Khan Qasim A, Pilch Daniel S
Department of Pharmacology, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, 675 Hoes Lane, Piscataway, NJ 08854-5635, USA.
J Mol Biol. 2007 Jan 19;365(3):561-9. doi: 10.1016/j.jmb.2006.10.032. Epub 2006 Oct 13.
Many agents (e.g. camptothecins, indolocarbazoles, indenoisoquinolines, and dibenzonaphthyridines) stimulate topoisomerase I (TOP1)-mediated DNA cleavage (a behavior termed topoisomerase I poisoning) by interacting with both the DNA and the enzyme at the site of cleavage (typically by intercalation between the -1 and +1 base-pairs). The bibenzimidazoles, which include Hoechst 33258 and 33342, are a family of DNA minor groove-directed agents that also stimulate topoisomerase I-mediated DNA cleavage. However, the molecular mechanism by which these ligands poison TOP1 is poorly understood. Toward this goal, we have used a combination of mutational, footprinting, and DNA binding affinity analyses to define the DNA binding site for Hoechst 33258 and a related derivative that results in optimal induction of TOP1-mediated DNA cleavage. We show that this DNA binding site is located downstream from the site of DNA cleavage, encompassing the base-pairs from position +4 to +8. The distal nature of this binding site relative to the site of DNA cleavage suggests that minor groove-directed agents like the bibenzimidazoles poison TOP1 via a mechanism distinct from compounds like the camptothecins, which interact at the site of cleavage.
许多药物（如喜树碱、吲哚咔唑、茚并异喹啉和二苯并萘啶）通过在切割位点与DNA和酶相互作用（通常通过插入-1和+1碱基对之间）来刺激拓扑异构酶I（TOP1）介导的DNA切割（一种称为拓扑异构酶I中毒的行为）。包括Hoechst 33258和33342在内的双苯并咪唑类药物是一类DNA小沟靶向药物，它们也能刺激拓扑异构酶I介导的DNA切割。然而，这些配体使TOP1中毒的分子机制尚不清楚。为了实现这一目标，我们结合了突变、足迹和DNA结合亲和力分析来确定Hoechst 33258和一种相关衍生物的DNA结合位点，该衍生物能最佳诱导TOP1介导的DNA切割。我们表明，这个DNA结合位点位于DNA切割位点的下游，涵盖从+4到+8位置的碱基对。相对于DNA切割位点，这个结合位点的远端性质表明，像双苯并咪唑类这样的小沟靶向药物通过一种不同于喜树碱类化合物的机制使TOP1中毒，喜树碱类化合物在切割位点相互作用。
