Abstract 4389: Hypoxia-inducible HIF1α-miR-210 signaling axis enhances chemoresistance in human hepatocellular carcinoma

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Dysregulation of microRNA is implicated in many human malignancies including hepatocellular carcinoma (HCC), yet little is known regarding the regulatory mechanisms of these small noncoding RNAs. Hypoxia is a prevalent tumor microenvironment in HCC because of its rapid growth often to large size, and plays a key role in modulating tumor aggressiveness. Apart from insufficient neovascularization of HCC tumors, hepatic ischemia induced during transarterial chemoembolization (TACE) also resulted in development of hypoxic HCC tumors. Therefore, studying the underlying mechanisms of hypoxia-induced chemoresistance may provide treatment benefits for HCC patients. Previously, we investigated the effects of hypoxia on microRNA expression in human HCCs, and characterized hypoxia-inducible microRNA-210 (miR-210) as an important player for the development of metastatic phenotypes. In the present study, we sought to investigate whether hypoxia confers chemoresistance to HCC cells, and whether hypoxic induction of hypoxia-inducible factor 1α (HIF1α)-miR-210 signaling axis promoted cell survival against cytotoxic treatments. Firstly, we treated human HCC cell line SMMC7721 with cisplatin under both normoxic and hypoxic conditions, and examined apoptosis of these cells by flow cytometry analysis after co-staining with annexin V and propidium iodide. We found that hypoxic SMMC-7721 cells were more resistant to both cisplatin and 5-fluorouracil under hypoxia when compared to normoxia. Moreover, we observed that HIF1α appears to play a detrimental role in mediating chemoresistance, as we demonstrated that the population of annexin V positive cells was significantly higher in HIF1α knockdown cells than in the non-targeted control cells upon cisplatin treatment. Similar observation was also obtained by in vivo subcutaneous tumor xenograft experiment, for which we demonstrated that HIF1α knockdown xenografts were more susceptible to cisplatin treatment. Finally, we also examined the importance of miR-210 in hypoxia-induced resistance to cisplatin using miR-210 LNA inhibitor. Under hypoxic conditions, we found that the population of apoptotic cells was higher in SMMC7721 transfected with miR-210 LNA inhibitor compared with that of control LNA transfectant (Annexin-V positive: 23.6% in negative control group at 1.0%O2 vs 28.0% in miR-210 LNA group at 1.0%O2; P<0.05). Taken altogether, we demonstrated that induction of HIF1α-miR-210 axis conferred chemoresistance to HCC cells under hypoxic conditions, and inhibition of miR-210 re-sensitized hypoxic HCC cells to these cytotoxic drugs. We are now underway to investigate the direct downstream cDNA target that contributes to the pro-survival effects mediated by miR-210 under cytotoxic conditions. Citation Format: Alan KL Kai, Regina CL Lo, Joyce MF Lee, Kwan Man, Carmen CL Wong, Jack CM Wong, Irene OL Ng. Hypoxia-inducible HIF1α-miR-210 signaling axis enhances chemoresistance in human hepatocellular carcinoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4389. doi:10.1158/1538-7445.AM2014-4389