Mechanistic Studies of Type II Topoisomerases and Topoisomerase-Targeted Agents

在此输入文本，它是应用程序的新摘要信息。此部分不得超过30行文本。 II型拓扑异构酶是普遍存在的酶，其是正确的染色体结构和分离所需的，并且在DNA复制、转录和重组中起重要作用。这些酶通过使完整的双螺旋（运输片段）通过它们在单独的DNA片段（门片段）中产生的瞬时双链断裂来松弛DNA并从遗传物质中去除结和缠结。人类编码两种密切相关的II型酶亚型，拓扑异构酶IIα和拓扑异构酶IIβ。拓扑异构酶IIα对增殖细胞的存活至关重要，拓扑异构酶IIβ在发育过程中起关键作用。然而，由于这些酶在其关键的催化功能期间产生必需的双链DNA断裂，因此它们具有双重角色。尽管它们对细胞生存至关重要，但每次它们的作用也会对基因组的完整性构成内在威胁。 除了它们的重要生理功能之外，拓扑异构酶IIα和IIβ是目前用于治疗人类癌症的一些最活跃和最广泛的处方药物的主要靶标。这些试剂通过稳定共价拓扑异构酶II切割的DNA复合物（切割复合物）来杀死细胞，所述共价拓扑异构酶II切割的DNA复合物是催化DNA链通过反应中的正常但短暂的中间体。当产生的酶相关DNA断裂以足够的浓度存在时，它们可以触发细胞死亡途径。靶向II型酶的抗癌药物被称为拓扑异构酶II毒药，因为它们将这些不可或缺的酶转化为在治疗细胞中产生DNA损伤的强效生理毒素。 虽然拓扑异构酶IIα和IIβ是癌症化疗的重要靶点，但有证据表明它们也有可能引发特定的白血病。一小部分接受拓扑异构酶II靶向药物治疗的癌症（和其他）患者最终发展为涉及染色体带11 q23处MLL基因的急性髓性白血病（AML）或涉及15：17易位的急性早幼粒细胞白血病。11 q23染色体易位也见于婴儿AML，当母亲在怀孕期间暴露于环境和饮食拓扑异构酶II毒物时，这些白血病的风险增加约3倍。 尽管II型拓扑异构酶对细胞生长和癌症的重要性，我们仍然有很多关于人类酶如何在体外，细胞和脊椎动物中与DNA和抗癌药物相互作用的研究。因此，所提出的目的是为了进一步定义拓扑异构酶II的催化机制和DNA相互作用，并评估新的拓扑异构酶II靶向药物和药物-DNA缀合物在体外、培养细胞和脊椎动物中增加酶介导的DNA断裂水平的机制。本研究的主要研究模型为人类拓扑异构酶IIα和IIβ、培养的人类细胞和非洲爪蟾提取物。细菌促旋酶和拓扑异构酶IV也将用于评估靶向原核和真核II型酶的药物的作用机制之间的关系。

Enter the text here that is the new abstract information for your application. This section must be no longer than 30 lines of text. Type II topoisomerases are ubiquitous enzymes that are required for proper chromosome structure and segregation and play important roles in DNA replication, transcription, and recombination. These enzymes relax DNA and remove knots and tangles from the genetic material by passing an intact double helix (transport segment) through a transient double-stranded break that they generate in a separate DNA segment (gate segment). Humans encode two closely related isoforms of the type II enzyme, topoisomerase IIα and topoisomerase IIβ. Topoisomerase IIα is essential for the survival of proliferating cells and topoisomerase IIβ plays critical roles during development. However, because these enzymes generate requisite double-stranded DNA breaks during their crucial catalytic functions, they assume a dual persona. Although essential to cell survival, they also pose an intrinsic threat to genomic integrity every time they act. Beyond their critical physiological functions, topoisomerase IIα and IIβ are the primary targets for some of the most active and widely prescribed drugs currently used for the treatment of human cancers. These agents kill cells by stabilizing covalent topoisomerase II-cleaved DNA complexes (cleavage complexes) that are normal, but fleeting, intermediates in the catalytic DNA strand passage reaction. When the resulting enzyme-associated DNA breaks are present in sufficient concentrations, they can trigger cell death pathways. Anticancer drugs that target type II enzymes are referred to as topoisomerase II poisons because they convert these indispensable enzymes to potent physiological toxins that generate DNA damage in treated cells. Although topoisomerase IIα and IIβ are important targets for cancer chemotherapy, evidence suggests that they also have the potential to trigger specific leukemias. A small percentage of cancer (and other) patients treated with topoisomerase II-targeted drugs eventually develop acute myeloid leukemias (AMLs) involving the MLL gene at chromosome band 11q23 or acute promyelocytic leukemias involving 15:17 translocations. The 11q23 chromosomal translocations also are seen in infant AMLs, and the risk of these leukemias rises ~3–fold when there is high maternal exposure during pregnancy to environmental and dietary topoisomerase II poisons. Despite the importance of type II topoisomerases to cell growth and cancer, we still have much to learn about how the human enzymes function and interact with DNA and anticancer drugs in vitro, in cells, and in vertebrate animals. Thus, the proposed aims are designed to further define the catalytic mechanism and DNA interactions of topoisomerase II and assess the mechanism by which novel topoisomerase II-targeted drugs and drug-DNA conjugates increase levels of enzyme-mediated DNA breaks in vitro, in cultured cells, and in vertebrate animals. The primary research models for this study will be human topoisomerase IIα and IIβ, cultured human cells, and Xenopus laevis extracts. Bacterial gyrase and topoisomerase IV also will be used to assess relationships between the mechanisms of action of drugs targeted to prokaryotic and eukaryotic type II enzymes.