Metal-intercalator-mediated self-association and one-dimensional aggregation in the structure of the excised major DNA adduct of a platinum-acridine agent

The crystal structure of the excised major DNA monoadduct, Pt(en)(ACRAMTU-S)(dGuo-N7)]3+ ("dGuo*"; en = ethane-1,2-diamine; ACRAMTU = 1-2-(acridin-9-ylamino)ethyl]-1,3-dimethylthiourea, acridinium cation; dGuo = 2'-deoxyguanosine), of a platinum-acridine cytotoxic agent is reported. The adduct dGuo*, previously identified in enzymatic digests of native DNA treated with this drug, is partially deprotonated and dimerizes through formation of a rare GG- mismatch base pair, which is sandwiched between the planar chromophores of the acridine nonleaving groups linked to platinum. NMR evidence exists that indicates that the dimeric form persists in neutral aqueous solution. The one-dimensional pi-stack produced by the dimers in the solid state is reminiscent of a coordinative-intercalative DNA binding mode.