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

The DNA target/ligand conjugates (HL X , X = P n and M n , 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.