Pulse radiolysis studies indicate that electron transfer is involved in radioprotection by Hoechst 33342 and methylproamine
Pulse radiolysis studies indicate that electron transfer is involved in radioprotection by Hoechst 33342 and methylproamine
复制标题
DOI：
10.1016/s0360-3016(98)00316-2
复制
发表时间：
1998-11-01
影响因子：
7
通讯作者：
Anderson, RF
中科院分区：
文献类型：
--
作者：
Martin, RF;Anderson, RF
目的：本研究的目的是获得证据来支持这一假设，即DNA结合的bibenzimidazole的辐射保护是由于减少由DNA结合的配体的瞬态辐射诱导的氧化物种的DNA，通过以下氧化的配体后脉冲辐解。第二个目的是比较甲基丙胺和Hoechst 33342在脉冲辐解系统中的活性，以寻求与辐射防护活性的相关性。脱氧鸟苷或DNA的溶液，有或没有Hoechst 33342或甲基丙胺，并含有硒酸钠和叔丁醇，进行脉冲辐解，配体的氧化，然后进行时间分辨分光光度法，结果如下：使用脱氧鸟苷（dG）的初始脉冲辐解实验确定了硒酸钠的脉冲辐解产生瞬时氧化剂SeO 3-，其将dG氧化成一种物质（推测为dG（.+）），光谱特性与先前使用Br-2（.-）亚硒酸根与dG反应的双分子速率常数（k（2））为1.2 × 10（9）M（-1）s（-1）。SeO 3.-的相应反应与DNA的反应要慢得多（k（2）3 x 10（7）M-1 s（-1））。尽管未结合的Hoechst 33342直接被SeO 2氧化。(k(2)2.3 × 10（9）M-1 s（-1）），Hoechst 33342与过量dG（或DNA）的混合物的实验表明，配体氧化由dG（.+）介导。(or DNA（氧化））例如，DNA-Hoechst溶液的连续稀释对配体氧化速率的影响很小，这与分子内速率决定步骤一致。当DNA浓度保持在1.0mM DNA bp时，增加配体浓度导致氧化速率线性增加;甲基原胺的增加比Hoechst 33342更陡。氧化配体的产率对配体占有率的依赖性的研究也表明甲基原胺比Hoechst 33342更有活性，对于Hoechst 33342和甲基丙胺，从配体到DNA（氧化物）的电子转移范围的估计值分别为14和31 bp，结论：在这个阶段，我们得出结论，这些DNA结合配体的辐射保护作用是由电子转移介导的，并且甲基丙胺的改进的辐射防护活性可归因于所观察到的动力学差异。然而，需要进一步的研究来证实这种相关性，如果这种相关性持续存在，脉冲辐解可能有助于评估新的类似物，以试图进一步提高甲基丙胺的辐射防护性能，甲基丙胺已经具有相当大的临床潜力。(C)1998年爱思唯尔科学公司
Purpose: The aim of the study was to obtain evidence to support the hypothesis that the radioprotection by DNA-binding bibenzimidazoles is due to reduction by the DNA-bound ligand of transient radiation-induced oxidizing species on DNA, by following oxidation of the ligand after pulse radiolysis. A second aim was to compare the activities of methylproamine and Hoechst 33342 in the pulse radiolysis system, with the view to seeking a correlation with radioprotective activity,Methods: Solutions of deoxyguanosine or DNA, with or without Hoechst 33342 or methylproamine, and containing sodium selenate and tert-butanol were subjected to pulse radiolysis, and the oxidation of the ligand followed by time-resolved spectrophotometry,Results: The initial pulse radiolysis experiments using deoxyguanosine (dG) established that pulse radiolysis of sodium selenate produces a transient oxidant SeO3.-, which oxidizes dG to a species (presumably dG(.+)), with spectral characteristics indistinguishable from those described in previous pulse radiolysis studies using Br-2(.-) as the oxidant, The estimate obtained for the bimolecular rate constant (k(2)) for the reaction of the selenite radical with dG, was 1.2 x 10(9) M(-1)s(-1). The corresponding reaction of SeO3.- with DNA is much slower (k(2) 3 x 10(7) M-1 s(-1)). Although unbound Hoechst 33342 is oxidized directly by SeO2.- (k(2) 2.3 x 10(9) M-1 s(-1)), experiments with mixtures of Hoechst 33342 with an excess of dG (or DNA) indicated that ligand oxidation was mediated by dG(.+) (or DNA(oxid)) For example, successive dilution of a DNA-Hoechst solution had little impact on the rate of ligand oxidation, consistent with an intramolecular rate-determining step. When the concentration of DNA was maintained at 1.0 mM DNA bp, increasing the concentration of the ligand resulted in a linear increase in the rate of oxidation; the increase being steeper for methylproamine than for Hoechst 33342, Investigation of the dependence of yield of oxidized ligand on ligand occupancy also indicated that the methylproamine was more active than Hoechst 33342, with the estimates for the range of electron transfer from the ligand to DNA(oxid) being 14 and 31 bp for Hoechst 33342 and methylproamine, respectively,Conclusions: At this stage we conclude that radioprotection by these DNA-binding ligands is mediated by electron transfer, and that the improved radioprotective activity of methylproamine may be attributable to the observed kinetic differences. However, further studies are required to confirm the correlation, and if it is sustained, pulse radiolysis could be useful in evaluating new analogues in an attempt to further improve the radioprotective properties of methylproamine, which already has considerable clinical potential. (C) 1998 Elsevier Science Inc.