Martin R F, Kelly D P, Roberts M, Green A, Denison L, Rose M, Reum M, Pardee M
Molecular Sciences Group, Peter MacCallum Cancer Institute, Melbourne, Australia.
Int J Radiat Oncol Biol Phys. 1994 Jun 15;29(3):549-53. doi: 10.1016/0360-3016(94)90454-5.
To evaluate the importance of the position of the halogen atom in iodinated DNA-binding bibenzimidazoles, with respect to sensitization of UV-A-induced DNA breakage.
Three analogues of iodoHoechst 33258, denoted ortho-, meta- and paraiodoHoechst, according to the site of iodine substitution, were synthesized. Plasmid DNA (pBR322) was used to assay UV-A-induced DNA single-strand breaks (ssbs). The location of the sites of strand breakage was determined by DNA sequencing gel analysis, using a 32P-endlabelled oligoDNA with a single binding site for the ligands.
A clear trend in decreasing activity of sensitization of UV-induced DNA ssbs was established: ortho- > meta-, para- > iodoHoechst 33258. The sequencing gel studies showed that orthoiodoHoechst was distinct from the other three compounds, with respect to the sites of DNA strand breakage and the chemistry of the cleavage reaction.
The position of iodine substitution in iodinated bibenzimidazoles determines the location of the carbon-centered radical on the ligand in the minor groove of DNA. DNA strand cleavage is mediated by abstraction of a nearby deoxyribosyl H-atom. Hence, the position of the radical species determines: which deoxyribosyl group is attacked (i.e., site of cleavage relative to the ligand binding site); which H-atom is abstracted, more specifically which of the five deoxyribosyl carbons is involved (i.e., the chemistry of the cleavage reaction), and the stereochemistry of the transition state for the H-atom abstraction (and hence the efficiency or extent of strand breakage). The ortho-compound represents the best example to date of iodinated DNA ligands designed as potential radiation sensitizers, as an extension of the well-established sensitization by halogenated DNA precursors.
评估碘化双苯并咪唑中卤原子位置对于紫外线A诱导的DNA断裂致敏作用的重要性。
根据碘取代位点，合成了碘代赫斯特33258的三种类似物，分别称为邻碘代赫斯特、间碘代赫斯特和对碘代赫斯特。使用质粒DNA（pBR322）检测紫外线A诱导的DNA单链断裂（ssbs）。通过DNA测序凝胶分析确定链断裂位点的位置，使用具有单个配体结合位点的32P末端标记寡聚DNA。
确定了紫外线诱导的DNA单链断裂致敏活性降低的明显趋势：邻碘代赫斯特＞间碘代赫斯特，对碘代赫斯特＞碘代赫斯特33258。测序凝胶研究表明，邻碘代赫斯特在DNA链断裂位点和裂解反应化学方面与其他三种化合物不同。
碘化双苯并咪唑中碘取代的位置决定了DNA小沟中配体上以碳为中心的自由基的位置。DNA链裂解是通过夺取附近的脱氧核糖基氢原子介导的。因此，自由基物种的位置决定：攻击哪个脱氧核糖基团（即相对于配体结合位点的裂解位点）；夺取哪个氢原子，更具体地说涉及五个脱氧核糖基碳中的哪一个（即裂解反应的化学性质），以及氢原子夺取过渡态的立体化学（从而决定链断裂的效率或程度）。邻位化合物代表了迄今为止设计为潜在辐射致敏剂的碘化DNA配体的最佳实例，这是卤化DNA前体既定致敏作用的扩展。
