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.