Region-specific DNA damage by AT-specific DNA-reactive drugs is predicted by drug binding specificity

Bizelesin and adozelesin are DNA-reactive antitumor drugs that alkylate adenines at the 3' ends of their preferred binding sites [5'T(A/T)(4)A3'and 5'(A/T)(3)(-4)A3', respectively]. We used these drugs to examine the determinants for region-specific damage of human genomic DNA. The distribution of bizelesin binding motifs in several regions analyzed "in silico" correlated well with the experimentally determined lesions in these regions assessed by quantitative polymerase chain reaction (QPCR) stop assay. In contrast to the typically low motif density, clusters of potential bizelesin binding sites were found in the matrix-associated regions (MAR domains) of the c-myc and apolipoprotein B (apoB) genes. Accordingly, lesions induced by bizelesin in these domains (2.13 and 7.06 lesions kbp(-1) microM(-1), respectively) markedly exceeded lesions in bulk DNA (0.87 lesions kbp(-1) microM(-1)) or in regions with typically low motif density (e.g., 0.75 and 0.87 lesions kbp(-1) microM(-1) in a beta-globin gene and c-myc origin of replication regions, respectively). Consistent with the more frequent, less localized adozelesin motif, actual lesions induced by adozelesin exceeded by severalfold lesions by bizelesin in four selected regions (within the c-myc and HPRT loci). Whereas adozelesin is likely to affect similar regions as bizelesin, adozelesin's more promiscuous binding probably compromises its relative specificity for such targets. In contrast, findings for bizelesin provide for the first time a proof of principle that a small molecular weight drug can preferentially damage specific regions in cellular DNA. Targeting of critical repetitive sequences, such as AT-rich MAR domains, which allow for clustering of drug binding motif, can be the paradigm for region specificity of small molecular weight agents.