Mixed-ligand copper(II) complexes based on 1,10-phenanthroline and related compounds are of interest to scientists due to their promising anticancer properties. In this study, four new water-soluble copper(II) complexes [Cu(dmbipy)L2], [Cu(phen)(H2O)L2], [Cu(dmphen)L2] and [Cu2(bipy)2L4], where HL – 4,5-dichloro-isothiazole-3-carboxylic acid, bipy – 2,2′-bipyridine, dmbipy – 2,2′-bi-4-picoline, phen – 1,10-phenanthroline, dmphen – 4,7-dimethyl-1,10-phenanthroline are reported. All complexes have been characterized by elemental and powder X-ray diffraction analysis, EPR and IR-spectroscopy. Molecular structures of the reported complexes have been determined by single crystal X–ray diffraction. Copper(II) ion, HL and heterocyclic N-donor ligands have been found to form 1:2:1 complexes that possess square bipyramid or square pyramidal geometry. The UV–vis spectroscopy and mass spectrometry have been applied to show the behavior of the compounds in solution. All complexes have been screened in vitro for their cytotoxic activity against Hep-2 and MCF-7 cell lines. They exhibit significant dose-dependent cytotoxic effect and [Cu(dmphen)L2] is found to be the most cytotoxic (IC50 = 0.97 ± 0.03 µM when compared to IC50 = 9.2 ± 0.5 µM for control, cisplatin – Hep-2 cell line). The investigation of DNA binding ability by UV–vis titration technique indicates that complexes obtained exhibit moderate binding affinity toward calf thymus DNA. Effect of [Cu(dmbipy)L2] and [Cu(dmphen)L2] on activity of drug-metabolizing enzymes cytochromes P450 has also been investigated. The addition of complexes to the hepatic microsomes of 3-MC or PB-treated rat, lead to a dose-dependent decrease of CYP's activities. The data obtained indicate that [Cu(dmphen)L2] and [Cu(phen)(H2O)L2] can be potential anticancer agents.