The inhibition of hypoxia-induced angiogenesis and metastasis by cinnamaldehyde is mediated by decreasing HIF-1α protein synthesis via PI3K/Akt pathway.

Tumor hypoxia is positively correlated with tumor aggressiveness and hence is a negative prognostic factor in cancer. As normal cells usually do not experience such low oxygen levels, hypoxic cell signaling has attracted significant attention for the development of tumor-selective treatment strategies. In response to hypoxia, the master transcriptional regulator, HIF-1α plays central role in cellular adaptation by transactivating several crucial downstream target genes, which are involved in angiogenesis, metastasis, and EMT. In this study, we investigated the effect of cinnamaldehyde (CA), the main active ingredient of Cinnamon cassia bark extract, on hypoxia-induced angiogenesis and metastasis. The study in vitro comprised two cell lines, viz, sarcoma 180 and B16F10 melanoma, which were further confirmed in their respective transplantable in vivo models. Results show that CA administration inhibited tumor angiogenesis, EMT, and metastasis. At the molecular level, this was accompanied by a reduction in VEGF secretion, VEGF receptor (FLK) phosphorylation, matrix metalloproteinase (MMP) expression, and activity as well as a reduction in the EMT-related factors TWIST and ZEB1. Next, we focused our study particularly on the modulation of HIF-1 α by CA, which revealed that CA decreased HIF-1 α protein level by inhibiting its synthesis without affecting its proteasomal degradation. Furthermore, the PI3/Akt/mTOR pathway, which plays an important role in HIF-1α transcription and translation, was also inhibited by CA both in vitro and in vivo. Thus, it can be concluded that CA decreased angiogenesis and metastasis in tumor cells by inhibiting HIF-1α protein accumulation probably by targeting the PI3/Akt/mTOR pathway. © 2019 BioFactors, 45(3):401-415, 2019.