Metal complexes to promote oxidative DNA cleavage by H 2 O 2 are desirable as anticancer drugs. A dicopper(II) complex of known p-cresol-derived methylene-tether ligand Hbcc [Cu 2 (bcc)] 3+ did not promote DNA cleavage by H 2 O 2 . Here, we synthesized a new p-cresol-derived amide-tether one, 2,6-bis(1,4,7,10tetrazacyclododecyl-1-carboxyamide)-p-cresol (Hbcamide). A dicopper(II) complex of the new ligand [Cu 2 (μ-OH)(bcamide)] 2+ was structurally characterized. This complex promoted the oxidative cleavage of supercoiled plasmid pUC19 DNA (Form I) with H 2 O 2 at pH 6.0−8.2 to give Forms II and III. The reaction was largely accelerated in a high pH region. A μ-1,1hydroperoxo species was formed as the active species and spectroscopically identified. The amide-tether complex is more effective in cytotoxicity against HeLa cells than the methylene-tether one.

Dicopper complexes [Cu2(μ-OH)(Ln)](ClO4)2 [n = 1 (1) and 2 (2)] with a novel phenanthrene amide-tether ligand conjugate (HL1) and the original p-cresol-2,6-bis(amidecyclen) (HL2) were synthesized. A phenanthrene unit of 1...

Dicopper complexes of a new p-cresol-2,6-bis(dpa) amide-tether ligand (HL1), [Cu 2 (μ-OH 2 )(μ-1,3-OAc)(L1)](ClO 4 ) 2 (1) and [Cu 2 (μ-1,1-OAc)(μ-1,3-OAc)(L1)]X (X = ClO 4 (2a), OAc (2b)) were synthesized and structurally characterized. 2b rapidly cleaves supercoiled plasmid DNA by activating H 2 O 2 at neutral pH to a linear DNA and shows remarkable cytotoxicity in comparison with related complexes. As 2b is more cytotoxic than HL1, the dicopper core is kept in the cell. A boron dipyrromethene (Bodipy)-modified complex of the p-cresol-2,6-bis(dpa) amide-tether ligand having a Bodipy pendant (HL2), [Cu 2 (μ-OAc) 2 (L2)](OAc) (3), was synthesized to visualize intracellular behavior, suggesting that 2b attacks the nucleolus and mitochondria. A comet assay clearly shows that 2b does not cleave nuclear DNA. The apoptotic cell death is evidenced from flow cytometry.

We found bursts of DNA double-strand breaks by a dicopper(II) complex with a p-cresol-2,6-bis(amide-tether-dpa) ligand (HL) [Cu2(μ-1,1-OAc)(μ-1,3-OAc)(L)]2+ (1) via reductive O2-activa-tion with sodium ascorbate (AscNa) under air, where 26% of supercoiled plasmid DNA was converted to linear form in 1 min. The reasons for bursts of DNA double-strand breaks by 1 were clarified in comparison with a Robson type dicopper complex [Cu2(μ-OH)(bpmp)]2+ (2) and an iron complex of N4Py ligand [Fe(MeCN)(N4Py)]2+ (3). Spectroscopic, electrochemical, and kinetic studies revealed that upon reaction with AscNa, 1 is rapidly reduced to Cu(I)Cu(II) and Cu(I)Cu(I) species, which are involved in rate-limiting three electron reduction of O2 to HO• responsible for the DNA cleavage. The HO• formation was monitored by emission spectral change of terephthalic acid (TA). DNA binding abilities of 1 and 3 were examined by isothermal titration calorimetry (ITC) and electronic absorption spectral and IR spectral changes. These revealed that the rapid HO• formation and the large binding number and rigid binding to DNA are key features of 1 to enable the burst of DNA double-strand breaks.

The DNA target/ligand conjugates (HLX, X = Pn and Mn, n = 1–3) were synthesized where various lengths of −CONH(CH2CH2O) n CH2CH2NHCO– 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 H2O2, μ-1,1-O2H 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 H2O2 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 H2O2 increased by mitochondrial dysfunction in cancer cells.