An exhaustive cell-based screen coupled with an intracellular-induced lux-based reporter identified bioactive molecules that inhibit host cell infection by intracellular pathogens.

INTRODUCTION: Antibiotic resistance poses a critical and escalating global health crisis, leading to higher morbidity and mortality associated with infectious diseases. This problem is significantly exacerbated by intracellular bacterial pathogens, which are often shielded from conventional antibiotics and foster the emergence of persister populations. Recently, host-directed therapy (HDT) has been emerging as a promising strategy that aims to modulate host cellular processes or immune responses to enhance bacterial clearance. Nonetheless, the inherent complexity of host biology makes identifying appropriate and safe modulators challenging, unpredictable, and highly complicated.

METHODS: Here, we present a cell-based high-throughput screen (HTS), coupled with an intracellular-induced reporter that was used to screen a library of nearly 37,000 small molecules with potentially pharmacological activity for compounds that inhibit host cell infection by intracellular pathogens.

RESULTS AND DISCUSSION: This multistage, screening protocol resulted in the identification of eight non-cytotoxic compounds that efficiently inhibited the intracellular growth of the Gram-negative bacterium Salmonella Typhimurium in human epithelial cells by ~2.5- to 6-fold, without inhibiting Salmonella growth in culture. Five of these eight molecules were also effective in controlling the intracellular replication of Salmonella in primary mouse macrophages by 1.5- to 38-fold. Strikingly, seven hits also inhibited the intracellular growth of the Gram-positive bacterial pathogen Listeria monocytogenes in epithelial cells by 1.5- to 10-fold. The structure-activity relationship approach successfully identified chemical analogs of one hit with enhanced biological activity as infection inhibitors. Overall, we describe a robust HTS platform that can be adapted for screening of compound libraries against other pathogens, and suggest that the identified compounds are potential candidates for downstream development of novel drugs against intracellular bacterial infections.