Identification of novel anti-bacterial compounds from a chemically highly diverse pathways-based library using phenotypic screens in amoebae host models

Abstract

Legionella pneumophila and tubercular Mycobacteria are the causative agents of potentially fatal diseases due to their pathogenesis but also to the emergence of antibiotic resistance that limits treatment strategies. The aim of our study is to explore the antimicrobial activity of a small ligand-based chemical library of 1,255 structurally diverse compounds. These compounds were screened in a combination of three assays, two monitoring the intracellular growth of the pathogenic bacteria, Mycobacterium marinum and L. pneumophila, and an additional anti-virulence \"plaque\" assay for M. marinum. We set up these assays using two amoeba strains, the genetically tractable Dictyostelium discoideum and the free-living amoeba Acanthamoeba castellanii. In summary, sixty-four compounds showed anti-infective/anti-virulence activity in at least one of the 3 assays. The intracellular assays hit rate varied between 1.7% (n=22) for M. marinum and 2.8% (n=35) for L pneumophila with 7 compounds in common between both pathogens. In parallel, 1.2 % (n= 15) of the tested compounds were able to restore D. discoideum growth in presence of M. marinum spiked in a lawn of Klebsiella pneumoniae. We also validated the generality of the hit compounds identified using the A. castellanii-M. marinum anti-infective screen in the powerful D. discoideum-M. marinum host-pathogen model. The characterization of anti-infective and antibacterial hits in the latter infection model revealed compounds able to reduce intracellular growth more than 50% at 30 M. Our studies underline the relevance of using a combination of low-cost and low-complexity assays with full 3R compliance associated with a rationalized focused library of compounds to help identifying new chemical scaffolds and dissect some of their properties prior to run further compounds development steps.