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Moscatilin Induces Apoptosis in Human Colorectal Cancer Cells: A Crucial Role of c-Jun NH₂-Terminal Protein Kinase Activation Caused by Tubulin Depolymerization and DNA Damage

Authors' Affiliations: ¹ Pharmacological Institute and ² School of Pharmacy, College of Medicine, National Taiwan University; and ³ National Research Institute of Chinese Medicine, Taipei, Taiwan, Republic of China

Requests for reprints: Che-Ming Teng, Pharmacological Institute, School of Pharmacy, College of Medicine, National Taiwan University, No. 1, Jen-Ai Road, Section 1, Taipei, Taiwan, Republic of China. Phone: 886-2-2322-1742; Fax: 886-2-2322-1742; E-mail: cmteng{at}ntu.edu.tw.

Purpose: To study the effect of moscatilin (purified from the stem of orchid Dendrobrium loddigesii) on the proliferation of human colorectal cancer HCT-116 cells in vitro and in vivo.

Experimental Design: The growth inhibition of moscatilin was screened on several human cancer cell lines. The effect of moscatilin on tubulin was detected in vitro. Following moscatilin treatment on HCT-116 cells, c-Jun NH₂-terminal protein kinase (JNK) and caspase activation was studied by Western blot analysis, and DNA damage was done by Comet assay. Specific JNK inhibitor SP600125 was cotreated to reverse moscatilin-induced apoptosis. Tumor growth inhibition of moscatilin was done on HCT-116 xenograft models.

Results: Moscatilin induced a time-dependent arrest of the cell cycle at G₂-M, with an increase of cells at sub-G₁. Moscatilin inhibited tubulin polymerization, suggesting that it might bind to tubulins. Moscatilin also induced the phosphorylation of JNK1/2. SP600125 significantly inhibited the activation of caspase-9 and caspase-3 and the subsequent moscatilin-induced apoptosis. The data suggest that JNK activation may contribute to moscatilin-mediated apoptosis signaling. A parallel experiment showed that SP600125 significantly inhibits Taxol- and vincristine-induced HCT-116 cell apoptosis. This suggests that the JNK activation may be a common mechanism for tubulin-binding agents. Moreover, moscatilin induces DNA damage, phosphorylation of H2AX and p53, and up-regulation of p21. Our HCT-116 xenograft models show the in vivo efficacy of moscatilin.

Conclusions: In summary, our results suggest that moscatilin induces apoptosis of colorectal HCT-116 cells via tubulin depolymerization and DNA damage stress and that this leads to the activation of JNK and mitochondria-involved intrinsic apoptosis pathway.