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Decrease in intensity of DNA fluorescence caused by interaction between DNA and platinum complexes
P Rauko1, K Povazanová, V Reichelová
1Cancer Research Institute, Slovak Academy of Sciences, Bratislava; Czechoslovakia.
Abstract:
The decrease of DNA fluorescence caused by an impaired capacity of ethidium bromide to intercalate into the DNA reflected structural changes caused in the DNA molecule by its interaction with platinum complexes. This fall in DNA fluorescence was proportional to the length of exposure of DNA to the platinum complexes, and depended on the environment in which the interaction took place. The therapeutically active cisplatinum (cis-DDP) was more efficient to inhibit fluorescence in a solution of 4 X 10(-3) mol NaCl than its therapeutically inactive trans-isomer (trans-DDP). For comparison, the inhibition of DNA fluorescence was also studied in a solution of 10(-2) mol NaClO4. The inhibitory effect was elicited more rapidly, but no difference was found between the two isomers. We concluded that the larger effect of cis-DDP on DNA was induced by the 4 X 10(-3) mol concentration of NaCl. Since also the intracellular concentration of chloride ions is 4 X 10(-3) mol, it cannot be ruled out that the interaction between DNA and cis-DDP and trans-DDP in vivo might be influenced by the intracellular environment.
Insights
Platinum complexes alter DNA structure, reducing fluorescence. The active cis-DDP shows greater DNA interaction in specific salt concentrations, suggesting in vivo relevance for cancer drug development.
Area of Science:
- Biochemistry
- Molecular Biology
- Pharmacology
Background:
- Platinum-based chemotherapy agents, like cisplatin, are crucial in cancer treatment.
- Understanding their interaction with DNA is key to their efficacy and side effects.
- Ethidium bromide fluorescence is a sensitive indicator of DNA structural integrity.
Purpose of the Study:
- To investigate the structural changes in DNA induced by platinum complexes.
- To compare the effects of cis-diamminedichloroplatinum(II) (cis-DDP) and its trans-isomer (trans-DDP) on DNA.
- To determine the influence of the surrounding ionic environment on these interactions.
Main Methods:
- Measuring the decrease in DNA fluorescence caused by ethidium bromide intercalation.
- Exposing DNA to cis-DDP and trans-DDP in solutions with varying salt concentrations (NaCl and NaClO4).
- Correlating fluorescence changes with exposure time and salt concentration.
Main Results:
- Platinum complex interaction with DNA caused structural changes, reducing ethidium bromide fluorescence.
- The extent of fluorescence reduction was proportional to exposure time and dependent on the salt environment.
- Cis-DDP significantly inhibited fluorescence more than trans-DDP in 4 x 10(-3) mol NaCl.
- In 10(-2) mol NaClO4, the inhibitory effect was faster, but no difference was observed between cis-DDP and trans-DDP.
Conclusions:
- The enhanced effect of cis-DDP in 4 x 10(-3) mol NaCl suggests this concentration is critical for its DNA interaction.
- Given the similar intracellular chloride concentration, the cellular environment likely influences the in vivo activity of cis-DDP and trans-DDP.
- These findings provide insights into the mechanism of action of platinum-based anticancer drugs.