DNA Damage by Tumor Cell-Specific N-Oxides

描述(申请人提供)：3-氨基-1，2，4-苯并三嗪1，4-二氧化物(替拉帕明，TPZ)是一种生物还原激活的DNA损伤剂，可以选择性地杀死几乎所有实体肿瘤中发现的缺氧细胞。这种化合物显示出巨大的临床前景，目前正在进行十多项不同的临床试验，包括几项III期研究。重要的是，TPZ通过一系列全新的化学反应损伤DNA，在该反应中，单电子还原的药物引发自由基介导的DNA损伤，然后药物或其代谢物将氧原子从其N-氧化物官能团转移到生成的DNA自由基，从而将它们转化为链切割位点。尽管人们对三苯丙胺的药用特性进行了广泛的研究，但它的许多与生物相关的化学特性仍然知之甚少。临床上对TPZ日益增长的兴趣提供了一个实际的动机来描述这种药物的相关化学特性。此外，这种新的化学基序能够有效地将细胞毒性DNA破坏自由基传递到缺氧细胞内部，其特征可能是药物化学和毒理学的基本兴趣。本提案中描述的工作分为三个具体目标：1.TPZ如何在DNA上产生根本性损伤？这种药物是否能将已知的DNA损伤剂羟基自由基传递到缺氧细胞？肿瘤细胞中发现的低氧和低pH条件如何结合起来促进药物对DNA的损伤？2.TPZ及其代谢产物将氧原子从其N-氧化物官能团转移到DNA自由基的化学机制是什么？这一史无前例的反应使药物能够在低氧条件下有效地损伤DNA，并可能在确定TPZ引起的最终DNA损伤的结构性质方面发挥核心作用。3.我们提出了一些研究，以表征TPZ介导的DNA链断裂和碱基损伤的结构性质。这些研究将探索这样一种可能性，即TPZ在不寻常的条件下工作，加上药物的独特化学性质，导致一系列独特的DNA损伤，使细胞面临DNA修复系统的社会挑战。

DESCRIPTION (provided by applicant): 3-Amino-1,2,4-benzotriazine 1,4-dioxide (tirapazamine, TPZ) is a bioreductively-activated DNA-damaging agent that selectively kills the hypoxic cells found in virtually all solid tumors. This compound shows great clinical promise and is currently being examined in more than ten different clinical trials, including several phase III studies. Importantly, TPZ damages DNA via a completely novel sequence of chemical reactions in which the one-electron reduced drug initiates radical-mediated DNA damage and then the drug or its metabolites transfer oxygen atoms from their N-oxide functional groups to the resulting DNA radicals, thus, converting them to strand cleavage sites. While the medicinal properties of TPZ have been extensively investigated, many of its biologically relevant chemical properties remain poorly understood. The growing clinical interest in TPZ provides a practical incentive to characterize the relevant chemistry of this drug. In addition, characterization of this new chemical motif that efficiently delivers cytotoxic DNA-damaging radicals to the interior of hypoxic cells may be of fundamental interest in both medicinal chemistry and toxicology. The work described in this proposal is divided into three Specific Aims: 1. How does TPZ generate radical lesions on DNA? Does the drug serve to deliver the known DNA-damaging agent hydroxyl radical to hypoxic cells? How do the conditions of low oxygen and low pH found in tumor cells combine to facilitate DNA damage by the drug? 2. What is the chemical mechanism by which TPZ and its metabolites transfer oxygen atoms from their N-oxide functional groups to DNA radicals? This unprecedented reaction allows the drug to efficiently damage DNA under hypoxic conditions and may play a central role in defining the structural nature of the final DNA lesions caused by TPZ. 3. We propose studies to characterize the structural nature of the DNA strand breaks and base damage mediated by TPZ. These studies will explore the possibility that the unusual conditions under which TPZ operates, along with the unique chemical properties of the drug, lead to a unique spectrum of DNA lesions that confront cells with social challenges to their DNA-repair systems.