PROTEIN-ASSOCIATED DNA BREAKS AS INDICATOR OF TOPOISOMERASE INHIBITION

DNA拓扑异构酶已被确定为癌症的主要靶点 化疗。从黄瓜中分离出两种类型的拓扑异构酶 真核细胞核。两种拓扑异构酶1和II都能松弛DNA 在DNA复制和复制中起着至关重要的作用 抄写。然而，拓扑异构酶II是唯一能 将DNA环锚定到核基质上，并重新分解 复制了DNA环。两个抗癌药物家族抑制 拓扑异构酶II：DNA嵌入物，如间苯丙氨酸(m-AMSA)， 阿霉素和椭圆形碱衍生物，以及 去甲基鬼臼毒素，如依托泊苷(VP-16)和 替尼平苷(Vm-26)。药物诱导的拓扑异构酶II抑制 导致蛋白质相关的DNA断裂的形成，这 可用碱洗脱法检测。我们现在已经证明， 特定的拓扑异构酶I抑制剂喜树碱也能产生 蛋白质相关的DNA断裂。我们最近的发现是DNA 拓扑异构酶抑制剂诱导的断裂与 强烈且不可逆的DNA合成抑制，以及 蜂毒灵预防拓扑异构酶抑制剂的细胞毒性 提示药物诱导的拓扑异构酶复合体可以发挥其作用 产生稳定的拓扑异构酶-DNA复合体的细胞毒作用 这会破坏DNA复制复合体的稳定性。最后，我们 发现一种耐药的人乳腺癌细胞株(MCF-7) 阿霉素有11种拓扑异构酶修饰，它们是 与药物摄取减少有关的通常是 多效性耐药细胞系。

DNA topoisomerases have been identified as major targets for cancer chemotherapy. Two types of topoisomerases have been isolated from eukaryotic cell nuclei. Both topoisomerases 1 & II relax DNA supercoiling and play a crucial role in DNA replication and transcription. However, topoisomerase II is the only enzyme able to anchor DNA loops to the nuclear matrix and to decatenate newly replicated DNA circles. Two families of anticancer drugs inhibit topoisomerase II: DNA intercalators, such as amsacrine (m-AMSA), adriamycin and ellipticine derivatives, and demethylepipodophyllotoxins, such as etoposide (VP-16) and teniposide (VM-26). Drug-induced topoisomerase II inhibition results in the formation of protein-associated DNA breaks, which can be detected by alkaline elution. We have shown now, that the specific topoisomerase I inhibitor, camptothecin produces also protein-associated DNA breaks. Our recent finding that the DNA breaks induced by topoisomerase inhibitors are associated with strong and poorly reversible DNA synthesis inhibition, and that aphidicolin prevents the cytotoxicity of topoisomerase inhibitors suggest that drug-induced topoisomerase complexes could exert their cytotoxic action by producing stable topoisomerase-DNA complexes which would destabilize DNA replication complexes. Finally, we have found that a human breast cancer cell line (MCF-7) resistant to adriamycin has topoisomerase 11 modifications, which are associated with the drug uptake reduction usually encountered in pleiotropic resistant cell lines.