Liver Cancer
Copyright ©The Author(s) 2002. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Gastroenterol. Oct 15, 2002; 8(5): 797-803
Published online Oct 15, 2002. doi: 10.3748/wjg.v8.i5.797
DNA-PKcs subunits in radiosensitization by hyperthermia on hepatocellular carcinoma hepG2 cell line
Zhao-Chong Zeng, Guo-Liang Jiang, Guo-Min Wang, Zhao-You Tang, Walter J. Curran, George Iliakis
Zhao-Chong Zeng, Department of Radiation Oncology, Zhongshan Hospital, Fudan University, Shanghai, 200032, China
Guo-Liang Jiang, Department of Radiation Oncology of Cancer Hospital, Fudan University, Shanghai, 200032, China
Guo-Min Wang, Department of Urology, Zhongshan Hospital, Fudan University, Shanghai, 200032, China
Zhao-You Tang, Liver Cancer Institute, Fudan University, Shanghai, 200032, China
Zhao-Chong Zeng, Walter J. Curran, George Iliakis, Department of Radiation Oncology of Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, PA 19107, USA
Author contributions: All authors contributed equally to the work.
Correspondence to: Dr. Zhao-Chong Zeng, Department of Radiation Oncology, Zhongshan Hospital, Fudan University. Shanghai, 200032, China. zeng@guomai.sh.cn
Telephone: +86-21-64041990 Ext.2763 Fax: +86-21-64037181
Received: August 24, 2001
Revised: August 26, 2001
Accepted: August 28, 2001
Published online: October 15, 2002
Abstract

AIM: To investigate the role of DNA-PKcs subunits in radiosensitization by hyperthermia on hepatocellular carcinoma HepG2 cell lines.

METHODS: HepG2 cells were exposed to hyperthermia and irradiation. Hyperthermia was given at 45.5 °C. Cell survival was determined by an in vitro clonogenic assay for the cells treated with or without hyperthermia at various time points. DNA DSB rejoining was measured using asymmetric field inversion gel electrophoresis (AFIGE). The DNA-PKcs activities were measured using DNA-PKcs enzyme assay system.

RESULTS: Hyperthermia can significantly enhance irradiation-killing cells. Thermal enhancement ratio as calculated at 10% survival was 2.02. The difference in radiosensitivity between two treatment modes manifested as a difference in the α components and the almost same β components, which α value was considerably higher in the cells of combined radiation and hyperthermia as compared with irradiating cells (1.07 Gy-1vs 0.44 Gy-1). Survival fraction showed 1 logarithm increase after an 8-hour interval between heat and irradiation, whereas DNA-PKcs activity did not show any recovery. The cells were exposed to heat 5 min only, DNA-PKcs activity was inhibited at the nadir, even though the exposure time was lengthened. Whereas the ability of DNA DSB rejoining was inhibited with the increase of the length of hyperthermic time. The repair kinetics of DNA DSB rejoining after treatment with Wortmannin is different from the hyperthermic group due to the striking high slow rejoining component.

CONCLUSION: Determination with the cell extracts and the peptide phosphorylation assay, DNA-PKcs activity was inactivated by heat treatment at 45.5 °C, and could not restore. Cell survival is not associated with the DNA-PKcs inactivity after heat. DNA-PKcs is not a unique factor affecting the DNA DSB repair. This suggests that DNA-PKcs do not play a crucial role in the enhancement of cellular radiosensitivity by hyperthermia.

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