title: Tirapazamine sensitizes hepatocellular carcinoma cells to topoisomerase I inhibitors via cooperative modulation of hypoxia-inducible factor-1α.
abstract: Topoisomerase I inhibitors are a class of anticancer drugs with a broad spectrum of clinical activity. However, they have limited efficacy in hepatocellular cancer. Here, we present in vitro and in vivo evidence that the extremely high level of hypoxia-inducible factor-1α (HIF-1α) in hepatocellular carcinoma is intimately correlated with resistance to topoisomerase I inhibitors. In a previous study conducted by our group, we found that tirapazamine could downregulate HIF-1α expression by decreasing HIF-1α protein synthesis. Therefore, we hypothesized that combining tirapazamine with topoisomerase I inhibitors may overcome the chemoresistance. In this study, we investigated that in combination with tirapazamine, topoisomerase I inhibitors exhibited synergistic cytotoxicity and induced significant apoptosis in several hepatocellular carcinoma cell lines. The enhanced apoptosis induced by tirapazamine plus SN-38 (the active metabolite of irinotecan) was accompanied by increased mitochondrial depolarization and caspase pathway activation. The combination treatment dramatically inhibited the accumulation of HIF-1α protein, decreased the HIF-1α transcriptional activation, and impaired the phosphorylation of proteins involved in the homologous recombination repair pathway, ultimately resulting in the synergism of these two drugs. Moreover, the increased anticancer efficacy of tirapazamine combined with irinotecan was further validated in a human liver cancer Bel-7402 xenograft mouse model. Taken together, our data show for the first time that HIF-1α is strongly correlated with resistance to topoisomerase I inhibitors in hepatocellular carcinoma. These results suggest that HIF-1α is a promising target and provide a rationale for clinical trials investigating the efficacy of the combination of topoisomerase I inhibitors and tirapazamine in hepatocellular cancers.
authors.affiliation: Corresponding Authors: Bo Yang and Qiao-Jun He, College of Pharmaceutical Sciences, Zhejiang University, #866 Yuhangtang Road, Hangzhou 310058, China, yang924@zju.edu.cn.
authors.forename: Tian-Yu
authors.initials: TY
authors.lastname: Cai
authors.forename: Xiao-Wen
authors.initials: XW
authors.lastname: Liu
authors.forename: Hong
authors.initials: H
authors.lastname: Zhu
authors.forename: Ji
authors.initials: J
authors.lastname: Cao
authors.forename: Jun
authors.initials: J
authors.lastname: Zhang
authors.forename: Ling
authors.initials: L
authors.lastname: Ding
authors.forename: Jian-Shu
authors.initials: JS
authors.lastname: Lou
authors.forename: Qiao-Jun
authors.initials: QJ
authors.lastname: He
authors.forename: Bo
authors.initials: B
authors.lastname: Yang
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D006528:Carcinoma, Hepatocellular / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology; D015687:Cell Hypoxia / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004264:DNA Topoisomerases, Type I / Q000096:biosynthesis* / Q000235:genetics; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics* / Q000378:metabolism; D008113:Liver Neoplasms / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology; D051379:Mice; D000077704:Tirapazamine; D059004:Topoisomerase I Inhibitors / Q000008:administration & dosage; D014227:Triazines / Q000008:administration & dosage; D023041:Xenograft Model Antitumor Assays
chemical_list: C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D059004:Topoisomerase I Inhibitors; D014227:Triazines; D000077704:Tirapazamine; D004264:DNA Topoisomerases, Type I