Scutebarbatine B Exerts Anti-Breast Cancer Activity by Inducing Cell Cycle Arrest and Apoptosis Through Multiple Pathways.

Breast cancer is the most commonly occurring cancer among women with high mortality. Identifying effective anticancer compounds to improve the overall survival is imperative. The present study was designed to evaluate the effects and underlying mechanisms of Scutebarbatine B (SBT-B), a diterpenoid alkaloid extracted from Scutellaria barbata D. Don (S. barbata), on breast cancer. Cell viability assay, 5-ethynyl-2'-deoxyuridine (EdU) assay, immunofluorescence, flow cytometry analysis, TdT-mediated dUTP-biotin nick end labeling (TUNEL) staining, Western blot analysis, 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA), and dihydroethidium (DHE) staining were performed to elucidate the anticancer mechanisms of SBT-B in vitro. Mice xenograft models were used to assess the anticancer properties in vivo. We demonstrated that SBT-B suppressed the proliferation of breast cancer cells in a dose-dependent manner. SBT-B treatment induced DNA damage response, G2/M phase arrest and downregulated the expression of cyclinB1, cyclinD1, Cdc2, and p-Cdc2. SBT-B could trigger apoptosis through increasing the cleavage of caspase-8, caspase-9 and PARP in breast cancer cells. Additionally, SBT-B elevated the generation of intracellular reactive oxygen species (ROS). Treatment with a ROS scavenger N-acetyl cysteine (NAC) partially blocked viability reduction and cleavage of caspase-8 and PARP induced by SBT-B. Moreover, SBT-B blocked pRB/E2F1 and Akt/mTOR pathways. Incubation with SBT-B increased the expression of IRE1 and phospho-JNK. In vivo, SBT-B exhibited significant suppression of tumor growth in xenograft models. We demonstrate firstly that SBT-B induces DNA damage, cell cycle arrest and apoptosis in breast cancer cells. ROS generation, suppression of oncogenic signaling and activation of IRE1/JNK pathway play an essential role in the anticancer activity of SBT-B. Our study highlights the potential of SBT-B as an alternative candidate to treat human breast cancer.