Position-specific trapping of topoisomerase I-DNA cleavage complexes by intercalated benzo[a]pyrene diol epoxide adducts at the 6-amino group of adenine
Y. Pommier et al., Position-specific trapping of topoisomerase I-DNA cleavage complexes by intercalated benzo[a]pyrene diol epoxide adducts at the 6-amino group of adenine, P NAS US, 97(20), 2000, pp. 10739-10744
Citations number
50
Categorie Soggetti
Multidisciplinary
Journal title
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
DNA topoisomerase I (top1) is the target of potent anticancer agents, inclu
ding camptothecins and DNA intercalators, which reversibly stabilize (trap)
top1 catalytic intermediates (cleavage complexes). The aim of the present
study was to define the structural relationship between the site(s) of cova
lently bound intercalating agents, whose solution conformations in DNA are
known, and the site(s) of top1 cleavage. Two diastereomeric pairs of oligon
ucleotide 22-mers, derived from a sequence used to determine the crystal st
ructure of top1-DNA complexes, were synthesized. One pair contained either
a trans-opened 10R- or 10S-benzo[a]pyrene 7,8-diol 9,10-epoxide adduct at t
he N-6-amino group of a central 2'-deoxyadenosine residue in the scissile s
trand, and the other pair contained the same two adducts in the non-scissil
e strand. These adducts were derived from the (+)-(7R,8S,9S,10R)- and (-)-(
7S,8R,9R,10S)-7,8-diol 9,10-epoxides in which the benzylic 7-hydroxyl group
and the epoxide oxygen are trans. On the basis of analogy with known solut
ion conformations of duplex oligonucleotides containing these adducts, we c
onclude that top1 cleavage complexes are trapped when the hydrocarbon adduc
t is intercalated between the base pairs flanking a preexisting top1 cleava
ge site, or between the base pairs immediately downstream (3' relative to t
he scissile strand) from this site. We propose a model with the +1 base rot
ated out of the duplex, and in which the intercalated adduct prevents relig
ation of the corresponding nucleotide at the 5' end of the cleaved DNA. The
se results suggest mechanisms whereby intercalating agents interfere with t
he normal function of human top1.