Tumor Biology

, Volume 36, Issue 11, pp 8985–8992 | Cite as

Inhibition of topoisomerase IIα sensitizes FaDu cells to ionizing radiation by diminishing DNA repair

Research Article


Despite the high efficiency of ionizing radiation (IR) to inactivate malignant tumours in general, an appreciable number of individual patients cannot be cured by standard IR. Head and neck tumours are not likely to be cured even by high-dose radiotherapy or chemotherapy. Accordingly, combined therapy is one of the most applicable strategies. Topoisomerase IIα is a ubiquitous enzyme that removes knots and tangles from the genetic material by generating and subsequently resealing of transient double-strand breaks. Due to its unique mechanism of action, topoisomerase IIα is the target of many chemotherapeutic agents such as etoposide. The aim of the present study is to examine the effect of inhibiting topoisomerase IIα by etoposide on the response of squamous cell carcinoma to IR. Results of the present study demonstrated a radiosensitizing effect for the topoisomerase IIα inhibitor etoposide on exponentially growing squamous cell carcinoma (FaDu) cell line especially at low radiation doses. This effect was found to be due to inhibition, by etoposide, of the repair of radiation-induced DNA damage. Cell cycle studies showed that the concentration of etoposide that sensitized the cells to radiation had no effect on the distribution of cells at different phases of the cell cycle. Synchronization of FaDu cells in different cell cycle phases revealed that proliferating G1 and G2 cells are responsible for sensitization of cells at low doses of ionizing radiation. It might, therefore, be concluded that topoisomerase II enzyme may be involved in the repair of radiation-induced DNA damage and consequently its inhibition constitute a strategy for sensitizing tumour cells to ionizing radiation.


Topoisomerase IIα Etoposide Ionizing radiation Double-strand breaks DNA repair FaDu cells 



Ionizing radiation


Double-strand break


Homologous recombination


Non-homologous end joining


Dimethyl sulfoxide


Room temperature


Conflicts of interest



  1. 1.
    Valerie K, Povirk L. Regulation and mechanisms of mammalian double-strand break repair. Oncogene. 2003;22:5792–812.CrossRefPubMedGoogle Scholar
  2. 2.
    Lobo PA, Liebner EJ, Chao JJ. Radiotherapy in the management of malignant melanoma. Int J Radiat Oncol Biol Phys. 1981;7:21–6.CrossRefPubMedGoogle Scholar
  3. 3.
    NG CE, Bussey M, Raaphorst GP. Inhibition of potentially lethal and sublethal damage repair by camptothecin and etoposide in human melanoma cell lines. Int J Radiat Biol. 1994;66:49–57.CrossRefPubMedGoogle Scholar
  4. 4.
    Jung M, Velena A, Chen B, Petukho PA, Kozikowski AP, Dritchiloa A, et al. Novel HDAC inhibitions with radiosensitizing properties. Radiat Res. 2005;163:488–93.CrossRefPubMedGoogle Scholar
  5. 5.
    Adachi N, Suzuki H, Liizumi S, Koyama H. Hypersensitivity of nonhomologous DNA end-joining mutants to VP-16 and ICRF-193. J Biol Chem. 2003;278:35897–902.CrossRefPubMedGoogle Scholar
  6. 6.
    Boeckman HJ, Trego KS, Henkels KM, Turchi JJ. Cisplatin sensitizes cancer cells to ionizing radiation via inhibition of non-homologous end joining. Mol Cancer Res. 2005;3:277–85.CrossRefPubMedPubMedCentralGoogle Scholar
  7. 7.
    Thompson LH, Schild D. The contribution of homologous recombination in preserving genome integrity in mammalian cells. Biochimie. 1999;81:87–105.CrossRefPubMedGoogle Scholar
  8. 8.
    Thompson LH, Schild D. Recombinationl DNA repair and human disease. Mutat Res. 2002;509:49–78.CrossRefPubMedGoogle Scholar
  9. 9.
    Rothkamm K, Krüger I, Thompson L, Löbrich M. Pathways of DNA double- strand break repair during the mammalian cell cycle. Mol Cell Biol. 2003;23:5706–15.CrossRefPubMedPubMedCentralGoogle Scholar
  10. 10.
    Cortes F, Pastor N. Ionizing radiation damage repair: a role for topoisomerases? Mutagenesis. 2001;16:365–8.CrossRefPubMedGoogle Scholar
  11. 11.
    Woessener RD, Mattern MR, Mirabelli CK, Johnson RK, Drake FH. Proliferation- and cell cycle-dependent differences in expression of the 170 kilodalton and 180 kilodalton forms of topoisomerase II in NIH 3T3 cells. Cell Growth Differ. 1991;2:209–14.Google Scholar
  12. 12.
    Adachi N, Nomoto M, Kohno K, Koyama H. Cell-cycle regulation of the DNA topoisomerase II alpha promoter is mediated by proximal CCAAT boxes: possible involvement of acetylation. Gene. 2000;245:49–57.CrossRefPubMedGoogle Scholar
  13. 13.
    Potter AJ, Rabinovitch PS. The cell cycle phases of DNA damage and repair initiated by topoisomerase II-targeting chemotherapeutic drugs. Mutat Res. 2005;572:27–44.CrossRefPubMedGoogle Scholar
  14. 14.
    Wang JC. Cellular roles of DNA topoisomerases: a molecular perspective. Nature. 2002;3:430–40.Google Scholar
  15. 15.
    Pastor N, Cortes F. Bufalin influences the repair of X-ray-induced DNA breaks in Chinese hamster cells. DNA Repair. 2003;2:1353–60.CrossRefPubMedGoogle Scholar
  16. 16.
    Timothy M, Khandank. Role of cell cycle in mediating sensitivity to radiotherapy. Int J Radiat Biol Phys. 2004;59:928–42.CrossRefGoogle Scholar
  17. 17.
    El-Awady RA, Dikomey E, Dahm-Daphi J. Radiosensitivity of human tumour cells is associated with the induction but not with the repair of DNA double- strand breaks. Br J Cancer. 2003;89:593–601.CrossRefPubMedPubMedCentralGoogle Scholar
  18. 18.
    Bohnke A, Westphal F, Schmidt A, El-Awady RA, Dahm- Daphi J. The role of mutations, protein function and DNA damage for the radiosensitivity of human tumour cells. Int J Radiat Biol. 2004;80:53–63.CrossRefPubMedGoogle Scholar
  19. 19.
    Annane D, Depondt J, Aubert P. Postoperative irradiation with or without concomitant chemotherapy for locally advanced head and neck cancer. J Clin Oncol. 2004;15:4893–900.CrossRefGoogle Scholar
  20. 20.
    Mateos S, Hajji N, Pastor N, Cortes F. Modulation of radiation response by inhibiting topoisomerase II catalytic activity. Mutat Res. 2006;599:105–15.CrossRefPubMedGoogle Scholar
  21. 21.
    Sancar A, Lindsey-Boltz LA, Unsal-Kacmaz K, Linn S. Molecular mechanisms of mammalian DNA repair and the DNA damage checkpoints. Annu Rev Biochem. 2004;73:39–85.CrossRefPubMedGoogle Scholar
  22. 22.
    Short SC, Woodcock M, Marpeles B, Joiner MC. Effect of cell cycle phase on low-dose hyper-radiosensitivity. Int J Radiat Biol. 2003;79:99–105.CrossRefPubMedGoogle Scholar
  23. 23.
    Rogakou EP, Redon BC, Bonner WM. Megabase chromatin domains involved in DNA double-strand breaks in vivo. J Cell Biol. 1999;146:905–16.CrossRefPubMedPubMedCentralGoogle Scholar
  24. 24.
    Sedelnikova OA, Rogakou EP, Panyutin IG, Booner WM. Quantitation detection of (125) IdU-induced DNA double-strand breaks with gamma- H2AX antibody. Radiat Res. 2002;158:486–92.CrossRefPubMedGoogle Scholar
  25. 25.
    Rothkamm K, Lobrich M. Evidence for a lack of double-strand break repair human cells exposed to very low x-ray doses. PNAS. 2003;100:5057–62.CrossRefPubMedPubMedCentralGoogle Scholar
  26. 26.
    Giocanti N, Hennequim C, Balosso J, Mahler M, Favaudon V. DNA repair and cell cycle interactions in radiation sensitization by the topoisomerase II poison etoposide. Cancer Res. 1993;53:2105–11.PubMedGoogle Scholar
  27. 27.
    Schrader C, Meusers P, Brittinger G, Teymoortash A, Siebmann J, Janssen D, et al. Topoisomerase IIα expression in mantle cell lymphoma: marker of cell proliferation and a prognostic factor for clinical outcome. Leukemia. 2004;18:1200–6.CrossRefPubMedGoogle Scholar
  28. 28.
    Kondapi AK, Padmaja G, Satyanarayana N, Mukhopadyaya R, Reitz MS. A biochemical analysis of topoisomerase IIα and β kinases activity found in HIV- 1 infected cells and virus. Arch Biochem Biophys. 2005;441:41–55.CrossRefPubMedGoogle Scholar
  29. 29.
    Chamberlain M. Recurrent brainstem gliomas treated with oral VP-16. J Neuroncol. 1993;5:133–9.CrossRefGoogle Scholar

Copyright information

© International Society of Oncology and BioMarkers (ISOBM) 2015

Authors and Affiliations

  1. 1.Clinical Biochemistry and Molecular Biology Unit, Cancer Biology Department, National Cancer InstituteCairo UniversityGizaEgypt

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