PARENT SESSION
1:30 PM to 3:30 PM
Monday, April 22, 2002
Poster Session 12 DNA Damage and Repair I
Room: Nevada Exhibition Center
(P17-164) DNA damage induction by 123I-estrogen decay.
Yasui, Linda*,1, Anderson, Kim1, Hughes, Alun2, DeSombre, Eugene2, 1 Northern Illinois University, DeKalb, IL2 Ben May Institute for Cancer Research, Chicago, IL
ABSTRACT-
DNA damage induction by 123I-estrogen decay was assayed in the estrogen receptor (ER) expressing human breast cancer cell line, MCF-7 and ER expressing chinese hamster ovary cells, CHOER. During a 30 min labeling time, 123I-estrogen binds to ER and then the 123I-estrogen-ER complex binds to a specific DNA sequence called estrogen response elements (EREs). Cells were labeled with varying concentrations of 123I-estrogen added to the cell medium (4.33-0 nM 123I-estrogen). Association of 123I-estrogen with EREs is maximal by 10 min. at 37oC in suspension cells. At the end of the labeling period, cells were frozen to -90oC to permit decay accumulation. After a period of decay accumulation, the cells were thawed immediately before being assayed. DNA damage was assayed using the neutral filter elution assay and constant field gel electrophoresis. In the neutral elution experiments, very little to no elution of 123I-estrogen treated cell DNA was observed. The mean value of the elution data equaled 0.73 for cells treated with 4.33 nM 123I-estrogen. Mean values for control cell samples not labeled with 123I-estrogen averaged 0.88. Constant field gel electrophoresis experiments showed no detectable DNA migration into the gel by visual inspection (using high ethidium bromide concentrations in the stain solution) and by scintillation counting of 14C-TdR prelabeled DNA. Others also find reduced DNA damage induction by 123I decay (Karamychev et al., 2000). When 123I is associated with the target DNA using triplex forming oligonucleotides, 123I decay was found to be considerably less damaging than 125I decay (0.8 to 0.34 breaks/decay for 125I compared to 0.03 breaks/decay for 123I)(Karamychev et al., 2000). In our experiments, 123I-estrogen was less cytotoxic (Do=165 decays/cell) compared to 125I-estrogen (Do=28 decays/cell). The reduced cytotoxic effect of 123I may be related to the reduced DNA dsb indcution by 123I-estrogen reported here. Supported by NIH R15CA74544 to LY and a Department of Energy Grant to ERD.
KEYWORDS: 123I-estrogen, DNA damage, Auger emitters