| Summary: | Hypoxia-inducible factor 1 (HIF-1) plays a pivotal role in tumor adaptation to microenvironmental hypoxia, and it also exerts important roles in angiogenesis and tumor development. Vanillic acid is a dietary phenolic compound reported to exhibit anticancer properties. However, the mechanisms by which vanillic acid inhibits tumor growth are not fully understood. Here, we investigated the effect of vanillic acid on HIF-1α activation. Vanillic acid significantly inhibits HIF-1α expression induced by hypoxia in various human cancer cell lines. Further analysis revealed that vanillic acid inhibited HIF-1α protein synthesis. Neither the HIF-1α protein degradation rate nor the steady-state HIF-1α mRNA levels were affected by vanillic acid. Moreover, vanillic acid inhibited HIF-1α expression by suppressing mammalian target of rapamycin/p70 ribosomal protein S6 kinase/eukaryotic initiation factor 4E-binding protein-1 and Raf/extracellular signal-regulated kinase (ERK) kinase (MEK)/ERK pathways. We found that vanillic acid dose-dependently inhibited VEGF and EPO protein expressions and disrupted tube formation. The results suggest that vanillic acid effectively inhibits angiogenesis. Flow cytometry analysis demonstrated that vanillic acid significantly induced G1 phase arrest and inhibited the proliferation of human colon cancer HCT116 cells. In vivo experiments confirmed that vanillic acid treatment caused significant inhibition of tumor growth in a xenografted tumor model. These studies reveal that vanillic acid is an effective inhibitor of HIF-1α and provides new perspectives into the mechanism of its antitumor activity.
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