Di-copper metallodrugs promote NCI-60 chemotherapy via singlet oxygen and superoxide production with tandem TA/TA and AT/AT oligonucleotide discrimination

Abstract

In order to expand the current repertoire of cancer treatments and to help circumvent limitations associated with resistance, the identification of new metallodrugs with high potency and novel mechanisms of action is of significant importance. Here we present a class of di-copper(II) complex based on the synthetic chemical nuclease [Cu(Phen)2]+ (where Phen = 1,10-phenanthroline) that is selective against solid epithelial cancer cells from the National Cancer Institute’s 60 human cell line panel (NCI-60). Two metallodrug leads are studied and in each case two [Cu(Phen)2]+ units are bridged by a dicarboxylate linker but the length and rigidity of the linkers differ distinctly. Both agents catalyze intracellular superoxide (O2•−) and singlet oxygen (1O2) formation with radical species mediating oxidative damage within nuclear DNA in the form of double strand breaks and to the mitochondria in terms of membrane depolarization. The complexes are effective DNA binders and can discriminate AT/AT from TA/TA steps of duplex DNA through induction of distinctive Z-like DNA or by intercalative interactions.

Polypyridyl‐Based Copper Phenanthrene Complexes: A New Type of Stabilized Artificial Chemical Nuclease

“…DNA cleavage in the presence of ROS scavengers : The assay was conducted according to the method recently reported by Slator et al . Briefly, to a final volume of 20 μL, 80 m m HEPES, 25 m m NaCl, 1 m m sodium l ‐ascorbate, and 400 ng of pUC19 DNA were treated with varying drug concentrations (Cu‐TPMA: 5, 10, 15, 20, 25 μ m ; Cu‐TPMA‐Phen, Cu‐TPMA‐DPQ, Cu‐TPMA‐DPPZ: 1, 2, 3, 4, 5 μ m ) in the presence of ROS scavengers [4,5‐dihydroxy‐1,3‐benzenedisulfonic acid (Tiron) (10 m m ), d ‐mannitol (10 m m ), N ′‐dimethylthiourea (10 m m ), l ‐methionine (10 m m ), KI (10 m m ), DMSO (10 %) and EDTA (100 μ m )].…”

“…[23] To characterizet he intercalative activity of Phen, DPQ and DPPZ complexes, topoisomerase-I (Topo I)-mediated relaxation of negativelys upercoiled DNA (pUC19) was examined. [27,58,59] This enzyme is fundamental in biological systemsb ecause DNA supercoiling is generated during cellular processes includ-Chem. Eur.J.…”

“…Significantly, the presence of phenazine ligands did not alter the electrochemical profile or ROS catalysis when compared with Cu‐Phen. We, as well as others, have identified the value of polynuclearity in providing enhanced cleavage capability and recently demonstrated that TA/TA and AT/AT oligonucleotide steps can be discriminated by a di‐Cu II ‐Phen complex containing an octanedioate bridge . Despite these developments, a limiting factor of Cu‐Phen systems is their poor stability in solution, in which speciation, ligand dissociation, and transmetalation occur.…”

“…We, as well as others, have identified the value of polynuclearity in providing enhanced cleavage capability [25,26] and recently demonstrated that TA/TAa nd AT/AToligonucleotide steps can be discriminated by ad i-Cu II -Phen complex containing an octanedioate bridge. [27] Despite these developments, al imiting factor of Cu-Phen systemsist heir poor stability in solution,inw hich speciation, ligand dissociation, and transmetalationoccur.T oh elp circumventt his limitation, AMNs were developed with both phenanthroline ligandsl inked by aliphatic chains (or "clips", for example,s erinol) to yield new complexes with improved DNA cleavage sensitivity. [28][29][30] Stabilizationo ft he copper complex may also be achieved by coordination to polypyridyl ligands and multidentate complexes e.g.,t ris(2-pyridylmethyl)amine, [31] 2,2',2''-tris(dipicolylamino)trimethylamine, [32] and structurally related ligands containing phenoxide or alkoxide bridges [33,34] , which have received considerable attention as inorganic modelso fe nzymec ofactors.…”

Oxidative DNA Cleavage with Clip‐Phenanthroline Triplex‐Forming Oligonucleotide Hybrids

“…If triplexes were incubated with low concentrations of ascorbate, almost no cleavage was detected because Cu I would quickly re‐oxidise to Cu II under aerobic conditions. In contrast, if high concentrations of ascorbate were used, a significant level of off‐target oxidative damage was observed due to the high concentration of diffusible free radicals generated (Table S3 and Figure S15) . Similarly, substoichiometric or equimolar AMN–TFO, with respect to the duplex, led to very little oxidative cleavage, which increased proportionally with the amount of AMN–TFO employed.…”