Wang X, Wang L K, Kingsbury W D, Johnson R K, Hecht S M
Department of Chemistry, University of Virginia, Charlottesville 22901, USA.
Biochemistry. 1998 Jun 30;37(26):9399-408. doi: 10.1021/bi980451k.
The effects of eleven camptothecin derivatives on calf thymus topoisomerase I-mediated cleavage of synthetic DNA duplex have revealed that the A ring of camptothecin is very important for its biochemical activity. Depending on the type, number, and location of substituents, highly active or inactive analogues were obtained. The persistence of CPT-induced topoisomerase I-DNA covalent binary complexes was investigated by using as substrates DNA containing several good topoisomerase I cleavage sites, or else a synthetic DNA duplex of defined structure with a single high-efficiency cleavage site. The ligation kinetics at a given topoisomerase I cleavage site were sometimes quite different in the presence of CPT derivatives whose structures were closely related. Even in the presence of a single CPT analogue, topoisomerase I-DNA covalent binary complexes underwent ligation with different kinetics, presumably reflecting a dependence on DNA sequences flanking the individual topoisomerase I cleavage sites. Individual camptothecin derivatives also exhibited a spectrum of inhibitory potentials in blocking the topoisomerase I-mediated rearrangement of branched, nicked, and gapped DNA duplex substrates; in some cases the potencies of inhibition observed in these assays for individual camptothecin analogues were quite different than those determined for stabilization of the unmodified DNA-topoisomerase I binary complex.
11种喜树碱衍生物对小牛胸腺拓扑异构酶I介导的合成DNA双链体切割的影响表明，喜树碱的A环对其生化活性非常重要。根据取代基的类型、数量和位置，可以得到高活性或无活性的类似物。通过使用含有多个良好拓扑异构酶I切割位点的DNA作为底物，或者使用具有单个高效切割位点的确定结构的合成DNA双链体，研究了喜树碱诱导的拓扑异构酶I-DNA共价二元复合物的持久性。在结构密切相关的喜树碱衍生物存在下，给定拓扑异构酶I切割位点的连接动力学有时会有很大差异。即使在存在单一喜树碱类似物的情况下，拓扑异构酶I-DNA共价二元复合物也会以不同的动力学进行连接，这可能反映了对各个拓扑异构酶I切割位点侧翼DNA序列的依赖性。单个喜树碱衍生物在阻断拓扑异构酶I介导的分支、带切口和有缺口的DNA双链体底物重排方面也表现出一系列抑制潜力；在某些情况下，在这些试验中观察到的单个喜树碱类似物的抑制效力与为稳定未修饰的DNA-拓扑异构酶I二元复合物所确定的效力有很大不同。
