STUDIES OF TOPOISOMERASE I INHIBITORS

核酶DNA拓扑异构酶I松弛超螺旋DNA和 参与DNA复制和转录。拓扑异构酶I 主要定位于核仁，是细胞毒的靶点 喜树碱类药物。这一类的几个类似物是 目前处于I/II期临床试验，以及这些试验的早期结果 试验表明，它们对几种类型的 “难治性”实体瘤。 据报道，细胞内因素影响细胞毒性 喜树碱包括核酶的量，药物诱导 共价拓扑异构酶I-DNA复合体的增加及其需求 正在进行的DNA合成。我们建议，在此之前， 未知的细胞事件也会显著影响细胞毒性 喜树碱。 因此，我们建议检验以下假设：1)喜树碱 通过改变亚细胞分布来限制自身的细胞毒性 拓扑异构酶I和其他核蛋白，并通过减少 核拓扑异构酶II的量，导致减少 拓扑异构酶I-DNA复合体和DNA合成减少； 2)间歇性、反复接触喜树碱，使 细胞维持核酶水平和核仁完整性，以及 因此，形成拓扑异构酶-DNA复合体的能力将具有 最大的细胞毒性作用；以及 3)基于生化观察，预测 拓扑替康在原发肿瘤或骨组织中的抗肿瘤作用 儿童神经母细胞瘤患者的骨髓转移 髓母细胞瘤可确诊。

The nuclear enzyme DNA topoisomerase I relaxes supercoiled DNA and participates in DNA replication and transcription. Topoisomerase I localizes predominantly to nucleoli, and is the cytotoxic target for drugs of the camptothecin class. Several analogues of this class are currently in Phase I/II clinical trials, and early results of these traials have shown them to have activity against several types of "refractory" solid tumors. Intracellular factors reported to influence the cytotoxicity of the camptothecins include the amount of nuclear enzyme, the drug-induced increase in covalent topoisomerase I-DNA complexes, and the requirement for ongoing DNA synthesis. We suggest that additional, previously unidentified cellular events also significantly affect the cytotoxicity of the camptothecins. Therefore, we propose to test the hypotheses that: 1) Camptothecins limit their own cytotoxicity by altering the subcellular distribution of topoisomerase I and other nuclear proteins and by decreasing the amount of nuclear topoisomerase II, resulting in decreased topoisomerase I-DNA complexes and decreased DNA synthesis; 2) Intermittent, repeated exposures to the camptothecins that allow cells to maintain nuclear enzyme levels and nucleolar integrity, and consequently the ability to form topoisomerase-DNA complexes, will have the greatest cytotoxic effect; and 3) Based on biochemical observations, markers that predict the antitumor effect of topotecan in samples of primary tumors or bone marrow metatases of pediatric patients with neuroblastoma or medulloblastoma cal be identified.