Hypoxia-mediated sorafenib resistance can be overcome by EF24 through Von Hippel-Lindau tumor suppressor-dependent HIF-1α inhibition in hepatocellular carcinoma

Abstract

The increasing incidence of hepatocellular carcinoma (HCC) is of great concern not only in the United States but throughout the world. Although sorafenib, a multikinase inhibitor with antiangiogenic and antiproliferative effects, currently sets the new standard for advanced HCC, tumor response rates are usually quite low. An understanding of the underlying mechanisms for sorafenib resistance is critical if outcomes are to be improved. In this study we tested the hypothesis that hypoxia caused by the antiangiogenic effects of sustained sorafenib therapy could induce sorafenib resistance as a cytoprotective adaptive response, thereby limiting sorafenib efficiency. We found that HCCs, clinically resistant to sorafenib, exhibit increased intratumor hypoxia compared with HCCs before treatment or HCCs sensitive to sorafenib. Hypoxia protected HCC cells against sorafenib and hypoxia-inducible factor 1 (HIF-1a) was required for the process. HCC cells acquired increased P-gp expression, enhanced glycolytic metabolism, and increased nuclear factor kappa B (NF-jB) activity under hypoxia. EF24, a molecule having structural similarity to curcumin, could synergistically enhance the antitumor effects of sorafenib and overcome sorafenib resistance through inhibiting HIF-1a by sequestering it in cytoplasm and promoting degradation by way of up-regulating Von Hippel-Lindau tumor suppressor (VHL). Furthermore, we found that sustained sorafenib therapy led to increased intratumor hypoxia, which was associated with sorafenib sensitivity in HCC subcutaneous mice tumor models. The combination of EF24 and sorafenib showed synergistically effects against metastasis both in vivo and in vitro. Synergistic tumor growth inhibition effects were also observed in subcutaneous and orthotopic hepatic tumors. Conclusion: Hypoxia induced by sustained sorafenib treatment confers sorafenib resistance to HCC through HIF-1a and NF-jB activation. EF24 overcomes sorafenib resistance through VHL-dependent HIF-1a degradation and NF-jB inactivation. EF24 in combination with sorafenib represents a promising strategy for HCC.

Mechanisms of resistance to sorafenib and the corresponding strategies in hepatocellular carcinoma

“…Although sorafenib downregulates the synthesis of hypoxia-inducible factor (HIF)-1α in HCC cells in vitro and in vivo [32] , the correlation of sorafenib resistance and hypoxic microenvironment is attractive because the antiangiogenic activity of sorafenib is speculated to lead to tumor starvation and subsequent tumor hypoxia [33] . A recent study [34] has shown that sorafenib-resistant HCC tissues had higher expression of HIF-1α than sorafenibsensitive and pre-treated HCC tissues. In xenograft models, the increased hypoxia because of sustained sorafenib therapy was associated with sorafenib sensitivity.…”

Tirapazamine Sensitizes Hepatocellular Carcinoma Cells to Topoisomerase I Inhibitors via Cooperative Modulation of Hypoxia-Inducible Factor-1α

“…Treatments were initiated when tumors reached a mean group size of about 100 mm 3 . Tumor volume (mm 3 ) was measured with calipers and calculated as (W 2 ÂL)/2, where W is the width and L is the length.…”

“…Conventional radio/chemotherapies are generally not prescribed for advanced hepatocellular carcinoma due to their low efficacies (2). We and other groups (3,4) have found that the expression of HIF-1a is increased in most hepatocellular carcinomas and is associated with poor outcomes. Because fibrogenesis during the development of cirrhosis ultimately destroys the normal blood supply to the liver, the blood supply is limited in hepatocellular carcinoma with cirrhosis, which ultimately leads to local hypoxia (5).…”

Targeting hypoxia-inducible factor-2α enhances sorafenib antitumor activity via β-catenin/C-Myc-dependent pathways in hepatocellular carcinoma

“…Previous studies have reported that sustained sorafenib treatment may promote hypoxia within tumors, which has been associated with sorafenib-resistance in HCC patients as well as subcutaneous mice models of HCC (10). In addition, it was reported that short-term sorafenib therapy reduced vascularization, resulting in increased tumor hypoxia (11).…”