SITE-SPECIFIC D(GPG) INTRASTRAND CROSS-LINKS FORMED BY DINUCLEAR PLATINUM COMPLEXES - BENDING AND NMR-STUDIES

The novel platinum drugs [{trans-PtCl(NH3)(2))(2)H2N(CH2)(n)NH2](2+) ( 1,1/t,t) are currently undergoing preclinical development. The bifunct ional DNA binding of these agents allows comparison with that of cispl atin [Farrell et al. (1995) Biochemistry, 34, 15480]. The major DNA le sion of cisplatin, the 1,2-d(Gpc) intrastrand adduct, produces a rigid , directed bend 30-35 degrees into the major groove of DNA. We have no w completed a structural analysis of the corresponding adduct formed w ith the dinuclear complexes. Gel retardation assays on 15-22 bp oligon ucleotides containing a central d(TGG*T) site show that the (Pt,Pt)-i ntrastrand adducts result in a flexible nondirectional bend. This bend is essentially independent of chain length (n = 2, 4, 6). Chemical re activity assays indicated a hypersensitivity of the thymine 5' to the adduct and an enhanced sensitivity of the 3'-thymine to OsO4. 2D H-1 N MR studies on a d(TG(1)G(2)T) adduct of [{trans-PtCl(NH3)(2)}2H2N(CH2) (6)NH2](2+) have delineated the structural features responsible for th ese 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 p latinated bases in both solid state and solution, the dinuclear adduct does not display the typical N-type sugar pucker. The base orientatio ns are anti (5'-T), anti (G(1)), anti/syn (G(2)), and anti (3'-T) whil e 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 unst acked, a reverse of the situation observed for cis-DDP.