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Site-Specific d(GpG) Intrastrand Cross-Links Formed by Dinuclear Platinum Complexes. Bending and NMR Studies

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journal contribution
posted on 24.12.1996 by J. Kašpárková, K. J. Mellish, Y. Qu, V. Brabec, N. Farrell
The novel platinum drugs [{trans-PtCl(NH3)2}2H2N(CH2)nNH2]2+ (1,1/t,t) are currently undergoing preclinical development. The bifunctional DNA binding of these agents allows comparison with that of cisplatin [Farrell et al. (1995) Biochemistry, 34, 15480]. The major DNA lesion of cisplatin, the 1,2-d(GpG) intrastrand adduct, produces a rigid, directed bend 30−35° into the major groove of DNA. We have now completed a structural analysis of the corresponding adduct formed with the dinuclear complexes. Gel retardation assays on 15−22 bp oligonucleotides containing a central d(TG*G*T) site show that the (Pt,Pt)-intrastrand adducts result in a flexible nondirectional bend. This bend is essentially independent of chain length (n = 2, 4, 6). Chemical reactivity assays indicated a hypersensitivity of the thymine 5‘ to the adduct and an enhanced sensitivity of the 3‘-thymine to OsO4. 2D 1H NMR studies on a d(TG1G2T) adduct of [{trans-PtCl(NH3)2}2H2N(CH2)6NH2]2+ have delineated the structural features responsible for these observations. In contrast to the cisplatin adduct, which displays a 100% N-type sugar of the 5‘-G and an anti base conformation of the platinated bases in both solid state and solution, the dinuclear adduct does not display the typical N-type sugar pucker. The base orientations are anti (5‘-T), anti (G1), anti/syn (G2), and anti (3‘-T) while the sugar conformations are N, S/N, N, and S, respectively. The 5‘-T remains stacked with its guanine neighbor while the 3‘-T becomes unstacked, a reverse of the situation observed for cis-DDP.