A copper(ii) peptide helicate selectively cleaves DNA replication foci in mammalian cells.

The use of copper-based artificial nucleases as potential anticancer agents has been hampered by their poor selectivity in the oxidative DNA cleavage process. An alternative strategy to solve this problem is to design systems capable of selectively damaging noncanonical DNA structures that play crucial roles in the cell cycle. We designed an oligocationic CuII peptide helicate that selectively binds and cleaves DNA three-way junctions (3WJs) and induces oxidative DNA damage via a ROS-mediated pathway both in vitro and in cellulo, specifically at DNA replication foci of the cell nucleus, where this DNA structure is transiently generated. To our knowledge, this is the first example of a targeted chemical nuclease that can discriminate with high selectivity 3WJs from other forms of DNA both in vitro and in mammalian cells. Since the DNA replication process is deregulated in cancer cells, this approach may pave the way for the development of a new class of anticancer agents based on copper-based artificial nucleases.

Analysis of non-canonical three- and four-way DNA junctions.

The development of compounds that can selectively bind with non-canonical DNA structures has expanded in recent years. Junction DNA, including three-way junctions (3WJs) and four-way Holliday junctions (HJs), offer an intriguing target for developmental therapeutics as both 3WJs and HJs are involved in DNA replication and repair processes. However, there are a limited number of assays available for the analysis of junction DNA binding. Here, we describe the design and execution of multiplex fluorescent polyacrylamide gel electrophoresis (PAGE) and microscale thermophoresis (MST) assays that enable evaluation of junction-binding compounds. Two well characterised junction-binding compounds-a C6 linked bis-acridine ligand and an iron(II)-bound peptide helicate, which recognise HJs and 3WJs, respectively-were employed as probes for both MST and PAGE experiments. The multiplex PAGE assay expands beyond previously reported fluorescent PAGE as it uses four individual fluorophores that can be combined to visualise single-strands, pseudo-duplexes, and junction DNA present during 3WJ and HJ formation. The use of MST to identify the binding affinity of junction binding agents is, to our knowledge, first reported example of this technique. The combined use of PAGE and MST provides complementary results for the visualisation of 3WJ and HJ formation and the direct binding affinity (Kd and EC50) of these agents. These assays can be used to aid the discovery and design of new therapeutics targeting non-canonical nucleic acid structures.

Canonical DNA minor groove insertion of bisbenzamidine-Ru(ii) complexes with chiral selectivity.

We report the first Ru(ii) coordination compounds that interact with DNA through a canonical minor groove insertion mode and with selectivity for A/T rich sites. This was made possible by integrating a bis-benzamidine minor groove DNA-binding agent with a ruthenium(ii) complex. Importantly, one of the enantiomers (Δ-[Ru(bpy)2 b4bpy]2+, Δ-4Ru) shows a considerably higher DNA affinity than the parent organic ligand and the other enantiomer, particularly for the AATT sequence, while the other enantiomer preferentially targets long AAATTT sites with overall lower affinity. Finally, we demonstrate that the photophysical properties of these new binders can be exploited for DNA cleavage using visible light.

Sulfonamide-imines as selective fluorescent chemosensors for the fluoride anion.

Two new sulfonamide-type fluorescent chemosensors in organic media are reported. The two receptors, [N,N'-bis(2-tosylaminobenzylidene)-1,2-diaminoethane and N,N'-bis(2-tosylaminobenzylidene)-1,3-diamino-2-propanol], display marked changes in the fluorescence emission intensities as a result of deprotonation by basic anions, and show high selectivity for fluoride over other inorganic anions, such as acetate or dihydrogenphosphate. These results suggest that the presence of the imine group as an intramolecular H-bond acceptor enhances the selectivity of these sensors compared to previous examples in the literature. The deprotonation mechanism has been demonstrated by spectrophotometric and spectrofluorimetric titrations as well as by NMR spectroscopy. The X-ray structures of both receptors are also discussed.