In vitro and in vivo characterization of FimH antagonists for anti-adhesion therapy - an alternative therapeutic approach against urinary tract infection

Uropathogenic Escherichia coli (UPEC) are the major cause of urinary tract infections (UTI), which is one of the most common infectious disease worldwide. Women belong to the most affected population, with every second woman experiencing at least one symptomatic UTI during her lifetime. Additionally, UTI is a major problem in the clinics, being the most common hospital acquired infection. To avoid complications like kidney infections, irreversible kidney damage or urosepsis, all symptomatic infections should be treated with antibiotics. The use of antibiotics for the treatment of UTI, is continuosly increasing the development of resistant pathogens against most of the currently available antimicrobials. Therefore, new treatment strategies targeting alternative mechanisms are urgently needed, avoiding selection pressure on bacteria and thereby implying a reduced risk of resistance. An alternative approach for the treatment of UTI is the anti-adhesion therapy using FimH antagonists. FimH is an adhesin, located on the distal tip of type 1 pili, expressed on the surface of UPEC. The type 1 pilus contains a carbohydrate recognition domain, binding to mannose glycans expressed on urothelial cells. This allows UPEC to adhere to and to invade host cells within the urinary tract epithelium and is the initial step for a successful establishment of a UTI. FimH antagonists are highly active anti-adhesion molecules, targeting the virulence factor FimH. In vitro and in vivo studies clearly indicate the potential of FimH antagonists for the prevention and treatment of UTI, with a higher therapeutic efficacy compared to antibiotics. The anti-adhesion therapy is focusing on the development of a new class of antimicrobials exhibiting less selection pressure and therefore a reduced potential for the emergence of resistance. In addition, a reduction of the antibiotic associated side effects (e.g. the disruption of the commensal microbiota) is expected. Thus, the availability of a novel class of antimicrobials based on an alternative mode of action would have a huge impact on the treatment of UTI, being a substantial contribution to public health

In vivo evaluation of FimH antagonists – a novel class of antimicrobials for the treatment of urinary tract infection

The discovery of antimicrobials as ?-lactam antibiotics or aminoglycosides revolutionized the treatment of infectious diseases. However, the extensive use rapidly created the problem of resistant pathogens, which are increasingly difficult to treat. FimH antagonists are a new class of antimicrobials, which target the bacterial adhesion to urothelial cells, a crucial first step in the establishment of urinary tract infections. Because of their different mode of action, FimH antagonists neither kill nor inhibit the growth of bacteria, they should have a reduced potential to generate resistant strains. This mini-review outlines the main problems associated with increasing development of antimicrobial resistance. Furthermore, it summarizes the currently available in vivo studies in mice for the treatment of urinary tract infections conducted with FimH antagonists

Development of an aggregation assay to screen FimH antagonists

Alpha-D-mannopyranosides are potent FimH antagonists, which inhibit the adhesion of Escherichia coli to highly mannosylated uroplakin Ia on the urothelium and therefore offer an efficient therapeutic opportunity for the treatment and prevention of urinary tract infection. For the evaluation of the therapeutic potential of FimH antagonists, their effect on the disaggregation of E. coli from Candida albicans and guinea pig erythrocytes (GPE) was studied. The mannose-specific binding of E. coli to yeast cells and erythrocytes is mediated by type 1 pili and can be monitored by aggregometry. Maximal aggregation of C. albicans or GPE to E. coli is reached after 600 s. Then the FimH antagonist was added and disaggregation determined by light transmission over a period of 1400 s. A FimH-deleted mutant of E. coli, which does not induce any aggregation, was used in a control experiment. The activities of FimH antagonists are expressed as IC(50)s, the half maximal inhibitory concentration of the disaggregation potential. n-Heptyl alpha-D-mannopyranoside (1) was used as a reference compound and exhibits an IC(50) of 77.14 microM , whereas methyl alpha-D-mannopyranoside (2) does not lead to any disaggregation at concentrations up to 800 microM. o-Chloro-p-[N-(2-ethoxy-3,4-dioxocyclobut-1-enyl)amino]phenyl alpha-D-mannopyranoside (3) shows a 90-fold and 2-chloro-4-nitrophenyl alpha-D-mannopyranoside (4) a 6-fold increased affinity compared to 1. Finally, 4-nitrophenyl alpha-D-mannopyranoside (5) exhibits an activity similar to 1. As negative control, D-galactose (6) was used. The standardized aggregation assay generates concentration-dependent, reproducible data allowing the evaluation of FimH antagonists according to their potency to inhibit E. coli adherence and can therefore be employed to select candidates for experimental and clinical studies for treatment and prevention of urinary tract infections

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