INHIBITION OF CISPLATIN-MEDIATED DNA DAMAGE INVITRO BY RIBONUCLEOTIDES

Effects of ribonucleotides on cis-diamminedichloroplatinum(II) (cispla tin)-mediated DNA damage were studied by incubating pUC18 DNA with cis platin in the presence of nucleotide, and by monitoring conformational change and sensitivity change to restriction enzyme HpaII of the DNA due to the platinum-DNA adduct formation. The cisplatin-mediated DNA d amage was inhibited in a dose-dependent fashion by ATP or GTP, substan tially at their physiological intracellular concentrations, and almost completely by 5 mM ATP or 2 mM GTP. The inhibitory effect of nucleoti de on the platination of DNA was in the order of GTP > ATP much greate r than CTP > UTP, and of nucleoside triphosphate > nucleoside diphosph ate > nucleoside monophosphate. Nucleoside did not show any significan t effect on platination of DNA. To elucidate the mechanism of the nucl eotide effects on platination of DNA, interaction between ATP or GTP a nd cisptatin was analyzed by high-performance liquid chromatography. T he results suggested that ATP inhibits cisplatin-mediated DNA damage b oth by forming a platinum-ATP adduct and by non-covalent ionic interac tion with cisplatin, while GTP acts largely by forming platinum-GTP ad ducts.