FimH antagonists and their therapeutic options in urinary tract infection : an example of an anti-adhesive therapy for infectious diseases

FimH antagonists are small molecule inhibitors, derived from α-D-mannose, which block the adhesion of uropathogenic Escherichia coli (UPEC) to bladder cells. The abolition of binding leads to clearance of the bacteria with the urine flow and prevents urinary tract infections (UTIs). Within this thesis, the merits as well as problems of an anti-adhesive therapy (in the context of the infection cycle of UTI) as an alternative approach to combat bacterial infections are described. Previous reports showed successful applications of FimH antagonists in vitro and in vivo. The antagonists reduced bacterial attachment to cells and surfaces and decreased bladder infections in a UTI mouse model. Within this thesis, FimH antagonists from our group were screened for their minimal anti-adhesive concentration (MAC90) using an in vitro cell infection assay. The minimal therapeutic concentration was analyzed in the context of the pharmacokinetic (PK) performance of individual antagonists. It could be shown, that a preventive application and the resulting peak concentration of a FimH antagonist in the urine relative to the MAC90 value is predictive for positive treatment outcome. Guided by this finding, several treatment regimens, including combination therapies with antibiotics, were successfully applied to reduce bladder infections in an experimental mouse model by up to three orders of magnitude. Furthermore, FimH antagonists were effective against catheter-associated UTI (CAUTI), assessed by a newly established 96-well screening assay, using catheter pieces and human urine. They prevented biofilm formation in concentrations as low as 6.25 µg/ml. Moreover, in all tested applications, FimH antagonists exhibited a synergistic effect with ciprofloxacin (CIP), implying the possibility of combination therapies. Antagonizing the FimH lectin proofed cumbersome, because depending on the UPEC strain, the FimH binding pocket exhibits different affinity states towards mannose ligands. This leads to different MAC90 values for every individual strain and a specific antagonist. Besides, different strains vary in their infection course over longer time periods, probably related to the different affinity state of the FimH lectin. Consequently, the differences in affinity in combination with the infection time course might strongly influence treatment regimens, which will be an important topic of future investigations

FimH antagonists - solubility vs. permeability

Urinary tract infections (UTIs) caused by uropathogenic Escherichia coli (UPEC) are among the most prevalent infections worldwide. Since frequent antibiotic treatment favors the emergence of antibiotic resistance, efficient non-antibiotic strategies are urgently needed. The first step of the pathogenesis of UTI is the bacterial adherence to urothelial host cells, a process mediated by the mannose-binding adhesin FimH located at the tip of bacterial pili. In a preliminary study, biphenyl α-d-mannopyranosides with an electron-withdrawing carboxylate on the aglycone were identified as potent FimH antagonists. Although passive permeability could be established by masking the carboxylate as an ester, insufficient solubility and fast hydrolysis did not allow to maintain the therapeutic concentration in the bladder for the requested period of time. By modifying the substitution pattern, molecular planarity and symmetry of the biphenyl aglycone could be disrupted leading to improved solubility. In addition, when heteroatoms were introduced to the aglycone, antagonists with further improved solubility, metabolic stability as well as passive permeability were obtained. The best representative, the pyrrolylphenyl mannoside 42f exhibited therapeutic urine concentration for up to 6 h and is therefore a promising oral candidate for UTI prevention and/or treatment

FimH Antagonists: Phosphate Prodrugs Improve Oral Bioavailability

The widespread occurrence of urinary tract infections has resulted in frequent antibiotic treatment, contributing to the emergence of antimicrobial resistance. Alternative approaches are therefore required. In the initial step of colonization, FimH, a lectin located at the tip of bacterial type 1 pili, interacts with mannosylated glycoproteins on the urothelial mucosa. This initial pathogen/host interaction is efficiently antagonized by biaryl α-d-mannopyranosides. However, their poor physicochemical properties, primarily resulting from low aqueous solubility, limit their suitability as oral treatment option. Herein, we report the syntheses and pharmacokinetic evaluation of phosphate prodrugs, which show an improved aqueous solubility of up to 140-fold. In a Caco-2 cell model, supersaturated solutions of the active principle were generated through hydrolysis of the phosphate esters by brush border-associated enzymes, leading to a high concentration gradient across the cell monolayer. As a result, the in vivo application of phosphate prodrugs led to a substantially increased Cmax and prolonged availability of FimH antagonists in urine

FimH Antagonists: Bioisosteres To Improve the in Vitro and in Vivo PK/PD Profile

Urinary tract infections (UTIs), predominantly caused by uropathogenic Escherichia coli (UPEC), belong to the most prevalent infectious diseases worldwide. The attachment of UPEC to host cells is mediated by FimH, a mannose-binding adhesin at the tip of bacterial type 1 pili. To date, UTIs are mainly treated with antibiotics, leading to the ubiquitous problem of increasing resistance against most of the currently available antimicrobials. Therefore, new treatment strategies are urgently needed. Here, we describe the development of an orally available FimH antagonist. Starting from the carboxylate substituted biphenyl α-d-mannoside 9, affinity and the relevant pharmacokinetic parameters (solubility, permeability, renal excretion) were substantially improved by a bioisosteric approach. With 3'-chloro-4'-(α-d-mannopyranosyloxy)biphenyl-4-carbonitrile (10j) a FimH antagonist with an optimal in vitro PK/PD profile was identified. Orally applied, 10j was effective in a mouse model of UTI by reducing the bacterial load in the bladder by about 1000-fold

Multi-model comparison of the volcanic sulfate deposition from the 1815 eruption of Mt. Tambora

International audienceThe eruption of Mt. Tambora in 1815 was the largest volcanic eruption of the past 500 years. The eruption had significant climatic impacts, leading to the 1816 "year without a summer", and remains a valuable event from which to understand the climatic effects of large stratospheric volcanic sulfur dioxide injections. The eruption also resulted in one of the strongest and most easily identifiable volcanic sulfate signals in polar ice cores, which are widely used to reconstruct the timing and atmospheric sulfate loading of past eruptions. As part of the Model Intercomparison Project on the climatic response to Volcanic forcing (VolMIP), five state-of-the-art global aerosol models simulated this eruption. We analyse both simulated background (no Tambora) and volcanic (with Tambora) sulfate deposition to polar regions and compare to ice core records. The models simulate overall similar patterns of background sulfate deposition, although there are differences in regional details and magnitude. However, the volcanic sulfate deposition varies considerably between the models with differences in timing, spatial pattern and magnitude. Mean simulated deposited sulfate on Antarctica ranges from 19 to 264 kg km−2 and on Greenland from 31 to 194 kg km−2, as compared to the mean ice-core-derived estimates of roughly 50 kg km−2 for both Greenland and Antarctica. The ratio of the hemispheric atmospheric sulfate aerosol burden after the eruption to the average ice sheet deposited sulfate varies between models by up to a factor of 15. Sources of this inter-model variability include differences in both the formation and the transport of sulfate aerosol. Our results suggest that deriving relationships between sulfate deposited on ice sheets and atmospheric sulfate burdens from model simulations may be associated with greater uncertainties than previously thought