Synthesis and characterization of an O6-2′-deoxyguanosine-alkyl-O6-2′-deoxyguanosine interstrand cross-link in a 5′-GNC motif and repair by human O6-alkylguanine-DNA alkyltransferase
作者:Francis P. McManus、Qingming Fang、Jason D. M. Booth、Anne M. Noronha、Anthony E. Pegg、Christopher J. Wilds
DOI:10.1039/c0ob00093k
日期:——
O6-2â²-Deoxyguanosine-alkyl-O6-2â²-deoxyguanosine interstrand DNA cross-links (ICLs) with a four and seven methylene linkage in a 5â²-GNC- motif have been synthesized and their repair by human O6-alkylguanine-DNA alkyltransferase (hAGT) investigated. Duplexes containing 11 base-pairs with the ICLs in the center were assembled by automated DNA solid-phase synthesis using a cross-linked 2â²-deoxyguanosine dimer phosphoramidite, prepared via a seven step synthesis which employed the Mitsunobu reaction to introduce the alkyl lesion at the O6 atom of guanine. Introduction of the four and seven carbon ICLs resulted in no change in duplex stability based on UV thermal denaturation experiments compared to a non-cross-linked control. Circular dichroism spectra of these ICL duplexes exhibited features of a B-form duplex, similar to the control, suggesting that these lesions induce little overall change in structure. The efficiency of repair by hAGT was examined and it was shown that hAGT repairs both ICL containing duplexes, with the heptyl ICL repaired more efficiently relative to the butyl cross-link. These results were reproducible with various hAGT mutants including one that contains a novel V148L mutation. The ICL duplexes displayed similar binding affinities to a C145S hAGT mutant compared to the unmodified duplex with the seven carbon containing ICLs displaying slightly higher binding. Experiments with CHO cells to investigate the sensitivity of these cells to busulfan and hepsulfam demonstrate that hAGT reduces the cytotoxicity of hepsulfam suggesting that the O6-2â²-deoxyguanosine-alkyl-O6-2â²-deoxyguanosine interstrand DNA cross-link may account for at least part of the cytotoxicity of this agent.
已合成了5²-GNC-结构中具有4个和7个亚甲基连接的O6-2²-脱氧鸟苷-烷基-O6-2²-脱氧鸟苷DNA链间交联(ICL),并研究了人类O6-烷基鸟嘌呤-DNA烷基转移酶(hAGT)对其的修复。使用交联的2²-脱氧鸟苷二聚体亚磷酰胺,通过自动DNA固相合成组装了包含11个碱基对的ICL双链,该亚磷酰胺是通过七步合成制备的,其中采用Mitsunobu反应在鸟嘌呤的O6原子引入烷基损伤。与非交联对照相比,引入4个和7个碳的ICL不会改变双链的稳定性(基于UV热变性实验)。这些ICL双链的圆二色光谱表现出与对照类似的B型双链特征,表明这些损伤不会引起整体结构变化。研究了hAGT的修复效率,结果表明,hAGT可以修复两种ICL双链,其中庚基ICL的修复效率比丁基交联更高。这些结果在各种hAGT突变体中具有可重复性,包括一种含有新型V148L突变的突变体。与未修饰的双链相比,ICL双链与C