Mechanism of action of TOP2-directed anticancer drugs

描述（由申请方提供）：本申请的长期目标是确定拓扑异构酶II（TOP 2）靶向抗癌药物的作用机制。除了其抗肿瘤活性外，TOP 2导向的抗癌药物（如VP-16）与治疗相关的急性骨髓性白血病（AML）的发生有关。事实上，我们的初步研究表明，VP-16在小鼠皮肤癌发生模型中表现为I期肿瘤促进剂。已知针对TOP2的抗癌药物将TOP2同工酶TOP2 α和TOP2 β捕获到其各自的与DNA的共价复合物中，称为可裂解复合物或裂解复合物。这两种TOP2同工酶在细胞周期中受到不同的调节，并且很可能执行不同的功能。然而，这两种TOP2同工酶在TOP导向的抗癌药物的抗肿瘤和致癌活性中的不同作用仍不清楚。我们最近的研究表明，由针对TOP2的抗癌药物VP-16诱导的TOP2 β而不是TOP2 α切割复合物触发了TOP2 β的泛素/26 S蛋白酶体依赖性降解（TOP2 β下调）。这是首次证明TOP2同工酶特异性细胞对TOP2靶向抗癌药物的反应。TOP2 β下调依赖于RNA转录，而不是新蛋白质合成。与TOP 2 β下调同时，RNA聚合酶II的大亚基（而不是其他蛋白质）也被26 S蛋白酶体降解。这些和其他结果表明，泛素/26 S蛋白酶体途径在被阻滞的RNA聚合酶延伸复合物附近局部活化，导致TOP 2 β-DNA共价复合物降解。我们进一步假设TOP 2 β-DNA共价复合物的降解导致TOP 2隐藏的双链断裂暴露，这可能导致肿瘤细胞死亡和DNA序列重排/致癌。阐明由TOP2同工酶形成的TOP2切割复合物的差异细胞反应可能为未来开发TOP2同工酶特异性抗癌药物奠定基础。本申请的目的是表征由针对TOP2的抗癌药物诱导的泛素/26 S蛋白酶体途径，并探索TOP2 β下调在肿瘤细胞死亡和癌变中的生物学后果。

DESCRIPTION (provided by applicant): The long-term goal of this application is to determine the mechanism of action of topoisomerase II (TOP2)-directed anticancer drugs. In addition to their antitumor activities, TOP2-directed anticancer drugs;uch as VP-16 have been associated with the development of therapy-related acute myelogenous leukaemia (AML). Indeed, our preliminary studies have shown that VP-16 behaves as a stage I tumor promoter in the mouse skin carcinogenesis model. TOP2-directed anticancer drugs are known to trap both TOP2 isozymes, TOP2 alpha and TOP2 beta, into their respective covalent complexes with DNA known as cleavable or cleavage complexes. These two TOP2 isozymes are regulated differently during the cell cycle and most likely perform different functions. However, the differential roles of these two TOP2 isozymes in the antitumor and carcinogenic activities of TOP-directed anticancer drugs remain unclear. Our recent studies have demonstrated that TOP2 beta but not TOP2 alpha cleavage complexes induced by the TOP2-directed anti-cancer drug, VP-16, trigger ubiquitin/26S proteasome-dependent degradation of TOP2 beta (TOP2beta down-regulation). This is the first demonstration of a TOP2 isozyme-specific cellular response to TOP2-directed anticancer drugs. TOP2beta down-regulation is dependent on RNA transcription but not new protein synthesis. Concurrent with TOP2 beta down-regulation, the large subunit of RNA polymerase II, but not other proteins, is also degraded by 26S proteasome. These and other results have suggested that a ubiquitin/26S proteasome pathway(s) is activated locally in the vicinity of the arrested RNA polymerase elongation complexes, leading to the degradation of the TOP2 beta-DNA covalent complex. We further hypothesize that degradation of the TOP2 beta-DNA covalent complex results in exposure of theTOP2-concealed double-strand breaks, which could contribute to both tumor cell death and DNA sequence rearrangements/carcinogenesis. Elucidation of the differential cellular responses to TOP2 cleavage complexes formed by TOP2 isozymes may form the foundation for future development of TOP2 isozyme-specific anticancer drugs. The objective of the current application is to characterize the ubiquitin/26S proteasome pathway induced by TOP2-directed anticancer drugs and to explore the biological consequences of TOP2 beta down-regulation in tumor cell death and carcinogenesis.