Repurposing Candesartan Cilexetil as Antibacterial Agent for MRSA Infection

Antibacterial and anti-biofilm activities of Derazantinib (ARQ-087) against Staphylococcus aureus

The global rise of multidrug-resistant pathogens, particularly methicillin-resistant Staphylococcus aureus (MRSA), represents a critical public health challenge. This study evaluates the antibacterial and anti-biofilm activities of Derazantinib (ARQ-087) against S. aureus. ARQ-087 exhibited minimum inhibitory concentration (MIC) values ranging from 4 to 16 µM against S. aureus reference laboratory strains and diverse clinical MRSA isolates, demonstrating strong antibacterial activity with minimal resistance development. Time-kill assays demonstrated a concentration- and time-dependent reduction in bacterial viability. Crystal violet staining assays revealed that ARQ-087 significantly inhibited MRSA biofilm formation in a dose-dependent manner. Additionally, ARQ-087 exhibited strong anti-biofilm activity against pre-formed biofilms, as shown by colony counts and confocal laser scanning microscopy, which indicated extensive biofilm disruption and bacterial cell death. Mechanistic studies revealed that ARQ-087 disrupts bacterial membrane integrity, as evidenced by SYTOX Green and DISC3(5) fluorescence assays, while inducing intracellular ATP depletion and reactive oxygen species generation, contributing to bacterial death. ARQ-087 also displayed negligible hemolytic activity and no acute toxicity observed in a Galleria mellonella infection model. In this model, ARQ-087 prolonged the survival of larvae infected with S. aureus. These findings highlight ARQ-087 as a promising therapeutic candidate for treating MRSA infections and biofilm-associated diseases. Further preclinical studies are needed to confirm its potential for clinical application.

Repurposing pinaverium bromide against Staphylococcus and its biofilms with new mechanisms

Antibiotic resistance by methicillin-resistant Staphylococcus aureus (MRSA) is an urgent threat to human health. The biofilm and persister cells formation ability of MRSA and Staphylococcus epidermidis often companied with extremely high antimicrobial resistance. Pinaverium bromide (PVB) is an antispasmodic compound mainly used for irritable bowel syndrome. Here we demonstrate that PVB could rapidly kill MRSA and S. epidermidis planktonic cells and persister cells avoiding resistance occurrence. Moreover, by crystal violet staining, viable cells counting and SYTO9/PI staining, PVB exhibited strong biofilm inhibition and eradication activities on the 96-well plates, glass surface or titanium discs. And the synergistic antimicrobial effects were observed between PVB and conventional antibiotics (ampicillin, oxacillin, and cefazolin). Mechanism study demonstrated the antimicrobial and antibiofilm effects by PVB were mainly mediated by proton motive force disrupting as well as reactive oxygen species inducing. Although, relatively poor pharmacokinetics were observed by systemic use, PVB could significantly reduce the viable bacterial cell loads and inflammatory infiltration in abscess in vivo caused by the biofilm forming strain ATCC 43,300. In all, our results indicated that PVB could be an alternative antimicrobial reagent for the treatment of MRSA, S. epidermidis and its biofilm related skin and soft tissue infections.

Bactericidal and anti-quorum sensing activity of repurposing drug Visomitin against Staphylococcus aureus

With the growing antibiotic resistance in Staphylococcus aureus, it is imperative to develop innovative therapeutic strategies against new targets to reduce selective survival pressures and incidence of resistance. In S. aureus, interbacterial communication relies on a quorum sensing system that regulates gene expression and physiological activities. Here, we identified that Visomitin, an antioxidant small molecule, exhibited bactericidal efficacy against methicillin-resistant S. aureus and its high tolerance phenotypes like intracellular bacteria and persister cells without inducing resistance. Critically, sub-minimal inhibitory concentrations (sub-MICs) of Visomitin could serve as a potent quorum-quencher reducing virulence production (such as haemolysin and staphyloxanthin), along with inhibiting biofilm formation, self-aggregation, and colony spreading of S. aureus. These effects were probably mediated by interfering with the S. aureus accessory gene regulator quorum sensing system. In summary, our findings suggest that Visomitin shows dual antimicrobial effects, including bactericidal effects at the concentrations above MIC and quorum sensing inhibition effects at sub-MICs, which holds promise for treating MRSA-related refractory infections.

Machine Learning-Assisted High-Throughput Screening for Anti-MRSA Compounds

BACKGROUND

Antimicrobial resistance is a major public health threat, and new agents are needed. Computational approaches have been proposed to reduce the cost and time needed for compound screening.

AIMS

A machine learning (ML) model was developed for the in silico screening of low molecular weight molecules.

METHODS

We used the results of a high-throughput Caenorhabditis elegans methicillin-resistant Staphylococcus aureus (MRSA) liquid infection assay to develop ML models for compound prioritization and quality control.

RESULTS

The compound prioritization model achieved an AUC of 0.795 with a sensitivity of 81% and a specificity of 70%. When applied to a validation set of 22,768 compounds, the model identified 81% of the active compounds identified by high-throughput screening (HTS) among only 30.6% of the total 22,768 compounds, resulting in a 2.67-fold increase in hit rate. When we retrained the model on all the compounds of the HTS dataset, it further identified 45 discordant molecules classified as non-hits by the HTS, with 42/45 (93%) having known antimicrobial activity.

CONCLUSION

Our ML approach can be used to increase HTS efficiency by reducing the number of compounds that need to be physically screened and identifying potential missed hits, making HTS more accessible and reducing barriers to entry.

Effective drug design screening in bacterial glycolytic enzymes via targeting alternative allosteric sites

Three glycolytic enzymes phosphofructokinase (PFK), glyceraldehyde-3-phosphate dehydrogenase (GADPH) and pyruvate kinase (PK) that belong to Staphylococcus aureus were used as targets for screening a dataset composed of 7229 compounds of which 1416 were FDA-approved. Instead of catalytic sites, evolutionarily less conserved allosteric sites were targeted to identify compounds that would selectively bind the bacteria's glycolytic enzymes instead of the human host. Seven different allosteric sites provided by three enzymes were used in independent screening experiments via docking. For each of the seven sites, a total of 723 compounds were selected as the top 10 % which displayed the highest binding affinities. All compounds were then united to yield the top 54 drug candidates shared by all seven sites. Next, 17 out of 54 were selected and subjected to in vitro experiments for testing their inhibition capability for antibacterial growth and enzymatic activity. Accordingly, four compounds displaying antibacterial growth inhibition above 40 % were determined as Candesartan cilexetil, Montelukast (sodium), Dronedarone (hydrochloride) and Thonzonium (bromide). In a second round of experiment, Candesartan cilexetil and Thonzonium displayed exceptionally high killing efficiencies on two bacterial strains of S.aureus (methicillin-sensitive and methicillin-resistant) with concentrations as low as 4 μg/mL and 0.5 μg/mL. Yet, their enzymatic assays were not in accordance with their killing effectiveness. Different inhibitory effects was observed for each compound in each enzymatic assay. A more effective target strategy would be to screen for drug compounds that woud inhibit a combination of glycolytic enzymes observed in the glycolytic pathway.

Bactericidal and biofilm eradication efficacy of a fluorinated benzimidazole derivative, TFBZ, against methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is a major inducement of nosocomial infections and its biofilm formation render the high tolerance to conventional antibiotics, which highlights the requirement to develop new antimicrobial agents urgently. In this study, we identified a fluorinated benzimidazole derivative, TFBZ, with potent antibacterial efficacy toward planktonic MRSA (MIC = 4 μg/mL, MBC = 8 μg/mL) and its persistent biofilms (≥99%, MBEC = 8 μg/mL). TFBZ manifested significant irreversible time-dependent killing against MRSA as characterized by diminished cell viability, bacterial morphological change and protein leakage. Furthermore, the results from CBD devices, crystal violet assay in conjunction with live/dead staining and scanning electron microscopy confirmed that TFBZ was capable of eradicating preformed MRSA biofilms with high efficiency. Simultaneously, TFBZ reduced the bacterial invasiveness and exerted negligible hemolysis and cytotoxicity toward mammalian cells, which ensuring the robust therapeutic effect on mouse skin abscess model. The transcriptome profiling and quantitative RT-PCR revealed that a set of encoding genes associated with cell adhesion, biofilm formation, translation process, cell wall biosynthesis was consistently downregulated in MRSA biofilms upon exposure to TFBZ. In conclusion, TFBZ holds promise as a valuable candidate for therapeutic applications against MRSA chronic infections.

Repurposing of the antimalarial agent tafenoquine to combat MRSA

IMPORTANCE

This study represents the first investigation into the antimicrobial effect of TAF against S. aureus and its potential mechanisms. Our data highlighted the effects of TAF against MRSA planktonic cells, biofilms, and persister cells, which is conducive to broadening the application of TAF. Through mechanistic studies, we revealed that TAF targets bacterial cell membranes. In addition, the in vivo experiments in mice demonstrated the safety and antimicrobial efficacy of TAF, suggesting that TAF could be a potential antibacterial drug candidate for the treatment of infections caused by multiple drug-resistant S. aureus.

Candesartan exhibits low intrinsic permeation capacity and affects buccal tissue viability and integrity: An ex vivo study in porcine buccal mucosa

Candesartan is a nonpeptide angiotensin II receptor blocker that selectively binds to angiotensin II receptor subtype 1. It is administered orally in its ester form (candesartan cilexetil). However, its poor aqueous solubility results in its low bioavailability; therefore, other routes of administration must be explored. The buccal mucosa has been extensively studied as an alternative route for drug delivery as it improves the bioavailability of drugs administered via the peroral route. Porcine buccal mucosa has been widely used as an ex vivo model to study the permeability of various diffusants; however, studies on candesartan are limited. This study aimed to evaluate the ex vivo permeation profile of candesartan and its effects on the viability and integrity of porcine buccal mucosa. Initially, we evaluated the viability, integrity, and barrier function of the buccal tissue before performing permeability tests using freshly excised tissues or tissues after 12 h of resection. Here, three indicators were used: caffeine, β-estradiol, and FD-20 penetration; mucosal metabolic activity, as determined using MTT reduction assay; and haematoxylin and eosin staining. Our results indicated that the porcine buccal mucosa preserved its viability, integrity, and barrier function before the permeation assay, allowing the passage of molecules with a molecular mass of less than 20 kDa, such as caffeine, but not β-estradiol and FD-20. Furthermore, we analyzed the intrinsic capacity of candesartan to diffuse through the fresh porcine buccal mucosa under two pH conditions. The concentration of candesartan in the receptor chamber of Franz diffusion cell was quantified using ultra-high liquid chromatography. In the permeation assay, candesartan exhibited a low intrinsic permeation capacity that impacted the buccal tissue viability and integrity, suggesting that using the buccal mucosa as an alternative route of administration requires developing a pharmaceutical formulation that reduces the adverse effects on mucosa and increasing the buccal permeability of candesartan.