Effect of radiation and ibuprofen on normoxic renal carcinoma cells overexpressing hypoxia-inducible factors by loss of von Hippel-Lindau tumor suppressor gene function.
OBJECTIVE
Tumor hypoxia is a major limiting factor for radiation therapy. Hypoxia-inducible factors (HIFs) are overexpressed in several human cancers and are considered prognostic markers and potential targets for cancer therapy. The purpose of the present study was to investigate the impact of HIFs on radiosensitivity.


METHODS
Renal clear cell carcinoma (RCC) cell lines overexpressing HIFs under normoxic conditions because of inactivation of von Hippel-Lindau tumor suppressor gene function (VHL-ve) and their matched pairs in which overexpression of HIFs was abolished by expression of functional VHL (VHL+ve) were irradiated. Radiosensitivity was determined by clonogenic assay. HIF and VHL protein levels were evaluated by Western blot analysis. RCC cells were also treated with ibuprofen, a radiosensitizer and HIF inhibitor in prostate cancer cells. The effect of ibuprofen on radiosensitization and HIF and VHL proteins was compared in RCC matched-pair cell lines.


RESULTS
The data showed only small differences in the radiosensitivity between the cells overexpressing HIFs and cells with basal HIF levels. The dose-modifying factors for C2, 786-0, and A498 RCC cells were 1.14, 1.14 and 1.15, respectively. Radiation did not alter HIF or VHL protein levels. Ibuprofen inhibited HIFs in VHL+ve cells expressing basal levels of HIFs. In VHL-ve cells overexpressing HIFs, the inhibition was very modest. Ibuprofen radiosensitized C2 RCC cells to the same extent irrespective of their HIF status.


CONCLUSIONS
Overexpression of HIFs in RCC cells harboring VHL mutations has only a modest effect on the radiosensitivity. Radiosensitization by ibuprofen appears to be independent of HIF status.
Palayoor
Sanjeewani T
ST
Radiation Oncology Branch, Center for Cancer Research and the Molecular Radiation Therapeutics Branch, Division of Cancer and Treatment and Diagnosis, National Cancer Institute, NIH, Bethesda, Maryland, USA. Palayoor@mail.nih.gov
Burgos
Melissa A
MA
Shoaibi
Azadeh
A
Tofilon
Philip J
PJ
Coleman
C Norman
CN
D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology; D051792:Basic Helix-Loop-Helix Proteins; D015153:Blotting, Western; D002277:Carcinoma / Q000188:drug therapy* / Q000532:radiotherapy*; D002460:Cell Line; D002470:Cell Survival; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007052:Ibuprofen / Q000494:pharmacology*; D015151:Immunoblotting; D007680:Kidney Neoplasms / Q000188:drug therapy* / Q000532:radiotherapy*; D009154:Mutation; D010100:Oxygen / Q000378:metabolism; D011379:Prognosis; D011836:Radiation Tolerance; D013997:Time Factors; D015534:Trans-Activators / Q000235:genetics / Q000502:physiology*; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*; D014162:Transfection; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000502:physiology*; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000502:physiology*; D015854:Up-Regulation; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism; D051794:Von Hippel-Lindau Tumor Suppressor Protein; D000099162:Endothelial PAS Domain-Containing Protein 1
D000894:Anti-Inflammatory Agents, Non-Steroidal; D051792:Basic Helix-Loop-Helix Proteins; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007052:Ibuprofen; D010100:Oxygen; D015534:Trans-Activators; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; D044767:Ubiquitin-Protein Ligases; D042461:Vascular Endothelial Growth Factor A; D051794:Von Hippel-Lindau Tumor Suppressor Protein; D000099162:Endothelial PAS Domain-Containing Protein 1; C497442:HIF1A protein, human; C497446:VHL protein, human