A new antibiotic with potent activity targets MscL

Constructing mechanosensitive signalling pathways de novo in synthetic cells

Biological mechanotransduction enables cells to sense and respond to mechanical forces in their local environment through changes in cell structure and gene expression, resulting in downstream changes in cell function. However, the complexity of living systems obfuscates the mechanisms of mechanotransduction, and hence the study of these processes in vitro has been critical in characterising the function of existing mechanosensitive membrane proteins. Synthetic cells are biomolecular compartments that aim to mimic the organisation, functionality and behaviours of biological systems, and represent the next step in the development of in vitro cell models. In recent years, mechanosensitive channels have been incorporated into synthetic cells to create de novo mechanosensitive signalling pathways. Here, I will discuss these developments, from the molecular parts used to construct existing pathways, the functionality of such systems, and potential future directions in engineering synthetic mechanotransduction. The recapitulation of mechanotransduction in synthetic biology will facilitate an improved understanding of biological signalling through the study of molecular interactions across length scales, whilst simultaneously generating new biotechnologies that can be applied as diagnostics, microreactors and therapeutics.

Less is more: CRISPR/Cas9-based mutations in DND1 gene enhance tomato resistance to powdery mildew with low fitness costs

Powdery mildew (PM), triggered by Oidium neolycopersici, represents a significant threat and a major concern for the productivity of tomato plants (Solanum lycopersicum L.). The presence of susceptibility (S) genes in plants facilitates pathogen proliferation and their dysfunction can lead to a recessively inherited broad-spectrum and durable type of resistance. Past studies have demonstrated that disrupting the function of DND1 (Defense No Death 1) increases plant resilience against various pathogens, such as powdery mildew (PM), but this comes at the cost of negatively affecting the overall health and vigor of the plant. To investigate the possibility of minimizing the adverse effects of the dnd1 mutation while boosting disease resistance, a CRISPR-Cas9 construct with four single guide RNAs targeting three exons of SlDND1 (Solyc02g088560.4.1) was designed and introduced into the tomato variety Moneymaker (MM) through Agrobacterium tumefaciens-mediated transformation. Three T1 lines (named E1, E3 and E4) were crossed with MM and then selfed to produce TF2 families. All the TF2 plants in homozygous state dnd1/dnd1, showed reduced PM symptoms compared to the heterozygous (DND1/dnd1) and wild type (DND1/DND1) ones. Two full knock-out (KO) mutant events (E1 and E4) encoding truncated DND1 proteins, exhibited clear dwarfness and auto-necrosis phenotypes, while mutant event E3 harbouring deletions of 3 amino acids, showed normal growth in height with less auto-necrotic spots. Analysis of the 3D structures of both the reference and the mutant proteins revealed significant conformational alterations in the protein derived from E3, potentially impacting its function. A dnd1/dnd1 TF2 line (TV181848-9, E3) underwent whole-genome sequencing using Illumina technology, which confirmed the absence of off-target mutations in selected genomic areas. Additionally, no traces of the Cas9 gene were detected, indicating its elimination through segregation. Our findings confirm the role of DND1 as an S-gene in tomato because impairment of this gene leads to a notable reduction in susceptibility to O. neolycopersici. Moreover, we provide, for the first time, a dnd1 mutant allele (E3) that exhibits fitness advantages in comparison with previously reported dnd1 mutant alleles, indicating a possible way to breed with dnd1 mutants.

The efficacy of the food-grade antimicrobial xanthorrhizol against Staphylococcus aureus is associated with McsL channel expression

Background

The emergence and spread of multidrug-resistant Staphylococcus aureus strains demonstrates the urgent need for new antimicrobials. Xanthorrhizol, a plant-derived sesquiterpenoid compound, has a rapid killing effect on methicillin-susceptible strains and methicillin-resistant strains of S. aureus achieving the complete killing of staphylococcal cells within 2 min using 64 μg/mL xanthorrhizol. However, the mechanism of its action is not yet fully understood.

Methods

The S. aureus cells treated with xanthorrhizol were studied using optical diffraction tomography. Activity of xanthorrhizol against the wild-type and mscL null mutant of S. aureus ATCC 29213 strain was evaluated in the time-kill assay. Molecular docking was conducted to predict the binding of xanthorrhizol to the SaMscL protein.

Results

Xanthorrhizol treatment of S. aureus cells revealed a decrease in cell volume, dry weight, and refractive index (RI), indicating efflux of the cell cytoplasm, which is consistent with the spontaneous activation of the mechanosensitive MscL channel. S. aureus ATCC 29213ΔmscL was significantly more resistant to xanthorrhizol than was the wild-type strain. Xanthorrhizol had an enhanced inhibitory effect on the growth and viability of exponentially growing S. aureus ATCC 29213ΔmscL cells overexpressing the SaMscL protein and led to a noticeable decrease in their viability in the stationary growth phase. The amino acid residues F5, V14, M23, A79, and V84 were predicted to be the residues of the binding pocket for xanthorrhizol. We also showed that xanthorrhizol increased the efflux of solutes such as K+ and glutamate from S. aureus ATCC 29213ΔmscL cells overexpressing SaMscL. Xanthorrhizol enhanced the antibacterial activity of the antibiotic dihydrostreptomycin, which targets the MscL protein.

Conclusion

Our findings indicate that xanthorrhizol targets the SaMscL protein in S. aureus cells and may have important implications for the development of a safe antimicrobial agent.

Observing mechanosensitive channels in action in living bacteria

Mechanosensitive (MS) channels act to protect the cytoplasmic membrane (CM) of living cells from environmental changes in osmolarity. In this report, we demonstrate the use of time-resolved second-harmonic light scattering (SHS) as a means of experimentally observing the relative state (open versus closed) of MS channels in living bacteria suspended in different buffer solutions. Specifically, the state of the MS channels was selectively controlled by changing the composition of the suspension medium, inducing either a transient or persistent osmotic shock. SHS was then used to monitor transport of the SHG-active cation, malachite green, across the bacterial CM. When MS channels were forced open, malachite green cations were able to cross the CM at a rate at least two orders of magnitude faster compared with when the MS channels were closed. These observations were corroborated using both numerical model simulations and complementary fluorescence experiments, in which the propensity for the CM impermeant cation, propidium, to stain cells was shown to be contingent upon the relative state of the MS channels (i.e., cells with open MS channels fluoresced red, cells with closed MS channels did not). Application of time-resolved SHS to experimentally distinguish MS channels opened via osmotic shock versus chemical activation, as well as a general comparison with the patch-clamp method is discussed.

The Effects of Airflow on the Mechanosensitive Channels of Escherichia coli MG1655 and the Impact of Survival Mechanisms Triggered

Understanding how bacteria respond to ventilated environments is a crucial concept, especially when considering accurate airflow modeling and detection limits. To properly design facilities for aseptic conditions, we must minimize the parameters for pathogenic bacteria to thrive. Identifying how pathogenic bacteria continue to survive, particularly due to their multi-drug resistance characteristics, is necessary for designing sterile environments and minimizing pathogen exposure. A conserved characteristic among bacterial organisms is their ability to maintain intracellular homeostasis for survival and growth in hostile environments. Mechanosensitive (MS) channels are one of the characteristics that guide this phenomenon. Interestingly, during extreme stress, bacteria will forgo favorable homeostasis to execute fast-acting survival strategies. Physiological sensors, such as MS channels, that trigger this survival mechanism are not clearly understood, leaving a gap in how bacteria translate physical stress to an intracellular response. In this paper, we study the role of mechanosensitive ion channels that are potentially triggered by aerosolization. We hypothesize that change in antimicrobial uptake is affected by aerosolization stress. Bacteria regulate their defense mechanisms against antimicrobials, which leads to varying susceptibility. Based on this information we hypothesize that aerosolization stress affects the antimicrobial resistance defense mechanisms of Escherichia coli (E. coli). We analyzed the culturability of knockout E. coli strains with different numbers of mechanosensitive channels and compared antibiotic susceptibility under stressed and unstressed airflow conditions. As a result of this study, we can identify how the defensive mechanisms of resistant bacteria are triggered for their survival in built environments. By changing ventilation airflow velocity and observing the change in antibiotic responses, we show how pathogenic bacteria respond to ventilated environments via mechanosensitive ion channels.

Targeting Inflammation in Acne: Current Treatments and Future Prospects

Acne is a common, chronic inflammatory condition affecting millions of people worldwide, with significant negative impact on quality of life and mental health. Acne is characterized by comedones, inflammatory papules, pustules, and nodulocystic lesions, with long-lasting sequelae including scarring and dyspigmentation, the latter of which is more common in skin of color. The four main pillars of acne pathophysiology include alteration of sebum production and concentration, hyperkeratinization of the follicular unit, Cutibacterium acnes strains, and an inflammatory immune response. Newer research has provided greater insight into these pathophysiologic categories. This greater understanding of acne pathogenesis has led to numerous new and emerging treatment modalities. These modalities include combinations of existing treatments, repurposing of existing agents historically used for other conditions, new topical treatments, novel antibiotics, topical and oral probiotics, and various procedural devices. This article will provide an overview of emerging treatments of acne and their link to our current and improved understanding of acne pathogenesis.

In vitro efficacy of different PEGylation designs on cathelicidin-like peptide with high antibacterial and antifungal activity

Recent reports on antibiotic resistance have highlighted the need to reduce the impact of this global health issue through urgent prevention and control. The World Health Organization currently considers antibiotic resistance as one of the most dangerous threats to global health. Therefore, Antimicrobial peptides (AMPs) are promising for the development of novel antibiotic molecules due to their high antimicrobial effects, non-inducing antimicrobial resistance (AMR) properties, and broad spectrum. Hence, in this study, we developed novel antimicrobial peptide/polymer conjugates to reduce the adverse effects of TN6 (RLLRLLLRLLR) peptide. We demonstrate how our constructs function in vitro in terms of antimicrobial activity, hemolytic activity, cytotoxicity, and protease resistance. Our findings show that our molecules are effective against different types of microorganisms such as Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, methicillin-resistant S. aureus, vancomycin-resistant Enteroccus faecium, and Candida albicans, which are known to be pathogenic and antibiotic-resistant. Our constructs generally showed low cytotoxicity relative to the peptide in HaCaT and 3T3 cells. Especially these structures are very successful in terms of hemotoxicity. In the bacteremia model with S. aureus, the naked peptide (TN6) was hemotoxic even at 1 µg/mL, while the hemotoxicity of the conjugates was considerably lower than the peptide. Remarkably in this model, the hemolytic activity of PepC-PEG-pepC conjugate decreased 15-fold from 2.36 to 31.12 µg/mL compared to the bacteria-free 60-min treatment. This is proof that in the case of bacteremia and sepsis, the conjugates specifically direct to bacterial cell membranes rather than red blood cells. In addition, the PepC-PEG-pepC conjugate is resistant to plasma proteases. Moreover, morphological and intracellular damage of the peptide/conjugates to Escherichia coli are demonstrated in SEM and TEM images. These results suggest our molecules can be considered potential next-generation broad-spectrum antibiotic molecule/drug candidates that might be used in clinical cases such as bacteremia and sepsis.

arfA antisense RNA regulates MscL excretory activity

Excretion of cytoplasmic protein (ECP) is a commonly observed phenomenon in bacteria, and this partial extracellular localisation of the intracellular proteome has been implicated in a variety of stress response mechanisms. In response to hypoosmotic shock and ribosome stalling in Escherichia coli, ECP is dependent upon the presence of the large-conductance mechanosensitive channel and the alternative ribosome-rescue factor A gene products. However, it is not known if a mechanistic link exists between the corresponding genes and the respective stress response pathways. Here, we report that the corresponding mscL and arfA genes are commonly co-located on the genomes of Gammaproteobacteria and display overlap in their respective 3' UTR and 3' CDS. We show this unusual genomic arrangement permits an antisense RNA-mediated regulatory control between mscL and arfA, and this modulates MscL excretory activity in E. coli These findings highlight a mechanistic link between osmotic, translational stress responses and ECP in E. coli, further elucidating the previously unknown regulatory function of arfA sRNA.

Approaches for the modulation of mechanosensitive MscL channel pores

MscL was the first mechanosensitive ion channel identified in bacteria. The channel opens its large pore when the turgor pressure of the cytoplasm increases close to the lytic limit of the cellular membrane. Despite their ubiquity across organisms, their importance in biological processes, and the likelihood that they are one of the oldest mechanisms of sensory activation in cells, the exact molecular mechanism by which these channels sense changes in lateral tension is not fully understood. Modulation of the channel has been key to understanding important aspects of the structure and function of MscL, but a lack of molecular triggers of these channels hindered early developments in the field. Initial attempts to activate mechanosensitive channels and stabilize functionally relevant expanded or open states relied on mutations and associated post-translational modifications that were often cysteine reactive. These sulfhydryl reagents positioned at key residues have allowed the engineering of MscL channels for biotechnological purposes. Other studies have modulated MscL by altering membrane properties, such as lipid composition and physical properties. More recently, a variety of structurally distinct agonists have been shown bind to MscL directly, close to a transmembrane pocket that has been shown to have an important role in channel mechanical gating. These agonists have the potential to be developed further into antimicrobial therapies that target MscL, by considering the structural landscape and properties of these pockets.

The Urgent Threat of Clostridioides difficile Infection: A Glimpse of the Drugs of the Future, with Related Patents and Prospects

Clostridioides difficile infection (CDI) is an urgent threat and unmet medical need. The current treatments for CDI are not enough to fight the burden of CDI and recurrent CDI (r-CDI). This review aims to highlight the future drugs for CDI and their related patented applications. The non-patent literature was collected from PubMed and various authentic websites of pharmaceutical industries. The patent literature was collected from free patent databases. Many possible drugs of the future for CDI, with diverse mechanisms of action, are in development in the form of microbiota-modulating agents (e.g., ADS024, CP101, RBX2660, RBX7455, SYN-004, SER-109, VE303, DAV132, MET-2, and BB128), small molecules (e.g., ridinilazole, ibezapolstat, CRS3123, DNV3837, MGB-BP-3, alanyl-L-glutamine, and TNP-2198), antibodies (e.g., IM-01 and LMN-201), and non-toxic strains of CD (e.g., NTCD-M3). The development of some therapeutic agents (e.g., DS-2969b, OPS-2071, cadazolid, misoprostol, ramoplanin, KB109, LFF571, and Ramizol) stopped due to failed clinical trials or unknown reasons. The patent literature reveals some important inventions for the existing treatments of CDI and supports the possibility of developing more and better CDI-treatment-based inventions, including patient-compliant dosage forms, targeted drug delivery, drug combinations of anti-CDI drugs possessing diverse mechanisms of action, probiotic and enzymatic supplements, and vaccines. The current pipeline of anti-CDI medications appears promising. However, it will be fascinating to see how many of the cited are successful in gaining approval from drug regulators such as the US FDA and becoming medicines for CDI and r-CDI.

Dynamic Interactions Between Brilliant Green and MscL Investigated by Solid-State NMR Spectroscopy and Molecular Dynamics Simulations

The mechanosensitive ion channel of large conductance (MscL) is a promising template for the development of new antibiotics due to its high conservation and uniqueness to microbes. Brilliant green (BG), a triarylmethane dye, has been identified as a new antibiotic targeted MscL. However, the detailed binding sites to MscL and the dynamic pathway of BG through the MscL channel remain unknown. Here, the dynamic interactions between BG and MscL were investigated using solid-state NMR spectroscopy and molecule dynamics (MD) simulations. Residue site-specific binding sites of BG to the MscL channel were identified by solid-state NMR. In addition, MD simulations revealed that BG conducts through the MscL channel via residues along the inner surface of the pore sequentially, in which the strong hydrophobic interactions between BG and hydrophobic residues F23 and I27 in the hydrophobic gate region of the MscL channel are major restrictions. Particularly, it was demonstrated that BG activates the MscL channel by reducing the hydrophobicity of the F23 in the gate region by water molecules that are bound to BG. Taken together, these simulations and experimental data provide novel insights into the dynamic interactions between BG and MscL, based on which new hydrophobic antibiotics and adjuvants targeting MscL can be developed.

Roles of Bacterial Mechanosensitive Channels in Infection and Antibiotic Susceptibility

Bacteria accumulate osmolytes to prevent cell dehydration during hyperosmotic stress. A sudden change to a hypotonic environment leads to a rapid water influx, causing swelling of the protoplast. To prevent cell lysis through osmotic bursting, mechanosensitive channels detect changes in turgor pressure and act as emergency-release valves for the ions and osmolytes, restoring the osmotic balance. This adaptation mechanism is well-characterized with respect to the osmotic challenges bacteria face in environments such as soil or an aquatic habitat. However, mechanosensitive channels also play a role during infection, e.g., during host colonization or release into environmental reservoirs. Moreover, recent studies have proposed roles for mechanosensitive channels as determinants of antibiotic susceptibility. Interestingly, some studies suggest that they serve as entry gates for antimicrobials into cells, enhancing antibiotic efficiency, while others propose that they play a role in antibiotic-stress adaptation, reducing susceptibility to certain antimicrobials. These findings suggest different facets regarding the relevance of mechanosensitive channels during infection and antibiotic exposure as well as illustrate that they may be interesting targets for antibacterial chemotherapy. Here, we summarize the recent findings on the relevance of mechanosensitive channels for bacterial infections, including transitioning between host and environment, virulence, and susceptibility to antimicrobials, and discuss their potential as antibacterial drug targets.

Elucidating the molecular basis of spontaneous activation in an engineered mechanosensitive channel

Mechanosensitive channel of large conductance (MscL) detects and responds to changes in the pressure profile of cellular membranes and transduces the mechanical energy into electrical and/or chemical signals. MscL can be activated using ultrasonic or chemical activation methods to improve the absorption of medicines and bioactive compounds into cells. However, re-engineering chemical signals such as pH change can trigger channel activation in MscL. This study elucidates the activation mechanism of an engineered MscL at an atomic level through a combination of equilibrium and non-equilibrium (NE) molecular dynamics (MD) simulations. Comparing the wild-type (WT) and engineered MscL activation processes suggests that the two systems are likely associated with different active states and different transition pathways. These findings indicate that (1) periplasmic loops play a key role in the activation process of MscL, (2) the loss of various backbone-backbone hydrogen bonds and salt bridge interactions in the engineered MscL channel causes the spontaneous opening of the channel, and (3) the most significant interactions lost during the activation process are between the transmembrane helices 1 and 2 in engineered MscL channel. The orientation-based biasing approach for producing and optimizing an open MscL model used in this work is a promising way to characterize unknown protein functional states and investigate the activation processes in ion channels and transmembrane proteins in general. This work paves the way for a computational framework for engineering more efficient pH-sensing mechanosensitive channels.

In Silico Screen Identifies a New Family of Agonists for the Bacterial Mechanosensitive Channel MscL

MscL is a highly conserved mechanosensitive channel found in the majority of bacterial species, including pathogens. It functions as a biological emergency release valve, jettisoning solutes from the cytoplasm upon acute hypoosmotic stress. It opens the largest known gated pore and has been heralded as an antibacterial target. Although there are no known endogenous ligands, small compounds have recently been shown to specifically bind to and open the channel, leading to decreased cell growth and viability. Their binding site is at the cytoplasmic/membrane and subunit interfaces of the protein, which has been recently been proposed to play an essential role in channel gating. Here, we have targeted this pocket using in silico screening, resulting in the discovery of a new family of compounds, distinct from other known MscL-specific agonists. Our findings extended the study of this functional region, the progression of MscL as a viable drug target, and demonstrated the power of in silico screening for identifying and improving the design of MscL agonists.

Curcumin activation of a bacterial mechanosensitive channel underlies its membrane permeability and adjuvant properties

Curcumin, a natural compound isolated from the rhizome of turmeric, has been shown to have antibacterial properties. It has several physiological effects on bacteria including an apoptosis-like response involving RecA, membrane permeabilization, inhibiting septation, and it can also work synergistically with other antibiotics. The mechanism by which curcumin permeabilizes the bacterial membrane has been unclear. Most bacterial species contain a Mechanosensitive channel of large conductance, MscL, which serves the function of a biological emergency release valve; these large-pore channels open in response to membrane tension from osmotic shifts and, to avoid cell lysis, allow the release of solutes from the cytoplasm. Here we show that the MscL channel underlies the membrane permeabilization by curcumin as well as its synergistic properties with other antibiotics, by allowing access of antibiotics to the cytoplasm; MscL also appears to have an inhibitory role in septation, which is enhanced when activated by curcumin.

Synergic activity of oligostyrylbenzenes with amphotericin B against Candida tropicalis biofilms

Antimicrobial drug resistance is a serious challenge in clinical settings worldwide, with biofilm formation having been associated with this problem. In the present study, the synergism of oligostyrylbenzene (OSB) compounds in combination with amphotericin B (AmB) against Candida tropicalis biofilms was investigated. In addition, the toxicity in human blood cells was determined. Synergistic combinations of OSBs and AmB were evaluated to consider future effects of OSBs in vivo. The checkerboard microdilution method was used to study the interactions of one anionic (1) and two cationic (2 and 3) OSBs with AmB. We investigated the effects of OSBs on reactive oxygen species (ROS) and the levels of the reactive nitrogen intermediates (RNIs). The cellular stress affected biofilm growth through an accumulation of ROS and RNI, at synergistic concentrations of OSBs and AmB. Furthermore, significant surface topography differences were noted upon treatment with the OSB 2/AmB combination, using confocal laser scanning microscopy in conjunction with the image analysis software COMSTAT. The results revealed a low toxicity to leukocytes and red blood cells at synergistic combinations of cationic OSBs with AmB. These findings demonstrated the antibiofilm effects of OSBs and the synergism of AmB with cationic OSBs against biofilms of C. tropicalis for the first time.

Investigational Treatment Agents for Recurrent Clostridioides difficile Infection (rCDI)

Clostridioides difficile infection (CDI) is a major cause of nosocomial diarrhea that is deemed a global health threat. C. difficile strain BI/NAP1/027 has contributed to the increase in the mortality, severity of CDI outbreaks and recurrence rates (rCDI). Updated CDI treatment guidelines suggest vancomycin and fidaxomicin as initial first-line therapies that have initial clinical cure rates of over 80%. Unacceptably high recurrence rates of 15–30% in patients for the first episode and 40% for the second recurrent episode are reported. Alternative treatments for rCDI include fecal microbiota transplant and a human monoclonal antibody, bezlotoxumab, that can be used in patients with high risk of rCDI. Various emerging potential therapies with narrow spectrum of activity and little systemic absorption that are in development include 1) Ibezapolstat (formerly ACX-362E), MGB-BP-3, and DS-2969b-targeting bacterial DNA replication, 2) CRS3213 (REP3123)-inhibiting toxin production and spore formation, 3) ramizol and ramoplanin-affecting bacterial cell wall, 4) LFF-571-blocking protein synthesis, 5) Alanyl-L-Glutamine (alanylglutamine)-inhibiting damage caused by C. difficile by protecting intestinal mucosa, and 6) DNV3837 (MCB3681)-prodrug consisting of an oxazolidinone–quinolone combination that converts to the active form DNV3681 that has activity in vitro against C. difficile. This review article provides an overview of these developing drugs that can have potential role in the treatment of rCDI and in lowering recurrence rates.

Conservation and divergence in NaChBac and NaV1.7 pharmacology reveals novel drug interaction mechanisms

Voltage-gated Na⁺ (Na_V) channels regulate homeostasis in bacteria and control membrane electrical excitability in mammals. Compared to their mammalian counterparts, bacterial Na_V channels possess a simpler, fourfold symmetric structure and have facilitated studies of the structural basis of channel gating. However, the pharmacology of bacterial Na_V remains largely unexplored. Here we systematically screened 39 Na_V modulators on a bacterial channel (NaChBac) and characterized a selection of compounds on NaChBac and a mammalian channel (human Na_V1.7). We found that while many compounds interact with both channels, they exhibit distinct functional effects. For example, the local anesthetics ambroxol and lidocaine block both Na_V1.7 and NaChBac but affect activation and inactivation of the two channels to different extents. The voltage-sensing domain targeting toxin BDS-I increases Na_V1.7 but decreases NaChBac peak currents. The pore binding toxins aconitine and veratridine block peak currents of Na_V1.7 and shift activation (aconitine) and inactivation (veratridine) respectively. In NaChBac, they block the peak current by binding to the pore residue F224. Nonetheless, aconitine has no effect on activation or inactivation, while veratridine only modulates activation of NaChBac. The conservation and divergence in the pharmacology of bacterial and mammalian Na_V channels provide insights into the molecular basis of channel gating and will facilitate organism-specific drug discovery.

Evaluation of the Novel Antimicrobial BCP3 in a Coating for Endotracheal Tubes

Ventilator-associated pneumonia (VAP) is a highly common hospital-acquired infection affecting people that require mechanical ventilation. The endotracheal tube (ETT) used during the ventilation process provides a surface that can allow bacterial colonization and biofilm formation, which can lead to VAP. Although various approaches, including ETT design and material selection, as well as antimicrobial coatings have been employed to minimize adverse events, VAP remains a significant unresolved clinical issue. In this study, we have utilized a novel styrylbenzene-based antimicrobial (BCP3) in a simple and robust coating that allows its long-term release at an effective level. BCP3 was applied onto PVC ETT segments blended together with poly(lactic-co-glycolic acid) via a facile dip-coating process with controlled loadings. In vitro studies demonstrated concentration-dependent release of BCP3 from the coatings for at least 31 days. Bacterial assays using major VAP culprits, Staphylococcus aureus and Pseudomonas aeruginosa, demonstrated significant growth inhibition, with a stronger effect on S. aureus. Despite its ability to inhibit bacterial growth, BCP3 showed no cytotoxicity toward mammalian (L929) fibroblasts, which makes it attractive from a clinical perspective. The coating procedure was successfully translated to coat the entire ETTs, making it highly amenable for large-scale manufacturing.

Novel MscL agonists that allow multiple antibiotics cytoplasmic access activate the channel through a common binding site

The antibiotic resistance crisis is becoming dire, yet in the past several years few potential antibiotics or adjuvants with novel modes of action have been identified. The bacterial mechanosensitive channel of large conductance, MscL, found in the majority of bacterial species, including pathogens, normally functions as an emergency release valve, sensing membrane tension upon low-osmotic stress and discharging cytoplasmic solutes before cell lysis. Opening the huge ~30Å diameter pore of MscL inappropriately is detrimental to the cell, allowing solutes from and even passage of drugs into to cytoplasm. Thus, MscL is a potential novel drug target. However, there are no known natural agonists, and small compounds that modulate MscL activity are just now being identified. Here we describe a small compound, K05, that specifically modulates MscL activity and we compare results with those obtained for the recently characterized MscL agonist 011A. While the structure of K05 only vaguely resembles 011A, many of the findings, including the binding pocket, are similar. On the other hand, both in vivo and molecular dynamic simulations indicate that the two compounds modulate MscL activity in significantly different ways.

Life with Bacterial Mechanosensitive Channels, from Discovery to Physiology to Pharmacological Target

General principles in biology have often been elucidated from the study of bacteria. This is true for the bacterial mechanosensitive channel of large conductance, MscL, the channel highlighted in this review. This channel functions as a last-ditch emergency release valve discharging cytoplasmic solutes upon decreases in osmotic environment. Opening the largest gated pore, MscL passes molecules up to 30 Å in diameter; exaggerated conformational changes yield advantages for study, including in vivo assays. MscL contains structural/functional themes that recur in higher organisms and help elucidate how other, structurally more complex, channels function. These features of MscL include (i) the ability to directly sense, and respond to, biophysical changes in the membrane, (ii) an α helix ("slide helix") or series of charges ("knot in a rope") at the cytoplasmic membrane boundary to guide transmembrane movements, and (iii) important subunit interfaces that, when disrupted, appear to cause the channel to gate inappropriately. MscL may also have medical applications: the modality of the MscL channel can be changed, suggesting its use as a triggered nanovalve in nanodevices, including those for drug targeting. In addition, recent studies have shown that the antibiotic streptomycin opens MscL and uses it as one of the primary paths to the cytoplasm. Moreover, the recent identification and study of novel specific agonist compounds demonstrate that the channel is a valid drug target. Such compounds may serve as novel-acting antibiotics and adjuvants, a way of permeabilizing the bacterial cell membrane and, thus, increasing the potency of commonly used antibiotics.

Novel compounds that specifically bind and modulate MscL: insights into channel gating mechanisms

The bacterial mechanosensitive channel of large conductance (MscL) normally functions as an emergency release valve discharging cytoplasmic solutes upon osmotic stress. Opening the large pore of MscL inappropriately is detrimental to the cell, and thus it has been speculated to be a potential antibiotic target. Although MscL is one of the best studied mechanosensitive channels, no chemical that influenced bacterial growth by modulating MscL is known. We therefore used a high-throughput screen to identify compounds that slowed growth in an MscL-dependent manner. We characterized 2 novel sulfonamide compounds identified in the screen. We demonstrated that, although both increase MscL gating, one of these compounds does not work through the folate pathway, as other antimicrobial sulfonamides; indeed, the sulfonamide portion of the compound is not needed for activity. The only mode of action appears to be MscL activation. The binding pocket is where an α-helix runs along the cytoplasmic membrane and interacts with a neighboring subunit; analogous motifs have been observed in several prokaryotic and eukaryotic channels. The data not only demonstrate that MscL is a viable antibiotic target, but also give insight into the gating mechanisms of MscL, and they may have implications for developing agonists for other channels.-Wray, R., Iscla, I., Kovacs, Z., Wang, J., Blount, P. Novel compounds that specifically bind and modulate MscL: insights into channel gating mechanisms.

A 14-day repeat dose oral gavage range-finding study of a first-in-class CDI investigational antibiotic, in rats

Drug resistant bacteria are winning the fight over antibiotics with some bacteria not responding to any antibiotics, threatening modern medicine as we know it. The development of new, effective and safe antibiotics is critical for addressing this issue. Ramizol, a first-in-class styrylbenzene based antibiotic, is an investigational drug indicated for Clostridium difficile infections (CDI). The objective of this range-finding study was to evaluate the potential general toxicity (based on toxicological endpoints selected) and toxicokinetics of Ramizol in male and female rats that may arise from repeated exposure via oral gavage over a test period of at least 14 days at doses of 50 mg/kg, 500 mg/kg and 1500 mg/kg. There were no mortalities in this study and no Ramizol-related clinical observations. Additionally, there were no changes in mean body weight, body weight gain, food consumption or food efficiency for male and female rats attributable to Ramizol administration. The observed pharmacokinetic behavior showed the presence of Ramizol in plasma at 24 hours post-dosing combined with increasing AUC(0-24) values during the course of this study in groups administered 1500 mg/kg/day, which suggests that at least some dosing groups will show accumulation of compound during repeated dose studies. These toxicology results have shown Ramizol is well-tolerated at very high concentrations in rats and support the further drug development of Ramizol as a first-in-class antibiotic for the treatment of CDI.

Comparison of the in vitro antibacterial activity of Ramizol, fidaxomicin, vancomycin, and metronidazole against 100 clinical isolates of Clostridium difficile by broth microdilution

Antibiotic drug development remains a major challenge with few candidates in clinical development. Ramizol, a first-in-class styrylbenzene antibiotic, is under development for the treatment of Clostridium difficile associated disease. Here, we investigate the in vitro antibacterial activity of Ramizol in comparison to fidaxomicin, vancomycin and metronidazole against 100 clinical isolates of C. difficile by the broth microdilution method. We show there is no apparent impact of ribotype, toxin-production, or resistance to fidaxomicin, vancomycin or metronidazole on the activity of Ramizol. Moreover, we show Ramizol has a narrower MIC range translating to potentially better control over the therapeutic dose. Together, these results support the further development of Ramizol for the treatment of C. difficile associated disease.

Comparison of Strategies to Overcome Drug Resistance: Learning from Various Kingdoms

Drug resistance, especially antibiotic resistance, is a growing threat to human health. To overcome this problem, it is significant to know precisely the mechanisms of drug resistance and/or self-resistance in various kingdoms, from bacteria through plants to animals, once more. This review compares the molecular mechanisms of the resistance against phycotoxins, toxins from marine and terrestrial animals, plants and fungi, and antibiotics. The results reveal that each kingdom possesses the characteristic features. The main mechanisms in each kingdom are transporters/efflux pumps in phycotoxins, mutation and modification of targets and sequestration in marine and terrestrial animal toxins, ABC transporters and sequestration in plant toxins, transporters in fungal toxins, and various or mixed mechanisms in antibiotics. Antibiotic producers in particular make tremendous efforts for avoiding suicide, and are more flexible and adaptable to the changes of environments. With these features in mind, potential alternative strategies to overcome these resistance problems are discussed. This paper will provide clues for solving the issues of drug resistance.

Nonpolar residues in the presumptive pore-lining helix of mechanosensitive channel MSL10 influence channel behavior and establish a nonconducting function

Mechanosensitive (MS) ion channels provide a universal mechanism for sensing and responding to increased membrane tension. MscS-like (MSL) 10 is a relatively well-studied MS ion channel from Arabidopsis thaliana that is implicated in cell death signaling. The relationship between the amino acid sequence of MSL10 and its conductance, gating tension, and opening and closing kinetics remains unstudied. Here, we identify several nonpolar residues in the presumptive pore-lining transmembrane helix of MSL10 (TM6) that contribute to these basic channel properties. F553 and I554 are essential for wild type channel conductance and the stability of the open state. G556, a glycine residue located at a predicted kink in TM6, is essential for channel conductance. The increased tension sensitivity of MSL10 compared to close homolog MSL8 may be attributed to F563, but other channel characteristics appear to be dictated by more global differences in structure. Finally, MSL10 F553V and MSL10 G556V provided the necessary tools to establish that MSL10's ability to trigger cell death is independent of its ion channel function.

Identification and Characterization of the Neisseria gonorrhoeae MscS-Like Mechanosensitive Channel

Mechanosensitive channels are ubiquitous in bacteria and provide an essential mechanism to survive sudden exposure to a hypo-osmotic environment by the sensing and release of increased turgor pressure. No mechanosensitive channels have thus far been identified and characterized for the human-specific bacterial pathogen Neisseria gonorrhoeae In this study, we identified and characterized the N. gonorrhoeae MscS-like mechanosensitive channel (Ng-MscS). Electrophysiological analyses by the patch clamp method showed that Ng-MscS is stretch activated and contains pressure-dependent gating properties. Further mutagenesis studies of critical residues forming the hydrophobic vapor lock showed that gain-of-function mutations in Ng-MscS inhibited bacterial growth. Subsequent analysis of the function of Ng-MscS in N. gonorrhoeae by osmotic down-shock assays revealed that the survival of Ng-mscS deletion mutants was significantly reduced compared with that of wild-type strains, while down-shock survival was restored upon the ectopic complementation of mscS Finally, to investigate whether Ng-MscS is important for N. gonorrhoeae during infections, competition assays were performed by using a murine vaginal tract infection model. Ng-mscS deletion mutants were outcompeted by N. gonorrhoeae wild-type strains for colonization and survival in this infection model, highlighting that Ng-MscS contributes to in vivo colonization and survival. Therefore, Ng-MscS might be a promising target for the future development of novel antimicrobials.

Ramizol® encapsulation into extended release PLGA micro- and nanoparticle systems for subcutaneous and intramuscular administration: in vitro and in vivo evaluation

OBJECTIVE

Novel antibiotic Ramizol^® is advancing to clinical trials for the treatment of gastrointestinal Clostridium difficile associated disease. Despite this, previous studies have shown a rapid plasma clearance upon intravenous administration and low oral bioavailability indicating pure drug is unsuitable for systemic infection treatment following oral dosing. The current study aims to investigate the development of poly-lactic-(co-glycolic) acid (PLGA) particles to overcome this limitation and increase the systemic half-life following subcutaneous and intramuscular dosing.

SIGNIFICANCE

The development of new antibiotic treatments will help in combatting the rising incidence of antimicrobial resistance.

METHODS

Ramizol^® was encapsulated into PLGA nano and microparticles using nanoprecipitation and emulsification solvent evaporation techniques. Formulations were analyzed for particle size, loading level and encapsulation efficiency as well as in vitro drug release profiles. Final formulation was advanced to in vivo pharmacokinetic studies in Sprague-Dawley rats.

RESULTS

Formulation technique showed major influence on particle size and loading levels with optimal loading of 9.4% and encapsulation efficiency of 92.06%, observed using emulsification solvent evaporation. Differences in formulation technique were also linked with subsequent differences in release profiles. Pharmacokinetic studies in Sprague-Dawley rats confirmed extended absorption and enhanced bioavailability following subcutaneous and intramuscular dosing with up to an 8-fold increase in T_max and T_1/2 when compared to the oral and IV routes.

CONCLUSIONS

Subcutaneous and intramuscular dosing of PLGA particles successfully increased systemic half-life and bioavailability of Ramizol^®. This formulation will allow further development of Ramizol^® for systemic infection eradication.

Bacterial Mechanosensitive Channels

Mechanosensitive (MS) channels protect bacteria against hypo-osmotic shock and fulfil additional functions. Hypo-osmotic shock leads to high turgor pressure that can cause cell rupture and death. MS channels open under these conditions and release unspecifically solutes and consequently the turgor pressure. They can recognise the raised pressure via the increased tension in the cell membrane. Currently, a better understanding how MS channels can sense tension on molecular level is developing because the interaction of the lipid bilayer with the channel is being investigated in detail. The MS channel of large conductance (MscL) and of small conductance (MscS) have been distinguished and studied in molecular detail. In addition, larger channels were found that contain a homologous region corresponding to MscS so that MscS represents a family of channels. Often several members of this family are present in a species. The importance of this family is underlined by the fact that members can be found not only in bacteria but also in higher organisms. While MscL and MscS have been studied for years in particular by electrophysiology, mutagenesis, molecular dynamics, X-ray crystallography and other biophysical techniques, only recently more details are emerging about other members of the MscS-family.

Bacterial Mechanosensors

Bacteria represent one of the most evolutionarily successful groups of organisms to inhabit Earth. Their world is awash with mechanical cues, probably the most ancient form of which are osmotic forces. As a result, they have developed highly robust mechanosensors in the form of bacterial mechanosensitive (MS) channels. These channels are essential in osmoregulation, and in this setting, provide one of the simplest paradigms for the study of mechanosensory transduction. We explore the past, present, and future of bacterial MS channels, including the alternate mechanosensory roles that they may play in complex microbial communities. Central to all of these functions is their ability to change conformation in response to mechanical stimuli. We discuss their gating according to the force-from-lipids principle and its applicability to eukaryotic MS channels. This includes the new paradigms emerging for bilayer-mediated channel mechanosensitivity and how this molecular detail may provide advances in both industry and medicine.

New strategies for targeting and treatment of multi-drug resistant Staphylococcus aureus

Staphylococcus aureus is a major cause of bacterial infection in humans, and has been notoriously able to acquire resistance to a variety of antibiotics. An example is methicillin-resistant S. aureus (MRSA), which despite having been initially associated with clinical settings, now is one of the key causative agents of community-acquired infections. Antibiotic resistance in S. aureus involves mechanisms ranging from drug efflux to increased expression or mutation of target proteins, and this has required innovative approaches to develop novel treatment methodologies. This review provides an overview of the major mechanisms of antibiotic resistance developed by S. aureus, and describes the emerging alternatives being sought to circumvent infection and proliferation, including new generations of classic antibiotics, synergistic approaches, antibodies, and targeting of virulence factors.

A Review of Experimental and Off-Label Therapies for Clostridium difficile Infection

In spite of increased awareness and the efforts taken to optimize Clostridium difficile infection (CDI) management, with the limited number of currently available antibiotics for C. difficile the halt of this increasing epidemic remains out of reach. There are, however, close to 80 alternative treatment methods with controversial anti-clostridial efficacy or in experimental phase today. Indeed, some of these therapies are expected to become acknowledged members of the recommended anti-CDI arsenal within the next few years. None of these alternative treatment methods can respond in itself to all the major challenges of CDI management, which are primary prophylaxis in the susceptible population, clinical cure of severe cases, prevention of recurrences, and forestallment of asymptomatic C. difficile carriage and in-hospital spread. Yet, the greater the variety of treatment choices on hand, the better combination strategies can be developed to reach these goals in the future. The aim of this article is to provide a comprehensive summary of these experimental and currently off-label therapeutic options.

Preclinical development of Ramizol, an antibiotic belonging to a new class, for the treatment of Clostridium difficile colitis

Antibiotic-resistant bacteria is a major threat to human health and is predicted to become the leading cause of death from disease by 2050. Despite the recent resurgence of research and development in the area, few antibiotics have reached the market, with most of the recently approved antibiotics corresponding to new uses for old antibiotics, or structurally similar derivatives thereof. We have recently reported an in silico approach that led to the design of an entirely new class of antibiotics for the bacteria-specific mechanosensitive ion channel of large conductance: MscL. Here, we present the preclinical development of one such antibiotic, Ramizol, a first generation antibiotic belonging to that class. We present the lack of interaction between Ramizol and other mammalian channels adding credibility to its MscL selectivity. We determine the pharmacokinetic profile in a rat model and show <0.1% of Ramizol is absorbed systemically. We show this non-systemic nature of the antibiotic translates to over 70% survival of hamsters in a Clostridium difficile colitis model. Lastly, initial in vitro data indicate that resistance to Ramizol occurs at a low frequency. In conclusion, we establish the potential of Ramizol as an effective new treatment for C. difficile associated disease.

Zolav(®) (a p-carboethoxy-tristyrylbenzene derivative) [corrected]: a new antibiotic for the treatment of acne

Background

Acne is a prominent skin condition affecting >80% of teenagers and young adults and ~650 million people globally. Isotretinoin, a vitamin A derivative, is currently the standard of care for treatment. However, it has a well-established teratogenic activity, a reason for the development of novel and low-risk treatment options for acne.

Objective

To investigate the effectiveness of Zolav^®, a novel antibiotic as a treatment for acne vulgaris.

Materials and methods

Minimum inhibitory concentration of Zolav^® against Propionibacterium acnes was determined by following a standard protocol using Mueller-Hinton broth and serial dilutions in a 96-well plate. Cytotoxicity effects on human umbilical vein endothelial cells and lung cells in the presence of Zolav^® were investigated by determining the growth inhibition (GI₅₀) concentration, total growth inhibition concentration, and the lethal concentration of 50% (LC₅₀). The tryptophan auxotrophic mutant of Escherichia coli strain, WP2 uvrA (ATCC 49979), was used for the AMES assay with the addition of Zolav^® tested for its ability to reverse the mutation and induce bacterial growth. The in vivo effectiveness of Zolav^® was tested in a P. acnes mouse intradermal model where the skin at the infection site was removed, homogenized, and subjected to colony-forming unit (CFU) counts.

Results

Susceptibility testing of Zolav^® against P. acnes showed a minimum inhibitory concentration of 2 µg/mL against three strains with no cytotoxicity and no mutagenicity observed at the highest concentrations tested, 30 µM and 1,500 µg/plate, respectively. The use of Zolav^® at a concentration of 50 µg/mL (q8h) elicited a two-log difference in CFU/g between the treatment group and the control.

Conclusion

This study demonstrates the potential of Zolav^® as a novel treatment for acne vulgaris.

Mechanisms of mechanosensing - mechanosensitive channels, function and re-engineering

Sensing and responding to mechanical stimuli is an ancient behavior and ubiquitous to all forms of life. One of its players 'mechanosensitive ion channels' are involved in processes from osmosensing in bacteria to pain in humans. However, the mechanism of mechanosensing is yet to be elucidated. This review describes recent developments in the understanding of a bacterial mechanosensitive channel. Force from the lipid principle of mechanosensation, new methods to understand protein-lipid interactions, the role of water in the gating, the use of engineered mechanosensitive channels in the understanding of the gating mechanism and application of the accumulated knowledge in the field of drug delivery, drug design and sensor technologies are discussed.

Antibacterial properties of 3-(phenylsulfonyl)-2-pyrazinecarbonitrile

The emergence of multidrug-resistant bacterial strains has heightened the need for new antimicrobial agents based on novel chemical scaffolds that are able to circumvent current modes of resistance. We recently developed a whole-animal drug-screening methodology in pursuit of this goal and now report the discovery of 3-(phenylsulfonyl)-2-pyrazinecarbonitrile (PSPC) as a novel antibacterial effective against resistant nosocomial pathogens. The minimum inhibitory concentrations (MIC) of PSPC against Staphylococcus aureus and Enterococcus faecium were 4 μg/mL and 8 μg/mL, respectively, whereas the MICs were higher against the Gram-negative bacteria Klebsiella pneumoniae (64 μg/mL), Acinetobacter baumannii (32 μg/mL), Pseudomonas aeruginosa (>64 μg/mL), and Enterobacter spp. (>64 μg/mL). However, co-treatment of PSPC with the efflux pump inhibitor phenylalanine arginyl β-naphthylamide (PAβN) or with sub-inhibitory concentrations of the lipopeptide antibiotic polymyxin B reduced the MICs of PSPC against the Gram-negative strains by >4-fold. A sulfide analog of PSPC (PSPC-1S) showed no antibacterial activity, whereas the sulfoxide analog (PSPC-6S) showed identical activity as PSPC across all strains, confirming structure-dependent activity for PSPC and suggesting a target-based mechanism of action. PSPC displayed dose dependent toxicity to both Caenorhabditis elegans and HEK-293 mammalian cells, culminating with a survival rate of 16% (100 μg/mL) and 8.5% (64 μg/mL), respectively, at the maximum tested concentration. However, PSPC did not result in hemolysis of erythrocytes, even at a concentration of 64 μg/mL. Together these results support PSPC as a new chemotype suitable for further development of new antibiotics against Gram-positive and Gram-negative bacteria.

Mechanical coupling of the multiple structural elements of the large-conductance mechanosensitive channel during expansion

The prokaryotic mechanosensitive channel of large conductance (MscL) is a pressure-relief valve protecting the cell from lysing during acute osmotic downshock. When the membrane is stretched, MscL responds to the increase of membrane tension and opens a nonselective pore to about 30 Å wide, exhibiting a large unitary conductance of ∼ 3 nS. A fundamental step toward understanding the gating mechanism of MscL is to decipher the molecular details of the conformational changes accompanying channel opening. By applying fusion-protein strategy and controlling detergent composition, we have solved the structures of an archaeal MscL homolog from Methanosarcina acetivorans trapped in the closed and expanded intermediate states. The comparative analysis of these two new structures reveals significant conformational rearrangements in the different domains of MscL. The large changes observed in the tilt angles of the two transmembrane helices (TM1 and TM2) fit well with the helix-pivoting model derived from the earlier geometric analyses based on the previous structures. Meanwhile, the periplasmic loop region transforms from a folded structure, containing an ω-shaped loop and a short β-hairpin, to an extended and partly disordered conformation during channel expansion. Moreover, a significant rotating and sliding of the N-terminal helix (N-helix) is coupled to the tilting movements of TM1 and TM2. The dynamic relationships between the N-helix and TM1/TM2 suggest that the N-helix serves as a membrane-anchored stopper that limits the tilts of TM1 and TM2 in the gating process. These results provide direct mechanistic insights into the highly coordinated movement of the different domains of the MscL channel when it expands.