Effects of a Second Local DNA Damage Event on the Toxicity of the Human Carcinogen 4-Aminobiphenyl: A Molecular Dynamics Study of a Damaged DNA Structure.

Exposure of humans to carcinogenic aromatic amines (AAs) occurs daily. AAs are bioactivated in cells into products that attack DNA, primarily leading to N-linked C8-dG adducts. Previous work on DNA containing a single AA-derived adduct (monoadducted DNA) has shown a structure-function relationship between the damaged DNA conformation and cellular outcomes. However, relatively little is known about the conformation and biological outcomes of DNA containing two bulky adducts (diadducted DNA) in close proximity. To fill this current void in the literature, the present work uses quintuplet 0.5 μs MD simulations to understand the structural impact of DNA exposure to the potent bladder carcinogen 4-aminobiphenyl (ABP), which is found in cigarette smoke and select dyes, and results in the widely studied N-linked ABP dG adduct. Specifically, 18 unique DNA duplexes were investigated that contain one or two ABP dG adducts in the anti and/or syn glycosidic orientation(s) in all combinations of three G positions in the Nar I mutation hotspot for AAs (5'-G 1 G 2 CG 3 CC). Monoadducted DNA displays sequence-dependent conformational heterogeneity, with the G 1 site having the greatest anti preference, and highlights the range of helical structures associated with the syn lesion orientation [i.e., stacked (S), intercalated (I), and wedge (W) conformations]. Diadducted DNA results in interesting lesion separation effects on the conformational heterogeneity, including a greater anti preference for neighboring adducts (G 1 G 2 ) and a greater syn preference for next-nearest neighbor damaged sites (G 2 G 3 ) compared to monoadducted DNA. As a result, an increase in the number of ABP dG adducts changes the conformational heterogeneity of ABP-exposed DNA depending on the relative positions of the lesions and thereby could result in increased or decreased toxicity upon human exposure to elevated levels of ABP.