Design and synthesis of etrasimod derivatives as potent antibacterial agents against Gram-positive bacteria

The emergence of multidrug-resistant bacteria along with a declining pipeline of clinically useful antibiotics has led to the urgent need for the development of more effective antibacterial agents. Inspired by our recent report on the antibacterial activity of etrasimod, an immunomodulating drug candidate, we prepared a series of etrasimod derivatives by varying substituents on the phenyl ring, altering the central tricyclic aromatic ring, and modifying the carboxyl group. From this series of compounds, indole derivative 24f was identified as the most potent antibacterial compound, with the minimum inhibitory concentration (MIC) values between 2.5 and 10 μM against various Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), S. epidermidis and enterococci. Moreover, 24f exhibited rapid bactericidal activity against S. aureus, low toxicity and hemolytic activity, and a synergistic effect with gentamicin against S. aureus, MRSA, and Enterococcus faecalis. Furthermore, it was shown that neither etrasimod nor 24f affects S. aureus cell membranes. Importantly, 24f did not induce resistance in S. aureus, representing a significant improvement compared to etrasimod. Finally, the antibacterial activity of etrasimod and 24f against S. aureus and MRSA was confirmed in vivo in a Caenorhabditis elegans infection model. Taken together, our study highlights the value of etrasimod and its derivatives as potential antibacterial candidates for combating infections caused by Gram-positive bacteria.

Impact of azithromycin, doxycycline and redox-active small molecules on amoxicillin-induced Chlamydia pneumoniae persistence

Amoxicillin is recommended as primary treatment for community-acquired bacterial pneumonia (CABP). 5-10% of CABP cases are caused by Chlamydia pneumoniae, an obligate intracellular bacterium which responds to beta-lactam antibiotics by converting to a persistent phenotype. To support rational pharmacotherapy of C. pneumoniae infections, we investigated how clinically relevant concentrations of azithromycin and doxycycline affect amoxicillin induced C. pneumoniae persistence. Given the known role of redox state alterations in the action of bactericidal antibiotics and widespread use of redox-active dietary supplements when experiencing respiratory symptoms, we also studied how redox active compounds affect the studied antibiotic treatments. Our data demonstrate that clinically applied amoxicillin concentrations (10 and 25 mg/l) fail to eradicate C. pneumoniae infection in respiratory epithelial cells. Transmission electron microscopy (TEM) of amoxicillin-treated C. pneumoniae infected cells reveal aberrant bacterial morphology characteristic of chlamydial stress response. Amoxicillin was also found to significantly limit the antichlamydial effect of azithromycin or doxycycline. However, based on quantitative culture and quantitative PCR data, azithromycin was superior to doxycycline in C. pneumoniae eradication either as monotherapy or in combination with amoxicillin. Amoxicillin was also found to decrease respiratory epithelial cell glutathione (GSH) levels, whereas redox-active dibenzocyclooctadiene lignans increased C. pneumoniae load in amoxicillin-treated cultures up to two-fold. These data highlight the impact of relative administration time on the efficacy of antichlamydial antibiotics and indicate unfavorable interactions between amoxicillin and redox-active small molecules.

Repurposing the Sphingosine-1-Phosphate Receptor Modulator Etrasimod as an Antibacterial Agent Against Gram-Positive Bacteria

New classes of antibiotics are urgently needed in the fight against multidrug-resistant bacteria. Drug repurposing has emerged as an alternative approach to accelerate antimicrobial research and development. In this study, we screened a library of sphingosine-1-phosphate receptor (S1PR) modulators against Staphylococcus aureus and identified five active compounds. Among them, etrasimod (APD334), an investigational drug for the treatment of ulcerative colitis, displayed the best inhibitory activity against S. aureus when growing as free-floating planktonic cells and within biofilms. In follow-up studies, etrasimod showed bactericidal activity and drastic reduction of viable bacteria within 1 h of exposure. It also displayed a potent activity against other Gram-positive bacteria, including penicillin- and methicillin-resistant S. aureus strains, S. epidermidis, and Enterococcus faecalis, with a minimum inhibitory concentration (MIC) ranging from 5 to 10 μM (2.3–4.6 μg/mL). However, no inhibition of viability was observed against Gram-negative bacteria Acinetobacter baumannii, Escherichia coli, and Pseudomonas aeruginosa, showing that etrasimod preferably acts against Gram-positive bacteria. On the other hand, etrasimod was shown to inhibit quorum sensing (QS) signaling in Chromobacterium violaceum, suggesting that it may block the biofilm formation by targeting QS in certain Gram-negative bacteria. Furthermore, etrasimod displayed a synergistic effect with gentamicin against S. aureus, thus showing potential to be used in antibiotic combination therapy. Finally, no in vitro toxicity toward mammalian cells was observed. In conclusion, our study reports for the first time the potential of etrasimod as a repurposed antibacterial compound against Gram-positive bacteria.

Screening of natural compounds identifies ferutinin as an antibacterial and anti-biofilm compound

Antibacterial screenings are most commonly targeted at planktonic bacteria but less effort is dedicated to the exploration of agents acting on biofilms. Here, a natural compounds library was screened against Staphylococcus aureus using a 384-well plate platform to identify compounds preventing biofilm formation. Five structurally diverse hits were selected for follow-up studies: honokiol, tschimganidin, ferutinin, oridonin and deoxyshikonin. The compounds were evaluated against different bacterial species for their capacity to prevent and disrupt biofilms. The development of resistance and cytotoxicity were also investigated. Ferutinin displayed the best antibacterial activity, with a minimum inhibitory, bactericidal and biofilm preventive concentration of 25 µM against S. aureus. It efficiently disrupted pre-formed biofilms (over 5-log reduction of viable cells) and reduced biofilm formation on a catheter in the presence of neutrophils. This work provides new information on the antibacterial activity of five natural compounds and identified ferutinin as a promising candidate against S. aureus biofilms.

Synthesis and Biological Evaluation of Fingolimod Derivatives as Antibacterial Agents

We recently identified fingolimod as a potent antibiofilm compound by screening FDA-approved drugs. To study if the antibacterial activity of fingolimod could be further improved and to explore in-depth structure-activity relationships, we synthesized 28 novel fingolimod derivatives and evaluated their efficacy against Staphylococcus aureus grown in planktonic/single cell and biofilms. The most effective derivatives were tested on preformed S. aureus biofilms and against Gram-negative bacteria Acinetobacter baumannii and Pseudomonas aeruginosa, using fingolimod as the reference compound. Seven derivatives were more effective against S. aureus, while five other derivatives showed improved activity against P. aeruginosa and/or A. baumannii, with no apparent change in cytotoxicity on human cells. The most interesting derivatives, compounds 43 and 55, displayed a broader spectrum of antibacterial activity, possibly exerted by the change of the para-hydrocarbon chain to a meta position for 43 and by an additional hydroxyl group for 55.

Surfaceome and Exoproteome Dynamics in Dual-Species Pseudomonas aeruginosa and Staphylococcus aureus Biofilms

Bacterial biofilms are an important underlying cause for chronic infections. By switching into the biofilm state, bacteria can evade host defenses and withstand antibiotic chemotherapy. Despite the fact that biofilms at clinical and environmental settings are mostly composed of multiple microbial species, biofilm research has largely been focused on single-species biofilms. In this study, we investigated the interaction between two clinically relevant bacterial pathogens (Staphylococcus aureus and Pseudomonas aeruginosa) by label-free quantitative proteomics focusing on proteins associated with the bacterial cell surfaces (surfaceome) and proteins exported/released to the extracellular space (exoproteome). The changes observed in the surfaceome and exoproteome of P. aeruginosa pointed toward higher motility and lower pigment production when co-cultured with S. aureus. In S. aureus, lower abundances of proteins related to cell wall biosynthesis and cell division, suggesting increased persistence, were observed in the dual-species biofilm. Complementary phenotypic analyses confirmed the higher motility and the lower pigment production in P. aeruginosa when co-cultured with S. aureus. Higher antimicrobial tolerance associated with the co-culture setting was additionally observed in both species. To the best of our knowledge, this study is among the first systematic explorations providing insights into the dynamics of both the surfaceome and exoproteome of S. aureus and P. aeruginosa dual-species biofilms.

Combined Effect of Naturally-Derived Biofilm Inhibitors and Differentiated HL-60 Cells in the Prevention of Staphylococcus aureus Biofilm Formation

Nosocomial diseases represent a huge health and economic burden. A significant portion is associated with the use of medical devices, with 80% of these infections being caused by a bacterial biofilm. The insertion of a foreign material usually elicits inflammation, which can result in hampered antimicrobial capacity of the host immunity due to the effort of immune cells being directed to degrade the material. The ineffective clearance by immune cells is a perfect opportunity for bacteria to attach and form a biofilm. In this study, we analyzed the antibiofilm capacity of three naturally derived biofilm inhibitors when combined with immune cells in order to assess their applicability in implantable titanium devices and low-density polyethylene (LDPE) endotracheal tubes. To this end, we used a system based on the coculture of HL-60 cells differentiated into polymorphonuclear leukocytes (PMNs) and Staphylococcus aureus (laboratory and clinical strains) on titanium, as well as LDPE surfaces. Out of the three inhibitors, the one coded DHA1 showed the highest potential to be incorporated into implantable devices, as it displayed a combined activity with the immune cells, preventing bacterial attachment on the titanium and LDPE. The other two inhibitors seemed to also be good candidates for incorporation into LDPE endotracheal tubes.

3D-Printed Drug Delivery Systems: The Effects of Drug Incorporation Methods on Their Release and Antibacterial Efficiency

Additive manufacturing technologies have been widely used in the medical field. More specifically, fused filament fabrication (FFF) 3D-printing technology has been thoroughly investigated to produce drug delivery systems. Recently, few researchers have explored the possibility of directly 3D printing such systems without the need for producing a filament which is usually the feedstock material for the printer. This was possible via direct feeding of a mixture consisting of the carrier polymer and the required drug. However, as this direct feeding approach shows limited homogenizing abilities, it is vital to investigate the effect of the pre-mixing step on the quality of the 3D printed products. Our study investigates the two commonly used mixing approaches-solvent casting and powder mixing. For this purpose, polycaprolactone (PCL) was used as the main polymer under investigation and gentamicin sulfate (GS) was selected as a reference. The produced systems' efficacy was investigated for bacterial and biofilm prevention. Our data show that the solvent casting approach offers improved drug distribution within the polymeric matrix, as was observed from micro-computed topography and scanning electron microscopy visualization. Moreover, this approach shows a higher drug release rate and thus improved antibacterial efficacy. However, there were no differences among the tested approaches in terms of thermal and mechanical properties.

Antioxidant and Antiaging Effects of Licorice on the Caenorhabditis elegans Model

The causative relationship between oxidative stress and aging remains controversial, but it is a fact that many of the pathologies of age-related diseases are associated with oxidative stress. Phytochemicals may reduce damage from oxidative stress; the intake of these through diet could represent a strategy to lessen their pathological consequences. The popular and widely consumed licorice (Glycyrrhiza glabra) is a rich source of potential antioxidants. The aim of this study was to investigate whether licorice increases the oxidative stress resistance and lifespan of the animal model Caenorhabditis elegans. Licorice roots ethanolic extract showed in vitro antioxidant activity, with an IC₅₀ of 51.17 μg/mL using 2,2-diphenyl-1-picrylhydrazyl (DPPH) as free radical. C. elegans pretreated with licorice showed an increase of survival rate when exposed to the oxidant juglone, being this increase up to ∼33.56%. This pretreated population also showed an increase in lifespan of 14.28% at a concentration of 250 μg/mL. In conclusion, we suggest that licorice has a high antioxidant capability both in vitro and in vivo and that this activity may explain the observed extension of lifespan.

Viola cornuta and Viola x wittrockiana: Phenolic compounds, antioxidant and neuroprotective activities on Caenorhabditis elegans

Different Viola species are known for their traditional use as analgesic, antitussive, febrifuge, hipnotic, analgesic and anti-inflammatory medicinal agents. Additionally, they are considered edible flowers in certain cultures. Thus, the aim of this work was to characterize the phenolic composition and to assess the neuroprotective properties of Viola cornuta and Viola x wittrockiana using in vitro and in vivo methodologies with Caenorhabditis elegans as model. The identification of the phenolic compounds was carried out with a LC-DAD-ESI/MSn. The antioxidant activity of the extracts was determined in vitro using Folin-Ciocalteu, DPPH and FRAP assays and in vivo with a juglone-induced oxidative stress in C. elegans. The neuroprotective properties were evaluated measuring the ability to inhibit CNS enzymes (MAO A, AChE), and the capability to avoid paralyzing the C. elegans CL4176, an Alzheimer disease model. The phenolic content was higher in V. x wittrockiana, being quercetin-3-O-(6-O-rhamnosylglucoside)-7-O-rhamnoside the predominant compound in the extract, which also exhibited a stronger antioxidant capacity in vitro and a higher response to lethal oxidative stress on C. elegans than V. cornuta. Only V. x wittrockiana showed inhibitory effect on CNS enzymes, such as acetylcholinesterase and monoamine oxidase A, but both had protective effect against the paralysis of C. elegans. These findings suggest that the studied V. cornuta and V. x wittrockiana could be interesting candidates for age related neurodegenerative disorder associated with oxidative stress.