lack of approved inhibitors. In this study, we propose the integration of catechol substructures into the design of thiol-based MBL inhibitors, aiming at mimicking bacterial siderophores for the active uptake by the iron acquisition system of bacteria. We synthesised two catechol-containing MBL inhibitors, as well as their dimethoxy counterparts, and tested them for in vitro inhibitory activity against NDM-1, VIM-1, and IMP-7. We demonstrated that the most potent catechol-containing MBL inhibitor is able to bind Fe³⁺ ions. Finally, we could show that this compound restores the antibiotic activity of imipenem in NDM-1-expressing K. pneumoniae, while leaving HUVEC cells completely unaffected. Thus, siderophore-containing MBL inhibitors might be a valuable strategy to overcome bacterial MBL-mediated resistance to beta lactam antibiotics.