Novel HldE-K inhibitors leading to attenuated Gram negative bacterial virulence.

We report here the optimization of an HldE kinase inhibitor to low nanomolar potency, which resulted in the identification of the first reported compounds active on selected E. coli strains. One of the most interesting candidates, compound 86, was shown to inhibit specifically bacterial LPS heptosylation on efflux pump deleted E. coli strains. This compound did not interfere with E. coli bacterial growth (MIC > 32 µg/mL) but sensitized this pathogen to hydrophobic antibiotics like macrolides normally inactive on Gram-negative bacteria. In addition, 86 could sensitize E. coli to serum complement killing. These results demonstrate that HldE kinase is a suitable target for drug discovery. They also pave the way toward novel possibilities of treating or preventing bloodstream infections caused by pathogenic Gram negative bacteria by inhibiting specific virulence factors.

From triclosan toward the clinic: discovery of nonbiocidal, potent FabI inhibitors for the treatment of resistant bacteria.

In this paper, we present some elements of our optimization program to decouple triclosan's specific FabI effect from its nonspecific cytotoxic component. The implementation of this strategy delivered highly specific, potent, and nonbiocidal new FabI inhibitors. We also disclose some preclinical data of one of their representatives, 83, a novel antibacterial compound active against resistant staphylococci and some clinically relevant Gram negative bacteria that is currently undergoing clinical trials.

Towards Gram-positive antivirulence drugs: new inhibitors of Streptococcus agalactiae Stk1.

A structure-activity relationship study from a screening hit and structure-based design strategy has led to the identification of bisarylureas as potent inhibitors of Streptococcus agalactiae Stk1. As this target has been directly linked to bacterial virulence, these inhibitors can be considered as a promising step towards antivirulence drugs.

Towards Gram-negative antivirulence drugs: new inhibitors of HldE kinase.

Gram-negative bacteria lacking heptoses in their lipopolysaccharide (LPS) display attenuated virulence and increased sensitivity to human serum and to some antibiotics. Thus inhibition of bacterial heptose synthesis represents an attractive target for the development of new antibacterial agents. HldE is a bifunctional enzyme involved in the synthesis of bacterial heptoses. Development of a biochemical assay suitable for high-throughput screening allowed the discovery of inhibitors 1 and 2 of HldE kinase. Study of the structure-activity relationship of this series of inhibitors led to highly potent compounds.

Identification of candidates for a subunit vaccine against extraintestinal pathogenic Escherichia coli.

Extraintestinal pathogenic Escherichia coli (ExPEC) strains cause a large spectrum of infections. The majority of ExPEC strains are closely related to the B2 or the D phylogenetic group. The aim of our study was to develop a protein-based vaccine against these ExPEC strains. To this end, we identified ExPEC-specific genomic regions, using a comparative genome analysis, between the nonpathogenic E. coli strain K-12 MG1655 and ExPEC strains C5 (meningitis isolate) and CFT073 (urinary tract infection isolate). The analysis of these genomic regions allowed the selection of 40 open reading frames, which are conserved among B2/D clinical isolates and encode proteins with putative outer membrane localization. These genes were cloned, and recombinant proteins were purified and assessed as vaccine candidates. After immunization of BALB/c mice, five proteins induced a significant protective immunity against a lethal challenge with a clinical E. coli strain of the B2 group. In passive immunization assays, antigen-specific antibodies afforded protection to naive mice against a lethal challenge. Three of these antigens were related to iron acquisition metabolism, an important virulence factor of the ExPEC, and two corresponded to new, uncharacterized proteins. Due to the large number of genetic differences that exists between commensal and pathogenic strains of E. coli, our results demonstrate that it is possible to identify targets that elicit protective immune responses specific to those strains. The five protective antigens could constitute the basis for a preventive subunit vaccine against diseases caused by ExPEC strains.