Liquiritigenin inhibits serum-induced HIF-1α and VEGF expression via the AKT/mTOR-p70S6K signalling pathway in HeLa cells.

Liquiritigenin (LQ) is a non-toxic dietary flavonoid with chemopreventive and anticancer properties. However, the mechanism of its antiangiogenesis remains unclear. Hypoxia-inducible factor-1α (HIF-1α) and its downstream target, vascular endothelial growth factor (VEGF), play a critical role in tumour angiogenesis and represent an attractive chemotherapeutic target. In this study, we investigated the effect of LQ on the molecular mechanism of angiogenesis. We found that LQ inhibited VEGF expression at both mRNA and protein levels. Liquiritigenin did not affect HIF-1α expression at the mRNA level, but it dramatically inhibited both serum- and mimicked hypoxic-induced HIF-1α protein accumulation in HeLa cells. Furthermore, we showed that LQ inhibited serum-induced expression of HIF-1α by reducing its stability and decreased the synthesis in a dose-dependent manner. Mechanistically, we demonstrated that LQ inhibited HIF-1α and VEGF expression involved in blocking the protein kinase B (PKB/Akt) signalling pathway, and the mechanisms correlated with dephosphorylation of the mammalian target of rapamycin (mTOR) and its effector ribosomal protein S6 kinase (p70S6K). In addition, LQ inhibited VEGF-induced formation of capillary-like structures in human umbilical vein endothelial cells (HUVEC). Taken together, our study provided valuable insights into the mechanism of antiangiogenic effect of LQ.

Xie SR ，Wang Y ，Liu CW ，Luo K ，Cai YQ ... -  《-》

Magnolol suppresses hypoxia-induced angiogenesis via inhibition of HIF-1α/VEGF signaling pathway in human bladder cancer cells.

The hypoxic environment in tumors is an important factor causing tumor angiogenesis by activating the key transcription factor, hypoxia-inducible factors-1α (HIF-1α). Magnolol isolated from Magnolia officinalis has been reported to exhibit an anticancer activity via elevation of apoptosis. However, whether magnolol inhibits tumor angiogenesis remains unknown. In the present study, we demonstrated that magnolol significantly inhibited angiogenesis in vitro and in vivo evidenced by the attenuation of hypoxia and vascular endothelial growth factor (VEGF)-induced tube formation of human umbilical vascular endothelial cells, vasculature generation in chicken chorioallantoic membrane and Matrigel plug. In hypoxic human bladder cancer cells (T24), treatment with magnolol inhibited hypoxia-stimulated H2O2 formation, HIF-1α induction including mRNA, protein expression, and transcriptional activity as well as VEGF secretion. Additionally, the enhanced degradation of HIF-1α protein via enhancing prolyl hydroxylase activity and the decreased newly-synthesized HIF-1α protein in hypoxic T24 cells may involve the reduction of HIF-1α protein accumulation by magnolol. Interestingly, magnolol also acts as a VEGFR2 antagonist, and subsequently attenuates the down-stream AKT/mTOR/p70S6K/4E-BP-1 kinase activation both in hypoxic T24 cells and tumor tissues. As expected, administration of magnolol greatly attenuated tumor growth, angiogenesis and the protein expression of HIF-1α, VEGF, CD31, a marker of endothelial cells, and carbonic anhydrase IX, an endogenous marker for hypoxia, in the T24 xenograft mouse model. Collectively, these findings strongly indicate that the anti-agngiogenic activity of magnolol is, at least in part, mediated by suppressing HIF-1α/VEGF-dependent pathways, and suggest that magnolol may be a potential drug for human bladder cancer therapy.

Chen MC ，Lee CF ，Huang WH ，Chou TC ... -  《-》

Notoginsenoside Ft1 promotes angiogenesis via HIF-1α mediated VEGF secretion and the regulation of PI3K/AKT and Raf/MEK/ERK signaling pathways.

Notoginsenoside Ft1 (Ft1) is a saponin isolated from Panax notoginseng, which has been used traditionally for the treatment of trauma injuries in East Asia. Here we show that Ft1 is a novel stimulator of angiogenesis. The results show that Ft1 induces proliferation, migration, and tube formation in cultured human umbilical vein endothelial cells (HUVECs). Ft1 increases translocalization of hypoxia-inducible factor-1α (HIF-1α) from cytoplasm to nuclei, where it binds to the vascular endothelial growth factor (VEGF) promoter, increasing the expression of VEGF mRNA and the subsequent secretion of the growth factor. Ft1 induces the activation of PI3K/AKT and Raf/MEK/ERK signaling pathways. Pharmacological inhibition with LY294002, wortmanin or PD98059 reduces Ft1-induced angiogenesis, indicating the important role played by these pathways. In addition, Ft1 induces phosphorylation of the mammalian target of rapamycin (mTOR), and siRNA-mediated mTOR knockdown decreases tube formation, proliferation, transport of HIF-1α into nuclei and VEGF mRNA expression in response to Ft1. Finally, in vivo, Ft1 promotes the formation of blood vessels in Matrigel plug and wound healing in mice. Taken together, the present results reveal that Ft1 stimulates angiogenesis via HIF-1α-mediated VEGF expression, with PI3K/AKT and Raf/MEK/ERK signaling cascades concurrently participating in the process.

Shen K ，Ji L ，Gong C ，Ma Y ，Yang L ，Fan Y ，Hou M ，Wang Z ... -  《-》

Silibinin inhibits hypoxia-inducible factor-1alpha and mTOR/p70S6K/4E-BP1 signalling pathway in human cervical and hepatoma cancer cells: implications for anticancer therapy.

The hypoxia-inducible factor 1 (HIF-1) plays a critical role for tumour adaptation to microenvironmental hypoxia, and represents an appealing chemotherapeutic target. Silibinin is a nontoxic flavonoid reported to exhibit anticancer properties. However, the mechanisms by which silibinin inhibits tumour growth are not fully understood. In this study, silibinin was found to inhibit hypoxia-induced HIF-1alpha accumulation and HIF-1 transcriptional activity in human cervical (HeLa) and hepatoma (Hep3B) cells. Neither HIF-1alpha protein degradation rate nor HIF-1alpha steady-state mRNA level was affected by silibinin. Rather, we found that suppression of HIF-1alpha accumulation by silibinin correlated with strong dephosphorylation of mammalian target of rapamycin (mTOR) and its effectors ribosomal protein S6 kinase (p70S6K) and eukaryotic initiation factor 4E-binding protein-1 (4E-BP1), a pathway known to regulate HIF-1alpha expression at the translational level. Silibinin also activated Akt, a mechanistic feature exhibited by established mTOR inhibitors in many tumour cells. Moreover, silibinin reduced hypoxia-induced vascular endothelial growth factor (VEGF) release by HeLa and Hep3B cells, and this effect was potentiated by the PI3K/Akt inhibitor LY294002. Finally, silibinin was found to be a potent inhibitor of cell proliferation. These results show that silibinin is an effective inhibitor of HIF-1 and provide new perspectives into the mechanism of its anticancer activity.

García-Maceira P ，Mateo J 《-》

Ascofuranone suppresses EGF-induced HIF-1α protein synthesis by inhibition of the Akt/mTOR/p70S6K pathway in MDA-MB-231 breast cancer cells.

Hypoxia-inducible factor (HIF)-1 plays an important role in tumor progression, angiogenesis and metastasis. In this study, we investigated the potential molecular mechanisms underlying the anti-angiogenic effect of ascofuranone, an isoprenoid antibiotic from Ascochyta viciae, in epidermal growth factor (EGF)-1 responsive human breast cancer cells. Ascofuranone significantly and selectively suppressed EGF-induced HIF-1α protein accumulation, whereas it did not affect the expression of HIF-1β. Furthermore, ascofuranone inhibited the transcriptional activation of vascular endothelial growth factor (VEGF) by reducing protein HIF-1α. Mechanistically, we found that the inhibitory effects of ascofuranone on HIF-1α protein expression are associated with the inhibition of synthesis HIF-1α through an EGF-dependent mechanism. In addition, ascofuranone suppressed EGF-induced phosphorylation of Akt/mTOR/p70S6 kinase, but the phosphorylation of ERK/JNK/p38 kinase was not affected by ascofuranone. These results suggest that ascofuranone suppresses EGF-induced HIF-1α protein translation through the inhibition of Akt/mTOR/p70S6 kinase signaling pathways and plays a novel role in the anti-angiogenic action.

Jeong YJ ，Cho HJ ，Magae J ，Lee IK ，Park KG ，Chang YC ... -  《-》