DNA Lesions as Endogenous Topoisomerase Poisons

描述（由申请人提供）：拓扑异构酶II是一种必需的酶，它通过在单独的DNA片段中产生的瞬时双链断裂传递完整的双螺旋，从而使DNA松弛，并从遗传物质中去除结和缠结。然而，由于拓扑异构酶II必须产生双链DNA断裂才能发挥其催化功能，因此该酶也对基因组完整性构成了内在威胁。除了其关键的细胞功能外，拓扑异构酶II是目前临床使用的一些最活跃的抗癌药物的主要靶点。这些药物通过增加共价拓扑异构酶的水平来起作用，这些共价拓扑异构酶是正常的，但在酶的催化循环中是短暂的中间产物。当产生的酶相关DNA断裂以高浓度存在时，它们会产生突变、染色体易位并触发细胞死亡途径。针对II型酶的抗癌药物被称为拓扑异构酶II毒药，因为它们将这种必需的酶转化为一种强大的生理毒素，使基因组片段化。虽然拓扑异构酶II是癌症治疗最重要的靶点之一，但有令人信服的证据表明，这种酶产生的DNA断裂也会引发特定类型的白血病。这表明拓扑异构酶靶向药物可能代表了诱导DNA重组、突变或细胞死亡途径的细胞成分的外源性对应物。先前的研究（许多来自申请人的实验室）表明，一个基本位点、DNA中最常见的病变和其他生理DNA病变刺激拓扑异构酶介导的DNA切割，其效力远远高于广泛使用的抗癌药物依托泊苷。因此，本研究的最终目标是进一步确定拓扑异构酶II与DNA损伤之间的相互作用，并确定DNA损伤是否作为内源性拓扑异构酶II毒素在细胞中起作用。本研究的模型将是人类拓扑异构酶α和β，以及培养的哺乳动物细胞系。相关性：拓扑异构酶II是临床上一些最重要的抗癌药物的靶标。然而，也有证据表明，这种酶会引发引发白血病的染色体断裂。目前的提议验证了DNA损伤作为抗癌药物内源性对应物的假设，并可能参与启动拓扑异构酶介导的白血病染色体易位。

DESCRIPTION (provided by applicant): Topoisomerase II is an essential enzyme that relaxes DNA and removes knots and tangles from the genetic material by passing an intact double helix through a transient double-stranded break that it generates in a separate DNA segment. However, since topoisomerase II must create double-stranded DNA breaks in order to carry out its catalytic functions, the enzyme also poses an intrinsic threat to genomic integrity. Beyond its critical cellular functions, topoisomerase II is the primary target for some of the most active anticancer drugs currently in clinical use. These drugs act by increasing levels of covalent topoisomerase ll-cleaved DNA complexes that are normal, but fleeting, intermediates in the catalytic cycle of the enzyme. When the resulting enzyme-associated DNA breaks are present in high concentrations, they generate mutations, chromosomal translocations, and trigger cell death pathways. Anticancer drugs targeted to the type II enzyme are referred to as topoisomerase II poisons because they convert this essential enzyme to a potent physiological toxin that fragments the genome. Although topoisomerase II is one of the most important targets for cancer treatment, there is compelling evidence that DNA breaks created by the enzyme also trigger specific types of leukemia. This suggests that topoisomerase ll-targeted drugs may represent exogenous counterparts of cellular components that induce DNA recombination, mutagenesis, or cell death pathways. Previous studies (many from the applicant's lab) indicate that a basic sites, the most commonly formed lesion in DNA, and other physiological DNA lesions stimulate topoisomerase ll-mediated DNA cleavage with a potency that is considerably higher than that of the widely prescribed anticancer drug etoposide. Thus, the ultimate goals of this proposal are to further define interactions between topoisomerase II and DNA damage and to determine whether DNA lesions function in cells as endogenous topoisomerase II poisons. The models for this study will be human topoisomerase ll alpha and beta, and cultured mammalian cell lines. RELEVANCE: Topoisomerase II is the target for some of the most important anticancer drugs in clinical use. However, there is also evidence that the enzyme triggers chromosomal breaks that trigger leukemia. The current proposal tests the hypothesis that DNA lesions act as endogenous counterparts of anticancer drugs and may be involved in initiating topoisomerase ll-mediated leukemic chromosomal translocations.