Drug Repurposing Approaches towards Defeating Multidrug-Resistant Gram-Negative Pathogens: Novel Polymyxin/Non-Antibiotic Combinations

Combination of aloe emodin, emodin, and rhein from Aloe with EDTA sensitizes the resistant Acinetobacter baumannii to polymyxins

Background

The continuous emergence and spread of polymyxin-resistant Acinetobacter baumannii pose a significant global health challenge, necessitating the development of novel therapeutic strategies. Aloe, with its long-standing history of medicinal use, has recently been the subject of substantial research for its efficacy against pathogenic infections.

Methods

This study investigates the potential application of anthraquinone components in aloe against polymyxin-resistant A. baumannii by liquid chromatography-mass spectrometry, in vitro activity assessment, and construction of animal infection models.

Results

The findings demonstrate that aloe emodin, emodin, rhein, and their mixtures in equal mass ratios (EAR) exhibit strain-specific antibacterial activities against polymyxin-resistant A. baumannii. Co-administration of EAR with EDTA synergistically and universally enhanced the antibacterial activity and bactericidal efficacy of polymyxins against polymyxin-resistant A. baumannii, while also reducing the frequency of polymyxin-resistant mutations in polymyxinssensitive A. baumannii. Following toxicity assessment on human hepatic and renal cell lines, the combination therapy was applied to skin wounds in mice infected with polymyxin-resistant A. baumannii. Compared to monotherapy, the combination therapy significantly accelerated wound healing and reduced bacterial burden.

Conclusions

The combination of EAR and EDTA with polymyxins offers a novel therapeutic approach for managing skin infections caused by polymyxinresistant A. baumannii.

Drug repurposing against antibiotic resistant bacterial pathogens

The growing prevalence of MDR and XDR bacterial pathogens is posing a critical threat to global health. Traditional antibiotic development paths have encountered significant challenges and are drying up thus necessitating innovative approaches. Drug repurposing, which involves identifying new therapeutic applications for existing drugs, offers a promising alternative to combat resistant pathogens. By leveraging pre-existing safety and efficacy data, drug repurposing accelerates the development of new antimicrobial therapy regimes. This review explores the potential of repurposing existing FDA approved drugs against the ESKAPE and other clinically relevant bacterial pathogens and delves into the identification of suitable drug candidates, their mechanisms of action, and the potential for combination therapies. It also describes clinical trials and patent protection of repurposed drugs, offering perspectives on this evolving realm of therapeutic interventions against drug resistance.

Drug metabolism of ciprofloxacin, ivacaftor, and raloxifene by Pseudomonas aeruginosa cytochrome P450 CYP107S1

Drug metabolism is one of the main processes governing the pharmacokinetics and toxicity of drugs via their chemical biotransformation and elimination. In humans, the liver, enriched with cytochrome P450 (CYP) enzymes, plays a major metabolic and detoxification role. The gut microbiome and its complex community of microorganisms can also contribute to some extent to drug metabolism. However, during an infection when pathogenic microorganisms invade the host, our knowledge of the impact on drug metabolism by this pathobiome remains limited. The intrinsic resistance mechanisms and rapid metabolic adaptation to new environments often allow the human bacterial pathogens to persist, despite the many antibiotic therapies available. Here, we demonstrate that a bacterial CYP enzyme, CYP107S1, from Pseudomonas aeruginosa, a predominant bacterial pathogen in cystic fibrosis patients, can metabolize multiple drugs from different classes. CYP107S1 demonstrated high substrate promiscuity and allosteric properties much like human hepatic CYP3A4. Our findings demonstrated binding and metabolism by the recombinant CYP107S1 of fluoroquinolone antibiotics (ciprofloxacin and fleroxacin), a cystic fibrosis transmembrane conductance regulator potentiator (ivacaftor), and a selective estrogen receptor modulator antimicrobial adjuvant (raloxifene). Our in vitro metabolism data were further corroborated by molecular docking of each drug to the heme active site using a CYP107S1 homology model. Our findings raise the potential for microbial pathogens modulating drug concentrations locally at the site of infection, if not systemically, via CYP-mediated biotransformation reactions. To our knowledge, this is the first report of a CYP enzyme from a known bacterial pathogen that is capable of metabolizing clinically utilized drugs.

Antibacterial activity of closantel against methicillin-resistant Staphylococcus aureus and itsbiofilm

OBJECTIVES

The antimicrobial resistance of Staphylococcus aureus (S. aureus) has become a challenge in the treatment of infectious diseases. It is of great clinical value to discovery effective antimicrobial agents against multi-drug resistant S. aureus and its biofilms. This study aims to explore the antibacterial activity of the antiparasitic drug closantel against methicillin-resistant S. aureus and its biofilms through drug repurposing.

METHODS

The sensitivity of S. aureus to closantel was assessed using microbroth dilution and disk diffusion methods. The bacteriostatic and bactericidal activities of closantel were determined by time-kill curves and colony count. Scanning electron microscopy combined with SYTOX Green and DiSC3(5) fluorescence probes were used to study the bactericidal mechanism of closantel. The influence of resistance was assessed by continuous exposure to sub-inhibitory concentrations of closantel. The anti-biofilm activity was evaluated using 96-well plates and crystal violet staining, and cytotoxicity was measured using the CCK-8 assay.

RESULTS

The minimal inhibitory concentration (MIC) of closantel for both methicillin-sensitive and methicillin-resistant S. aureus ranged from 0.125 to 1.000 μg/mL. Disk diffusion tests showed that 80 μg of closantel created an inhibition zone, which increased in diameter with higher drug amounts. Sub-inhibitory concentrations (0.031 μg/mL) of closantel significantly inhibited S. aureus proliferation, reducing bacterial turbidity from 0.26±0.00 to 0.11±0.01 (t=16.06, P<0.001), with stronger inhibition at higher concentrations. Closantel at 0.25×MIC inhibited S. aureus proliferation for 12 hours, while 1×MIC inhibited it for over 24 hours, with the number of viable bacteria decreasing as the drug concentration increased. Mechanistic studies indicated that closantel effectively disrupted the integrity of S. aureus cell membranes, significantly increasing SYTOX Green and DiSC3(5) fluorescence intensity. Even after 25 days of continuous exposure to sub-inhibitory concentrations of closantel, no resistance developed. Closantel at 0.0625 μg/mL significantly inhibited biofilm formation, reducing it from 1.29±0.16 to 0.62±0.04 (t=11.62, P<0.001), showing a clear dose-dependent effect. Closantel at 2 μg/mL also significantly eradicated established biofilms, reducing biofilm mass from 1.62±0.34 to 0.51±0.39 (t=4.84, P<0.01). Additionally, closantel exhibited extremely low cytotoxicity, with half-maximal lethal concentrations for HepG2 liver cancer cells and normal LO2 liver cells both exceeding 64 μg/mL.

CONCLUSIONS

Closantel exhibits strong antibacterial activity against S. aureus and its biofilm with low cytotoxicity against human cells, making it a promising candidate for new therapeutic strategies against S. aureus-related infections.

Polymyxin B-Enriched Exogenous Lung Surfactant: Thermodynamics and Structure

The use of an exogenous pulmonary surfactant (EPS) to deliver other relevant drugs to the lungs is a promising strategy for combined therapy. We evaluated the interaction of polymyxin B (PxB) with a clinically used EPS, the poractant alfa Curosurf (PSUR). The effect of PxB on the protein-free model system (MS) composed of four phospholipids (diC16:0PC/16:0-18:1PC/16:0-18:2PC/16:0-18:1PG) was examined in parallel to distinguish the specificity of the composition of PSUR. We used several experimental techniques (differential scanning calorimetry, small- and wide-angle X-ray scattering, small-angle neutron scattering, fluorescence spectroscopy, and electrophoretic light scattering) to characterize the binding of PxB to both EPS. Electrostatic interactions PxB-EPS are dominant. The results obtained support the concept of cationic PxB molecules lying on the surface of the PSUR bilayer, strengthening the multilamellar structure of PSUR as derived from SAXS and SANS. A protein-free MS mimics a natural EPS well but was found to be less resistant to penetration of PxB into the lipid bilayer. PxB does not affect the gel-to-fluid phase transition temperature, Tm, of PSUR, while Tm increased by ∼+ 2 °C in MS. The decrease of the thickness of the lipid bilayer (dL) of PSUR upon PxB binding is negligible. The hydrophobic tail of the PxB molecule does not penetrate the bilayer as derived from SANS data analysis and changes in lateral pressure monitored by excimer fluorescence at two depths of the hydrophobic region of the bilayer. Changes in dL of protein-free MS show a biphasic dependence on the adsorbed amount of PxB with a minimum close to the point of electroneutrality of the mixture. Our results do not discourage the concept of a combined treatment with PxB-enriched Curosurf. However, the amount of PxB must be carefully assessed (less than 5 wt % relative to the mass of the surfactant) to avoid inversion of the surface charge of the membrane.

Modulating the antibacterial effect of the existing antibiotics along with repurposing drug metformin

Owing to the extensive prevalence of resistant bacteria to numerous antibiotic classes, antimicrobial resistance (AMR) poses a well-known hazard to world health. As an alternate approach in the field of antimicrobial drug discovery, repurposing the available medications which are also called antibiotic resistance breakers has been pursued for the treatment of infections with antimicrobial resistance pathogens. In this study, we used Haloperidol, Metformin and Hydroxychloroquine as repurposing drugs in in vitro (Antibacterial Antibiotic Sensitivity Test and Minimum Inhibitory Concentration-MIC) and in vivo (Shigellosis in Swiss albino mice) tests in combination with traditional antibiotics (Oxytetracycline, Erythromycin, Doxycycline, Gentamicin, Ampicillin, Chloramphenicol, and Penicillin) against a group of AMR resistance bacteria (Bacillus cereus, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Shigella boydii). After observing the results of the conducted in vitro experiments we studied the effects of the above non antibiotic drugs in combination with the said antibiotics. As an repurposing adjuvant antibiotic drug, Metformin exhibited noteworthy activity in almost all in vitro, in vivo and in silico tests (Zone of inhibition for 30 to 43 mm for E.coli in combination with Doxycycline; MIC value decreased 50 µM to 0.781 µM with Doxycycline on S. boydii).In rodents Doxycycline and Metformin showed prominent against Shigellosis in White blood cell count (6.47 ± 0.152 thousand/mm3) and Erythrocyte sedimentation rate (10.5 ± 1.73 mm/hr). Our findings indicated that Metformin and Doxycycline combination has a crucial impact on Shigellosis. The molecular docking study was performed targeting the Acriflavine resistance protein B (AcrB) (PDB ID: 4CDI) and MexA protein (PDB ID: 6IOK) protein with Metformin (met8) drug which showed the highest binding energy with - 6.4 kcal/mol and - 5.5 kcal/mol respectively. Further, molecular dynamics simulation revealed that the docked complexes were relatively stable during the 100 ns simulation period. This study suggest Metformin and other experimented drugs can be used as adjuvants boost up antibiosis but further study is needed to find out the safety and efficacy of this non-antibiotic drug as potent antibiotic adjuvant.

Synergistic Activity and Mechanism of Sanguinarine with Polymyxin B against Gram-Negative Bacterial Infections

Compounds that potentiate the activity of clinically available antibiotics provide a complementary solution, except for developing novel antibiotics for the rapid emergence of multidrug-resistant Gram-negative bacteria (GNB). We sought to identify compounds potentiating polymyxin B (PMB), a traditional drug that has been revived as the last line for treating life-threatening GNB infections, thus reducing its nephrotoxicity and heterogeneous resistance in clinical use. In this study, we found a natural product, sanguinarine (SA), which potentiated the efficacy of PMB against GNB infections. The synergistic effect of SA with PMB was evaluated using a checkerboard assay and time-kill curves in vivo and the murine peritonitis model induced by Escherichia coli in female CD-1 mice in vivo. SA assisted PMB in accelerating the reduction in bacterial loads both in vitro and in vivo, improving the inflammatory responses and survival rate of infected animals. The subsequent detection of the intracellular ATP levels, membrane potential, and membrane integrity indicated that SA enhanced the bacterial-membrane-breaking capacity of PMB. A metabolomic analysis showed that the inhibition of energy metabolism, interference with nucleic acid biosynthesis, and the blocking of L-Ara4N-related PMB resistance may also contribute to the synergistic effect. This study is the first to reveal the synergistic activity and mechanism of SA with PMB, which highlights further insights into anti-GNB drug development.

Epigenetic therapeutics in dental pulp treatment: Hopes, challenges and concerns for the development of next-generation biomaterials

This opinion-led review paper highlights the need for novel translational research in vital-pulp-treatment (VPT), but also discusses the challenges in translating evidence to clinics. Traditional dentistry is expensive, invasive and relies on an outmoded mechanical understanding of dental disease, rather than employing a biological perspective that harnesses cell activity and the regenerative-capacity. Recent research has focussed on developing minimally-invasive biologically-based 'fillings' that preserve the dental pulp; research that is shifting the paradigm from expensive high-technology dentistry, with high failure rates, to smart restorations targeted at biological processes. Current VPTs promote repair by recruiting odontoblast-like cells in a material-dependent process. Therefore, exciting opportunities exist for development of next-generation biomaterials targeted at regenerative processes in the dentin-pulp complex. This article analyses recent research using pharmacological-inhibitors to therapeutically-target histone-deacetylase (HDAC) enzymes in dental-pulp-cells (DPCs) that stimulate pro-regenerative effects with limited loss of viability. Consequently, HDAC-inhibitors have the potential to enhance biomaterial-driven tissue responses at low concentration by influencing the cellular processes with minimal side-effects, providing an opportunity to develop a topically-placed, inexpensive bio-inductive pulp-capping material. Despite positive results, clinical translation of these innovations requires enterprise to counteract regulatory obstacles, dental-industry priorities and to develop strong academic/industry partnerships. The aim of this opinion-led review paper is to discuss the potential role of therapeutically-targeting epigenetic modifications as part of a topical VPT strategy in the treatment of the damaged dental pulp, while considering the next steps, material considerations, challenges and future for the clinical development of epigenetic therapeutics or other 'smart' restorations in VPT.

CRISPR-Based Gene Editing in Acinetobacter baumannii to Combat Antimicrobial Resistance

Antimicrobial resistance (AMR) poses a significant threat to the health, social, environment, and economic sectors on a global scale and requires serious attention to addressing this issue. Acinetobacter baumannii was given top priority among infectious bacteria because of its extensive resistance to nearly all antibiotic classes and treatment options. Carbapenem-resistant A. baumannii is classified as one of the critical-priority pathogens on the World Health Organization (WHO) priority list of antibiotic-resistant bacteria for effective drug development. Although available genetic manipulation approaches are successful in A. baumannii laboratory strains, they are limited when employed on newly acquired clinical strains since such strains have higher levels of AMR than those used to select them for genetic manipulation. Recently, the CRISPR-Cas (Clustered regularly interspaced short palindromic repeats/CRISPR-associated protein) system has emerged as one of the most effective, efficient, and precise methods of genome editing and offers target-specific gene editing of AMR genes in a specific bacterial strain. CRISPR-based genome editing has been successfully applied in various bacterial strains to combat AMR; however, this strategy has not yet been extensively explored in A. baumannii. This review provides detailed insight into the progress, current scenario, and future potential of CRISPR-Cas usage for AMR-related gene manipulation in A. baumannii.

Bifunctional antibiotic hybrids: A review of clinical candidates

Antibiotic resistance is a top threat to human health and a priority across the globe. This problematic issue is accompanied by the decline of new antibiotics in the pipeline over the past 30 years. In this context, an urgent need to develop new strategies to combat antimicrobial resistance is in great demand. Lately, among the possible approaches used to deal with antimicrobial resistance is the covalent ligation of two antibiotic pharmacophores that target the bacterial cells through a dissimilar mode of action into a single hybrid molecule, namely hybrid antibiotics. This strategy exhibits several advantages, including better antibacterial activity, overcoming the existing resistance towards individual antibiotics, and may ultimately delay the onset of bacterial resistance. This review sheds light on the latest development of the dual antibiotic hybrids pipeline, their potential mechanisms of action, and challenges in their use.