Gene-specific formation and repair of cisplatin intrastrand adducts and interstrand cross-links in Chinese hamster ovary cells

We have used three methods to study the formation and repair of intrastrand adducts and interstrand cross-links in the DNA of Chinese hamster ovary cells induced by the anticancer drug cis-diamminedichloroplatinum II (cisplatin). Using atomic absorption spectroscopy, we found that 21% of the total genomic cisplatin adducts were removed at 8 h and 42% at 24 h. We used ABC excinuclease digestion, coupled with out previously reported methodology to quantify DNA in specific genomic regions. These adducts were removed faster in the transcribed dihydrofolate reductase and c-myc genes compared to a noncoding fragment, a region containing the little or nontranscribed c-fos oncogene, and to the overall genome. Interstrand cross-links in specific sequences were quantified by Southern hybridization of denatured-renatured DNA separated on a neutral gel. We found that cross-links were removed more efficiently from the gene regions than intrastrand adducts and, at high levels of cross-linking, removal was similar from transcribed and from nontranscribed regions.