Cholesterol-dependent activity of dapsone against non-replicating persistent mycobacteria

Area of Science:

• Microbiology
• Drug Discovery
• Tuberculosis Research

Background:

• Latent tuberculosis infection (LTBI) affects one-third of the global population.
• The reservoir of latent Mycobacterium tuberculosis is largely resistant to current antimicrobial treatments.
• Existing treatments for LTBI focus on inhibiting bacterial resuscitation rather than preventing or treating the latent state, leading to limited in vivo efficacy.

Purpose of the Study:

• To develop an in vitro method for analyzing physiologically relevant non-replicating persistence (NRP) in Mycobacterium bovis BCG.
• To identify novel antimicrobial compounds effective against cholesterol-dependent NRP M. bovis BCG.
• To elucidate the mechanism of action and potential drug targets for compounds active against NRP M. bovis BCG.

Main Methods:

• Established an in vitro NRP model using cholesterol as the sole carbon source and hypoxia to induce persistence in M. bovis BCG.
• Conducted a phenotypic screen of an approved-drug library against cholesterol-dependent NRP M. bovis BCG.
• Performed overexpression trials of target enzymes to identify the molecular target of active compounds.

Main Results:

• The minimal cholesterol media NRP assay demonstrated increased in vitro resistance to front-line anti-tubercular drugs.
• Dapsone was identified as a bactericidal molecule against cholesterol-dependent NRP M. bovis BCG.
• FolP2, a dihydropteroate synthase homologue, was identified as the likely target of dapsone in NRP M. bovis BCG, with its overexpression conferring resistance.

Conclusions:

• The study introduces a novel in vitro methodology for screening drugs against non-replicating persistent tuberculosis bacteria.
• Dapsone exhibits bactericidal activity against a challenging persistent form of M. bovis BCG, suggesting its potential inclusion in tuberculosis treatment regimens.
• Understanding drug resistance mechanisms in NRP bacteria, like the role of FolP2, is crucial for developing more effective anti-tubercular therapies.