A synthetic dinuclear copper(II) hydrolase and its potential as antitumoral: Cytotoxicity, cellular uptake, and DNA cleavage

We have studied the protonation equilibria of a dicopper(II) complex [Cu-2(mu-OH)(C21H33ON6)] (ClO4)(2)center dot H2O, (1), in aqueous solution, its interactions with DNA, its cytotoxic activity, and its uptake in tumoral cells. C21H33ON6 corresponds to the ligand 4-methyl-2,6-bis[(6-methyl-1,4-diazepan-6-yl)iminomethyl]phenol. From spectrophotometric data the following pKa values were calculated 3.27, 4.80 and 6.10. Complex 1 effectively promotes the hydrolytic cleavage of double-strand plasmid DNA under anaerobic and aerobic conditions. The following kinetic parameters were calculated k(cat) of 2.73 x 10(-4) s(-1), K-M of 1.36 x 10(-4) M and catalytic efficiency of 2.01 s(-1) M-1, a 2.73 x 10(7) fold increase in the rate of the reaction compared to the uncatailyzed hydrolysis rate of DNA. Competition assays with distamycin reveal minor groove binding. Complex 1 inhibited the growth of two tumoral cell lines, GLC4 and K562, with the IC50 values of 14.83 mu M and 34.21 mu M, respectively. There is a good correlation between cell growth inhibition and intracellular copper content. When treated with 1, cells accumulate approximately twice as much copper as with CuCl2. Copper-DNA adducts are formed inside cells when they are exposed to the complex. In addition, at concentrations that compound 1 inhibits tumoral cell growth it does not affect macrophage viability. These results show that complex 1 has a good therapeutic prospect. (C) 2009 Elsevier Inc. All rights reserved.