2-Methoxyestradiol synergizes with sorafenib to suppress hepatocellular carcinoma by simultaneously dysregulating hypoxia-inducible factor-1 and -2

Abstract Sorafenib is the approved systemic drug of choice for advanced hepatocellular carcinoma (HCC), but has demonstrated limited benefits because of drug resistance. 2-Methoxyestradiol (2ME2) has been shown to be a promising anticancer drug against various types of cancers and acts by dysregulating hypoxia-inducible factor (HIF)-1. Hypoxic cancer cells are extremely resistant to therapies since they elicit strong survival ability due to the cellular adaptive response to hypoxia, which is controlled by HIF-1 and HIF-2. The present study has demonstrated that sorafenib downregulated the expression of HIF-1α, making the hypoxic response switch from HIF-1α- to HIF-2α-dependent pathways, resulting in upregulation of HIF-2α, which contributes to the insensitivity of hypoxic HCC cells to sorafenib. HIF-2α played a dominant role in regulating VEGF, thus sorafenib in turn increased the expression of VEGF (a downstream molecule of both HIF-1 and HIF-2) and cyclin D1 (a downstream molecule of HIF-2), but reduced the expression of LDHA (a downstream molecule of HIF-1), in hypoxic HCC cells. 2ME2 significantly reduced the expression of both HIF-1α and HIF-2α, and their downstream molecules, VEGF, LDHA and cyclin D1, rendering hypoxic HCC cells to increased sensitivity to 2ME2. 2ME2 also inhibited the nuclear translocation of HIF-1α and HIF-2α proteins, but had no effect on their mRNA expression. 2M2 synergized with sorafenib to suppress the proliferation and induction of apoptosis of HCC cells in vitro and in vivo , and inhibited tumoral angiogenesis. These results indicate that 2ME2 given in combination with sorafenib acts synergistically for treating HCC.