FimH Antagonists: Phosphate Prodrugs Improve Oral Bioavailability

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.

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.

Programmable site-specific delivery of an alkaline phosphatase-activatable prodrug and a mitochondria-targeted cyclopeptide for combination therapy in colon cancer

The design of advanced carriers that enable time- or stimulus-programmed drug release holds great promise to enhance the treatment efficacy in tumors. Here, hyaluronic acid (HA)-coated liposomes were designed to efficiently deliver multi-organelle-targeted and ALP/GSH dual-responsive prodrugs for combination therapy on colon tumors. In this system (designated CPTP/RA-HALipo), the unique natural cyclopeptide RA-V was linked covalently to a near-infrared (NIR) fluorophore through a disulfide linker, which was subsequently loaded in the cationic liposome core of CPTP/RA-HALipo, while the ALP-activatable phosphate CPT (CPTP) was encapsulated in the HA shell. In the tumor microenvironment, the HA shell of CPTP/RA-HALipo was partially degraded by HAase, thereby allowing the release of CPTP. The released phosphate prodrug CPTP was activated through hydrolysis of the phosphate esters by brush border-associated enzymes. The cationic liposome coated with the remaining HA could selectively enter CD44 overexpressed cells via receptor-mediated endocytosis into the lysosome, in which the acidic microenvironment degraded the liposomes to release the mitochondria-targeted theranostic agent RA-S-S-Cy. More significantly, the GSH-activatable NIR fluorescence of Cy5.5 made it possible to realize in vivo and in situ dynamic monitoring of drug release in a noninvasive manner. The organelle-specific and multi-stimuli responsive nanoparticles have shown precise control over drug delivery and release, leading to superior in vitro and/or in vivo anti-cancer efficacy. This approach represents a novel interactive drug delivery system that can synergistically differentiate the extracellular, cell membranal and intracellular targets to promote spatial and temporal control of drug release.

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.

Application of molecular dynamics simulation in self-assembled cancer nanomedicine

Self-assembled nanomedicine holds great potential in cancer theragnostic. The structures and dynamics of nanomedicine can be affected by a variety of non-covalent interactions, so it is essential to ensure the self-assembly process at atomic level. Molecular dynamics (MD) simulation is a key technology to link microcosm and macroscale. Along with the rapid development of computational power and simulation methods, scientists could simulate the specific process of intermolecular interactions. Thus, some experimental observations could be explained at microscopic level and the nanomedicine synthesis process would have traces to follow. This review not only outlines the concept, basic principle, and the parameter setting of MD simulation, but also highlights the recent progress in MD simulation for self-assembled cancer nanomedicine. In addition, the physicochemical parameters of self-assembly structure and interaction between various assembled molecules under MD simulation are also discussed. Therefore, this review will help advanced and novice researchers to quickly zoom in on fundamental information and gather some thought-provoking ideas to advance this subfield of self-assembled cancer nanomedicine.

In-vitro dynamic dissolution/bioconversion/permeation of fosamprenavir using a novel tool with an artificial biomimetic permeation barrier and microdialysis-sampling

Fosamprenavir is a phosphate ester prodrug that, upon dissolution, is cleaved to the poorly soluble yet readily absorbable parent drug amprenavir. In this study, a novel cell-free in vitro setup with quasi-continuous monitoring of the dynamic dissolution/bio-conversion/permeation of fosamprenavir was designed and tested. It consists of side-by-side diffusion cells, where the donor and acceptor compartments are separated by the biomimetic barrier PermeaPad®, and sampling from the donor compartment is accomplished via a microdialysis probe. Externally added bovine alkaline phosphatase induced bioconversion in the donor compartment. Microdialysis sampling allowed to follow the enzymatic conversion of fosamprenavir to amprenavir by the bovine alkaline phosphatase in an (almost) real-time manner eliminating the need to remove or inactivate the enzyme. Biomimetic conversion rates in the setup were established by adding appropriate amounts of the alkaline phosphatase. A substantial (6.5-fold) and persistent supersaturation of amprenavir was observed due to bioconversion at lower (500 µM) concentrations, resulting in a substantially increased flux across the biomimetic barrier, nicely reflecting the situation in vivo. At conditions with an almost 10-fold higher dose than the usual human dose, some replicates showed premature precipitation and collapse of supersaturation, while others did not. In conclusion, the proposed novel tool appears very promising in gaining an in-depth mechanistic understanding of the bioconversion/permeation interplay, including transient supersaturation of phosphate-ester prodrugs like fosamprenavir.

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.

Investigation on the solid-phase synthesis of silybin prodrugs and their timed-release

Prodrugs are ingenious derivatives of therapeutic agents designed to improve the pharmacokinetic profile of the drug. Here, we report an efficient and regioselective solid phase approach for obtaining new prodrugs of 9″-silybins conjugated with 3'-ribonucleotide units (uridine and adenosine) as pro-moieties. Uridine and adenosine conjugates were obtained in good yields (41-50%), beginning with silibinin and its diastereomers (silybin A and silybin B), using a NovaSyn® support functionalized with an ad hoc linker, which allowed selective detachment of only the desired products. As expected, the solubility of both uridine and adenosine conjugates was higher than that of the parental natural product (5 mg/mL and 3 mg/mL for uridine and adenosine, respectively). Our investigations revealed that uridine conjugates were quickly cleaved by RNase A, releasing silybin drugs, even at low enzyme concentrations. No toxic effects were found for any ribonucleotide conjugate on differentiated neuroblastoma SH-SY5Y cells when tested at increasing concentrations. All results strongly encourage further investigations of uridine-silybin prodrugs as potential therapeutic agents for both oral and intravenous administration. The present synthetic approach represents a valuable strategy to the future design of new prodrugs with modified nucleoside pro-moieties to modulate the pharmacokinetics of silybins or different natural products with strong pharmacological activities but poor bioavailability.

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.

Solid-phase synthesis of curcumin mimics and their anticancer activity against human pancreatic, prostate, and colorectal cancer cell lines

Curcumin is a bioactive natural compound with a wide range of pharmacological properties, including antitumor activity; however, its clinical application has been limited because of its low solubility, stability, and bioavailability. In this study, a solid phase approach was proposed for the combinatorial synthesis of a mini library of the mimics of curcumin in good purity and yield. The non-effective findings in pancreatic cancer cells switched to strong growth inhibition and cell death efficacy for PC3 prostate cancer cells, and mimic 9, in which tyrosol (TYR) and homovanillyl alcohol (HVA) units were linked by a phosphodiester bond, was quite effective not only in cell growth inhibition but also in causing strong cell death under the study conditions and treatments that were not effective in PANC1 cells. The results got more exciting when we also consider the findings in SW480 human colorectal carcinoma cell line, where the growth inhibitor effects were more in line with that of the PC3 cells, but the lack of cell death effect was more in line with the PANC1 cells.

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.

Glycans in drug discovery

Glycans are key players in many biological processes. They are essential for protein folding and stability and act as recognition elements in cell-cell and cell-matrix interactions. Thus, being at the heart of medically relevant biological processes, glycans have come onto the scene and are considered hot spots for biomedical intervention. The progress in biophysical techniques allowing access to an increasing molecular and structural understanding of these processes has led to the development of effective therapeutics. Indeed, strategies aimed at designing glycomimetics able to block specific lectin-carbohydrate interactions, carbohydrate-based vaccines mimicking self- and non-self-antigens as well as the exploitation of the therapeutic potential of glycosylated antibodies are being pursued. In this mini-review the most prominent contributions concerning recurrent diseases are highlighted, including bacterial and viral infections, cancer or immune-related pathologies, which certainly show the great promise of carbohydrates in drug discovery.

Pro-Nifuroxazide Self-Assembly Leads to Triggerable Nanomedicine for Anti-cancer Therapy

Transcription factor STAT3 has been shown to regulate genes that are involved in stem cell self-renewal and thus represents a novel therapeutic target of great biological significance. However, many small-molecule agents with potential effects through STAT3 modulation in cancer therapy lack aqueous solubility and high off-target toxicity, hence impeding efficient bioavailability and activity. This work, for the first time, reports a prodrug-based strategy for selective and safer delivery of STAT3 inhibitors designed toward metastatic and drug-resistant breast cancer. We have synthesized a novel lipase-labile SN-2 phospholipid prodrug from a clinically investigated STAT3 inhibitor, nifuroxazide (Pro-nifuroxazide), which can be regioselectively cleaved by the membrane-abundant enzymes in cancer cells. Pro-nifuroxazide self-assembled to sub 20 nm nanoparticles (NPs), and the cytotoxic ability was screened in ER(+)-MCF-7 and ER(-)-MD-MB231 cells at 48-72 h using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetra-zolium bromide proliferation assay. Results indicated that Pro-nifuroxazide NPs are multifold more effective toward inhibiting cancer cells in a time-dependent manner compared to parent nifuroxazide. A remarkable improvement in the local concentration of drugs to as high as ∼240 fold when assembled into NPs is presumably the reason for this functional improvement. We also introduced molecular dynamics simulations to generate Pro-nifuroxazide nano-assembly, as a model assembly from triggerable anti-cancer drugs, to provide molecular insights correlating physicochemical and anti-cancer properties. In silico properties of Pro-nifuroxazide including size, chemistry of NPs and membrane interactions with individual molecules could be validated by in vitro functional activities in cells of breast cancer origin. The in vivo anti-cancer efficiencies of Pro-nifuroxazide NPs in nude mice xenografts with MCF-7 revealed remarkable growth inhibition of as high as 400%. Histopathological analysis corroborated these findings to show significantly high nuclear fragmentation and retracted cytoplasm. Immunostaining on tumor section demonstrated a significantly lower level of pSTAT-3 by Pro-nifuroxazide NP treatment, establishing the inhibition of STAT-3 phosphorylation. Our strategy for the first time proposes a translatable prodrug agent self-assembled into NPs and demonstrates remarkable enhancement in IC50, induced apoptosis, and reduced cancer cell population through STAT-3 inhibition via reduced phosphorylation.

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.

Development of Mannopyranoside Therapeutics against Adherent-Invasive Escherichia coli Infections

Preventing bacterial adhesion to host cells is a provocative and alternative approach to traditional antibiotic treatments given the increasing microbial resistance. A brief overview of common antibiotic treatments is described in light of their respective resistance and remaining susceptibility. This strategy has been seriously considered in the context of adherent-invasive infections in Crohn's disease and urinary tract infections in particular. The adhesions of various pathogenic Escherichia coli strains to host cells are primarily mediated through carbohydrate-protein interactions involving bacterial organelles called fimbriae that can recognize specific glycoconjugate receptors on host cells. Of particular interest are the FimH and PapG fimbriae, which bind to mannosylated glycoproteins and glycolipids of the galabiose series, respectively. Therefore, blocking FimH- and PapG-mediated bacterial adhesion to uroepithelial cells by high-affinity carbohydrate antagonists constitutes a challenging therapeutic target of high interest. This is of particular interest since bacterial adhesion to host cells is a parameter unlikely to be the subject of bacterial mutations without affecting the carbohydrate ligand binding interactions at the basis of the recognition and infection processes. To date, there have been several families of potent FimH antagonists that include natural O-linked as well as unnatural analogues of α-d-mannopyranosides. These observations led to a thorough understanding of the intimate binding site interactions that helped to reveal the so-called "tyrosine gate mechanism" at the origin of the strong necessary interactions with sugar-possessing hydrophobic aglycones. By modification of the aglycones of single monosaccharidic d-mannopyranosides, it was possible to replace the natural complex oligomannoside structure by simpler ones. An appealing and successful series of analogues have been disclosed, including nanomolecular architectures such as dendrimers, polymers, and liposomes. In addition, the data were compared to the above multivalent architectures and confirmed the possibility of working with small sugar candidates. This Account primarily concentrates on the most promising types of FimH inhibitors belonging to the family of α-C-linked mannopyranosides. However, one of the drawbacks associated with C-mannopyranosides has been that they were believed to be in the inverted chair conformation, which is obviously not recognized by the E. coli FimH. To decipher this situation, various synthetic approaches, conformational aspects, and restrictions are discussed using molecular modeling, high-field NMR spectroscopy, and X-ray analysis. These combined techniques pointed to the fact that several α-C-linked mannopyranosides do exist in the required ⁴C₁ chair conformation. Ultimately, recent findings in this growing field of interest culminated in the identification of drug candidates that have reached clinical phase I.

Pathoblockers or antivirulence drugs as a new option for the treatment of bacterial infections

The rapid development of antimicrobial resistance is threatening mankind to such an extent that the World Health Organization expects more deaths from infections than from cancer in 2050 if current trends continue. To avoid this scenario, new classes of anti-infectives must urgently be developed. Antibiotics with new modes of action are needed, but other concepts are also currently being pursued. Targeting bacterial virulence as a means of blocking pathogenicity is a promising new strategy for disarming pathogens. Furthermore, it is believed that this new approach is less susceptible towards resistance development. In this review, recent examples of anti-infective compounds acting on several types of bacterial targets, e.g., adhesins, toxins and bacterial communication, are described.

Effective anti-adhesives of uropathogenic Escherichia coli

Urinary tract infections (UTIs) caused by uropathogenic Escherichia coli (UPEC) are among the most common infectious diseases in humans. Due to their frequent occurrence in the community and nosocomial settings, as well as the development of resistance to the commonly prescribed antimicrobial agents, an enormous financial burden is placed on healthcare systems around the world. Therefore, novel approaches to the prevention and treatment of UTIs are needed. Although UPEC may harbour a plethora of virulence factors, type I fimbriae and P pili are two of the most studied adhesive organelles, since the attachment to host cells in the urinary tract is a crucial step towards infection. Design of receptor analogues that competitively bind to UPEC surface adhesins placed at the top of pili organelles led to the development of anti-adhesive drugs that are increasingly recognized as important and promising alternatives to antibiotic treatment of UTIs.

Monosaccharide Derivatives with Low-Nanomolar Lectin Affinity and High Selectivity Based on Combined Fluorine-Amide, Phenyl-Arginine, Sulfur-π, and Halogen Bond Interactions

The design of small and high-affinity lectin inhibitors remains a major challenge because the natural ligand binding sites of lectin are often shallow and have polar character. Herein we report that derivatizing galactose with un-natural structural elements that form multiple non-natural lectin-ligand interactions (orthogonal multipolar fluorine-amide, phenyl-arginine, sulfur-π, and halogen bond) can provide inhibitors with extraordinary affinity (low nanomolar) for the model lectin, galectin-3, which is more than five orders of magnitude higher than the parent galactose; moreover, is selective over other galectins.

Sites for Dynamic Protein-Carbohydrate Interactions of O- and C-Linked Mannosides on the E. coli FimH Adhesin

Antagonists of the Escherichia coli type-1 fimbrial adhesin FimH are recognized as attractive alternatives for antibiotic therapies and prophylaxes against acute and recurrent bacterial infections. In this study α-d-mannopyranosides O- or C-linked with an alkyl, alkene, alkyne, thioalkyl, amide, or sulfonamide were investigated to fit a hydrophobic substituent with up to two aryl groups within the tyrosine gate emerging from the mannose-binding pocket of FimH. The results were summarized into a set of structure-activity relationships to be used in FimH-targeted inhibitor design: alkene linkers gave an improved affinity and inhibitory potential, because of their relative flexibility combined with a favourable interaction with isoleucine-52 located in the middle of the tyrosine gate. Of particular interest is a C-linked mannoside, alkene-linked to an ortho-substituted biphenyl that has an affinity similar to its O-mannosidic analog but superior to its para-substituted analog. Docking of its high-resolution NMR solution structure to the FimH adhesin indicated that its ultimate, ortho-placed phenyl ring is able to interact with isoleucine-13, located in the clamp loop that undergoes conformational changes under shear force exerted on the bacteria. Molecular dynamics simulations confirmed that a subpopulation of the C-mannoside conformers is able to interact in this secondary binding site of FimH.

Rational design strategies for FimH antagonists: new drugs on the horizon for urinary tract infection and Crohn's disease

INTRODUCTION

The bacterial adhesin FimH is a virulence factor and an attractive therapeutic target for urinary tract infection (UTI) and Crohn's Disease (CD). Located on type 1 pili of uropathogenic E. coli (UPEC), the FimH adhesin plays an integral role in the pathogenesis of UPEC. Recent efforts have culminated in the development of small-molecule mannoside FimH antagonists that target the mannose-binding lectin domain of FimH, inhibiting its function and preventing UPEC from binding mannosylated host cells in the bladder, thereby circumventing infection. Areas covered: The authors describe the structure-guided design of mannoside ligands, and review the structural biology of the FimH lectin domain. Additionally, they discuss the lead optimization of mannosides for therapeutic application in UTI and CD, and describe various assays used to measure mannoside potency in vitro and mouse models used to determine efficacy in vivo. Expert opinion: To date, mannoside optimization has led to a diverse set of small-molecule FimH antagonists with oral bioavailability. With clinical trials already initiated in CD and on the horizon for UTI, it is the authors, opinion that mannosides will be a 'first-in-class' treatment strategy for UTI and CD, and will pave the way for treatment of other Gram-negative bacterial infections.

Eutirucallin: A Lectin with Antitumor and Antimicrobial Properties

Eutirucallin is a lectin isolated from the latex of Euphorbia tirucalli, a plant known for its medical properties. The present study explores various characteristics of Eutirucallin including stability, cytotoxicity against tumor cells, antimicrobial and antiparasitic activities. Eutirucallin was stable from 2 to 40 days at 4°C, maintained hemagglutinating activity within a restricted range, and showed optimal activity at pH 7.0–8.0. Eutirucallin presented antiproliferative activity for HeLa, PC3, MDA-MB-231, and MCF-7 tumor cells but was not cytotoxic for non-tumorigenic cells such as macrophages and fibroblasts. Eutirucallin inhibited the Ehrlich ascites carcinoma in vivo and it was also observed that Eutirucallin inhibited 62.5% of Escherichia coli growth. Also, Eutirucallin showed to be effective when tested directly against Toxoplasma gondii infection in vitro. Therefore, this study sheds perspectives for pharmacological applications of Eutirucallin.

Assembly and inhibitory activity of monovalent mannosides terminated with aromatic methyl esters: The effect of naphthyl groups

A series of monovalent α-D-mannoside ligands terminated with aromatic methyl esters have been synthesized in excellent yields using the Cu(I) catalyzed azide-alkyne 1,3-dipolar cycloaddition ("click chemistry"). These mannosides were designed to have a unique aglycone moiety (tail) that combines a triazole ring attached to aromatic methyl esters via a six carbon alkyl chain. The mannose unit of these ligands was linked at the ortho, meta, and para positions of substituted methyl benzoates and 1-, 3-, and 6-substituted methyl 2-napthaoates. In hemagglutination assays, ligands (32A-38A) showed better inhibitory activities than the standard inhibitor, methyl α-D-mannopyranoside. Overall, the naphthyl-based mannoside ligand (37A) showed the best activity and therefore merits further development.

Antivirulence C-Mannosides as Antibiotic-Sparing, Oral Therapeutics for Urinary Tract Infections

Gram-negative uropathogenic Escherichia coli (UPEC) bacteria are a causative pathogen of urinary tract infections (UTIs). Previously developed antivirulence inhibitors of the type 1 pilus adhesin, FimH, demonstrated oral activity in animal models of UTI but were found to have limited compound exposure due to the metabolic instability of the O-glycosidic bond (O-mannosides). Herein, we disclose that compounds having the O-glycosidic bond replaced with carbon linkages had improved stability and inhibitory activity against FimH. We report on the design, synthesis, and in vivo evaluation of this promising new class of carbon-linked C-mannosides that show improved pharmacokinetic (PK) properties relative to O-mannosides. Interestingly, we found that FimH binding is stereospecifically modulated by hydroxyl substitution on the methylene linker, where the R-hydroxy isomer has a 60-fold increase in potency. This new class of C-mannoside antagonists have significantly increased compound exposure and, as a result, enhanced efficacy in mouse models of acute and chronic UTI.