Hsiang Y H, Hertzberg R, Hecht S, Liu L F
J Biol Chem. 1985 Nov 25;260(27):14873-8.
Camptothecin, a cytotoxic drug, is a strong inhibitor of nucleic acid synthesis in mammalian cells and a potent inducer of strand breaks in chromosomal DNA. Neither the equilibrium dialysis nor the unwinding measurement indicates any interaction between camptothecin and purified DNA. However, camptothecin induces extensive single strand DNA breaks in reactions containing purified mammalian DNA topoisomerase I. DNA breakage in vitro is immediate and reversible. Analyses of camptothecin-induced DNA breaks show that topoisomerase I is covalently linked to the 3' end of the broken DNA. In addition, camptothecin inhibits the catalytic activity of mammalian DNA topoisomerase I. We propose that camptothecin blocks the rejoining step of the breakage-reunion reaction of mammalian DNA topoisomerase I. This blockage results in the accumulation of a cleavable complex which resembles the transient intermediate proposed for eukaryotic DNA topoisomerase I. The inhibition of nucleic acid synthesis and the induction of DNA strand breaks observed in vivo may be related to the formation of this drug-induced cleavable complex.
喜树碱是一种细胞毒性药物，是哺乳动物细胞中核酸合成的强抑制剂，也是染色体DNA链断裂的有效诱导剂。平衡透析和解旋测量均未表明喜树碱与纯化的DNA之间存在任何相互作用。然而，喜树碱在含有纯化的哺乳动物DNA拓扑异构酶I的反应中诱导大量单链DNA断裂。体外DNA断裂是即时且可逆的。对喜树碱诱导的DNA断裂的分析表明，拓扑异构酶I与断裂DNA的3'末端共价连接。此外，喜树碱抑制哺乳动物DNA拓扑异构酶I的催化活性。我们提出，喜树碱阻断了哺乳动物DNA拓扑异构酶I的断裂-重连反应的重新连接步骤。这种阻断导致可裂解复合物的积累，该复合物类似于为真核DNA拓扑异构酶I提出的瞬时中间体。体内观察到的核酸合成抑制和DNA链断裂诱导可能与这种药物诱导的可裂解复合物的形成有关。
