Book of Abstracts: Albany 2009
June 16-20 2009
© Adenine Press (2008)
Kinetics of DNA Stability in the Presence of Cisplatin and Transplatin
It has been shown in an earlier study that a negative shift of DNA melting temperature (Tm) caused by cisplatin is strongly increased if melting experiment is carried out in alkaline medium (E.N. Galyuk et al. J. Biomol. Struct. Dynam. 25, 407-418 (2008)). Transplatin also decreases Tm at pH>10 but the decrease is lower than that for cisplatin. This result allows us to increase sensitivity of melting measurements for DNA complexes with platinum compounds. Using it, we have demonstrated in the present study that the development of platination is stopped in alkaline medium (0.1 M NaCl, pH 10.5-10.8). All these findings gave an opportunity to measure kinetics of DNA stability under platination in 0.01M NaClO4 at various temperatures and compare these results with other properties of DNA complexes with platinum compounds. We have found that, in the presence of cisplatin, DNA stability is monotonously decreased with the time of incubation in 0.01 M NaClO4. The beginning of the effect of cisplatin on the melting temperature was registered in 2 minutes. At 37°C, the time of a half of the maximal decrease of Tm is ~1 h. The reaction is four-fold slower and four-fold faster at 25°C and 50°C, respectively. At 25 and 37°C, the maximal decrease in the melting temperature is almost the same but the maximal shift value is lower under a 50°C incubation. In contrast to cisplatin, kinetics is not monotonous for transplatin. A decrease in Tm during 3 h incubation at 37°C is changed by an increase. However, the melting temperature does not reach the value corresponding to control unplatinated DNA even after a 48 hour incubation. To evaluate kinetics of DNA interstrand crosslinking by cis- and transplatin, platination was stopped after various time interval of incubation, and then DNA was subjected to denaturation by heating to 100o°C followed by quick cooling or by freeze-thaw procedure in alkaline medium. The second type of denaturation was found recently (E.N. Galyuk et al. J. Biomol. Struct. Dynam. 26, 517-524 (2009)). It was shown that a weak interstrand crosslinking appears after a 15 minute incubation but it becomes sufficiently effective to restore the double helix after a 24 hour incubation.
Dmitri Y. Lando1, 2
1 Institute of Bioorganic Chemistry