Induction of AT-specific DNA-interstrand crosslinks by bizelesin in genomic and simian virus 40 DNA

Abstract

Bizelesin is a bifunctional AT-specific DNA alkylating drug. Our study characterized the ability of bizelesin to induce interstrand crosslinks, a potential lethal lesion. In genomic DNA of BSC-1 cells, bizelesin formed from approx. 0.3 to 6.03±0.85 interstrand crosslinks per 10 6 base pairs, at 5–100 nM drug concentration, respectively, comparable to the number of total adducts previously determined in the same system (J.M. Woynarowski, M.M. McHugh, L.S. Gawron, T.A. Beerman, Biochemistry 34 (1995) 13042–13050). Bizelesin did not induce DNA-protein crosslinks or strand breaks. A model defined target, intracellular simian virus 40 (SV40) DNA, was employed to map at the nucleotide level sites of bizelesin adducts, including potential interstrand crosslinks. Preferential adduct formation was observed at AT tracts which are abundant in the SV40 matrix associated region and the origin of replication. Many sites, including each occurrence of 5′-T(A/T) 4A-3′, co-mapped on both DNA strands suggesting interstrand crosslinks, although monoadducts were also formed. Bizelesin adducts in naked SV40 DNA were found at similar sites. The localization of bizelesin-induced crosslinks in AT-rich tracts of replication-related regions is consistent with the potent anti-replicative properties of bizelesin. Given the apparent lack of other types of lesions in genomic DNA, interstrand crosslinks localized in AT-rich tracts, and to some extent perhaps also monoadducts, are likely to be lethal effects of bizelesin.