Triptolide suppresses proliferation, hypoxia-inducible factor-1α and c-Myc expression in pancreatic cancer cells

Triptolide (TL) is known to suppress the proliferation of a number of pancreatic cancer cell lines in vitro. Marked antitumor effects were also observed in a xenograft model of pancreatic cancer. Hypoxia-inducible factor-1α (HIF-1α) is highly expressed in pancreatic cancer cells lines. The present study therefore tested the hypothesis that suppression of HIF-1α is associated with the antitumor activity of TL. Quantitative polymerase chain reaction and western blot analysis were used to determine the level of gene expression. A xenograft tumor model of pancreatic cancer was established in athymic nude mice and the tumor size was measured to evaluate the outcome of TL treatment. Immunohistochemistry was used to detect the expression of HIF-1α and vascular endothelial growth factor (VEGF), and to assess microvessel density. Microarray was used to investigate gene expression in pancreatic cancer cells following TL treatment. The expression of HIF-1α was shown to be reduced in pancreatic cell lines following treatment with TL, and this effect occurred in a dose-dependent manner. In a xenograft model of pancreatic cancer, reduced levels of HIF-1α were also observed in mice that were treated with TL. Furthermore, the expression of VEGF, which is a direct target of HIF-1α, was also suppressed, and the microvessel density of tumor tissues was consequently reduced. A microarray analysis of gene expression was performed in order to investigate the potential mechanisms underlying the antitumor activity of TL. The results showed that 11 genes, including c-Myc, SOX9 and Ets2, were downregulated at an early stage following treatment with TL. A recent study indicated that overexpression of c-Myc in colon cancer cells promotes increased expression of HIF-1α and VEGF. Therefore, TL may suppress HIF-1α through a c-Myc-dependent mechanism, which is involved in antitumor effects in mouse models of pancreatic cancer.