Inhibition of the STAT3 signaling pathway is involved in the antitumor activity of cepharanthine in SaOS2 cells.
OBJECTIVE
To investigate the molecular mechanisms underlying the antitumor activity of cepharanthine (CEP), an alkaloid extracted from Stephania cepharantha Hayata.


METHODS
Human osteosarcoma cell line SaOS2 was used. MTT assay, Hoechst 33342 nuclear staining, flow cytometry, Western blotting and nude mouse xenografts of SaOS2 cells were applied to examine the antitumor activity of CEP in vitro and in vivo. The expression levels of STAT3 and its downstream signaling molecules were measured with Western blotting and immunochemistry analysis. The activity of STAT3 was detected based on the phosphorylation level of STAT3, luciferase gene reporter assay and translocation of STAT3 to the nucleus.


RESULTS
Treatment of SaOS2 cells with CEP (2.5-20 μmol/L) inhibited the cell growth in a concentration- and time-dependent manner. CEP (10 μmol/L) caused cell cycle arrest at G(1) phase and induced apoptosis of SaOS2 cells. CEP (10 and 15 μmol/L) significantly decreased the expression of STAT3 in SaOS2 cells. Furthermore, CEP (5 and 10 μmol/L) significantly inhibited the expression of target genes of STAT3, including the anti-apoptotic gene Bcl-xL and the cell cycle regulators c-Myc and cyclin D1. In nude mouse xenografts of SaOS2 cells, CEP (20 mg·kg(-1)·d(-1), ip for 19 d) significantly reduced the volume and weight of the tumor.


CONCLUSIONS
Our findings suggest that inhibition of STAT3 signaling pathway is involved in the anti-tumor activity of CEP.
Institute of Vascular Medicine, Medical Research Center, Peking University Third Hospital, Beijing, China.
Zan
Z
Chen
Chen
C
Huang
Yan-ling
YL
Yang
Yi
Y
Ding
Han-qiang
HQ
Ou-Yang
You-yi
YY
Zhang
Ming
M
Xu
D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D044182:Benzylisoquinolines / Q000494:pharmacology*; D059447:Cell Cycle Checkpoints / Q000187:drug effects; D045744:Cell Line, Tumor / Q000187:drug effects; D019938:Cyclin D1 / Q000235:genetics / Q000378:metabolism; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism; D011897:Random Allocation; D050796:STAT3 Transcription Factor / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*; D051020:bcl-X Protein / Q000378:metabolism; D052117:Benzodioxoles
D000972:Antineoplastic Agents, Phytogenic; D044182:Benzylisoquinolines; D019938:Cyclin D1; D016271:Proto-Oncogene Proteins c-myc; D050796:STAT3 Transcription Factor; D051020:bcl-X Protein; C006947:cepharanthine; D052117:Benzodioxoles