Functionality of hypoxia-induced BAX expression in a human glioblastoma xenograft model.
The effectiveness of radiation therapy for human brain tumors is limited by the presence of radiation-resistant hypoxic cells. In order to improve patient outcomes, therapeutic methods that increase hypoxic cell killing must be developed. To investigate the possibility of using the hypoxic tumor microenvironment itself as a target for gene therapy, we stably transfected U-251 MG human glioblastoma cells with constructs containing the suicide gene Bax under the regulation of a nine-copy concatemer of hypoxia responsive elements (HREs). Previously, we demonstrated that the expression of BAX protein under anoxic conditions in transfected U-251 MG clones leads to increased cell killing in vitro. Our recent studies revealed that HIF-1alpha induction under anoxic conditions occurs prior to the increase in BAX expression, thereby implicating HIF-1 induction as the basis of BAX upregulation. To test the effect of BAX-mediated cell killing in vivo, we implanted five stably transfected clones subcutaneously into the flanks of athymic mice. Compared to nontransfected controls, tumor growth in four of five clones was significantly retarded. Histopathological analysis demonstrated decreased hypoxic fractions and increased amounts of apoptosis in clone-derived tumors. These results suggest that the tumor microenvironment is sufficiently hypoxic to trigger HRE-mediated cell killing via the BAX apoptotic pathway.
Ozawa
Tomoko
T
Brain Tumor Research Center, Department of Neurological Surgery, University of California-San Francisco, San Francisco, CA 94143-0520, USA.
Hu
Jethro L
JL
Hu
Lily J
LJ
Kong
Eileen L
EL
Bollen
Andrew W
AW
Lamborn
Kathleen R
KR
Deen
Dennis F
DF
D000818:Animals; D017209:Apoptosis; D015687:Cell Hypoxia; D004268:DNA-Binding Proteins / Q000235:genetics*; D005260:Female; D005909:Glioblastoma / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D051379:Mice; D009687:Nuclear Proteins / Q000235:genetics*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics*; D014162:Transfection; D014407:Tumor Cells, Cultured; D023041:Xenograft Model Antitumor Assays; D051028:bcl-2-Associated X Protein
C494826:BAX protein, human; C494827:Bax protein, mouse; D004268:DNA-Binding Proteins; C497442:HIF1A protein, human; C497443:Hif1a protein, mouse; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D009687:Nuclear Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D014157:Transcription Factors; D051028:bcl-2-Associated X Protein