The role of base excision repair in the repair of DNA adducts formed by a series of nitrogen mustard-containing analogues of distamycin of increasingbinding site size
N. Brooks et al., The role of base excision repair in the repair of DNA adducts formed by a series of nitrogen mustard-containing analogues of distamycin of increasingbinding site size, ANTI-CAN DR, 14(1), 1999, pp. 11-18
The role of base excision repair in the repair of alkylation damage produce
d by a series of sequence specific oligopyrrole-containing analogues of dis
tamycin A that tether benzoic acid mustard (BAM) has been examined. Whereas
BAM alkylates and cross-links in the major groove of DNA, attachment to py
rrole units produces monoalkylations in the minor groove of DNA at AT tract
s. Both sequence specificity of alkylation and cytotoxicity increase from o
ne to three attached pyrrole units (compounds 1-3), and with 3 alkylation i
s selective for purine-N3 in the sequence 5'-TTTTGPu (where Pu = guanine or
adenine), In a model bacterial (Escherichia coli) system repair of the seq
uence specific minor groove alkylations produced by 2 and 3 does not appear
to involve BER, since neither a formamidopyrimidine-DNA glycosylase repair
deficient E. coli mutant (BH 20, fpg(-) mutant) nor a 3-methyladenine-DNA
glycosylase repair deficient mutant (GC 4803, tag(-)alkA(-) mutant) showed
increased cytotoxicity to 2 or 3 compared with the wild type, AB 1157, The
monopyrrole compound 1 was, however, similar to 4-fold more cytotoxic to th
e GC 4803 mutant compared with wild type and BH 20, suggesting a role for t
he 3-methyladenine-DNA glycosylase in the recognition and excision of the a
dducts formed by 1. In contrast, increased sensitivity (>10-fold) was obser
ved for the conventional nitrogen mustard BAM in the BH 20 strain, suggesti
ng a role for the formamidopyrimidine-DNA glycosylase in the repair of the
lesions produced by the agent. In a cell-free system the E. coli 3-methylad
enine-DNA glycosylase (AlkA) was shown to remove alkylations at 5'-TTTTGPu
sequences. However, the efficiency in removing the adducts formed by the ol
igopyrrole compounds decreased dramatically from compound 1 to compound 3.
Increasing the size of the DNA adduct formed in the minor groove therefore
decreased the efficiency of recognition and removal of the adduct by the DN
A glycosylase.