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

The DNA target/ligand conjugates (HLX , X = P n and M n , n = 1-3) were synthesized where various lengths of -CONH(CH2 CH2 O) n CH2 CH2 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 [Cu2 (μ-OH)(LX )](ClO4 )2 ( 1X ) are examined and compared with those of [Cu2 (μ-OH)(L)](ClO4 )2 ( 1 ) to clarify roles of DNA targets. Upon reaction of 1X with H2 O2 , μ-1,1-O2 H complexes are formed for DNA cleavage. 1P1 , 1P2 , and 1P3 are 22-, 11-, 3-fold more active for conversion of Form II to III in the cleavage of supercoiled plasmid DNA with H2 O2 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 1P1 , 1P2 , and 1P3 , which are 30-, 12-, and 9.9-fold cytotoxic against HeLa cells than 1 . DNA dsb and cytotoxicity are 44% correlated in 1P1-3 but 5% in 1M1-3 , suggesting specific DNA binding of P-linkers and nonspecific binding of M-linkers in biological cells. 1P1-3 exert cancer cell-selective cytotoxicity against lung and pancreas cancer and normal cells where the short P-linker enhances the selectivity, but 1M1-3 do not. Intracellular visualization, apoptosis assay, and caspase activity assay clarify mitochondrial apoptosis caused by 1P1-3 . The highest cancer cell selectivity of 1P1 may be enabled by the short P-linker promoting dsb of mitochondrial DNA with H2 O2 increased by mitochondrial dysfunction in cancer cells.