Antibacterial activity evaluation and mode of action study of novel thiazole-quinolinium derivatives

In silico method and bioactivity evaluation to discover novel antimicrobial agents targeting FtsZ protein: Machine learning, virtual screening and antibacterial mechanism study

This research paper utilizes a fused-in-silico approach alongside bioactivity evaluation to identify active FtsZ inhibitors for drug discovery. Initially, ROC-guided machine learning was employed to obtain almost 13182 compounds from three libraries. After conducting virtual screening to assess the affinity of 2621 acquired compounds, cluster analysis and bonding model analysis led to the discovery of five hit compounds. Additionally, antibacterial activity assays and time-killing kinetics revealed that T3995 could eliminate Staphylococcus aureus ATCC6538 and Bacillus subtilis ATCC9732, with MIC values of 32 and 2 μg/mL. Further morphology and FtsZ polymerization assays indicated that T3995 could be an antimicrobial inhibitor by targeting FtsZ protein. Moreover, hemolytic toxicity evaluation demonstrated that T3995 is safe at or below 16 ug/mL concentration. Additionally, bonding model analysis explained how the compound T3995 can display antimicrobial activity by targeting the FtsZ protein. In conclusion, this study presents a promising FtsZ inhibitor that was discovered through a fused computer method and bioactivity evaluation.

Current scenario of indole hybrids with antibacterial potential against Acinetobacter baumannii pathogens: A mini-review

Acinetobacter baumannii with the capability to "escape" almost all currently available antibacterials is eroding the safety of basic medical interventions and is an increasing cause of mortality globally, prompting a substantial requirement for new classes of antibacterial agents. Indoles participate in the regulation of persistent bacterial formation, biofilm formation, plasmid stability, and drug resistance. In particular, indole hybrids demonstrated promising antibacterial activity against both drug-sensitive and drug-resistant A. baumannii pathogens, representing a fertile source for the discovery of novel therapeutic agents for clinical deployment in controlling A. baumannii infections. This mini-review outlines the current innovations of indole hybrids with antibacterial activity against A. baumannii pathogens, covering articles published from 2020 to the present, to open new avenues for exploring novel anti-A. baumannii candidates.

The therapeutic potential of indole hybrids, dimers, and trimers against drug-resistant ESKAPE pathogens

Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter (ESKAPE) species as causative agents are characterized by increased levels of resistance toward multiple classes of first-line as well as last-resort antibiotics and represent serious global health concerns, creating a critical need for the development of novel antibacterials with therapeutic potential against drug-resistant ESKAPE species. Indole derivatives with structural and mechanistic diversity demonstrated broad-spectrum antibacterial activity against various clinically important pathogens including drug-resistant ESKAPE. Moreover, several indole-based agents that are exemplified by creatmycin have already been used in clinics or under clinical trials for the treatment of bacterial infections, demonstrating that indole derivatives hold great promise for the development of novel antibacterials. This review is an endeavor to highlight the current scenario of indole hybrids, dimers, and trimers with therapeutic potential against drug-resistant ESKAPE pathogens, covering articles published from 2020 to the present, to open new avenues for the exploration of novel antidrug-resistant ESKAPE candidates.

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.

Ionic Liquids in Pharmaceutical and Biomedical Applications: A Review

The unique properties of ionic liquids (ILs), such as structural tunability, good solubility, chemical/thermal stability, favorable biocompatibility, and simplicity of preparation, have led to a wide range of applications in the pharmaceutical and biomedical fields. ILs can not only speed up the chemical reaction process, improve the yield, and reduce environmental pollution but also improve many problems in the field of medicine, such as the poor drug solubility, product crystal instability, poor biological activity, and low drug delivery efficiency. This paper presents a systematic and concise analysis of the recent advancements and further applications of ILs in the pharmaceutical field from the aspects of drug synthesis, drug analysis, drug solubilization, and drug crystal engineering. Additionally, it explores the biomedical field, covering aspects such as drug carriers, stabilization of proteins, antimicrobials, and bioactive ionic liquids.

Thiazole-based analogues as potential antibacterial agents against methicillin-resistant Staphylococcus aureus (MRSA) and their SAR elucidation

In recent years, the overuse of antibiotics has resulted in the emergence of antibiotic resistance, which is a serious global health problem. Methicillin-resistant Staphylococcus aureus (MRSA) is a common and virulent bacterium in clinical practice. Numerous researchers have focused on developing new candidate drugs that are effective, less toxic, and can overcome MRSA resistance. Thiazole derivatives have been found to exhibit antibacterial activity against drug-sensitive and drug-resistant pathogens. By hybridizing thiazole with other antibacterial pharmacophores, it is possible to obtain more effective antibacterial candidate drugs. Thiazole derivatives have shown potential in developing new drugs that can overcome drug resistance, reduce toxicity, and improve pharmacokinetic characteristics. This article reviews the recent progress of thiazole compounds as potential antibacterial compounds and examines the structure-activity relationship (SAR) in various directions. It covers articles published from 2018 to 2023, providing a comprehensive platform to plan and develop new thiazole-based small MRSA growth inhibitors with minimal side effects.

Bithionol Restores Sensitivity of Multidrug-Resistant Gram-Negative Bacteria to Colistin with Antimicrobial and Anti-biofilm Effects

Being among the few last-resort antibiotics, colistin (COL) has been used to treat severe infectious diseases, such as those caused by multidrug-resistant Gram-negative bacteria (MDR GNB). However, the appearance of colistin-resistant (COL-R) GNB has been frequently reported. Therefore, novel antimicrobial strategies need to be urgently sought to address this resistance challenge. In the present study, antimicrobial drug screening conducted revealed that bithionol (BT), approved by the Food and Drug Administration and used as an anthelminthic drug for paragonimiasis, exhibited a synergistic antibacterial effect with COL. Clinically isolated COL-R GNB were used as candidates to evaluate the synergistic antibacterial activity. The results revealed that BT could significantly reverse the sensitivity of COL-R GNB to COL. Furthermore, the combined application of BT and COL can reduce bacterial biofilm formation and have a scavenging effect on the mature biofilm in vitro. The damage caused to the bacterial cell membrane integrity by the BT/COL combination was observed under a fluorescence microscope. The fluorescence intensity of reactive oxygen species also increased in the experimental group. The BT/COL combination also exhibited a synergistic antibacterial effect in vivo. Importantly, BT was confirmed to be safe at the highest concentrations that exerted synergistic effects on all tested strains. In conclusion, our findings demonstrated that BT exerted synergistic antimicrobial and anti-biofilm effects when combined with COL against MDR organisms, especially COL-R GNB, in vitro and in vivo. The findings thus provide a reference for the clinical response to the serious challenge of MDR GNB and the exploitation of the potential antibacterial activities of existing clinical non-antibacterial drugs.

Models versus pathogens: how conserved is the FtsZ in bacteria?

Combating anti-microbial resistance by developing alternative strategies is the need of the hour. Cell division, particularly FtsZ, is being extensively studied for its potential as an alternative target for anti-bacterial therapy. Bacillus subtilis and Escherichia coli are the two well-studied models for research on FtsZ, the leader protein of the cell division machinery. As representatives of gram-positive and gram-negative bacteria, respectively, these organisms have provided an extensive outlook into the process of cell division in rod-shaped bacteria. However, research on other shapes of bacteria, like cocci and ovococci, lags behind that of model rods. Even though most regions of FtsZ show sequence and structural conservation throughout bacteria, the differences in FtsZ functioning and interacting partners establish several different modes of division in different bacteria. In this review, we compare the features of FtsZ and cell division in the model rods B. subtilis and E. coli and the four pathogens: Staphylococcus aureus, Streptococcus pneumoniae, Mycobacterium tuberculosis, and Pseudomonas aeruginosa. Reviewing several recent articles on these pathogenic bacteria, we have highlighted the functioning of FtsZ, the unique roles of FtsZ-associated proteins, and the cell division processes in them. Further, we provide a detailed look at the anti-FtsZ compounds discovered and their target bacteria, emphasizing the need for elucidation of the anti-FtsZ mechanism of action in different bacteria. Current challenges and opportunities in the ongoing journey of identifying potent anti-FtsZ drugs have also been described.

Thiazole: A Versatile Standalone Moiety Contributing to the Development of Various Drugs and Biologically Active Agents

For many decades, the thiazole moiety has been an important heterocycle in the world of chemistry. The thiazole ring consists of sulfur and nitrogen in such a fashion that the pi (π) electrons are free to move from one bond to other bonds rendering aromatic ring properties. On account of its aromaticity, the ring has many reactive positions where donor–acceptor, nucleophilic, oxidation reactions, etc., may take place. Molecules containing a thiazole ring, when entering physiological systems, behave unpredictably and reset the system differently. These molecules may activate/stop the biochemical pathways and enzymes or stimulate/block the receptors in the biological systems. Therefore, medicinal chemists have been focusing their efforts on thiazole-bearing compounds in order to develop novel therapeutic agents for a variety of pathological conditions. This review attempts to inform the readers on three major classes of thiazole-bearing molecules: Thiazoles as treatment drugs, thiazoles in clinical trials, and thiazoles in preclinical and developmental stages. A compilation of preclinical and developmental thiazole-bearing molecules is presented, focusing on their brief synthetic description and preclinical studies relating to structure-based activity analysis. The authors expect that the current review may succeed in drawing the attention of medicinal chemists to finding new leads, which may later be translated into new drugs.

Design and synthesis of quinolinium-based derivatives targeting FtsZ for antibacterial evaluation and mechanistic study

The discovery of small molecular inhibitors targeting essential and conserved bacterial drug targets such as FtsZ protein is a promising approach to fight against multi-drug resistant bacteria. In the present study, two new series of FtsZ inhibitors based on a 1-methylquinolinium scaffold were synthesized. The inhibitors possess a variety of substituent groups including the cyclic or linear amine skeleton at the 2- and 4-position of the quinolinium ring for structure-activity relationship study. In general, the inhibitors bearing a cyclic amine substituent at the 4-position of the quinolinium ring showed better antibacterial activity (MIC down to 0.25 μg/mL) than that at the 2-position, especially against Gram-positive bacteria. Among the twenty FtsZ inhibitors examined in various assays, A3 was identified to exhibit excellent antibacterial activity against S. aureus (MIC = 0.5-1 μg/mL), S. epidermidis (MIC = 0.25 μg/mL) and E. faecium (MIC = 1-8 μg/mL). More importantly, A3 showed low hemolytic toxicity (IC₅ = 64 μg/mL) and was found not readily to induce drug resistance. A3 at 2-8 μg/mL promoted the polymerization of FtsZ and interrupted the bacterial division. Furthermore, the ligand-FtsZ interaction study conducted with circular dichroism and molecular docking revealed that A3 induced secondary structure changes of FtsZ protein upon binding to the interdomain cleft of the protein. A3 is thus a potent inhibitor of FtsZ and shows potential to be used as a new antibacterial agent against drug-resistant bacteria.

Design, Molecular Docking, Synthesis, Characterization and Biological Activities of Novel Thiazole Derivatives

Aim:

The study aims to design & synthesize novel thiazole derivatives as potent antitubercular agents with minimal side effects.

Background:

The emergence and rapid spread of multi-drug resistant infectious microbial flora embracing a variety of bacterial as well as mycobacterium strains are causing a threat to public health worldwide.

Objective:

Owing to the importance, we designed compounds with thiazole functionality coupled with Schiff base and thiosemicarbazide, predicted the molecular properties and antitubercular potency of designed compounds by the in-silico method, and synthesized fifteen novel thiazole analogs, characterized and tested in vivo antitubercular, antibacterial and antioxidant potencies.

Methods:

Molinspiration online tool was used to predict the molecular properties and molecular docking was used to predict the antitubercular potency. FT-IR, 1H-NMR, 13C-NMR, Mass spectroscopy and bases of elemental analysis are employed to confirm the structure of compounds. 10-Fold serial dilution method, agar streak dilution test and DPPH radical scavenging methods are used to estimate antitubercular, antibacterial and antioxidant potency of title analogs, respectively.

Results:

Multi-step synthesis was used to synthesize a variety of novel thiazole derivatives coupled with Schiff base and thiosemicarbazide. Synthesized title compounds displayed a varying degree of antitubercular, antibacterial and antioxidant activities (mild to good). The title compounds possessing deactivating group exhibited superior activities than activating group, while unsubstituted analogs displayed intermediate activities. In addition, para-substituted analogs showed slightly higher activity than the corresponding meta substituted analogs.

Conclusion:

Among fifteen tested title compounds, the potent compound of this series was found to be 1-(4-nitrobenzylidene)-4-(4-(4-methoxyphenyl)thiazol-2-yl)thiosemicarbazide (BTS14), which might be extended as a novel class of antitubercular and antibacterial agents.

Targeting the Achilles Heel of FtsZ: The Interdomain Cleft

Widespread antimicrobial resistance among bacterial pathogens is a serious threat to public health. Thus, identification of new targets and development of new antibacterial agents are urgently needed. Although cell division is a major driver of bacterial colonization and pathogenesis, its targeting with antibacterial compounds is still in its infancy. FtsZ, a bacterial cytoskeletal homolog of eukaryotic tubulin, plays a highly conserved and foundational role in cell division and has been the primary focus of research on small molecule cell division inhibitors. FtsZ contains two drug-binding pockets: the GTP binding site situated at the interface between polymeric subunits, and the inter-domain cleft (IDC), located between the N-terminal and C-terminal segments of the core globular domain of FtsZ. The majority of anti-FtsZ molecules bind to the IDC. Compounds that bind instead to the GTP binding site are much less useful as potential antimicrobial therapeutics because they are often cytotoxic to mammalian cells, due to the high sequence similarity between the GTP binding sites of FtsZ and tubulin. Fortunately, the IDC has much less sequence and structural similarity with tubulin, making it a better potential target for drugs that are less toxic to humans. Over the last decade, a large number of natural and synthetic IDC inhibitors have been identified. Here we outline the molecular structure of IDC in detail and discuss how it has become a crucial target for broad spectrum and species-specific antibacterial agents. We also outline the drugs that bind to the IDC and their modes of action.

Molecular Recognition and Imaging of Human Telomeric G-Quadruplex DNA in Live Cells: A Systematic Advancement of Thiazole Orange Scaffold To Enhance Binding Specificity and Inhibition of Gene Expression

A series of fluorescent ligands, which were systematically constructed from thiazole orange scaffold, was investigated for their interactions with G-quadruplex structures and antitumor activity. Among the ligands, compound 3 was identified to exhibit excellent specificity toward telomere G4-DNA over other nucleic acids. The affinity of 3-Htg24 was almost 5 times higher than that of double-stranded DNA and promoter G4-DNA. Interaction studies showed that 3 may bind to both G-tetrad and the lateral loop near the 5'-end. The intracellular colocalization with BG4 and competition studies with BRACO19 reveal that 3 may interact with G4-structures. Moreover, 3 reduces the telomere length and downregulates hTERC and hTERT mRNA expression in HeLa cells. The cytotoxicity of 3 against cancer cells (IC₅₀ = 12.7-16.2 μM) was found to be generally higher than noncancer cells (IC₅₀ = 52.3 μM). The findings may support that the ligand is telomere G4-DNA specific and may provide meaningful insights for anticancer drug design.

The study of 9,10-dihydroacridine derivatives as a new and effective molecular scaffold for antibacterial agent development

The emergence of worldwide spreading drug-resistant bacteria has been a serious threat to public health during the past decades. The development of new and effective antibacterial agents to address this critical issue is an urgent action. In the present study, we investigated the antibacterial activity of two 9,10-dihydroacridine derivatives and their mechanism. Both compounds were found possessing strong antibacterial activity against some selected Gram-positive bacteria including MRSA, VISA and VRE. The biological study suggests that the compounds promoted FtsZ polymerization and also disrupted Z-ring formation at the dividing site and consequently, the bacterial cell division is interrupted and causing cell death.