Radical-induced DNA damage by a synthetic analogue of copper(II)-bleomycin

The capacity of free-radical formation and concomitant radical-induced DNA damage by [Cu(PMA)]X (X = ClO4-, BF4-), the first crystalline synthetic analogue of Cu(II)-BLM, have been studied. In phosphate buffer, [Cu(PMA)]+ can be reduced by thiols like DTT to a Cu(I) species that can be reoxidized with dioxygen. During oxygenation of the Cu(I) analogue, appreciable amounts of .OH radical are formed. This fact has been established by spin-trapping experiments. Effects of SOD and catalase as well as pH on the ESR signal of the spin adduct have identified a set of reactions that eventually leads to .OH radical formation by [Cu(PMA)]+. Interestingly, the same reaction scheme has been proposed earlier for Cu(II)-BLM. In the presence of DTT and dioxygen, [Cu(PMA)]+ inflicts significant damage to plasmid DNA. That the damage does not arise from iron contamination has been established. The DNA damage is hindered when SOD or catalase is present in the incubation mixture. Less strand scission is observed at higher pH. Modulation of DNA cleavage efficiency with systematic variations in DTT concentration indicates that the conflicting reports on the ability of Cu(II)-BLM to mediate in vitro DNA damage might have resulted from the different DTT concentrations used by different groups.