The reactions of the anticancer complex trans-[PtCl2{(E)-HN=C(OMe)Me}2] (trans-EE) with a series of ribo and deoxyribodinucleotides have been studied by HPLC and 2D [1H, 15N] HMQC NMR spectroscopy and compared with those of the inactive trans isomer of cisplatin, trans-[PtCl2(NH3)2] (trans-DDP). Reactions of trans-EE with r(ApG) and d(ApG) take place through solvolysis of the starting substrate and subsequent formation of trans G-N7/monochloro and G-N7/monoaqua adducts. Slowly, the monofunctional adducts evolve to a bifunctional adduct forming an unprecedented and unexpected A-N3/G-N7 platinum cross-link spanning two trans positions. For stereochemical reasons, trans platinum complexes cannot form N7/N7 cross-links between adjacent purines in di- or polynucleotides. For the reverse sequence r(GpA), no chelate structure was formed even after a two-week reaction. The reaction of trans-DDP with r(ApG) produces many more products than the analogous reaction with trans-EE. One of these products was identified as the A-N3/G-N7 trans-chelate.

The influence of the presence of DNA on the kinetics of cisplatin (cis-[PtCl2(NH3)2]) aquation (replacement of Cl- by H2O) and anation (replacement of H2O by Cl-) involved in the hydrolysis of cisplatin have been determined by two-dimensional [1H,15N] HMQC NMR spectroscopy. Single-stranded dT20 and double-stranded [d(AT)10]2 oligonucleotides were used as DNA models, avoiding guanines which are known to react rapidly with aquated cisplatin forms. Reactions starting from cis-[PtCl2(15NH3)2], or from a stoichiometric mixture of cis-[Pt(15NH3)2(H2O)2]2+ and Cl- (all 0.5 mM Pt(II); in ionic strength, adjusted to 0.095 M or 0.011 M with NaClO4, pH between 3.0 and 4.0) were followed in an NMR tube in both the absence and presence of 0.7 mM dT20 or [d(AT)10]2. In the presence of dT20, we observed a slight and ionic-strength-independent decrease (15-20 %) of the first aquation rate constant, and a more significant decrease of the second anation rate constant. The latter was more important at low ionic strength, and can be explained by efficient condensation of cis-[Pt(15NH3)2(H2O)2]2+ on the surface of single-stranded DNA, in a region depleted of chloride anions. At low ionic strength, we observed an additional set of [1H,15N] HMQC spectral signals indicative of an asymmetric species of PtN2O2 coordination, and we assigned them to phosphate-bound monoadducts of cis-[Pt(15NH3)2(H2O)2]2+. Double-stranded [d(AT)10]2 slowed down the first aquation step also by approximately 15 %; however, we could not determine the influence on the second hydrolysis step because of a significant background reaction with cis-[Pt(NH3)2(H2O)2]2+.

The focus of this review is on recently published papers (2000-2005) where NMR spectroscopy has been applied as the principal method in the study of anticancer platinum drugs. The paper gives an overview of the basic NMR techniques particularly relevant for studying interaction between platinum compounds and nucleic acid constituents. The latest NMR studies on the well-known anticancer drug cisplatin, with focus on kinetics and cisplatin-DNA structures are reported. Also cisplatin analogues clinically approved or currently in clinical trials are discussed. In addition two new classes of anticancer platinum drugs are described: trans-oriented Pt iminoether complexes and multinuclear Pt complexes. Reaction kinetics and structural changes induced by these novel Pt drugs are discussed in relation to cisplatin. NMR studies of non-DNA platinum drug targets including peptides, proteins and phospholipid membranes are also treated.

Reactions of [PtCl(dien)](+) (dien=diethylenetriamine), Mn(2+) and Zn(2+) ions with three different double-helical oligodeoxyribonucleotides, which contain the central sequence GGXY (XY=AT, TA or CC) have been monitored by NMR spectroscopy. 2 D [(1)H, (15)N] HSQC/HMQC NMR spectroscopy using (15)N-labeled Pt(dien) shows that the rate of formation of 3'-G-N 7 and 5'-G-N 7 platinated adducts is highly sequence dependent. The relative rates of platination of 5'-G versus 3'-G are largest for the sequence -GGCC-, for which only a small fraction of the 3'-G adduct is formed; for -GGTA-, the rate of 5'-G platination is about eight times that of 3'-G, and for -GGAT- the ratio is 1.2. These values are in qualitative agreement with those obtained for G-N 7/Mn(2+) selectivity as determined by paramagnetic line broadening of the adjacent G-H 8, and also G-N 7/Zn(2+) selectivity as determined by G-H 8 chemical shift changes. Fluctuation in the nucleophilicity of G-N 7 may be explained by variation of the pi-stacking interaction between base residues along the double helix. The reaction mixtures containing platinated 3'-G and 5'-G fractions were separated by HPLC. Since the duplexes are self-complementary, the platinated single strands were readily annealed to duplexes with twofold symmetry and analyzed by 2 D [(1)H, (1)H] NOESY NMR spectroscopy. Unexpectedly, the 5'-G-H 8 resonance signals of both 5'-G and 3'-G platinated duplexes showed large downfield shifts in the range delta=0.3-0.6 ppm, while the 3'-G-H 8 resonance signals in both cases exhibited no, or only slight, upfield shifts. Resonance signals for several other protons in the central region undergo large chemical shift variations induced by platination, indicating that monofunctional binding to DNA leads to appreciable conformational changes.