Antagonizing the adhesion of type 1 fimbriae - mediated Escherichia coli - a novel therapy for urinary tract infections

Urinary tract infections (UTIs), primarily caused by uropathogenic E. coli (UPEC), affect millions of people and account for significant morbidity and high medical costs. The key step in the pathogenesis of UTIs is the bacterial adhesion to urothelial cells, which is mediated by the virulence factor FimH located on type 1 pili. Blocking FimH and therefore the adhesion with FimH antagonists offers a new therapeutic approach for the prevention and treatment of UTIs. However, the antagonists developed so far have hardly met the requirements for clinical applications due to poor pharmacokinetic (PK) properties. In vivo studies indicated that with biphenyl α-D-mannosides as FimH antagonists, high doses were necessary to achieve the minimal concentrations required for anti-adhesive effects in the bladder. Additionally, the binding mode of an antagonist to the carbohydrate recognition domain of FimH can switch from an “in-docking mode” to an “out-docking mode”, depending on the structure of the antagonist. Further studies indicated that the existence of the high- and low-affinity state of FimH could complicate the binding affinity.
To achieve oral bioavailability, to improve binding affinity, and to explore the binding mode, we chemically modified the biphenyl FimH antagonists with diverse strategies. To establish the designed compound libraries, traditional synthesis and dynamic combinatorial techniques were applied. The binding affinity and the thermodynamic profile of the antagonists were evaluated by a cell-free competitive binding assay, a competitive fluorescence polarization assay, a cell-based flow cytometry assay, and isothermal titration calorimetry (ITC). Furthermore, the PK properties were determined by in vitro and in vivo assays. As results, structure-activity and structure-property relationships were established for structurally diversified FimH antagonists. The reported strategies led to FimH antagonists with significantly improved PD/PK profile regarding effectiveness of the anti-adhesive treatment.