New Investigations with Lupane Type A-Ring Azepane Triterpenoids for Antimycobacterial Drug Candidate Design

Area of Science:

• Medicinal Chemistry
• Microbiology
• Pharmacology

Background:

• Tuberculosis (TB) remains a global health challenge, exacerbated by drug-resistant strains.
• Novel therapeutic agents are urgently needed to combat Mycobacterium tuberculosis (MTB) and nontuberculous mycobacteria (NTM).
• Triterpenoids represent a promising class of natural products with diverse biological activities.

Purpose of the Study:

• To synthesize and evaluate novel lupane type A-ring azepano-triterpenoids for antitubercular activity.
• To investigate the efficacy of these compounds against drug-sensitive and drug-resistant MTB strains, as well as against Mycobacterium abscessus and Mycobacterium avium.
• To explore the mechanism of action and potential for combination therapy.

Main Methods:

• Synthesis of twenty azepano-triterpenoids from betulin derivatives.
• Antitubercular activity testing against M. tuberculosis (H37Rv), mono-resistant MTB strains, M. abscessus, and M. avium.
• Molecular docking and machine learning drug-drug similarity analysis.
• Fractional Inhibitory Concentration (FIC) testing for drug combinations.
• Ex vivo assessment of effectiveness in THP-1 infected macrophages.

Main Results:

• Seventeen of twenty synthesized compounds exhibited antitubercular activity.
• Six compounds were highly active against the H37Rv strain, with compound 7 showing potent activity (MIC 0.5 µM).
• Four derivatives were also highly active against three mono-resistant MTB strains.
• Compound 7 demonstrated a rifampicin-like mechanism, inhibiting M. tuberculosis RNA polymerase (RNAP).
• Compound 7 showed additive effects with rifampin, isoniazid, and ethambutol.
• Most compounds, particularly compound 14, were highly active against M. avium.
• Ex vivo effectiveness correlated with increased cell permeability.
• Compounds exhibited low cytotoxicity and did not induce antibacterial resistance.

Conclusions:

• Azepano-triterpenoids are a promising class of compounds with significant antitubercular and anti-mycobacterial activity.
• Compound 7 is a potent lead candidate for novel tuberculosis therapies, potentially overcoming existing resistance mechanisms.
• Combination therapy with compound 7 may enhance treatment efficacy against M. tuberculosis.
• The compounds show broad-spectrum activity, including against challenging NTM like M. avium.