Influence of dT20 and [d(AT)10]2 on Cisplatin Hydrolysis Studied by Two-Dimensional [1H,15N] HMQC NMR Spectroscopy
✍ Scribed by Jo Vinje; Einar Sletten; Jiří Kozelka
- Publisher
- John Wiley and Sons
- Year
- 2005
- Tongue
- English
- Weight
- 345 KB
- Volume
- 11
- Category
- Article
- ISSN
- 0947-6539
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✦ Synopsis
Abstract
The influence of the presence of DNA on the kinetics of cisplatin (cis‐[PtCl~2~(NH~3~)~2~]) aquation (replacement of Cl^−^ by H~2~O) and anation (replacement of H~2~O by Cl^−^) involved in the hydrolysis of cisplatin have been determined by two‐dimensional [^1^H,^15^N] HMQC NMR spectroscopy. Single‐stranded dT~20~ 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‐[PtCl~2~(^15^NH~3~)~2~], or from a stoichiometric mixture of cis‐[Pt(^15^NH~3~)~2~(H~2~O)~2~]^2+^ and Cl^−^ (all 0.5 mM Pt^II^; in ionic strength, adjusted to 0.095 M or 0.011 M with NaClO~4~, pH between 3.0 and 4.0) were followed in an NMR tube in both the absence and presence of 0.7 mM dT~20~ or [d(AT)~10~]~2~. In the presence of dT~20~, 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(^15^NH~3~)~2~(H~2~O)~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 [^1^H,^15^N] HMQC spectral signals indicative of an asymmetric species of PtN~2~O~2~ coordination, and we assigned them to phosphate‐bound monoadducts of cis‐[Pt(^15^NH~3~)~2~(H~2~O)~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(NH~3~)~2~(H~2~O)~2~]^2+^.