Genotoxic potential of N-(benzothiazolyl)sulfonamide copper(II) complexes on yeast cells transformed with YEGFP expression constructs containing the RAD54 or RNR2 promoter

Four ternary complexes [Cu(L)(2)(phen)] where L is an N(benzothiazol-2-yl)sulfonamide derivative have been prepared and their ability to cleave DNA has been studied. The complexes were structurally characterized with the aid of single-crystal X-ray crystallography. Whereas the molecular structure of the [Cu(L1)(2)(phen)] (1) [HL1 = N-(6-chlorobenzothiazol-2-yl)benzenesulfonamide] and [Cu(L3)(2)(phen)] (3) [HL3 = N-(benzothiazol-2-yl)benzenesulfonamide] complexes can best be described as having a distorted square-planar geometry, that of the [Cu(L4)(2)(phen)] (4) [HL4 = N(benzothiazol-2-yl)toluenesulfonamide] complex shows a strictly square-planar geometry. The [Cu(L2)(2),(phen)MeOH] (2) [HL2 = N-(6-chlorobenzothiazol-2-yl)toluenesulfonamide] complex displays an axially elongated square-pyramidal coordination geometry in which the phen ligand binds at the basal plane. Viscosity and fluorescence measurements indicated that [Cu(L4)2(phen)] (4) has a propensity for binding calf thymus DNA. The four complexes were found to be efficient chemical nucleases, with ascorbate/H2O2 activation giving rise to hydroxyl and superoxide radicals as active cleaving species. The nuclease activity of 4 is not only the highest of the four complexes, but also much higher than that of the copper-phenanthroline complex. The ability of the complexes to cleave DNA within cells has been tested by monitoring the expression of the yEGFP gene containing reporter plasmid. The significant induction of fluorescence by complex 4 indicates that it is able to cleave DNA inside the cell.