Interaction of Topotecan,DNA Topoisomerase I Inhibitor,with Double-Stranded Polydeoxyribonculeotides.5.Topotecan is Capable of Producing Single-and Double-Strand Breaks in Circular Supercoiled DNA in the Absence of the Enzyme

摘要

A study was made of the temperature,concentration,and time dependences for the emergence of breaks in the sugar-phosphate backbone of a circular supercoiled DNA (scDNA) in the presence of a camptothecin derivative topotecan (TPT) and in the absence of DNA topoisomerase I (topo I).The experiments were carried out in low ionic strength solutions (10 mM sodium cacodylate) at neutral pH (6.8).The incubation time necessary for the appearance of double-strand breaks in scDNA in the presence of TPT correlated with the time of formation of strong TPT-DNA complex.This is the first demonstration that molecules of the camptothecin family can cause double-strand breaks in scDNA in the absence of the enzyme.A model is suggested for the complex composed of two crossed DNA duplexes bound through a bridge of two dimers of the TPT lactone form.According to this model,two carbonyl groups of D rings of different TPT dimers form hydrogen bonds with 2-amino groups of guanines located in the neighboring base pairs of different strands of one DNA duplex.At the same time,two other carbonyl groups of D rings of TPT dimers form hydrogen bonds with 2-amino groups of guanines 5 bp apart in one and the same strand of the second DNA duplex.