Radiosensitization and DNA repair inhibition by pentoxifylline in NIH3T3 p53 transfectants.
OBJECTIVE
To examine the role of p53 mutations in the modulation of DNA repair and radiotoxicity by pentoxifylline.


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.
Binder
A
A
Department 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
Theron
T
T
Donninger
H
H
Parker
M
M
Bohm
L
L
D016475:3T3 Cells; D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D004247:DNA / Q000737:chemistry / Q000528:radiation effects; D004260:DNA Repair / Q000187:drug effects*; D004307:Dose-Response Relationship, Radiation; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism / Q000528:radiation effects; D016195:G2 Phase / Q000528:radiation effects; D005720:Gamma Rays; D051379:Mice; D016297:Mutagenesis, Site-Directed; D010431:Pentoxifylline / Q000494:pharmacology*; D011836:Radiation Tolerance / Q000187:drug effects*; D011837:Radiation-Protective Agents / Q000494:pharmacology*; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis* / Q000235:genetics
D011837:Radiation-Protective Agents; D016159:Tumor Suppressor Protein p53; D004247:DNA; D010431:Pentoxifylline