Kinetics of Reaction of cis-Diamminedichloroplatinum(II) with DNA

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Abstract
A method based on cation exchange chromatography was developed to determine the adducts formed in the reaction of cis‐diamminedichloroplatinum(II) (cis‐Pt) with DNA. DNA was incubated with various concentrations of cis‐Pt for various periods of time, ethanol precipitated, and enzymatically digested to nucleosides and Pt‐containing oligonucleotides. The unmodified nucleosides were separated from the positively charged intra‐ and interstrand cis‐Pt‐adducts with a weak cation exchanger, CM‐Sephadex C‐25, and the adducts were further purified by HPLC. The main adduct was shown to be an intrastrand cross‐link of cis‐Pt bound to the N‐7 atoms of two neighboring guanines. The minor adducts were intra‐ and interstrand cross‐links of cis‐Pt with adenine and guanine and an interstrand cross‐link of cis‐Pt with two guanines. At low levels of DNA‐modification (cis‐Pt:nucleotide = 1:50–1:1000) the intrastrand cross‐link of cis‐Pt with two guanines consisted of 60–70% of the total platination of DNA. At higher levels of DNA‐modification (>1:20), the amount of undigested products increased, indicating shielding of DNA by cis‐Pt from nucleolytic enzymes.
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