Cecchini Sylvain, Girouard Sonia, Huels Michael A, Sanche Léon, Hunting Darel J
Group in the Radiation Sciences, Department of Nuclear Medicine and Radiobiology, Faculty of Medicine, Université de Sherbrooke, Québec, Canada J1H 5N4.
Biochemistry. 2005 Feb 15;44(6):1932-40. doi: 10.1021/bi048105s.
Interstrand cross-links (ICL) represent one of the most toxic types of DNA damage for dividing cells. They are induced both by natural products (e.g., psoralens + UVA) and by several chemical agents, some of which are used in chemotherapy (e.g., carboplatin and mitomycin C). Although repair mechanisms exist for interstrand cross-links, these lesions can induce mutations, chromosomal rearrangements, and cell death. Here, we report, for the first time, the formation of ICL by gamma-rays in brominated DNA. It is well established that the radiosensitization properties of bromodeoxyuridine (BrdUrd) result primarily from the electrophilic nature of the bromine, making it a good leaving group and leading to the irreversible formation of a uridinyl radical (dUrd(*)) or uridinyl anion (dUrd-) upon addition of an electron. We observe that the radiolytic loss of the bromine atom is greatly suppressed in double-stranded compared to single-stranded DNA. We have used a model DNA containing a bulge, formed by five mismatched bases, and have observed a linear dose-response for the formation of strand breaks on the single-stranded regions of both the brominated strand and the opposite nonbrominated strand. Surprisingly, we have observed the formation of interstrand cross-links exclusively in the mismatched region. Thus, we propose that the radiosensitization effects of bromodeoxyuridine in vivo will almost certainly be limited to single strand regions such as found in transcription bubbles, replication forks, mismatched DNA, and possibly the loop region of telomeres. Our results suggest that interstrand cross-links may contribute to the radiosensitization effects of BrdUrd. These findings may have profound implications for the clinical use of bromodeoxyuridine as a radiosensitizer, as well as for the development of targeted radiosensitizers.
链间交联（ICL）是分裂细胞中最具毒性的DNA损伤类型之一。它们可由天然产物（如补骨脂素+紫外线A）和几种化学试剂诱导产生，其中一些化学试剂用于化疗（如卡铂和丝裂霉素C）。尽管存在修复链间交联的机制，但这些损伤可诱导突变、染色体重排和细胞死亡。在此，我们首次报道了γ射线在溴化DNA中诱导形成链间交联。众所周知，溴脱氧尿苷（BrdUrd）的放射增敏特性主要源于溴的亲电性质，使其成为一个良好的离去基团，并在添加电子后导致不可逆地形成尿苷基自由基（dUrd(*)）或尿苷基阴离子（dUrd-）。我们观察到，与单链DNA相比，双链DNA中溴原子的辐射分解损失受到极大抑制。我们使用了一种含有由五个错配碱基形成的凸起的模型DNA，并观察到溴化链和相对的非溴化链的单链区域上链断裂形成的线性剂量响应。令人惊讶的是，我们仅在错配区域观察到链间交联的形成。因此，我们提出，溴脱氧尿苷在体内的放射增敏作用几乎肯定仅限于单链区域，如转录泡、复制叉、错配DNA以及可能的端粒环区域中发现的单链区域。我们的结果表明，链间交联可能有助于溴脱氧尿苷的放射增敏作用。这些发现可能对溴脱氧尿苷作为放射增敏剂的临床应用以及靶向放射增敏剂的开发具有深远意义。
