Targeted constitutive activation of signal transducer and activator of transcription 3 in human hepatocellular carcinoma cells by cucurbitacin B

Purpose 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. Conclusion 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.