Effective Small Molecule Antibacterials from a Novel Anti-Protein Secretion Screen

Area of Science:

• Microbiology
• Drug Discovery
• Molecular Biology

Background:

• Antibiotic resistance necessitates novel antibacterial agents.
• Protein export pathways, like the Sec pathway, are essential for bacterial survival and represent promising drug targets.
• The Sec pathway is absent in eukaryotes, offering selective targeting opportunities.

Purpose of the Study:

• To develop and apply a high-throughput screening (HTS) assay to identify inhibitors of the bacterial Sec protein export pathway.
• To evaluate the antibacterial activity of identified inhibitors against a range of bacterial pathogens.
• To explore potential new targets within the protein secretion machinery.

Main Methods:

• A novel HTS assay was developed using alkaline phosphatase (PhoA) secretion and activity.
• A library of approximately 240,000 small molecules was screened.
• Hit compounds were confirmed, analoged, and tested for antibacterial activity against 19 bacterial species, including WHO priority pathogens.

Main Results:

• Fourteen high-throughput secretion inhibitors (HSIs) were identified with IC50 < 60 µM.
• Seven HSIs, from three structural families, demonstrated bactericidal activity.
• HSI#6 showed potent, broad-spectrum activity against 13 bacterial species (IC50 0.4–8.7 µM).
• Some HSIs inhibited Gram-positive bacteria and E. coli strains, with specific compounds indicating limited outer membrane penetration.

Conclusions:

• The developed HTS assay is effective for identifying novel inhibitors of bacterial protein secretion.
• The identified HSIs, particularly HSI#6, represent promising starting points for developing new antibiotics.
• These compounds may target novel components of the protein secretion pathway, distinct from SecA.