Abstract

The nuclease activity of the bisphenanthroline Cu(I) complex, [CuI(phen)2]+ (phen=1,10-phenanthroline), has been largely studied and there is a consensus that the predominant mechanism of DNA damage is through the generation of reactive oxygen species, ROS. Studies on the nuclease activity of Cu(I) coordinated to 2,9-dimethyl-1,10-phenanthroline (dmp), [CuI(dmp)2]+, did not show the same behaviour, and a poor reactivity has been informed. The lower activity of this dmp derivative has been ascribed to the redox stability of the 1+ oxidation state, which restricts the ROS-generating cycle. In addition, no information about the mechanism of DNA cleavage has been reported, meanwhile assays on cell cultures are limited. In this work, we present studies on the nuclease activity of [CuI(dmp)2]+, and the mechanism involved in the DNA cleavage. Gel-electrophoresis experiments using radical scavengers and EPR measurements were performed to detect the ROS involved, while hydroxyl radical, HO·, was identified as the responsible of DNA damage. Regarding the redox mechanism involved in the ROS generation, EPR and kinetic methods allowed to determine that recuperation of the Cu(I) state from the oxidized Cu(II) complex is mediated by water, in absence of common reductants. In addition, MTT assays were performed on tumour cells lines MG-63, MDA-231 and MCF-7. Interestingly, the complex [CuI(dmp)2]+ showed a higher anti-tumour activity compared to [CuI(phen)2]+, in agreement with the higher concentration of intracellular-ROS detected when the cells where incubated with [CuI(dmp)2]+.