An Azobenzene G-quadruplex Ligand Exhibits Promising Antibacterial Activity against Escherichia coli

Abstract

AbstractWith the rise in bacterial antimicrobial resistance (AMR) and decline in antibiotic discovery, global healthcare is at a point of jeopardy. There is great need for the development of novel antimicrobials that target bacteria that have become resistant to our existing antibiotics, in particular Gram-negative species such as Escherichia coli which is responsible for opportunistic infections of already compromised patients. Here we demonstrate that a novel pyridinium-functionalised azobenzene scaffold L20, identified as a candidate ligand able target G-quadruplex (G4) structures in bacterial genomes/transcriptomes, shows promising antibacterial activity (MIC values ≤ 4 µg/ml) against multi-drug resistant E. coli. Tandem Mass Tag (TMT) proteomics applied to cultures of the E. coli type strain ATCC 25922 treated with sub-lethal concentrations of L20, identified seven G4-containing sequences as potential targets for L20. FRET (fluorescence resonance energy transfer) stabilisation assays indicate L20 binds these selected sequences with variable and moderate affinity, in contrast to two comparator G4 ligands (stiff-stilbene L5 and pyridostatin (PDS)) that better stabilise G4 structures but exhibit a lower antimicrobial activity. However, proteomic experiments also reveal that, alongside its superior antibacterial activity, L20 treatment influences expression levels of more G4-associated proteins than either L5 or PDS, and upregulates multiple essential proteins involved in translation. These findings identify strategies discovering potential G4 ligands as approaches that can lead to antibacterial candidates active against priority targets such as multi-drug resistant E. coli, and that targeting G4 sequences, and ligands such as L20, warrant further exploration as potential novel therapeutics with G4-mediated modes of action.