Saikosaponin D Inhibits Proliferation and Promotes Apoptosis Through Activation of MKK4–JNK Signaling Pathway in Pancreatic Cancer Cells

INTRODUCTION: Pancreatic cancer remains one of the most lethal malignancies and has few treatment options. Saikosaponin D (SSD), a major bioactive triterpene saponin isolated from Bupleurum chinense, has been reported to exert cytotoxicity properties toward many cancer cells. However, the effects of SSD on pancreatic cancer have been little scrutinized. METHODS: Here, we investigated the effect of SSD on the proliferation and apoptosis of human pancreatic cancer BxPC3 and PANC1 cells and the mouse pancreatic cancer cell line Pan02. Cell viability was determined by MTT assays and cell apoptosis analyzed by DAPI staining and flow cytometry. Expression levels of apoptosis-regulating markers and activity of the MKK4–JNK signaling pathway were determined by Western blotting. The inhibitor SP600125 was applied to confirm the role of the JNK pathway in SSD efficiency. RESULTS: SSD significantly inhibited the proliferation of BxPC3, PANC1, and Pan02 cells in a concentration- and time-dependent manner. Flow-cytometry analysis indicated obvious apoptosis induction after SSD exposure. Furthermore, SSD significantly triggered cleavage of caspase 3 and caspase 9 proteins and increased the expression of FoxO3a. In addition, activity of the MKK4–JNK pathway was dramatically increased after treatment with SSD in BxPC3 cells. SSD obviously stimulated phosphorylation of JNK, cJun, and SEK1/MKK4 proteins within 30 minutes. The addition of SP600125 blocked the activation of SSD on the MKK4–JNK regulatory pathway and reversed the effects of SSD on proliferation inhibition and apoptosis induction in BxPC3 cells. CONCLUSION: These results revealed that SSD was capable of suppressing tumor growth and promoting apoptosis of pancreatic cancer cells via targeting the MKK4–JNK signaling pathway, indicating the possibility of further developing SSD as a potential therapeutic candidate for pancreatic cancer.