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Radiother Oncol. 2009 Sep;92(3):334-8. doi: 10.1016/j.radonc.2009.06.005. Epub 2009 Jul 7.

2-Methoxyestradiol-induced radiosensitization is independent of SOD but depends on inhibition of Akt and DNA-PKcs activities.

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  • 1Department of Radiation Oncology, University of Tuebingen, Germany.

Abstract

BACKGROUND AND PURPOSE:

2-Methoxyestradiol (2-ME) is described as an inhibitor of the superoxide dismutase (SOD) enzyme activity. However, it attenuates PI3K/Akt pathway and induces radiosensitization in human tumor cells as well. Since the activation of catalytic subunit of DNA-protein kinase (DNA-PKcs) is partially regulated by Akt activity, in the present study we investigated whether 2-ME-induced radiosensitization is dependent on inhibition of Akt and DNA-PKcs activities or on SOD targeting.

MATERIALS AND METHODS:

This study was performed using the lung carcinoma cell line A549. Ionizing radiation-induced SOD activity was analyzed by superoxide dismutase activity assay. Applying Western blotting, the pattern of radiation-induced SOD expression and activation of Akt as well as DNA-PKcs was analyzed. Colony formation assay and gammaH2AX foci assay were performed to measure radiosensitization and DNA-double strand break (DNA-DSB) repair. To downregulate SOD expression small interfering RNA (siRNA) was used.

RESULTS:

Irradiation with 4Gy stimulated SOD enzyme activity as early as 1min after radiation exposure. Expression of Cu/Zn-SOD (SOD1) as well as Mn-SOD (SOD2) was increased by single doses of 1-4Gy within 24-36h. 2-ME blocked radiation-induced SOD enzyme activity but not protein expression and enhanced radiation sensitivity. Pretreatment with 2-ME blocked IR-induced Akt as well as DNA-PKcs phosphorylation and impaired the repair of DNA-DSB. SiRNA targeting of SOD1 and SOD2 affected neither DNA-PKcs phosphorylation nor post-irradiation survival while inhibition of Akt by specific inhibitor abrogated 2-ME-induced radiosensitization.

CONCLUSION:

These results may indicate that 2-ME-induced radiosensitization is independent of SOD inhibition but mainly depends on inhibition of Akt and DNA-PKcs activities.

PMID:
19589609
[PubMed - indexed for MEDLINE]
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