Z‐Guggulsterone Inhibits Triple‐Negative Breast Cancer Progression by Blocking Autophagosome–Lysosome Fusion via <scp>OGT</scp> ‐Mediated <scp>SNAP29</scp> O‐ <scp>GlcNAcylation</scp>

Triple-negative breast cancer (TNBC) remains a clinical challenge due to its heterogeneity and lack of targeted therapies. This study aimed to evaluate the antitumor effects and underlying mechanisms of Z-guggulsterone (Z-GS), a natural product, in TNBC. Human TNBC cell lines (MDA-MB-231 and MDA-MB-468) were treated with Z-GS to assess proliferation, cell-cycle progression, apoptosis, and reactive oxygen species (ROS) accumulation. Autophagic flux and the OGT-SNAP29 signaling axis were investigated via Western blotting, immunofluorescence, molecular docking, and molecular dynamics simulation. In vivo, the antitumor efficacy and safety were evaluated using TNBC xenografts in zebrafish and BALB/c nude mice. Z-GS selectively suppressed TNBC cell proliferation, induced cell-cycle arrest and apoptosis, and increased intracellular ROS. Mechanistically, Z-GS upregulated O-GlcNAc transferase (OGT) expression, enhanced SNAP29 O-GlcNAcylation, disrupted SNARE complex assembly, inhibited autophagosome-lysosome fusion, and blocked late-stage autophagic flux. In vivo, Z-GS significantly inhibited TNBC xenograft growth without detectable toxicity. Z-GS functions as a novel late-stage autophagy inhibitor and exhibits selective anti-TNBC activity, bridging natural product pharmacology and cancer treatment.