Discovery Of Novel Antibacterials Research Articles

The Antibacterial Activity of Quinazoline and Quinazolinone Hybrids

Bacterial infections cause substantial morbidity and mortality across the world and pose serious threats to humankind. Drug resistance, especially multidrug resistance resulting from different defensive mechanisms in bacteria, is the leading cause of failure the chemotherapy, making it an urgent need to develop more effective antibacterials. Quinazoline and quinazolinone frameworks have received considerable attention due to their diversified therapeutic potential. In particular, quinazoline/quinazolinone hybrids could exert antibacterial activity through various mechanisms and are useful scaffolds for the discovery of novel antibacterials. This review principally emphases on the antibacterial potential, structure-activity relationships (SARs), and mechanism of action of quinazoline and quinazolinone hybrids, covering articles published between 2017 and 2021.

Moxifloxacin and Sulfamethoxazole-Based Nanocarriers Exhibit Potent Antibacterial Activities.

Antibiotic resistance is a major concern given the rapid emergence of multiple-drug-resistant bacteria compared to the discovery of novel antibacterials. An alternative strategy is enhancing the existing available drugs. Nanomedicine has emerged as an exciting area of research, showing promise in the enhanced development of existing antimicrobials. Herein, we synthesized nanocarriers and loaded these with available clinically approved drugs, namely Moxifloxacin and Sulfamethoxazole. Bactericidal activity against Gram-negative (Serratia marcescens, Pseudomonas aeruginosa, Klebsiella pneumoniae, and Salmonella enterica) and Gram-positive (methicillin-resistant Staphylococcus aureus, Streptococcus pneumoniae, and Bacillus cereus) bacteria was investigated. To characterize the nanocarriers and their drug-loaded forms, Fourier-transform infrared spectroscopy, dynamic light scattering, and atomic force microscopy were utilized. Antibacterial assays and hemolysis assays were carried out. Moreover, lactate dehydrogenase assays were performed to determine cytotoxicity against human cells. The results depicted the successful formation of drug–nanocarrier complexes. The potent antibacterial activities of the drug-loaded nanocarriers were observed and were significantly enhanced in comparison to the drugs alone. Hemolysis and cytotoxicity assays revealed minimal or negligible cytotoxic effects against human red blood cells and human cells. Overall, metronidazole-based nanocarriers loaded with Moxifloxacin and Sulfamethoxazole showed enhanced bactericidal effects against multiple-drug-resistant bacteria compared with drugs alone, without affecting human cells. Our findings show that drug-loaded nanocarriers hold promise as potent chemotherapeutic drugs against multiple-drug-resistant bacteria.

The search for novel treatment strategies for Streptococcus pneumoniae infections.

ABSTRACTThis review provides an overview of the most important novel treatment strategies against Streptococcus pneumoniae infections published over the past 10 years. The pneumococcus causes the majority of community-acquired bacterial pneumonia cases, and it is one of the prime pathogens in bacterial meningitis. Over the last 10 years, extensive research has been conducted to prevent severe pneumococcal infections, with a major focus on (i) boosting the host immune system and (ii) discovering novel antibacterials. Boosting the immune system can be done in two ways, either by actively modulating host immunity, mostly through administration of selective antibodies, or by interfering with pneumococcal virulence factors, thereby supporting the host immune system to effectively overcome an infection. While several of such experimental therapies are promising, few have evolved to clinical trials. The discovery of novel antibacterials is hampered by the high research and development costs versus the relatively low revenues for the pharmaceutical industry. Nevertheless, novel enzymatic assays and target-based drug design, allow the identification of targets and the development of novel molecules to effectively treat this life-threatening pathogen.

Synthesis and Evaluation of Aryl/Heteroaryl Benzohydrazide and Phenylacetamide Derivatives as Broad‐Spectrum Antibacterial Agents

AbstractA series of novel aryl/heteroaryl benzohydrazide (3 a–d) and aryl/heteroaryl phenylacetamide derivatives (5 a–g) were designed, synthesized and characterized by spectral techniques. The synthesized compounds were screened against pathogenic bacteria to assess their in vitro antibacterial properties. From the eleven synthesized compounds, 3 b(0.7 μg/mL) and 3 c(0.6 μg/mL) exhibited potent activity against a panel of organisms especially against S. aureus. Further, time‐kill study confirmed the bactericidal activity of 3 b and 3 c against S. aureus, that may be because of conjoined benzothiazole and benzohydrazide moieties in their structures. Extra‐precision docking and binding free energy calculation were also performed for the title compounds, in which 3 c(‐6.23 kcal/mol) exhibited higher binding affinity against S. aureus ParE (SaParE). Molecular dynamic simulation of 50 ns was used to find out the stability of predicted binding conformation of 3 c/SaParE. Besides, assessment of in silico ADMET properties illustrates that the title compounds were in agreement with Lipinski's rule parameters. The study could offer a unique framework that may lead to the discovery of novel antibacterials.

X-ray Crystallography Deciphers the Activity of Broad-Spectrum Boronic Acid β-Lactamase Inhibitors.

Recent decades have witnessed a dramatic increase of multidrug resistant (MDR) bacteria, compromising the efficacy of available antibiotics, and a continual decline in the discovery of novel antibacterials. We recently reported the first library of benzo[b]thiophen-2-ylboronic acid inhibitors sharing broad spectrum activity against β-lactamases (BLs). The ability of these compounds to inhibit structurally and mechanistically different types of β-lactamases has been here structurally investigated. An extensive X-ray crystallographic analysis of boronic acids (BAs) binding to proteins representative of serine BLs (SBLs) and metallo β-lactamases (MBLs) have been conducted to depict the role played by the boronic group in driving molecular recognition, especially in the interaction with MBLs. Our derivatives are the first case of noncyclic boronic acids active against MBLs and represent a productive route toward potent broad-spectrum inhibitors.

Bacterial histidine kinases as novel antibacterial drug targets.

Bacterial histidine kinases (HKs) are promising targets for novel antibacterials. Bacterial HKs are part of bacterial two-component systems (TCSs), the main signal transduction pathways in bacteria, regulating various processes including virulence, secretion systems and antibiotic resistance. In this review, we discuss the biological importance of TCSs and bacterial HKs for the discovery of novel antibacterials, as well as published TCS and HK inhibitors that can be used as a starting point for structure-based approaches to develop novel antibacterials.

The re-emerging role of microbial natural products in antibiotic discovery.

New classes of antibacterial compounds are urgently needed to respond to the high frequency of occurrence of resistances to all major classes of known antibiotics. Microbial natural products have been for decades one of the most successful sources of drugs to treat infectious diseases but today, the emerging unmet clinical need poses completely new challenges to the discovery of novel candidates with the desired properties to be developed as antibiotics. While natural products discovery programs have been gradually abandoned by the big pharma, smaller biotechnology companies and research organizations are taking over the lead in the discovery of novel antibacterials. Recent years have seen new approaches and technologies being developed and integrated in a multidisciplinary effort to further exploit microbial resources and their biosynthetic potential as an untapped source of novel molecules. New strategies to isolate novel species thought to be uncultivable, and synthetic biology approaches ranging from genome mining of microbial strains for cryptic biosynthetic pathways to their heterologous expression have been emerging in combination with high throughput sequencing platforms, integrated bioinformatic analysis, and on-site analytical detection and dereplication tools for novel compounds. These different innovative approaches are defining a completely new framework that is setting the bases for the future discovery of novel chemical scaffolds that should foster a renewed interest in the identification of novel classes of natural product antibiotics from the microbial world.

Toward the computer-aided discovery of FabH inhibitors. Do predictive QSAR models ensure high quality virtual screening performance?

Antibiotic resistance has increased over the past two decades. New approaches for the discovery of novel antibacterials are required and innovative strategies will be necessary to identify novel and effective candidates. Related to this problem, the exploration of bacterial targets that remain unexploited by the current antibiotics in clinical use is required. One of such targets is the β-ketoacyl-acyl carrier protein synthase III (FabH). Here, we report a ligand-based modeling methodology for the virtual-screening of large collections of chemical compounds in the search of potential FabH inhibitors. QSAR models are developed for a diverse dataset of 296 FabH inhibitors using an in-house modeling framework. All models showed high fitting, robustness, and generalization capabilities. We further investigated the performance of the developed models in a virtual screening scenario. To carry out this investigation, we implemented a desirability-based algorithm for decoys selection that was shown effective in the selection of high quality decoys sets. Once the QSAR models were validated in the context of a virtual screening experiment their limitations arise. For this reason, we explored the potential of ensemble modeling to overcome the limitations associated to the use of single classifiers. Through a detailed evaluation of the virtual screening performance of ensemble models it was evidenced, for the first time to our knowledge, the benefits of this approach in a virtual screening scenario. From all the obtained results, we could arrive to a significant main conclusion: at least for FabH inhibitors, virtual screening performance is not guaranteed by predictive QSAR models.

Exploring the Mode of Action of Bioactive Compounds by Microfluidic Transcriptional Profiling in Mycobacteria

Most candidate anti-bacterials are identified on the basis of their whole cell anti-bacterial activity. A critical bottleneck in the early discovery of novel anti-bacterials is tracking the structure activity relationship (SAR) of the novel compounds synthesized during the hit to lead and lead optimization stage. It is often very difficult for medicinal chemists to visualize if the novel compounds synthesized for understanding SAR of a particular scaffold have similar molecular mechanism of action (MoA) as that of the initial hit. The elucidation of the molecular MoA of bioactive inhibitors is critical. Here, a new strategy and routine assay for MoA de-convolution, using a microfluidic platform for transcriptional profiling of bacterial response to inhibitors with whole cell activity has been presented. First a reference transcriptome compendium of Mycobacterial response to various clinical and investigational drugs was built. Using feature reduction, it was demonstrated that subsets of biomarker genes representative of the whole genome are sufficient for MoA classification and deconvolution in a medium-throughput microfluidic format ultimately leading to a cost effective and rapid tool for routine antibacterial drug-discovery programs.

Current Challenges in the Discovery of Novel Antibacterials from Microbial Natural Products

Microbial natural products have been for decades one of the most successful sources of drugs to treat infectious diseases. The high occurrence of resistances to all major classes of known antibiotics represents today a new challenge and new classes of antibacterial compounds are urgently needed to respond to this unmet clinical need. While natural products discovery programs have been gradually abandoned by big pharma, smaller biotechnology companies and other research organizations are taking the lead in the discovery of novel antibacterials. A survey of recent patents has shown that in spite of the efforts, few novel compounds are being developed that can overcome most of the emerging multi-resistant and pan-resistant pathogens. In order to respond to the current challenges of discovering novel antibiotics, new approaches are required to be developed to further exploit the microbial resources and their biosynthetic potential as an untapped source of novel metabolites. Strategies to mine microbial collections for orphan biosynthetic pathways and novel species thought to be uncultivable, are emerging as a need within antibacterial drug discovery programs, in combination with high throughput screening and chemical dereplication of novel compounds. Different innovative methods that are being developed to respond to the new challenges that are faced today by drug discovery programs will ensure the evolution of these strategies into a completely new framework that will address the renovated interest in the discovery of novel classes of antibiotics.

Structure-based Discovery of Novel Antibacterials

Structure-based Discovery of Novel Antibacterials

Mechanistic studies of the enoyl‐ACP reductase from Yersinia pestis and its inhibition by diaryl ether compounds

Yersinia pestis is a gram‐negative bacterium which causes bubonic and pneumonic plague. Due to the microbe's ability to spread rapidly and cause high mortality, the Centers for Disease Control and Prevention (CDC) have classified this organism as a Category A pathogen as it can be easily utilized as a biological weapon. Currently, streptomycin or gentamicin is used for the treatment of this disease. However, neither of the drugs can be orally administered, thus limiting their potential usefulness. The bacterial fatty acid synthesis (FAS‐II) pathway is essential for bacterial viability and it has also been validated as an attractive target for the discovery of novel antibacterials. We have cloned, over‐expressed and purified FabV, the FAS‐II enoyl‐ACP reductase from Yersinia pestis (ypFabV). In vitro kinetic experiments demonstrated that the recombinant enzyme can efficiently catalyze the reduction of the synthetic substrate using Trans‐2‐dodecenoyl‐CoA (DD‐CoA) as the substrate and NADH as the cofactor. Structural activity relationship (SAR) studies have lead us to the identification of a series of diaryl ether inhibitors with Ki values as low as 0.50 μM and MIC values as low as 0.5 μg/ml.

Discovery of novel antibacterials

Importance of the field: Antibiotics have existed in the environment for millennia, but it has only been in the past 80 years that humans have used them systematically to treat infections. This battle between humans and bacteria has led to an alarming increase in resistance to all clinically useful antibacterial agents. Thus, there is an imperative need for new agents to combat these resistant strains of bacteria.Areas covered in this review: The topics covered include natural product screening, identification and validation of new antibacterial targets and approaches for the discovery and optimization of antibacterial compounds. Last, an assessment of the major challenges facing antibacterial discovery is presented.What the reader will gain: The current strategies and methodologies for discovering and designing new antibacterial agents are evaluated as to their potential for generating the next round of therapeutics. Each topic is presented in a general, basic manner and will hopefully be a useful resource for students and newcomers to the field.Take home message: New antibacterial agents are desperately needed to fight the increasing number of antibiotic resistant pathogenic bacteria. New methodologies as well as traditional approaches should both be used for discovering antibiotics to meet this serious medical need.

Slow-Onset Inhibition of the FabI Enoyl Reductase from Francisella tularensis: Residence Time and in Vivo Activity

Francisella tularensis is a highly virulent and contagious Gram-negative intracellular bacterium that causes the disease tularemia in mammals. The high infectivity and the ability of the bacterium to survive for weeks in a cool, moist environment have raised the possibility that this organism could be exploited deliberately as a potential biological weapon. Fatty acid biosynthesis (FAS-II) is essential for bacterial viability and has been validated as a target for the discovery of novel antibacterials. The FAS-II enoyl reductase ftuFabI has been cloned and expressed, and a series of diphenyl ethers have been identified that are subnanomolar inhibitors of the enzyme with MIC90 values as low as 0.00018 microg mL(-1). The existence of a linear correlation between the Ki and MIC values strongly suggests that the antibacterial activity of the diphenyl ethers results from direct inhibition of ftuFabI within the cell. The compounds are slow-onset inhibitors of ftuFabI, and the residence time of the inhibitors on the enzyme correlates with their in vivo activity in a mouse model of tularemia infection. Significantly, the rate of breakdown of the enzyme-inhibitor complex is a better predictor of in vivo activity than the overall thermodynamic stability of the complex, a concept that has important implications for the discovery of novel chemotherapeutics that normally rely on equilibrium measurements of potency.

Efficient synthesis of a bacterial translocase MraY inhibitor

The bacterial translocase MraY has recently been demonstrated as a prime target for the development of new antibiotics. We describe a straightforward synthesis of a new inhibitor 1 of this enzyme. The two key steps involve a tandem nucleophilic epoxide ring opening of C2-symmetrical bis-epoxide and subsequent O-heterocyclisation, followed by O-glycosylation. The in vitro biological evaluation of 1 at 2 mM showed an 81% of inhibition of the MraY activity. Therefore, congeners of 1 should permit detailed SAR investigations for the discovery of novel antibacterials.

Inhibition of FabI in Fatty Acid Synthesis Pathway ‐ Novel Chemotherapeutics Against Francisella Tularensis

Francisella tularensis is a highly virulent and contagious gram-negative intracellular bacterium that causes the disease tularemia in mammals. The high infectivity and the ability of the bacterium to survive for weeks in a cool, moist environment, have raised the possibility that this organism can be exploited deliberately as a potential biological weapon. Fatty acid synthesis (FAS) is essential for bacterial viability and it has also been validated as an attractive target for the discovery of novel antibacterials. Based on the result that there is a single enoyl reductase homologue in this bacterium, we hypothesize that this enzyme is a sensitive target for the development of novel antibiotics against tularemia. We have successfully cloned, overexpressed and purified the F. tularensis FabI (ftuFabI) and demonstrated that the gene encoded by FTT0782 is an enoyl reductase that catalyzes the NADH dependent reduction of enoyl-CoA substrates. We have solved the X-ray crystal structure of this protein to 2.5 ?resolution, and identified a series of diphenyl ethers which are nanomolar inhibitors of enzyme activity and that inhibit bacterial growth with MIC99 values as low as 0.2 ug/mL.

MraY Inhibitors as Novel Antibacterial Agents

MraY presents all necessary biological requirements to be considered as a target of interest for the discovery of novel antibacterials. Furthermore, several inhibitors aimed at this enzyme have been discovered. Amphomycin, which is currently used as a topical antibacterial in the veterinary industry is one of them, but the major source of future developments resides in the nucleoside based inhibitors group. This group has been subdivided into classes: Tunicamycins, Ribosamino-uridines, Uridylpeptides and Capuramycins. Analysis of pharmacological behaviours observed with several compounds within these classes, shows that broad-spectrum antibacterial activity, including relevant resistant strains and in vivo efficacy without toxicity are achievable. Among them, Caprazamycins, Muraymycins, Riburamycins and Capuramycins present the most promising profiles.