Enhanced response to radiotherapy in tumours deficient in the function of hypoxia-inducible factor-1.
OBJECTIVE
To test the hypothesis that deficiency in expression of the transcription factor, HIF-1, renders tumours more radioresponsive than HIF-1 proficient tumours.


METHODS
Tumours comprising mouse hepatoma cells lacking HIF-1beta (and thereby HIF-1 function) were grown in nude mice and radiation-induced growth delay compared with that seen for wild-type tumours and tumours derived from HIF-1beta negative cells where HIF-1 function had been restored.


RESULTS
The xenografts that lack HIF-1 activity take longer to establish their growth and are more radioresponsive than both parental xenografts and those with restored HIF-1 function. Pre-treatment of the HIF-1 deficient xenografts with the hypoxic radiosensitizer misonidazole, had little effect on radioresponse. In contrast this treatment radiosensitized the parental xenografts. In spite of this, no difference in oxygenation status was found between the tumour types as measured by Eppendorf O(2)-electrodes and by binding of the hypoxic cell marker NITP. Admixing wild type and HIF-1 deficient cells in the same tumour at ratios of 1 in 10 and 1 in 100 restores the growth of the mixed tumours to that of a 100% HIF-1 proficient cell population. However, when comparing the effects of radiation on the mixed tumours, radioresponsiveness is maintained in those tumours containing the high proportion of HIF-1 deficient cells.


CONCLUSIONS
The differences in radioresponse do not correlate with tumour oxygenation, suggesting that the hypoxic cells within the HIF-1 deficient tumours do not contribute to the outcome of radiotherapy. Thus, hypoxia impacts on tumour radioresponsiveness not simply because of the physio-chemical mechanism of oxygen with radiation-induced radicals causing damage 'fixation', but also because hypoxia/HIF-1 promotes expression of genes that allow tumour cells to survive under these adverse conditions. Further, the results from the cell mixing experiments uncouple the growth promoting effects of HIF-1 and the underlying mechanism by which HIF-1 may increase radiation resistance in solid tumours.
Williams
Kaye J
KJ
School of Pharmacy and Pharmaceutical Sciences, University of Manchester, Manchester M13 9PL, UK.
Telfer
Brian A
BA
Xenaki
Dia
D
Sheridan
Mary R
MR
Desbaillets
Isabelle
I
Peters
Hans J W
HJ
Honess
Davina
D
Harris
Adrian L
AL
Dachs
Gabi U
GU
van der Kogel
Albert
A
Stratford
Ian J
IJ
D000818:Animals; D006528:Carcinoma, Hepatocellular / Q000503:physiopathology* / Q000532:radiotherapy* / Q000662:veterinary; D002453:Cell Cycle; D015687:Cell Hypoxia; D004268:DNA-Binding Proteins / Q000096:biosynthesis* / Q000235:genetics*; D005260:Female; D006801:Humans; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D008113:Liver Neoplasms / Q000503:physiopathology* / Q000532:radiotherapy* / Q000662:veterinary; D051379:Mice; D008819:Mice, Nude; D009687:Nuclear Proteins / Q000096:biosynthesis* / Q000235:genetics*; D011836:Radiation Tolerance; D014157:Transcription Factors / Q000096:biosynthesis* / Q000235:genetics*; D014183:Transplantation, Heterologous; D016896:Treatment Outcome
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; D014157:Transcription Factors