Characterization of in vitro DNA breakage and crosslinking induced by bis(isopropylamine)-trans-dihydroxy-cis-dichloroplatinum(IV)

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Abstract
Bis(isopropylamine)-trans-dihydroxy-cis-dichloroplatinum (IV) (CHIP or JM-9), a derivative of [the antineoplastic drug] cisplatin, had 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 [bacteriophage] PM2 DNA. DNA cross-linking activity was detected by alkaline sucrose gradient analysis and by the snap-back assay employing PM2 DNA. 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) inhibited 99% and 25% of DNA breakage and cross-linking activities, respectively, suggesting DNA breakage and cross-linking may be independently mediated.