DNA strand breaks and hypoxia response inhibition mediate the radiosensitisation effect of nitric oxide donors on prostate cancer under varying oxygen conditions

Grant D. Stewart (1, 2, 3) , Jyoti Nanda (1) , Elad Katz (3) , Karen J. Bowman (4) , Jill G. Christie (5) , D.J. Gordon Brown (1) , Duncan B. Mclaren (5) , Antony C.P. Riddick (1) , James A. Ross (2) , George D.D. Jones (4) , Fouad K. Habib (1)

1 Department of Urology
2 Tissue Injury and Repair Group
3 Edin. - University of Edinburgh
4 Department of Cancer Studies and Molecular Medicine
5 Department of Clinical Oncology

Prostate cancer cells can exist in a hypoxic microenvironment, causing radioresistance. Nitric oxide (NO) is a radiosensitiser of mammalian cells. NO-NSAIDs are a potential means of delivering NO to prostate cancer cells. This study aimed to determine the effect and mechanism of action of NO-sulindac and radiation, on prostate cancer cells and stroma, under normoxia (21% oxygen) and chronic hypoxia (0.2% oxygen). Using clonogenic assays, at a surviving fraction of 10% the sensitisation enhancement ratios of radiation plus NO-sulindac over radiation alone on PC-3 cells were 1.22 and 1.42 under normoxia and hypoxia, respectively. 3D culture of PC-3 cells revealed significantly reduced sphere diameter in irradiated spheres treated with NO-sulindac. Neither NO-sulindac nor sulindac radiosensitised prostate stromal cells under normoxia or hypoxia. HIF-1α protein levels were reduced by NO-sulindac exposure and radiation at 21% and 0.2% oxygen. Alkaline Comet assay analysis suggested an increased rate of single strand DNA breaks and slower repair of these lesions in PC-3 cells treated with NO-sulindac prior to irradiation. There was a higher level of γ-H2AX production and hence double strand DNA breaks following irradiation of NO-sulindac treated PC-3 cells. At all radiation doses and oxygen levels tested, treatment of 2D and 3D cultures of PC-3 cells with NO-sulindac prior to irradiation radiosensitised PC-3, with minimal effect on stromal cells. Hypoxia response inhibition and increased DNA double strand breaks are potential mechanisms of action. Neoadjuvent and concurrent use of NO-NSAIDs have the potential to improve radiotherapy treatment of prostate cancer under normoxia and hypoxia.

Mots clés: hypoxia; prostate cancer; nitric oxide donors; radiation; radiosensitisation

Grant D. Stewart, Jyoti Nanda, Elad Katz, Karen J. Bowman, Jill G. Christie, et al.. DNA strand breaks and hypoxia response inhibition mediate the radiosensitisation effect of nitric oxide donors on prostate cancer under varying oxygen conditions. Biochemical Pharmacology, 2010, 81 (2), pp.203. ⟨10.1016/j.bcp.2010.09.022⟩. ⟨hal-00649890⟩