Characterization of in vitro deoxyribonucleic acid breakage and cross-linking induced by bis-isopropylamine)-trans-dihydroxy-cis-dichloroplatinum(IV).

Bis(isopropylamine)-trans-dihydroxy-cis-dichloroplatinum(IV) (CHIP or JM-9), a derivative of Cisplatin, was found to have DNA breakage and interstrand cross-linking activities in vitro. DNA breakage was detected by alkaline and neutral sucrose gradient analysis, agarose gel electrophoresis, and alkaline ethidium bromide fluorescence assay employing covalently closed circular PM2 DNA. DNA cross-linking activity was detected by alkaline sucrose gradient analysis and by the "snap-back" assay employing PM2 DNAs. Non-sulfhydryl-containing reducing agents, e.g., NaBH4 and NADPH, stimulated both cross-linking and breakage activities. Alkaline buffers, cyanide, or sulfhydryl group containing agents inhibited both types of activities. The hydroxyl free radical scavenger sodium benzoate (100 mM) was found to inhibit 99% and 25% of DNA breakage and cross-linking activities, respectively, suggesting DNA breakage and cross-linking may be independently mediated.