Generation of anti-virulence compounds against the type three secretion system of Escherichia coli O157:H7

Escherichia coli is normally found in the intestinal microbiota of most mammals and is regarded as a commensal bacterium. However, several strains have evolved as pathogens through the acquisition of pathogenicity islands. E. coli O157:H7 is a commensal bacterium for cattle, but can be transmitted to humans where it acts as a pathogen. In humans, E. coli O157:H7 infections cause bloody diarrhoea, haemorrhagic colitis and in some cases haemolytic uremic syndrome (HUS), which can lead to death. Treatment of this bacterial infection is rather complicated as traditional antibiotics have demonstrated to worsen the clinical symptoms and the outcome of the infection. Therefore, the discovery of new treatments for this infection is of great relevance. Anti-virulence (AV) compounds are one of the most promising classes of drugs for the treatment of E. coli O157:H7 infections, as they selectively target key virulence factors. This approach selectively decreases the ability of the pathogen to cause disease rather than its ability to survive, thus reducing the chances for the development of resistance. The type three secretion system (T3SS) is a key virulence factor for E. coli O157:H7 as it enables the tight attachment of the bacterium to the host cell and the secretion of effector proteins to initiate the colonisation process. The T3SS is a very attractive target for the development of selective AV compounds for E. coli O157:H7. Salicylidene acylhydrazides (SA) are the most well-studied class of AV compounds targeting the T3SS in several Gram-negative bacteria. ME0055 was found to be one of the best SA compounds against the T3SS in E. coli O157:H7, but it is considered as a promiscuous binder since its effects derived from a modulation of several metabolic pathways rather than a direct interaction with the T3SS. However, ME0055 provides an excellent starting point for chemical optimisation and the generation of more stable and potent T3SS inhibitors. The aim of this work was to chemically modify the ME0055 scaffold in order to create a small focused library of new anti-virulence compounds. Three new active scaffolds based on the SA compound’s core were found to be active against E. coli O157:H7 T3SS. Further biological studies also revealed the main protein target of this new class of anti-virulence compounds, enabling future investigations in the pursuit of new and more potent molecules against the T3SS