Physicochemical and pharmacokinetic characterization of carbohydrate mimetics

Urinary tract infection by uropathogenic Escherichia coli is one of the most frequent infectious diseases requiring an antibiotic treatment. Since the recurrent exposure to antibiotics leads to the emergence of antibacterial resistance, alternative prevention and treatment strategies are urgently needed. The interaction of the bacterial lectin FimH with mannosylated glycoproteins on the surface of the bladder mucosa is the initial step triggering the infection. Biaryl α-D-mannopyranosides were identified as potent FimH antagonists preventing this first contact. The present thesis describes the development of two biaryl mannosides, that are, the biphenyl mannoside bearing a para-carboxylate on the terminal ring of the aglycone and the 5-nitroindolinyl phenyl mannoside, towards drug-likeness. For this purpose, various approaches, such as the introduction of ester or phosphate prodrugs, the replacement of essential substituents with bioisosteres, the optimization of the substitution pattern, or the introduction of aromatic heterocycles, were explored. Several assays addressing the characterization of the physicochemical and in vitro pharmacokinetic properties, i.e. pKa, lipophilicity, aqueous solubility, membrane permeability, plasma protein binding, chemical and metabolic stability, were implemented for the identification of the most successful strategies providing high oral bioavailability, metabolic stability, and sustained renal clearance as major route of drug elimination. As a result of our thorough studies, two approaches proved most advantageous for the development of orally available FimH antagonists: first, the prodrug approach, i.e. the introduction of an alkyl promoiety masking the carboxylic acid substituent of the biphenyl mannoside or the creation of phosphate monoester prodrugs conferring high aqueous solubility, and second, the replacement of the carboxylic acid with bioisosteres providing optimal physicochemical properties for oral absorption and renal excretion

Prodruggability of Carbohydrates - Oral FimH Antagonists

The bacterial lectin FimH is a promising therapeutic target for the nonantibiotic prevention and treatment of urinary tract infections. In this communication, an ester prodrug approach is described to achieve oral bioavailability for FimH antagonists. By introducing short-chain acyl promoieties at the C-6 position of a biphenyl α- d -mannopyranoside, prodrugs with an excellent absorption potential were obtained. The human carboxylesterase 2 was identified as a main enzyme mediating rapid bioconversion to the active principle. Despite their propensity to hydrolysis within the enterocytes during absorption, these ester prodrugs present a considerable progress in the development of orally available FimH antagonists

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

Urinary Tract Infection: Which Conformation of the Bacterial Lectin FimH Is Therapeutically Relevant?

Frequent antibiotic treatment of urinary tract infections has resulted in the emergence of antimicrobial resistance, necessitating alternative treatment options. One such approach centers around FimH antagonists that block the bacterial adhesin FimH, which would otherwise mediate binding of uropathogenic Escherichia coli to the host urothelium to trigger the infection. Although the FimH lectin can adopt three distinct conformations, the evaluation of FimH antagonists has mainly been performed with a truncated construct of FimH locked in one particular conformation. For a successful therapeutic application, however, FimH antagonists should be efficacious against all physiologically relevant conformations. Therefore, FimH constructs with the capacity to adopt various conformations were applied. By examining the binding properties of a series of FimH antagonists in terms of binding affinity and thermodynamics, we demonstrate that depending on the FimH construct, affinities may be overestimated by a constant factor of 2 orders of magnitude. In addition, we report several antagonists with excellent affinities for all FimH conformations