Roles of DNA Target in Cancer Cell-Selective Cytotoxicity by Dicopper Complexes with DNA Target/Ligand Conjugates

[Image: see text] The DNA target/ligand conjugates (HL(X), X = Pn and Mn, n = 1–3) were synthesized where various lengths of −CONH(CH(2)CH(2)O)(n)CH(2)CH(2)NHCO– linkers with a 9-phenanthrenyl (P) or methyl (M) terminal as DNA targets replace the methyl group of 2,6-di(amide-tether cyclen)-p-cresol ligand (HL). DNA binding, DNA cleavage, cellular uptake, and cytotoxicity of [Cu(2)(μ-OH)(L(X))](ClO(4))(2) (1(X)) are examined and compared with those of [Cu(2)(μ-OH)(L)](ClO(4))(2) (1) to clarify roles of DNA targets. Upon reaction of 1(X) with H(2)O(2), μ-1,1-O(2)H complexes are formed for DNA cleavage. 1(P1), 1(P2), and 1(P3) are 22-, 11-, 3-fold more active for conversion of Form II to III in the cleavage of supercoiled plasmid DNA with H(2)O(2) than 1, where the short P-linker may fix a dicopper moiety within a small number of base pairs to facilitate DNA double-strand breaks (dsb). This enhances the proapoptotic activity of 1(P1), 1(P2), and 1(P3), which are 30-, 12-, and 9.9-fold cytotoxic against HeLa cells than 1. DNA dsb and cytotoxicity are 44% correlated in 1(P1–3) but 5% in 1(M1–3), suggesting specific DNA binding of P-linkers and nonspecific binding of M-linkers in biological cells. 1(P1–3) exert cancer cell-selective cytotoxicity against lung and pancreas cancer and normal cells where the short P-linker enhances the selectivity, but 1(M1–3) do not. Intracellular visualization, apoptosis assay, and caspase activity assay clarify mitochondrial apoptosis caused by 1(P1–3). The highest cancer cell selectivity of 1(P1) may be enabled by the short P-linker promoting dsb of mitochondrial DNA with H(2)O(2) increased by mitochondrial dysfunction in cancer cells.