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Radiosensitization and DNA repair inhibition by pentoxifylline in NIH3T3 p53 transfectants
A Binder1, T Theron, H Donninger
1Department of Radiation Oncology, Radiobiology Laboratory, University of Stellenbosch, Faculty of Health and Tygerberg Hospital, PO Box 19063, Tygerberg 7505, South Africa. abin@sun.ac.za
Purpose:
To examine the role of p53 mutations in the modulation of DNA repair and radiotoxicity by pentoxifylline.
Materials And Methods:
NIH3T3 murine cells transfected with mutant p53 constructs were examined for the influence of pentoxifylline on radiotoxicity to Co(60) gamma-irradiation by colony assay. DNA repair (0-100 Gy) was measured by constant-field gel electrophoresis. Apoptosis was assessed by flow cytometry with the annexin-V-binding assay.
Results:
In the two p53 hot-spot mutant cell lines p53-S269R and p53- + 15, the SF(10) radiotoxicity enhancement factors induced by the pentoxifylline were 8.0 and 9.7, respectively. In the p53 deletion mutant p53-DeltaA cell line, the radiotoxicity enhancement factor was 2.6. No radiosensitization was obtained in the untransfected p53 wild-type cell line U-Wt and in the transfected p53 double-wild-type p53-Wt cell line. When pentoxifylline was added after irradiation at the time of maximum G2 block expression, no radiosensitization was observed in any of the five cell lines. Constant-field gel electrophoresis analyses after 20 h of repair showed that pentoxifylline suppresses DNA double-strand break repair in all p53 mutant cell lines, as indicated by repair inhibition factors of 2.0-2.3. No repair suppression was found in the p53 wild-type cell lines.
Conclusions:
p53 mutations are a general requirement for radiosensitization by pentoxifylline and the level of radiosensitization depends upon the location of the p53 mutation.