Effect of distance between decaying 125I and DNA on Auger-electron induced double-strand break yield
Effect of distance between decaying 125I and DNA on Auger-electron induced double-strand break yield
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DOI：
10.3109/09553002.2012.706360
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发表时间：
2012-12-01
影响因子：
2.6
通讯作者：
Kassis, Amin I.
中科院分区：
文献类型：
--
作者：
Balagurumoorthy, Pichumani;Xu, Xiang;Kassis, Amin I.
目的：为了研究碘-125对DNA的距离对俄歇电子诱导双链断裂（Auger electron induced-double-strand break，DSB）的影响，我们合成了一系列碘-125标记的Hoechst（H）衍生物（（IE）-I-125-H，（IB）-I-125-H，I-125-C-8-H和I-125-C-12-H）。虽然所有四种分子都有一个共同的DNA小沟结合双苯并咪唑基序，但它们被设计成将I-125定位在距离DNA螺旋不同的距离处。将每种Hoechst衍生物与超螺旋（SC）H-3-pUC 19质粒DNA（比例3：1）+/-中心点OH清除剂二甲基亚砜（DMSO）（0.2M）一起在磷酸盐缓冲盐水（PBS）中于4 ℃孵育。在琼脂糖凝胶上随时间分析等分试样，并测定I-125原子每次衰变的DSB产率。结果：在不存在DMSO的情况下，当I-125原子与DNA螺旋的距离为10.5 ~ 13.9埃时，DSB产率单调下降（（IEH）-I-125：0.52 ± 0.01;（IB）-I-125-H：0.24 +/- 0.03; I-125-C-8-H：0.18 +/- 0.02; I-125-C-12-H：0.10 +/- 0.00）。在DMSO存在下，（IEH）-I-125（0.49 +/- 0.02）和（IB）-I-125-H（0.26 +/- 0.04）的DSB产率基本保持不变，表明DSB完全由直接效应产生。引人注目的是，I-125-C-8-H或I-125-C-12-H在DMSO存在下在类似条件下不产生可检测的DSB，这表明当I-125原子位于距离DNA>12埃时，DSB完全由间接效应产生。这些结果表明，在I-125原子和DNA螺旋之间的临界距离处，DSB的产生从"全部“直接机制转变为”全部“间接机制，后一种情况与溶液中游离的I-125的衰变相当。这些实验结果与基于微剂量学的理论预期相关。
Purpose: To determine the possible effects of I-125-to-DNA distance on the magnitude and mechanism of Auger-electron induced-double-strand break (DSB) production.Materials and methods: We have synthesized a series of I-125-labeled Hoechst (H) derivatives ((IE)-I-125-H, (IB)-I-125-H, I-125-C-8-H and I-125-C-12-H). While all four molecules share a common DNA minor groove binding bis-benzimidazole motif, they are designed to position I-125 at varying distances from the DNA helix. Each Hoechst derivative was incubated at 4 degrees C in phosphate buffered saline (PBS) together with supercoiled (SC) H-3-pUC19 plasmid DNA (ratio 3: 1) +/- the center dot OH scavenger dimethyl sulfoxide (DMSO) (0.2 M). Aliquots were analyzed on agarose gels over time and DSB yields per decay of I-125 atom were determined. Docking of the iodinated compounds on a DNA molecule was carried out to determine the distance between the iodine atom and the central axis of DNA.Results: In the absence of DMSO, the results show that the DSB yields decrease monotonically as the I-125 atom is distanced - by 10.5 angstrom to 13.9 angstrom - from the DNA helix ((IEH)-I-125: 0.52 +/- 0.01; (IB)-I-125-H: 0.24 +/- 0.03; I-125-C-8-H: 0.18 +/- 0.02; I-125-C-12-H: 0.10 +/- 0.00). In the presence of DMSO, DSB yields for (IEH)-I-125 (0.49 +/- 0.02) and (IB)-I-125-H (0.26 +/- 0.04) remain largely unchanged indicating that DSB are entirely produced by direct effects. Strikingly, I-125-C-8-H or I-125-C-12-H, did not produce detectable DSB in the presence of DMSO under similar conditions suggesting when I-125 atom is positioned >12 angstrom from the DNA, DSB are entirely produced by indirect effects.Conclusion: These results suggest that at a critical distance between the I-125 atom and the DNA helix, DSB production switches from an 'all' direct to an 'all' indirect mechanism, the latter situation being comparable to the decay of I-125 free in solution. These experimental findings were correlated with theoretical expectations based on microdosimetry.