HIF-1α blockade enhances the therapeutic efficacy of hypoxia for the treatment of hepatocellular carcinoma (HCC)

Abstract

Background and Objective: Transarterial embolization (TAE) is the major alternative for the treatment of non-resectable hepatocellular carcinoma (HCC). Although the hypoxic condition generated by hepatic artery blockade could induce tumor cell death, hypoxia-related angiogenesis and subsequent tumor re-growth might lead to treatment failure. Therefore, we designed the present study to investigate whether suppression of the activity of HIF-1α, a key player in hypoxia-induced angiogenesis, could enhance the therapeutic efficacy of hypoxia. Materials and Methods: In vitro, hypoxia was induced by culturing the tumor cells with 0.1% O2. YC-1, a HIF-1α blocker, was administered to the tumor cells at different concentrations under hypoxic condition. The proliferation and viability of the cells were determined by MTT assay and Annexin-V labeling, respectively. Molecular mechanism related to HIF-1α was determined by Western blot and luciferase promoter assay. In vivo, an orthotopic HCC model was generated by injection of tumor cells into the left lobe of the rat liver. Hypoxia was induced by hepatic artery ligation (HAL). YC-1 was administered through intra-tumoral injection right after hepatic artery ligation. Survival time was recorded and the histology of tumor tissue was studied. Results: In vitro, YC-1 administration decreased the viability of tumor cells but did not cause any change in the number of apoptotic cells. Hypoxia upregulated the expression of HIF-1α, which could be suppressed by YC-1 administration. The suppressive effect of YC-1 on HIF-1α could be blocked by overexpression of murine double minute 2 (MDM2), a potential upstream molecule of HIF-1α, and YC-1 affected MDM2 expression at a transcriptional level. In vivo, HAL stimulated HIF-1α upregulation in the tumor tissue with a peak level at 24 hr. Administration of YC-1 significantly prolonged the survival of tumor-bearing rats. Both HAL and HAL combined with YC-1 induced tumor tissue necrosis. YC-1 administration decreased the number of HIF-1α+ cells as well as vWF+ cells, which is a marker for angiogenesis in the tumor tissue. In addition, MDM2 mRNA level was downregulated in the combined treatment group, which was consistent with the in vitro results. Conclusion: The present study revealed that blockade of HIF-1α-related pathway could enhance the efficacy of hypoxia for the treatment of HCC. YC-1 achieved anti-HIF-1α effects through MDM2 dependent pathways.