Structure-based drug design and optimization of mannoside bacterial FimH antagonists

Beyond antibiotics: CRISPR/Cas9 triumph over biofilm-associated antibiotic resistance infections

A complex structure known as a biofilm is formed when a variety of bacterial colonies or a single type of cell in a group sticks to a surface. The extracellular polymeric compounds that encase these cells, often consisting of proteins, eDNA, and polysaccharides, exhibit strong antibiotic resistance. Concerns about biofilm in the pharmaceutical industry, public health, and medical fields have sparked a lot of interest, as antibiotic resistance is a unique capacity exhibited by these biofilm-producing bacteria, which increases morbidity and death. Biofilm formation is a complicated process that is controlled by several variables. Insights into the processes to target for the therapy have been gained from multiple attempts to dissect the biofilm formation process. Targeting pathogens within a biofilm is profitable because the bacterial pathogens become considerably more resistant to drugs in the biofilm state. Although biofilm-mediated infections can be lessened using the currently available medications, there has been a lot of focus on the development of new approaches, such as bioinformatics tools, for both treating and preventing the production of biofilms. Technologies such as transcriptomics, metabolomics, nanotherapeutics and proteomics are also used to develop novel anti-biofilm agents. These techniques help to identify small compounds that can be used to inhibit important biofilm regulators. The field of appropriate control strategies to avoid biofilm formation is expanding quickly because of this spurred study. As a result, the current article addresses our current knowledge of how biofilms form, the mechanisms by which bacteria in biofilms resist antibiotics, and cutting-edge treatment approaches for infections caused by biofilms. Furthermore, we have showcased current ongoing research utilizing the CRISPR/Cas9 gene editing system to combat bacterial biofilm infections, particularly those brought on by lethal drug-resistant pathogens, concluded the article with a novel hypothesis and aspirations, and acknowledged certain limitations.

Mannose-Presenting "Glyco-Colicins" Convert the Bacterial Cell Surface into a Multivalent Adsorption Site for Adherent Bacteria

Biofilm formation is integral to the pathogenesis of numerous adherent bacteria and contributes to antimicrobial resistance (AMR). The rising threat of AMR means the need to develop novel nonbactericidal antiadhesion approaches against such bacteria is more urgent than ever. Both adherent-invasive Escherichia coli (AIEC, implicated in inflammatory bowel disease) and uropathogenic E. coli (UPEC, responsible for ∼80% of urinary tract infections) adhere to terminal mannose sugars on epithelial glycoproteins through the FimH adhesin on their type 1 pilus. Although mannose-based inhibitors have previously been explored to inhibit binding of adherent bacteria to epithelial cells, this approach has been limited by monovalent carbohydrate-protein interactions. Herein, we pioneer a novel approach to this problem through the preparation of colicin E9 bioconjugates that bind to the abundant BtuB receptor in the outer membrane of bacteria, which enables multivalent presentation of functional motifs on the cell surface. We show these bioconjugates label the surface of live E. coli and furthermore demonstrate that mannose-presenting "glyco-colicins" induce E. coli aggregation, thereby using the bacteria, itself, as a multivalent platform for mannose display, which triggers binding to adjacent FimH-presenting bacteria.

Design, synthesis, biological evaluation and docking study of some new aryl and heteroaryl thiomannosides as FimH antagonists

FimH is a mannose-recognizing lectin that is expressed by Escherichia coli guiding its ability to adhere and infect cells. It is involved in pathogenesis of urinary tract infections and Chron's disease. Several X-ray structure-guided ligand design studies were extensively utilized in the discovery and optimization of small molecule aryl mannoside FimH antagonists. These antagonists retain key specific interactions of the mannose scaffolds with the FimH carbohydrate recognition domains. Thiomannosides are attractive and stable scaffolds, and this work reports the synthesis of some of their new aryl and heteroaryl derivatives as FimH antagonists. FimH-competitive binding assays as well as biofilm inhibition of the new compounds (24-32) were determined in comparison with the reference n-heptyl α-d-mannopyranoside (HM). The affinity among these compounds was found to be governed by the structure of the aryl and heteroarylf aglycones. Two compounds 31 and 32 revealed higher activity than HM. Molecular docking and total hydrophobic to topological polar surface area ratio calculations attributed to explain the obtained biological results. Finally, the SAR study suggested that introducing an aryl or heteroaryl aglycone of sufficient hydrophobicity and of proper orientation within the tyrosine binding site considerably enhance binding affinity. The potent and synthetically feasible FimH antagonists described herein hold potential as leads for the development of sensors for detection of E. coli and treatment of its diseases.

Does size matter? - Comparing pyranoses with septanoses as ligands of the bacterial lectin FimH

The pharmacological modulation of disease-relevant carbohydrate-protein interactions represents an underexplored area of medicinal chemistry. One particular challenge in the design of glycomimetic compounds is the inherent instability of the glycosidic bond toward enzymatic cleavage. This problem has traditionally been approached by employing S-, N-, or C-glycosides with reduced susceptibility toward glycosidases. The application of ring-extended glycomimetics is an innovative approach to circumvent this issue. On the example of the bacterial adhesin FimH, it was explored how design principles from pyranose glycomimetics transfer to analogous septanose structures. A series of ring-extended FimH antagonists exhibiting the well-proven pharmacophore necessary for targeting the tyrosine-gate of FimH was synthesized. The resulting septanoses were evaluated for their affinity to the conformationally rigid isolated lectin domain of FimH (FimHLD), as well as a structurally flexible full-length FimH (FimHFL) construct. Some elements of potent mannoside-based FimH antagonists could be successfully transferred to septanose-based ligands, ultimately resulting in a 32-fold increase in binding affinity. Interestingly, the canonical ca. 100-fold loss of binding affinity between FimHLD and FimHFL is partly mitigated by the more flexible septanose antagonists, hinting at potentially differing interaction features of the flexible glycomimetics with intermediately populated states during the conformational transition of FimHFL.

Discovery of Orally Bioavailable FmlH Lectin Antagonists as Treatment for Urinary Tract Infections

FmlH, a bacterial adhesin of uropathogenic Escherichia coli (UPEC), has been shown to provide a fitness advantage in colonizing the bladder during chronic urinary tract infections (UTIs). Previously reported ortho-biphenyl glycosides based on βGal and βGalNAc have excellent binding affinity to FmlH and potently block binding to its natural carbohydrate receptor, but they lack oral bioavailability. In this paper, we outline studies where we have optimized compounds for improved pharmacokinetics, leading to the discovery of novel analogues with good oral bioavailability. We synthesized galactosides with the anomeric O-linker replaced with more stable S- and C-linked linkers. We also investigated modifications to the GalNAc sugar and modifications to the biphenyl aglycone. We identified GalNAc 69 with an IC50 of 0.19 μM against FmlH and 53% oral bioavailability in mice. We also obtained a FimlH-bound X-ray structure of lead compound 69 (AM4085) which has potential as a new antivirulence therapeutic for UTIs.

Target identification, and optimization of dioxygenated amide derivatives as potent antibacterial agents with FabH inhibitory activity

The enzyme FabH plays a critical role in the initial step of fatty acid biosynthesis, which is vital for the survival of bacteria. As a result, FabH has emerged as an appealing target for the development of novel antibacterial agents. In this study, employing the chemical proteomics method, we validated the previously identified skeleton amide derivatives bearing dioxygenated rings, potentially formed through metabolic processes. Building upon the proteomics findings, we then synthesized and evaluated 32 compounds containing N-heterocyclic amides for their antimicrobial activity for future optimizing the deoxygenated amides. Several compounds demonstrated potent antimicrobial properties with low toxicity, particularly compound 25, which exhibited remarkable potential as an agent with an MIC range of 1.25-3.13 μg/mL against the tested bacterial strains and an IC50 of 2.0 μM against E. coli-derived FabH. Furthermore, we evaluated nine analogues with relatively low MIC values through cytotoxicity and hemolytic activity assessments, Lipinski's rule-of-five criteria, and in silico ADMET predictions to ascertain their druggability potential. Notably, a detailed docking simulation was performed to investigate the binding interactions of compound 25 within the binding pocket of E. coli FabH, which encouragingly revealed strong binding interactions. Based on our findings, compound 25 emerges as the optimal candidate for in vivo therapy aimed at treating infected skin defects. Remarkably, the application of compound 25 demonstrated a significant reduction in the duration of wound infection and notably accelerated the healing process of infected wounds, achieving an impressive 94 % healing rate by day 10.

Click chemistry inspired facile one-pot synthesis of mannosyl triazoles and their hemagglutination inhibitory properties: The effect of alkyl chain spacer length between the triazole and phthalimide moieties in the aglycone backbone

An efficient one-pot synthesis of a new series of mannosyl triazoles has been achieved through CuAAC reaction where the alkyl chain spacer between the phthalimide moiety and the triazole ring in the aglycone backbone is varied from one methylene to six methylene units. The target compounds were evaluated in terms of their inhibitory potency against FimH using hemagglutination inhibition (HAI) assay. It was found that the length of four methylene units was the optimum for the fitting/binding of the compound to FimH as exemplified by compound 11 (HAI = 1.9 μM), which was approximately 200 times more potent than the reference ligand 1(HAI = 385 μM). The successful implementation of one-pot protocol with building blocks 1-7 and the architecture of ligand 11 will be the subject of our future work for developing more potent FimH inhibitors.

Identifying FmlH lectin-binding small molecules for the prevention of Escherichia coli-induced urinary tract infections using hybrid fragment-based design and molecular docking

Nearly 50% of women are affected by urinary tract infections (UTIs) during their lifetimes. The most common agent to cause UTIs is Uropathogenic Escherichia coli (UPEC). UPEC expresses fibers known as chaperone-usher pathway pili with adhesins that specifically bind to receptors as they colonize various host tissues. UPEC uses an F9/Yde/Fml pilus, tipped with FmlH, which interacts with terminal galactoside/galactosaminoside units in glycoproteins in the epithelial cells of the bladder and kidney. The extensive use of traditional antibiotics has led to the rise of various antibiotic-resistant strains of UPEC. An alternative therapeutic approach is to use an anti-adhesion strategy mediated by competitive tight-binding FmlH inhibitors. In the current study, we have applied various computational modeling techniques, including fragment-based e-pharmacophore virtual screening, molecular docking, molecular dynamics simulations and binding free energy calculations for the design of small molecules that exhibit binding to FmlH. Our modeling protocol successfully predicted ligand moieties, such as a thiazole group, which were previously found as components of UPEC adhesin pili inhibitors, thereby validating our designed screening protocol. The screening protocol developed here could be utilized for design of ligands for other homologous protein targets. We also identified several novel galactosaminoside-containing molecules that, according to the computational modeling, are predicted to interact strongly with FmlH and hence we predict will be good FmlH inhibitors. Additionally, we have prepared and supplied a database of ∼190K small molecules obtained from virtual screening, which can serve as an excellent resource for the discovery of novel FmlH inhibitors.

Glycomimetics for the inhibition and modulation of lectins

Carbohydrates are essential mediators of many processes in health and disease. They regulate self-/non-self- discrimination, are key elements of cellular communication, cancer, infection and inflammation, and determine protein folding, function and life-times. Moreover, they are integral to the cellular envelope for microorganisms and participate in biofilm formation. These diverse functions of carbohydrates are mediated by carbohydrate-binding proteins, lectins, and the more the knowledge about the biology of these proteins is advancing, the more interfering with carbohydrate recognition becomes a viable option for the development of novel therapeutics. In this respect, small molecules mimicking this recognition process become more and more available either as tools for fostering our basic understanding of glycobiology or as therapeutics. In this review, we outline the general design principles of glycomimetic inhibitors (Section 2). This section is then followed by highlighting three approaches to interfere with lectin function, i.e. with carbohydrate-derived glycomimetics (Section 3.1), novel glycomimetic scaffolds (Section 3.2) and allosteric modulators (Section 3.3). We summarize recent advances in design and application of glycomimetics for various classes of lectins of mammalian, viral and bacterial origin. Besides highlighting design principles in general, we showcase defined cases in which glycomimetics have been advanced to clinical trials or marketed. Additionally, emerging applications of glycomimetics for targeted protein degradation and targeted delivery purposes are reviewed in Section 4.

Emerging Non-Antibiotic Options Targeting Uropathogenic Mechanisms for Recurrent Uncomplicated Urinary Tract Infection

Urinary tract infections (UTIs) are the most frequent bacterial infections in the clinical setting. Even without underlying anatomic or functional abnormalities, more than 40% of women experience at least one UTI in their lifetime, of which 30% develop recurrent UTIs (rUTIs) within 6 months. Conventional management with antibiotics for rUTIs may eventually lead to the development of multidrug-resistant uropathogens. Targeting of the pathogenicity of rUTIs, the evolution of uropathogenic Escherichia coli (UPEC), and inadequate host defenses by immune responses should be explored to provide non-antibiotic solutions for the management of rUTIs. The adaptive evolution of UPEC has been observed in several aspects, including colonization, attachment, invasion, and intracellular replication to invade the urothelium and survive intracellularly. Focusing on the antivirulence of UPEC and modulating the immunity of susceptible persons, researchers have provided potential alternative solutions in four categories: antiadhesive treatments (i.e., cranberries and D-mannose), immunomodulation therapies, vaccines, and prophylaxis with topical estrogen therapy and probiotics (e.g., Lactobacillus species). Combination therapies targeting multiple pathogenic mechanisms are expected to be a future trend in UTI management, although some of these treatment options have not been well established in terms of their long-term efficacy. Additional clinical trials are warranted to validate the therapeutic efficacy and durability of these techniques.

Insightful Improvement in the Design of Potent Uropathogenic E. coli FimH Antagonists

Selective antiadhesion antagonists of Uropathogenic Escherichia coli (UPEC) type-1 Fimbrial adhesin (FimH) are attractive alternatives for antibiotic therapies and prophylaxes against acute or recurrent urinary tract infections (UTIs) caused by UPECs. A rational small library of FimH antagonists based on previously described C-linked allyl α-D-mannopyranoside was synthesized using Heck cross-coupling reaction using a series of iodoaryl derivatives. This work reports two new members of FimH antagonist amongst the above family with sub nanomolar affinity. The resulting hydrophobic aglycones, including constrained alkene and aryl groups, were designed to provide additional favorable binding interactions with the so-called FimH "tyrosine gate". The newly synthesized C-linked glycomimetic antagonists, having a hydrolytically stable anomeric linkage, exhibited improved binding when compared to previously published analogs, as demonstrated by affinity measurement through interactions by FimH lectin. The crystal structure of FimH co-crystallized with one of the nanomolar antagonists revealed the binding mode of this inhibitor into the active site of the tyrosine gate. In addition, selected mannopyranoside constructs neither affected bacterial growth or cell viability nor interfered with antibiotic activity. C-linked mannoside antagonists were effective in decreasing bacterial adhesion to human bladder epithelial cells (HTB-9). Therefore, these molecules constituted additional therapeutic candidates' worth further development in the search for potent anti-adhesive drugs against infections caused by UPEC.

Type 1 piliated uropathogenic Escherichia coli hijack the host immune response by binding to CD14

A key attribute of persistent or recurring bacterial infections is the ability of the pathogen to evade the host’s immune response. Many Enterobacteriaceae express type 1 pili, a pre-adapted virulence trait, to invade host epithelial cells and establish persistent infections. However, the molecular mechanisms and strategies by which bacteria actively circumvent the immune response of the host remain poorly understood. Here, we identified CD14, the major co-receptor for lipopolysaccharide detection, on mouse dendritic cells (DCs) as a binding partner of FimH, the protein located at the tip of the type 1 pilus of Escherichia coli. The FimH amino acids involved in CD14 binding are highly conserved across pathogenic and non-pathogenic strains. Binding of the pathogenic strain CFT073 to CD14 reduced DC migration by overactivation of integrins and blunted expression of co-stimulatory molecules by overactivating the NFAT (nuclear factor of activated T-cells) pathway, both rate-limiting factors of T cell activation. This response was binary at the single-cell level, but averaged in larger populations exposed to both piliated and non-piliated pathogens, presumably via the exchange of immunomodulatory cytokines. While defining an active molecular mechanism of immune evasion by pathogens, the interaction between FimH and CD14 represents a potential target to interfere with persistent and recurrent infections, such as urinary tract infections or Crohn’s disease.

The Association between Biofilm Formation and Antimicrobial Resistance with Possible Ingenious Bio-Remedial Approaches

Biofilm has garnered a lot of interest due to concerns in various sectors such as public health, medicine, and the pharmaceutical industry. Biofilm-producing bacteria show a remarkable drug resistance capability, leading to an increase in morbidity and mortality. This results in enormous economic pressure on the healthcare sector. The development of biofilms is a complex phenomenon governed by multiple factors. Several attempts have been made to unravel the events of biofilm formation; and, such efforts have provided insights into the mechanisms to target for the therapy. Owing to the fact that the biofilm-state makes the bacterial pathogens significantly resistant to antibiotics, targeting pathogens within biofilm is indeed a lucrative prospect. The available drugs can be repurposed to eradicate the pathogen, and as a result, ease the antimicrobial treatment burden. Biofilm formers and their infections have also been found in plants, livestock, and humans. The advent of novel strategies such as bioinformatics tools in treating, as well as preventing, biofilm formation has gained a great deal of attention. Development of newfangled anti-biofilm agents, such as silver nanoparticles, may be accomplished through omics approaches such as transcriptomics, metabolomics, and proteomics. Nanoparticles’ anti-biofilm properties could help to reduce antimicrobial resistance (AMR). This approach may also be integrated for a better understanding of biofilm biology, guided by mechanistic understanding, virtual screening, and machine learning in silico techniques for discovering small molecules in order to inhibit key biofilm regulators. This stimulated research is a rapidly growing field for applicable control measures to prevent biofilm formation. Therefore, the current article discusses the current understanding of biofilm formation, antibiotic resistance mechanisms in bacterial biofilm, and the novel therapeutic strategies to combat biofilm-mediated infections.

Small Carbohydrate Derivatives as Potent Antibiofilm Agents

Biofilm formation by most pathogenic bacteria is considered as one of the key mechanisms associated with virulence and antibiotic resistance. Biofilm-forming bacteria adhere to the surfaces of biological or implant medical devices and create communities within their self-produced extracellular matrix that are difficult to treat by existing antibiotics. There is an urgent need to synthesize and screen structurally diverse molecules for their antibiofilm activity that can remove or minimize the bacterial biofilm. The development of carbohydrate-based small molecules as antibiofilm agents holds a great promise in addressing the problem of the eradication of biofilm-related infections. Owing to their structural diversity and specificity, the sugar scaffolds are valuable entities for developing antibiofilm agents. In this perspective, we discuss the literature pertaining to carbohydrate-based natural antibiofilm agents and provide an overview of the design, activity, and mode of action of potent synthetic carbohydrate-based molecules.

Small molecules as next generation biofilm inhibitors and anti-infective agents

Biofilms are consortia of microbes attached to surfaces that could be biotic or abiotic in nature. The bacterial cells are enclosed within a microbial synthesized extrapolymeric substances (EPS). The presence of a thick EPS matrix around the cells, protects it from antimicrobials. As the biofilms are difficult to be eradicated in the tissues and implants, the infections due to biofilms are chronic, persistent as well as recurrent in nature. Biofilm formation in multidrug resistant pathogens is a major public health concern. In this review, we have discussed traditional drug discovery approaches and high throughput screening assays involved in the discovery of small molecules for their application as biofilm inhibitory agents. The small molecules target different phases of biofilm growth in pathogenic bacteria. Here, we have focused on three specific application of small molecules, as anti-adhesion agents that prevent adherence and attachment of cells to surfaces; signal inhibitors that disrupt communication between cells resulting in hampered biofilm growth and development; and finally as agents that induce release of cells from mature biofilms. Some of the biofilm inhibitors have also potentiated the antibiotic efficacy leading to complete eradication of biofilms. It is highly pertinent now to focus on developing these as therapeutics and anti-biofilm agents for coating medical implants and devices in clinical settings.

Role of D-mannose in urinary tract infections - a narrative review

Urinary tract infections (UTIs) are one of the most prevalent bacterial diseases worldwide. Despite the efficacy of antibiotics targeted against UTI, the recurrence rates remain significant among the patients. Furthermore, the development of antibiotic resistance is a major concern and creates a demand for alternative treatment options. D-mannose, a monosaccharide naturally found in fruits, is commonly marketed as a dietary supplement for reducing the risk for UTIs. Research suggests that supplemented D-mannose could be a promising alternative or complementary remedy especially as a prophylaxis for recurrent UTIs. When excreted in urine, D-mannose potentially inhibits Escherichia coli, the main causative organism of UTIs, from attaching to urothelium and causing infection. In this review, we provide an overview of UTIs, E. coli pathogenesis and D-mannose and outline the existing clinical evidence of D-mannose in reducing the risk of UTI and its recurrence. Furthermore, we discuss the potential effect mechanisms of D-mannose against uropathogenic E.coli.

Combatting persisted and biofilm antimicrobial resistant bacterial by using nanoparticles

Some bacteria can withstand the existence of an antibiotic without undergoing any genetic changes. They are neither cysts nor spores and are one of the causes of disease recurrence, accounting for about 1% of the biofilm. There are numerous approaches to eradication and combating biofilm-forming organisms. Nanotechnology is one of them, and it has shown promising results against persister cells. In the review, we go over the persister cell and biofilm in extensive detail. This includes the biofilm formation cycle, antibiotic resistance, and treatment with various nanoparticles. Furthermore, the gene-level mechanism of persister cell formation and its therapeutic interventions with nanoparticles were discussed.

Targeting the BspC-vimentin interaction to develop anti-virulence therapies during Group B streptococcal meningitis

Bacterial infections are a major cause of morbidity and mortality worldwide and the rise of antibiotic resistance necessitates development of alternative treatments. Pathogen adhesins that bind to host cells initiate disease pathogenesis and represent potential therapeutic targets. We have shown previously that the BspC adhesin in Group B Streptococcus (GBS), the leading cause of bacterial neonatal meningitis, interacts with host vimentin to promote attachment to brain endothelium and disease development. Here we determined that the BspC variable (V-) domain contains the vimentin binding site and promotes GBS adherence to brain endothelium. Site directed mutagenesis identified a binding pocket necessary for GBS host cell interaction and development of meningitis. Using a virtual structure-based drug screen we identified compounds that targeted the V-domain binding pocket, which blocked GBS adherence and entry into the brain in vivo. These data indicate the utility of targeting the pathogen-host interface to develop anti-virulence therapeutics.

A Biomimetic Nonantibiotic Nanoplatform for Low-Temperature Photothermal Treatment of Urinary Tract Infections Caused by Uropathogenic Escherichia coli

Urinary tract infections (UTIs) caused by uropathogenic Escherichia coli (UPEC) remain a matter of concern, as the clinical use of multiple antibiotics induces antibiotic resistance in bacteria, resulting in the failure of treatments. Despite the emergence of anti-adhesion strategies that can prevent the development of bacterial drug resistance, these strategies are mainly used for disease prevention rather than effective treatment. Photothermal therapy (PTT) has emerged as an efficient alternative for the elimination of bacteria. Nevertheless, high local temperatures related to PTT probably cause damage to surrounding healthy tissue. Herein, a biomimetic nonantibiotic nanoplatform for low-temperature photothermal treatment of UTIs is developed. The nanoplatform comprises polydopamine (PDA) photothermal core and biphenyl mannoside (Man) shell with multivalent high-affinity to UPEC. Scanning electron microscope (SEM) shows PDA-Man possessed ultra-strong targeting binding ability toward UPEC. It is the fact that this impulse UPEC to form a large bacterial cluster. Consequently, the high photothermal energy of the PDA-Man appears predominantly in the affected bacterial area, while the overall environment remains at a low temperature. The fabricated nanoplatform shows excellent photothermal bactericidal effects, approximately 100% in a UTI model. Overall, this low-temperature photothermal nanoplatform provides an appropriate strategy for the elimination of bacteria in clinical applications.

Exploring Anticancer Activities and Structure-Activity Relationships of Binuclear Oxidovanadium(IV) Complexes

Dimeric mixed-ligand oxidovanadium complexes [V₂O₂(1,3-pdta)(bpy)₂]·9H₂O (1) and [V₂O₂(1,3-pdta)(phen)₂]·6H₂O (2) feature a symmetric binuclear structure bridged by 1,3-pdta, which is different from our previous reported asymmetric binuclear complex [V₂O₂(edta)(phen)₂]·11H₂O (3).In this study, a wide range of analytical techniques were carried out to fully characterize the complexes 1 and 2 and further investigate their structural stabilities. Density functional theory calculations of 1 and 2 also suggest that they might have good reactivity with biomolecules as anticancer agents. To assess and screen the antitumor activities of compounds 1-3 together with their four corresponding monomeric complexes [VO(ida)(phen)], [VO(ida)(bpy)], [VO(OH)(phen)₂]Cl, and [VO(Hedta)]^-, we have performed in vitro experiments with hepatocellular carcinoma HepG2 and SMMC-7721 cell lines by MTT analyses. Complex 2 was found to have the highest inhibitory potency against the growth of HepG2 and SMMC-7721 cells (IC₅₀ = 2.07 ± 0.72 μM for HepG2; 13.00 ± 3.06 μM for SMMC-7721) compared to other compounds. The structure-activity relationship studies showed that the antitumor effect of compound 2 is higher than that of other compounds. After studying the monomeric compounds of 1-3, their effects were also ranked. Moreover, complex 2 displayed stronger binding affinity toward calf thymus DNA (K_b = 5.71 × 10⁴ M^-1) and cleavage activities than the other complexes (K_b = 1.34 × 10⁴ M^-1 for 1 and 5.22 × 10⁴ M^-1 for 3, respectively). We further extended the cellular mechanisms of drug action and found that 2 could block DNA synthesis and cell division of HepG2 and 7721 cells and further induce apoptosis by flow cytometry assays. In short, these results indicate that binuclear oxidovanadium compounds could have potential as simple, effective, and safe antitumor agents.

Fast Identification and Quantification of Uropathogenic E. coli through Cluster Analysis

Rapid diagnostic tools to detect, identify, and enumerate bacteria are key to maintaining effective antibiotic stewardship and avoiding the unnecessary prescription of broad-spectrum agents. In this study, a 15 min agglutination assay is developed that relies on the use of mannose-functionalized polymeric microspheres in combination with cluster analysis. This allows for the identification and enumeration of laboratory (BW25113), clinical isolate (NCTC 12241), and uropathogenic Escherichia coli strains (NCTC 9001, NCTC 13958, J96, and CFT073) at clinically relevant concentrations in tryptic soy broth (10³-10⁸ CFU/mL) and in urine (10⁵-10⁸ CFU/mL). This fast, simple, and efficient assay offers a step forward toward efficient point-of-care diagnostics for common urinary tract infections.

Molecular basis for inhibition of adhesin-mediated bacterial-host interactions through a peptide-binding domain

Infections typically begin with pathogens adhering to host cells. For bacteria, this adhesion can occur through specific ligand-binding domains. We identify a 20-kDa peptide-binding domain (PBD) in a 1.5-MDa RTX adhesin of a Gram-negative marine bacterium that colonizes diatoms. The crystal structure of this Ca²⁺-dependent PBD suggests that it may bind the C termini of host cell-surface proteins. A systematic peptide library analysis reveals an optimal tripeptide sequence with 30-nM affinity for the PBD, and X-ray crystallography details its peptide-protein interactions. Binding of the PBD to the diatom partner of the bacteria can be inhibited or competed away by the peptide, providing a molecular basis for inhibiting bacterium-host interactions. We further show that this PBD is found in other bacteria, including human pathogens such as Vibrio cholerae and Aeromonas veronii. Here, we produce the PBD ortholog from A. veronii and demonstrate, using the same peptide inhibitor, how pathogens may be prevented from adhering to their hosts.

α-d-Mannoside ligands with a valency ranging from one to three: Synthesis and hemagglutination inhibitory properties

Six mono-, di-, and trivalent α-d-mannopyranosyl conjugates built on aromatic scaffolds were synthesized in excellent yields by Cu(I) catalyzed azide-alkyne cycloaddition reaction (CuAAC). These conjugates were designed to have unique, flexible tails that combine a mid-tail triazole ring, to interact with the tyrosine gate, with a terminal phenyl group armed with benzylic hydroxyl groups to avoid solubility problems as well as to provide options to connect to other supports. Biological evaluation of the prepared conjugates in hemagglutination inhibition (HAI) assay revealed that potency increases with valency and the trivalent ligand 6d (HAI = 0.005 mM) is approximately sevenfold better than the best meta-oriented monovalent analogues 2d and 4d (HAI ≈ 0.033 mM) and so may serve as a good starting point to find new lead ligands.

D-Mannoside FimH Inhibitors as Non-Antibiotic Alternatives for Uropathogenic Escherichia coli

FimH is a type I fimbria of uropathogenic Escherichia coli (UPEC), recognized for its ability to adhere and infect epithelial urinary tissue. Due to its role in the virulence of UPEC, several therapeutic strategies have focused on the study of FimH, including vaccines, mannosides, and molecules that inhibit their assembly. This work has focused on the ability of a set of monosubstituted and disubstituted phenyl mannosides to inhibit FimH. To determine the 3D structure of FimH for our in silico studies, we obtained fifteen sequences by PCR amplification of the fimH gene from 102 UPEC isolates. The fimH sequences in BLAST had a high homology (97–100%) to our UPEC fimH sequences. A search for the three-dimensional crystallographic structure of FimH proteins in the PDB server showed that proteins 4X5P and 4XO9 were found in 10 of the 15 isolates, presenting a 67% influx among our UPEC isolates. We focused on these two proteins to study the stability, free energy, and the interactions with different mannoside ligands. We found that the interactions with the residues of aspartic acid (ASP 54) and glutamine (GLN 133) were significant to the binding stability. The ligands assessed demonstrated high binding affinity and stability with the lectin domain of FimH proteins during the molecular dynamic simulations, based on MM-PBSA analysis. Therefore, our results suggest the potential utility of phenyl mannoside derivatives as FimH inhibitors to mitigate urinary tract infections produced by UPEC; thus, decreasing colonization, disease burden, and the costs of medical care.

Exploiting pilus-mediated bacteria-host interactions for health benefits

Surface pili (or fimbriae) are an important but conspicuous adaptation of several genera and species of Gram-negative and Gram-positive bacteria. These long and non-flagellar multi-subunit adhesins mediate the initial contact that a bacterium has with a host or environment, and thus have come to be regarded as a key colonization factor for virulence activity in pathogens or niche adaptation in commensals. Pili in pathogenic bacteria are well recognized for their roles in the adhesion to host cells, colonization of tissues, and establishment of infection. As an 'anti-adhesive' ploy, targeting pilus-mediated attachment for disruption has become a potentially effective alternative to using antibiotics. In this review, we give a description of the several structurally distinct bacterial pilus types thus far characterized, and as well offer details about the intricacy of their individual structure, assembly, and function. With a molecular understanding of pilus biogenesis and pilus-mediated host interactions also provided, we go on to describe some of the emerging new approaches and compounds that have been recently developed to prevent the adhesion, colonization, and infection of piliated bacterial pathogens.

Novel Strategies to Combat Bacterial Biofilms

Biofilms are considered as a severe problem in the treatment of bacterial infections; their development causes some noticeable resistance to antibacterial agents. Biofilms are responsible for at least two-thirds of all infections, displaying promoted resistance to classical antibiotic treatments. Therefore, finding new alternative therapeutic approaches is essential for the treatment and inhibition of biofilm-related infections. Therefore, this review aims to describe the potential therapeutic strategies that can inhibit bacterial biofilm development; these include the usage of antiadhesion agents, AMPs, bacteriophages, QSIs, aptamers, NPs and PNAs, which can prevent or eradicate the formation of biofilms. These antibiofilm agents represent a promising therapeutic target in the treatment of biofilm infections and development of a strong capability to interfere with different phases of the biofilm development, including adherence, polysaccharide intercellular adhesion (PIA), quorum sensing molecules and cell-to-cell connection, bacterial aggregation, planktonic bacteria killing and host-immune response modulation. In addition, these components, in combination with antibiotics, can lead to the development of some kind of powerful combined therapy against bacterial biofilm-related infections.

Recent development in the design of small 'drug-like' and nanoscale glycomimetics against Escherichia coli infections

Glycoconjugates are involved in several pathological processes. Glycomimetics that can favorably emulate complex carbohydrate structures, while competing with natural ligands as inhibitors, are gaining considerable attention owing to their improved hydrolytic stability, binding affinity, and pharmacokinetic (PK) properties. Of particular interest are the families of α-d-mannopyranoside analogs, which can be used as inhibitors against adherent invasive Escherichia coli infections. Bacterial resistance to modern antibiotics triggers the search for new alternative antibacterial strategies that are less susceptible to acquiring resistance. In this review, we highlight recent progress in the chemical syntheses of this family of compounds, one of which having reached clinical trials against Crohn's disease (CD).

Discovery of Bacterial Fimbria-Glycan Interactions Using Whole-Cell Recombinant Escherichia coli Expression

Chaperone-usher (CU) fimbriae are the most abundant Gram-negative bacterial fimbriae, with 38 distinct CU fimbria types described in Escherichia coli alone. Some E. coli CU fimbriae have been well characterized and bind to specific glycan targets to confer tissue tropism. For example, type 1 fimbriae bind to α-d-mannosylated glycoproteins such as uroplakins in the bladder via their tip-located FimH adhesin, leading to colonization and invasion of the bladder epithelium. Despite this, the receptor-binding affinity of many other E. coli CU fimbria types remains poorly characterized. Here, we used a recombinant E. coli strain expressing different CU fimbriae, in conjunction with glycan array analysis comprising >300 glycans, to dissect CU fimbria receptor specificity. We initially validated the approach by demonstrating the purified FimH lectin-binding domain and recombinant E. coli expressing type 1 fimbriae bound to a similar set of glycans. This technique was then used to map the glycan binding affinity of six additional CU fimbriae, namely, P, F1C, Yqi, Mat/Ecp, K88, and K99 fimbriae. The binding affinity was determined using whole-bacterial-cell surface plasmon resonance. This work describes new information in fimbrial specificity and a rapid and scalable system to define novel adhesin-glycan interactions that underpin bacterial colonization and disease.

Developments in Mannose-Based Treatments for Uropathogenic Escherichia coli-Induced Urinary Tract Infections

During their lifetime almost half of women will experience a symptomatic urinary tract infection (UTI) with a further half experiencing a relapse within six months. Currently UTIs are treated with antibiotics, but increasing antibiotic resistance rates highlight the need for new treatments. Uropathogenic Escherichia coli (UPEC) is responsible for the majority of symptomatic UTI cases and thus has become a key pathological target. Adhesion of type one pilus subunit FimH at the surface of UPEC strains to mannose-saturated oligosaccharides located on the urothelium is critical to pathogenesis. Since the identification of FimH as a therapeutic target in the late 1980s, a substantial body of research has been generated focusing on the development of FimH-targeting mannose-based anti-adhesion therapies. In this review we will discuss the design of different classes of these mannose-based compounds and their utility and potential as UPEC therapeutics.

Novel approaches to glycomimetic design: development of small molecular weight lectin antagonists

Introduction: The direct binding of carbohydrates or those presented on glycoproteins or glycolipids to proteins is the primary effector of many biological responses. One class of carbohydrate-binding proteins, lectins are important in all forms of life. Their functions in animals include regulating cell adhesion, glycoprotein synthesis, metabolism, and mediating immune system response while in bacteria and viruses a lectin-mediated carbohydrate-protein interaction between host cells and the pathogen initiates pathogenesis of the infection.Areas covered: In this review, the authors outline the structural and functional pathogenesis of lectins from bacteria, amoeba, and humans. Mimics of a carbohydrate are referred to as glycomimetics, which are much smaller in molecular weight and are devised to mimic the key binding interactions of the carbohydrate while also allowing additional contacts with the lectin. This article emphasizes the various approaches used over the past 10-15 years in the rational design of glycomimetic ligands.Expert opinion: Medicinal chemistry efforts enabled by X-ray structural biology have identified small-molecule glycomimetic lectin antagonists that have entered or are nearing clinical trials. A common theme in these strategies is the use of biaryl ring systems to emulate the carbohydrate interactions with the lectin.

Does targeting Arg98 of FimH lead to high affinity antagonists?

Bacterial resistance has become an important challenge in the treatment of urinary tract infections. The underlying resistance mechanisms can most likely be circumvented with an antiadhesive approach, antagonizing the lectin FimH located at the tip of fimbriae of uropathogenic E. coli. Here we report on a novel series of FimH antagonists based on the 1-(α-d-mannopyranosyl)-4-phenyl-1,2,3-triazole scaffold, designed to incorporate carboxylic acid or ester functions to interact with FimH Arg98. The most potent representative of the series, ester 11e, displayed a K_d value of 7.6 nM for the lectin domain of FimH with a general conclusion that all esters outperform carboxylates in terms of affinity. Surprisingly, all compounds from this new series exhibited improved binding affinities also for the R98A mutant, indicating another possible interaction contributing to binding. Our study on 1-(α-d-mannopyranosyl)-4-phenyl-1,2,3-triazole-based FimH antagonists offers proof that targeting Arg98 side chain by a "chemical common sense", i.e. by introduction of the acidic moiety to form ionic bond with Arg98 is most likely unsuitable approach to boost FimH antagonists' potency.

Targeting Biofilms Therapy: Current Research Strategies and Development Hurdles

Biofilms are aggregate of microorganisms in which cells are frequently embedded within a self-produced matrix of extracellular polymeric substance (EPS) and adhere to each other and/or to a surface. The development of biofilm affords pathogens significantly increased tolerances to antibiotics and antimicrobials. Up to 80% of human bacterial infections are biofilm-associated. Dispersal of biofilms can turn microbial cells into their more vulnerable planktonic phenotype and improve the therapeutic effect of antimicrobials. In this review, we focus on multiple therapeutic strategies that are currently being developed to target important structural and functional characteristics and drug resistance mechanisms of biofilms. We thoroughly discuss the current biofilm targeting strategies from four major aspects—targeting EPS, dispersal molecules, targeting quorum sensing, and targeting dormant cells. We explain each aspect with examples and discuss the main hurdles in the development of biofilm dispersal agents in order to provide a rationale for multi-targeted therapy strategies that target the complicated biofilms. Biofilm dispersal is a promising research direction to treat biofilm-associated infections in the future, and more in vivo experiments should be performed to ensure the efficacy of these therapeutic agents before being used in clinic.

Reciprocal Cooperation of Type A Procyanidin and Nitrofurantoin Against Multi-Drug Resistant (MDR) UPEC: A pH-Dependent Study

Uropathogenic Escherichia coli (UPEC) accounts for the majority of complicated and uncomplicated urinary tract infections. The use of phytomolecules in the treatment of UTI is fast gaining attention. The current report identifies a multidrug-resistant strain (QSLUPEC7), which is a strong biofilm producer, among the considered clinical isolates. The antimicrobial and antibiofilm activity was evaluated for the phytomolecule, Type A procyanidin (TAP) from Cinnamomum zeylanicum against QSLUPEC7. TAP treatment did not affect the growth of the MDR strain but affected the biofilm formation (~70% inhibition). The confocal microscopic examination reveals the biofilm inhibition and the live cells in the biofilm corroborates the antimicrobial results. Further, the synergy studies of TAP and nitrofurantoin (NIT) were carried out at different pH. TAP acts synergistically with nitrofurantoin at different pH considered. A closer look in the results reveals that at pH 5.8, maximum growth inhibition is recorded. The gene expression analysis shows that TAP alone and in combination with NIT downregulates the major fimbriae adhesins of UPEC. The results conclude that the TAP has an antibiofilm activity against the multidrug-resistant strain of UPEC, without affecting the growth. Also, TAP reciprocally cooperates with nitrofurantoin at different pH by downregulating the adhesins of UPEC.

FimH and Anti-Adhesive Therapeutics: A Disarming Strategy Against Uropathogens

Chaperone-usher fimbrial adhesins are powerful weapons against the uropathogens that allow the establishment of urinary tract infections (UTIs). As the antibiotic therapeutic strategy has become less effective in the treatment of uropathogen-related UTIs, the anti-adhesive molecules active against fimbrial adhesins, key determinants of urovirulence, are attractive alternatives. The best-characterized bacterial adhesin is FimH, produced by uropathogenic Escherichia coli (UPEC). Hence, a number of high-affinity mono- and polyvalent mannose-based FimH antagonists, characterized by different bioavailabilities, have been reported. Given that antagonist affinities are firmly associated with the functional heterogeneities of different FimH variants, several FimH inhibitors have been developed using ligand-drug discovery strategies to generate high-affinity molecules for successful anti-adhesion therapy. As clinical trials have shown d-mannose's efficacy in UTIs prevention, it is supposed that mannosides could be a first-in-class strategy not only for UTIs, but also to combat other Gram-negative bacterial infections. Therefore, the current review discusses valuable and effective FimH anti-adhesive molecules active against UTIs, from design and synthesis to in vitro and in vivo evaluations.

Ortho-Substituted α-Phenyl Mannoside Derivatives Promoted Early-Stage Adhesion and Biofilm Formation of E. coli 83972

Prevention of catheter-associated urinary tract infection (CAUTI) over long-term usage of urinary catheters remains a great challenge. Bacterial interference using nonpathogenic bacteria, such as E. coli 83972, have been investigated in many pilot-scale clinical studies as a potentially nonantibiotic based strategy for CAUTI prevention. We have demonstrated that preforming a dense and stable biofilm of the nonpathogenic E. coli greatly enhances their capability to prevent pathogen colonization. Such nonpathogenic biofilms were formed by E. coli 83972 expressing type 1 fimbriae (fim+ E. coli 83972) on mannoside-presenting surfaces. In this work, we report the synthesis of a series of mannoside derivatives with a wide range of binding affinities, all being equipped with a handle for covalent attachment to silicone surfaces. We established a high-throughput competitive assay based on mannoside-modified particles and flow-cytometry to directly measure the binding affinity between the mannoside ligands and fim+ E. coli 83972. We demonstrated that the bacterial adhesion and biofilm formation were strongly correlated to the binding affinity of the immobilized mannoside ligands. Mass spectrometry based proteomic analysis indicated a substantial difference in the proteome of the extracellular polymeric substance (EPS) secreted by biofilms on different mannoside surfaces, which might be related to the biofilm stability.

Deposition of Host Matrix Proteins on Breast Implant Surfaces Facilitates Staphylococcus Epidermidis Biofilm Formation: In Vitro Analysis

BACKGROUND

Staphylococcus epidermidis is a primary cause of breast implant-associated infection. S epidermidis possesses several virulence factors that enable it to bind both abiotic surfaces and host factors to form a biofilm. In addition S epidermidis colocalizes with matrix proteins coating explanted human breast implants.

OBJECTIVES

The authors sought to identify matrix proteins that S epidermidis may exploit to infect various breast implant surfaces in vitro.

METHODS

A combination of in vitro assays was used to characterize S epidermidis strains isolated from human breast implants to gain a better understanding of how these bacteria colonize breast implant surfaces. These included determining the (1) minimum inhibitory and bactericidal concentrations for irrigation solutions commonly used to prevent breast implant contamination; (2) expression and carriage of polysaccharide intercellular adhesin and serine-aspartate repeat proteins, which bind fibrinogen (SdrG) and collagen (SdrF), respectively; and (3) biofilm formation on varying implant surface characteristics, in different growth media, and supplemented with fibrinogen and Types I and III collagen. Scanning electron microscopy and immunofluorescence staining analyses were performed to corroborate findings from these assays.

RESULTS

Textured breast implant surfaces support greater bacterial biofilm formation at baseline, and the addition of collagen significantly increases biomass on all surfaces tested. We found that S epidermidis isolated from breast implants all encoded SdrF. Consistent with this finding, these strains had a clear affinity for Type I collagen, forming dense, highly structured biofilms in its presence.

CONCLUSIONS

The authors found that S epidermidis may utilize SdrF to interact with Type I collagen to form biofilm on breast implant surfaces.

LEVEL OF EVIDENCE: 5

Interaction with the host: the role of fibronectin and extracellular matrix proteins in the adhesion of Gram-negative bacteria

The capacity of pathogenic microorganisms to adhere to host cells and avoid clearance by the host immune system is the initial and most decisive step leading to infections. Bacteria have developed different strategies to attach to diverse host surface structures. One important strategy is the adhesion to extracellular matrix (ECM) proteins (e.g., collagen, fibronectin, laminin) that are highly abundant in connective tissue and basement membranes. Gram-negative bacteria express variable outer membrane proteins (adhesins) to attach to the host and to initiate the process of infection. Understanding the underlying molecular mechanisms of bacterial adhesion is a prerequisite for targeting this interaction by “anti-ligands” to prevent colonization or infection of the host. Future development of such “anti-ligands” (specifically interfering with bacteria-host matrix interactions) might result in the development of a new class of anti-infective drugs for the therapy of infections caused by multidrug-resistant Gram-negative bacteria. This review summarizes our current knowledge about the manifold interactions of adhesins expressed by Gram-negative bacteria with ECM proteins and the use of this information for the generation of novel therapeutic antivirulence strategies.

Dispersal and inhibition of biofilms associated with infections

As bacteria aggregate and form biofilms on surfaces in the human body such as tissues, indwelling medical devices, dressings and implants, they can cause a significant health risk. Bacterial biofilms possess altered phenotypes: physical features that facilitate antibiotic resistance and evasion of the host immune response. Since metabolic and physical factors contribute to biofilm maturation and persistence, an objective in antibiofilm therapy is to target these factors to deliver innovative approaches for solving these important health problems. Currently, there is little research on the direct immunological effects resulting from the introduction of foreign components to the body pertaining to biofilm inhibition methods. Detailed research involving animal models is necessary to better understand the biological side effects of synthetic peptides, genetically modified bacteriophages and isolated proteins and any resistance that may develop from these approaches.

RMSD analysis of structures of the bacterial protein FimH identifies five conformations of its lectin domain

FimH is a bacterial adhesin protein located at the tip of Escherichia coli fimbria that functions to adhere bacteria to host cells. Thus, FimH is a critical factor in bacterial infections such as urinary tract infections and is of interest in drug development. It is also involved in vaccine development and as a model for understanding shear-enhanced catch bond cell adhesion. To date, over 60 structures have been deposited in the Protein Data Bank showing interactions between FimH and mannose ligands, potential inhibitors, and other fimbrial proteins. In addition to providing insights about ligand recognition and fimbrial assembly, these structures provide insights into conformational changes in the two domains of FimH that are critical for its function. To gain further insights into these structural changes, we have superposed FimH's mannose binding lectin domain in all these structures and categorized the structures into five groups of lectin domain conformers using RMSD as a metric. Many structures also include the pilin domain, which anchors FimH to the fimbriae and regulates the conformation and function of the lectin domain. For these structures, we have also compared the relative orientations of the two domains. These structural analyses enhance our understanding of the conformational changes associated with FimH ligand binding and domain-domain interactions, including its catch bond behavior through allosteric action of force in bacterial adhesion.

Small Molecule Anti-biofilm Agents Developed on the Basis of Mechanistic Understanding of Biofilm Formation

Microbial biofilms are the cause of persistent infections associated with various medical implants and distinct body sites such as the urinary tract, lungs, and wounds. Compared with their free living counterparts, bacteria in biofilms display a highly increased resistance to immune system activities and antibiotic treatment. Therefore, biofilm infections are difficult or impossible to treat with our current armory of antibiotics. The challenges associated with biofilm infections have urged researchers to pursue a better understanding of the molecular mechanisms that are involved in the formation and dispersal of biofilms, and this has led to the identification of several steps that could be targeted in order to eradicate these challenging infections. Here we describe mechanisms that are involved in the regulation of biofilm development in Pseudomonas aeruginosa, Escherichia coli, and Acinetobacter baumannii, and provide examples of chemical compounds that have been developed to specifically inhibit these processes. These compounds include (i) pilicides and curlicides which inhibit the initial steps of biofilm formation by E. coli; (ii) compounds that interfere with c-di-GMP signaling in P. aeruginosa and E. coli; and (iii) compounds that inhibit quorum-sensing in P. aeruginosa and A. baumannii. In cases where compound series have a defined molecular target, we focus on elucidating structure activity relationship (SAR) trends within the particular compound series.

Disperse red 15 (DR15) impedes biofilm formation of uropathogenic Escherichia coli

Catheter associated urinary tract infection (CAUTI) is a highly prevalent hospital-acquired infection that is predominantly caused by uropathogenic Escherichia coli (UPEC). It adheres on catheter surface using type I pili as the initial step of pathogenesis that progresses to form biofilm. In this study, potential inhibitors against FimH adhesin of type I pili were screened computationally that yielded ten compounds. These were further validated in vitro against adhesion and biofilm formation. The compounds, 1-Amino-4-hydroxyanthraquinone (Disperse Red 15 or DR15) and 4-(4'-chloro-4-biphenylylsulfonylamino) benzoic acid (CB1) impaired adhesion and biofilm formation without inhibiting the planktonic growth. Also, both compounds inhibited cell assemblages like autoaggregation and swarming motility by unknown mechanisms. DR15 was further derivatised into N-(4-hydroxy-9,10-dioxo-9,10-dihydroanthracen-1-yl) undec-10-enamide that self-assembled with linseed oil, which was used as the coating material on urinary Foley catheters. The thin-film coating on the catheter did not leach when incubated in artificial urine and effectively restricted biofilm formation of UPEC. Altogether, the thin-film coating of urinary catheter with DR15 inhibited biofilm formation of UPEC and this application could potentially help to reduce CAUTI incidents in healthcare facilities.

Comparative Study of Aryl O-, C-, and S-Mannopyranosides as Potential Adhesion Inhibitors toward Uropathogenic E. coli FimH

A set of three mannopyranoside possessing identical 1,1'-biphenyl glycosidic pharmacophore but different aglyconic atoms were synthesized using either a palladium-catalyzed Heck cross coupling reaction or a metathesis reaction between their corresponding allylic glycoside derivatives. Their X-ray structures, together with their calculated 3D structures, showed strong indicators to explain the observed relative binding abilities against E. coli FimH as measured by a improved surface plasmon resonance (SPR) method. Amongst the O-, C-, and S-linked analogs, the C-linked analog showed the best ability to become a lead candidate as antagonist against uropathogenic E. coli with a Kd of 11.45 nM.

Bioisosteres of Carbohydrate Functional Groups in Glycomimetic Design

The aberrant presentation of carbohydrates has been linked to a number of diseases, such as cancer metastasis and immune dysregulation. These altered glycan structures represent a target for novel therapies by modulating their associated interactions with neighboring cells and molecules. Although these interactions are highly specific, native carbohydrates are characterized by very low affinities and inherently poor pharmacokinetic properties. Glycomimetic compounds, which mimic the structure and function of native glycans, have been successful in producing molecules with improved pharmacokinetic (PK) and pharmacodynamic (PD) features. Several strategies have been developed for glycomimetic design such as ligand pre-organization or reducing polar surface area. A related approach to developing glycomimetics relies on the bioisosteric replacement of carbohydrate functional groups. These changes can offer improvements to both binding affinity (e.g., reduced desolvation costs, enhanced metal chelation) and pharmacokinetic parameters (e.g., improved oral bioavailability). Several examples of bioisosteric modifications to carbohydrates have been reported; this review aims to consolidate them and presents different possibilities for enhancing core interactions in glycomimetics.

Glycointeractome of Neisseria gonorrhoeae: Identification of Host Glycans Targeted by the Gonococcus To Facilitate Adherence to Cervical and Urethral Epithelial Cells

Multidrug-resistant strains of Neisseria gonorrhoeae are emerging worldwide, and novel treatment and prevention strategies are needed. Glycans are ubiquitously expressed by all human cells and can be specifically targeted by pathogens to facilitate association with host cells. Here we identify and characterize the N. gonorrhoeae host-glycan binding profile (glycointeractome), which revealed numerous interactions, including high-affinity binding to mannosyl glycans. We identify gonococcal potential mannose-binding proteins and show that N. gonorrhoeae uses mannosyl glycans expressed on the surface of cervical and urethral epithelia to facilitate adherence. Furthermore, a mannose-binding lectin or a mannoside compound was able to reduce this adherence. By characterizing the glycointeractome of N. gonorrhoeae, we were able to elucidate a novel mechanism used by this important pathogen to interact with human cells, and this interaction could be exploited to develop novel therapeutics to treat antibiotic-resistant gonorrhea.

Neisseria gonorrhoeae is a significant threat to global health for which a vaccine and novel treatment options are urgently needed. Glycans expressed by human cells are commonly targeted by pathogens to facilitate interactions with the host, and thus characterization of these interactions can aid identification of bacterial receptors that can be exploited as vaccine and/or drug targets. Using glycan array analysis, we identified 247 specific interactions between N. gonorrhoeae and glycans representative of those found on human cells. Interactions included those with mannosylated, fucosylated, and sialylated glycans, glycosaminoglycans (GAGs), and glycans terminating with galactose (Gal), N-acetylgalactosamine (GalNAc), and N-acetylglucosamine (GlcNAc). By investigating the kinetics of interactions with selected glycans, we demonstrate that whole-cell N. gonorrhoeae has a high affinity for mannosylated glycans (dissociation constant [K_D], 0.14 to 0.59 μM), which are expressed on the surface of cervical and urethral epithelial cells. Using chromatography coupled with mass spectrometric (MS) analysis, we identified potential mannose-binding proteins in N. gonorrhoeae. Pretreatment of cells with mannose-specific lectin (concanavalin A) or free mannose competitor (α-methyl-d-mannopyranoside) substantially reduced gonococcal adherence to epithelial cells. This suggests that N. gonorrhoeae targets mannosyl glycans to facilitate adherence to host cells and that mannosides or similar compounds have the potential to be used as a novel treatment option for N. gonorrhoeae.

Reaching the End of the Line: Urinary Tract Infections

Urinary tract infections (UTIs) cause a substantial health care burden. UTIs (i) are most often caused by uropathogenic Escherichia coli (UPEC), (ii) primarily affect otherwise healthy females (50% of women will have a UTI), (iii) are associated with significant morbidity and economic impact, (iv) can become chronic, and (v) are highly recurrent. A history of UTI is a significant risk factor for a recurrent UTI (rUTI). In otherwise healthy women, an acute UTI leads to a 25 to 50% chance of rUTI within months of the initial infection. Interestingly, rUTIs are commonly caused by the same strain of E. coli that led to the initial infection, arguing that there exist host-associated reservoirs, like the gastrointestinal tract and underlying bladder tissue, that can seed rUTIs. Additionally, catheter-associated UTIs (CAUTI), caused by Enterococcus and Staphylococcus as well as UPEC, represent a major health care concern. The host's response of depositing fibrinogen at the site of infection has been found to be critical to establishing CAUTI. The Drug Resistance Index, an evaluation of antibiotic resistance, indicates that UTIs have become increasingly difficult to treat since the mid-2000s. Thus, UTIs are a "canary in the coal mine," warning of the possibility of a return to the preantibiotic era, where some common infections are untreatable with available antibiotics. Numerous alternative strategies for both the prevention and treatment of UTIs are being pursued, with a focus on the development of vaccines and small-molecule inhibitors targeting virulence factors, in the hopes of reducing the burden of urogenital tract infections in an antibiotic-sparing manner.

Strategies for the Development of Glycomimetic Drug Candidates

Carbohydrates are a structurally-diverse group of natural products which play an important role in numerous biological processes, including immune regulation, infection, and cancer metastasis. Many diseases have been correlated with changes in the composition of cell-surface glycans, highlighting their potential as a therapeutic target. Unfortunately, native carbohydrates suffer from inherently weak binding affinities and poor pharmacokinetic properties. To enhance their usefulness as drug candidates, 'glycomimetics' have been developed: more drug-like compounds which mimic the structure and function of native carbohydrates. Approaches to improve binding affinities (e.g., deoxygenation, pre-organization) and pharmacokinetic properties (e.g., limiting metabolic degradation, improving permeability) have been highlighted in this review, accompanied by relevant examples. By utilizing these strategies, high-affinity ligands with optimized properties can be rationally designed and used to address therapies for novel carbohydrate-binding targets.