ANTINEOPLASTIC v lEUKEMOGENIC EPIPODOPHYLLOTOXIN EFFECTS

描述（由申请人提供）：本研究的目的是了解使用DNA拓扑异构酶II抑制剂进行抗癌治疗后导致白血病MLL易位的DNA损伤的性质。CYP 3A 4启动子具有多态性，CYP 3A 4基因型赋予易感性。CYP 3A 4将依托泊苷转化为依托泊苷儿茶酚;儿茶酚易于氧化为醌。这些代谢物是遗传毒素。MLL与许多伴侣基因中的一个结合形成易位。基因组断点连接序列包含DNA损伤和修复的证据。几个基因组断裂点连接序列表明精确或接近精确的染色体间DNA重组，但额外的断裂点的克隆是必不可少的，以辨别损伤谱。依托泊苷及其代谢产物在体外诱导MLL及其伴侣基因易位断点处的DNA拓扑异构酶II切割。我们认为依托泊苷及其代谢产物可以刺激一系列不同的DNA损伤，这些损伤被修复形成断点连接，并且基因组断点连接序列的异质性反映了损伤及其分辨率的异质性。待测试的DNA损伤包括依托泊苷母体药物直接诱导DNA拓扑异构酶II切割、依托泊苷醌或活性氧物质诱导DNA拓扑异构酶II切割形成DNA加合物、与DNA拓扑异构酶II共价复合物的复制叉碰撞和DNA拓扑异构酶II非依赖性损伤。目的1将使用质谱法检查光谱并定量MLL bcr DNA底物中依托泊苷代谢产物的DNA加合物的相对重要性。目的2：利用DNA微阵列技术研究依托泊苷及其代谢产物对人CD 34+造血祖细胞MLL和基因组中DNA拓扑异构酶II共价复合物的诱导作用。为了回答在断点连接的产生中是否发生了精确重组、核酸外切蚕食、大缺失、插入、倒位、重复和非同源末端连接，目的3将表征白血病患者中两种衍生染色体的基因组序列。解决DNA拓扑异构酶II抑制剂的白血病发生机制与靶向预防这种通常致命的抗癌治疗并发症高度相关。

DESCRIPTION (provided by applicant): The objective of this work is to understand the nature of the DNA damage leading to MLL translocations in leukemias following anticancer treatment with DNA topoisomerase II inhibitors. The CYP3A4 promoter is polymorphic and CYP3A4 genotype confers susceptibility. CYP3A4 converts etoposide to etoposide catechol; the catechol is readily oxidized to a quinone. These metabolites are genotoxins. MLL joins with one of many partner genes to form the translocations. The genomic breakpoint junction sequences contain evidence of DNA damage and repair. Several genomic breakpoint junction sequences indicate precise or near-precise interchromosomal DNA recombinations, but the cloning of additional breakpoints is essential to discern the damage spectrum. Etoposide and its metabolites induce DNA topoisomerase II cleavage at the translocation breakpoints in MLL and in its partner genes in vitro. We propose that etoposide and its metabolites can stimulate a series of different DNA lesions, which are repaired to form the breakpoint junctions, and that the heterogeneity in genomic breakpoint junction sequences reflects heterogeneity in the damage and its resolution. The DNA lesions to be tested include the direct induction of DNA topoisomerase II cleavage by etoposide parent drug, induction of DNA topoisomerase II cleavage from DNA adduct formation by etoposide quinone or reactive oxygen species, replication fork collisions with DNA topoisomerase II covalent complexes and DNA topoisomerase II-independent damage. Aim 1 will examine the spectrum and quantify the relative importance of DNA adducts from etoposide metabolites in an MLL bcr DNA substrate using mass spectrometry. Aim 2 will investigate the induction of functional DNA topoisomerase II covalent complexes in MLL and in the genome by etoposide and etoposide metabolites in human CD34+ hematopoietic progenitor cells using DNA arrays. To answer whether, how often and to what degree precise recombinations, exonucleolytic nibbling, large deletions, insertions, inversions, duplications and nonhomologous end-joining have occurred in creation of the breakpoint junctions, Aim 3 will characterize the genomic sequences of both derivative chromosomes in the leukemias in patients. Solving the mechanism of leukemogenesis of the DNA topoisomerase II inhibitors is highly relevant to the targeted prevention of this usually fatal complication of anticancer treatment.