title: Tumor cycling hypoxia induces chemoresistance in glioblastoma multiforme by upregulating the expression and function of ABCB1.
abstract: Tumor cycling hypoxia is now a well-recognized phenomenon in animal and human solid tumors. However, how tumor cycling hypoxia impacts chemotherapy is unclear. In the present study, we explored the impact and the mechanism of cycling hypoxia on tumor microenvironment-mediated chemoresistance. Hoechst 33342 staining and hypoxia-inducible factor-1 (HIF-1) activation labeling together with immunofluorescence imaging and fluorescence-activated cell sorting were used to isolate hypoxic tumor subpopulations from human glioblastoma xenografts. ABCB1 expression, P-glycoprotein function, and chemosensitivity in tumor cells derived from human glioblastoma xenografts or in vitro cycling hypoxic stress-treated glioblastoma cells were determined using Western blot analysis, drug accumulation and efflux assays, and MTT assay, respectively. ABCB1 expression and P-glycoprotein function were upregulated under cycling hypoxia in glioblastoma cells concomitant with decreased responses to doxorubicin and BCNU. However, ABCB1 knockdown inhibited these effects. Moreover, immunofluorescence imaging and flow cytometric analysis for ABCB1, HIF-1 activation, and Hoechst 3342 in glioblastoma revealed highly localized ABCB1 expression predominantly in potentially cycling hypoxic areas with HIF-1 activation and blood perfusion in the solid tumor microenvironment. The cycling hypoxic tumor cells derived from glioblastoma xenografts exhibited higher ABCB1 expression, P-glycoprotein function, and chemoresistance, compared with chronic hypoxic and normoxic cells. Tumor-bearing mice that received YC-1, an HIF-1α inhibitor, exhibited suppressed tumor microenvironment-induced ABCB1 induction and enhanced survival rate in BCNU chemotherapy. Cycling hypoxia plays a vital role in tumor microenvironment-mediated chemoresistance through the HIF-1-dependent induction of ABCB1. HIF-1 blockade before and concurrent with chemotherapy could suppress cycling hypoxia-induced chemoresistance.
authors.affiliation: Institute of Medicine, Chung Shan Medical University, Taichung, Taiwan.
authors.forename: Chii-Wen
authors.initials: CW
authors.lastname: Chou
authors.forename: Chi-Chung
authors.initials: CC
authors.lastname: Wang
authors.forename: Chung-Pu
authors.initials: CP
authors.lastname: Wu
authors.forename: Yu-Jung
authors.initials: YJ
authors.lastname: Lin
authors.forename: Yu-Chun
authors.initials: YC
authors.lastname: Lee
authors.forename: Ya-Wen
authors.initials: YW
authors.lastname: Cheng
authors.forename: Chia-Hung
authors.initials: CH
authors.lastname: Hsieh
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000818:Animals; D014408:Biomarkers, Tumor / Q000378:metabolism; D015153:Blotting, Western; D001932:Brain Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology*; D049109:Cell Proliferation; D019008:Drug Resistance, Neoplasm; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D005909:Glioblastoma / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D008156:Luciferases / Q000378:metabolism; D008297:Male; D051379:Mice; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D014407:Tumor Cells, Cultured; D015854:Up-Regulation; D023041:Xenograft Model Antitumor Assays
chemical_list: C513055:ABCB1 protein, human; D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D014408:Biomarkers, Tumor; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D008156:Luciferases