Anti-Mycobacterium tuberculosis activity of 17-hydroxy-jolkinolide B by interacting with RNA polymerase

Euphorbia fischeriana has been traditionally used in Chinese medicine for tuberculosis (TB) treatment since ancient times. In this study, we first report the identification of an abietane-type diterpenoid, 17-hydroxy-jolkinolide B (HJKB), from E. fischeriana, which exhibits potent antimycobacterial activity against both Mycobacterium tuberculosis H37Ra strain and clinical isolates. The minimum inhibitory concentrations (MICs) of HJKB against diverse M. tuberculosis strains range from 1 to 12 μg/mL. Notably, HJKB demonstrates significant bactericidal activity against intracellular M. tuberculosis H37Ra in macrophage models, accompanied by anti-inflammatory effects at concentrations of 2-5 μg/mL. Using a combination of chemoproteomic analysis and pull-down assays, we explored the preliminary antimycobacterial mechanism of HJKB. Results indicate that HJKB interacts with the target proteins RpoB and RpoC in M. tuberculosis H37Ra, a finding further corroborated by molecular docking studies. RpoB and RpoC are essential subunits of the DNA-directed RNA polymerase holoenzyme, which is critical for bacterial ribosomal transcription regulation. In summary, HJKB represents a bioactive constituent of E. fischeriana with anti-TB efficacy, acting as a transcription inhibitor against M. tuberculosis. This study not only elucidates its antimycobacterial mechanism but also provides a preclinical foundation for the development of natural product-based TB therapeutics.