Targeted constitutive activation of signal transducer and activator of transcription 3 in human hepatocellular carcinoma cells by cucurbitacin B.
OBJECTIVE
To determine the effect of cucurbitacin B on human hepatocellular carcinoma cell growth and apoptosis, and to explore the potential mechanisms.


METHODS
In vitro viability of human hepatocellular carcinoma cell line (HepG2) was investigated using a 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide (MTT) assay. Morphologic changes of cells were evaluated through light microscopy. Cell cycle distribution was evaluated with flow cytometry following PI staining. Apoptosis was evaluated respectively with flow cytometry and fluorescent microscopy following Annexin V-FITC/PI and Hoechst 33258 staining. Western blot assays were performed to determine the expression of pSTAT3 and Bcl-2. Finally, in vivo effect of cucurbitacin B on the growth of HepG2 cells was determined in nude mice.


RESULTS
The MTT assay showed that cucurbitacin B inhibited HepG2 cell viability in a dose and time-dependent manner. Cucurbitacin B treatment resulted in accumulation of cells at the S phase of cell cycle as well as apoptosis. Marked morphological changes, including condensation of chromatin, nuclear fragmentation and apoptotic bodies were clearly shown on Hoechst 33258 staining. Western blot showed that cucurbitacin B inhibited STAT3 phosphorylation and down-regulated the expression of Bcl-2. Growth of HepG2 tumor in nude mice was also inhibited by cucurbitacin B.


CONCLUSIONS
Our results suggest that cucurbitacin B may have a therapeutic value in suppressing the growth of human hepatocellular carcinoma. The mechanism may be attributable to the suppression of STAT3 phosphorylation.
Department of Clinical Pharmacology, China Medical University, Shenyang, China. zhangmeixia@mail.cmu.edu.cn
Meixia
M
Zhang
Hongliang
H
Zhang
Chunyan
C
Sun
Xiaolei
X
Shan
Xiaolin
X
Yang
Jesse
J
Li-Ling
Yihui
Y
Deng
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D006528:Carcinoma, Hepatocellular / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D002453:Cell Cycle / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D005434:Flow Cytometry; D006801:Humans; D008114:Liver Neoplasms, Experimental / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D051379:Mice; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D050796:STAT3 Transcription Factor / Q000378:metabolism*; D015996:Survival Rate; D014315:Triterpenes / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D023041:Xenograft Model Antitumor Assays
D019253:Proto-Oncogene Proteins c-bcl-2; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D014315:Triterpenes; C041246:cucurbitacin B