Analysis and quantitation of the DNA damage produced in cells by the cisplatin analog cis-[3H]dichloro(ethylenediamine)platinum (II).

The anticancer drug cisplatin elicits its cytotoxicity through damaging DNA. A sensitive method for following this interaction involves the use of an analog cis-[3H]dichloro(ethylenediamine)platinum(II) (cis-[3H]DEP). Cells are incubated with this analog, the DNA is purified, the enzyme is digested, and the deoxyribonucleoside-bound adducts are separated by HPLC. Other radioactive peaks can be detected by HPLC. These have been identified as arising from contaminating RNA and from the incorporation of tritium into unmodified nucleosides. A rapid DNA purification procedure that overcomes the first problem is presented. The latter problem is overcome by incubation of cells in hypoxanthine, aminopterin, and thymidine (HAT medium). Direct quantitation of levels of DNA platination can be determined in a single HPLC run by comparing the radioactivity in a specific adduct peak to the absorbance of the unmodified deoxyribonucleosides. Modifications to the synthesis of cis-[3H]DEP, the enzyme digestion of DNA, and the HPLC methodology are also described.