INFLUENCE OF CISPLATIN INTRASTRAND CROSS-LINKING ON THE CONFORMATION,THERMAL-STABILITY, AND ENERGETICS OF A 20-MER DNA DUPLEX

cis-Diamminedichloroplatinum(II) (cisplatin) is a widely used anticanc er drug that binds to and crosslinks DNA. The major DNA adduct of the drug results from coordination of two adjacent guanine bases to platin um to form the intrastrand crosslink cis- [Pt(NH3)(2){d(GpG)-N7(1), -N 7(2)}] (cis-Pt-GG). In the present study, spectroscopic and calorimetr ic techniques were employed to characterize the influence of this cros slink on the conformation, thermal stability, and energetics of a site -specifically platinated 20-mer DNA duplex, CD spectroscopic and therm al denaturation data revealed that the crosslink alters the structure of the host duplex, consistent with a shift from a B-like to an A-like conformation; lowers its thermal stability by approximate to 9 degree s C; and reduces its thermodynamic stability by 6.3 kcal/mol at 25 deg rees C, most of which is enthalpic in origin; but it does not alter th e two-state melting behavior exhibited by the parent, unmodified duple x, despite the significant crosslink-induced changes noted above. The energetic consequences of the cis-Pt-GG crosslink are discussed in rel ation to the structural perturbations it induces in DNA and to how the se crosslink-induced perturbations might modulate protein binding.