Selective, Disruptive Luminescent Ru(II) Polypyridyl Probes of G-Quadruplex

Abstract

Sensors capable of transducing G-quadruplex DNA binding are important both in solution and for imaging and interrogation in cellulo. Ru(II)-based light switches incorporating dipyridylphenazine (dppz) ligands are effective probes for recognition and imaging of DNA and its polymorphs including G-quadruplex, although selectivity is a limitation. While the majority of Ru(II)-based light switches reported to date, stabilize the quadruplex, imaging/theranostic probes that can disrupt G4s are of potentially enormous value in study and therapy for a range of disease states. We report here, on a Ru(II) complex (Ru-PDC3) that assembles the light switch capability of a Ru(II) dipyridylphenazine complex with the well-known G4-selective ligand Phen-DC3, into a single structure. The complex shows the anticipated light switch effect and strong affinity for G4 structures. Affinity depended on the G4 topology and sequence, but across all structures bar one, it was roughly an order of magnitude greater than for duplex or single-stranded DNA. Moreover, photophysical and Raman spectral data showed clear discrimination between duplex DNA and G4-bound structures offering the prospect of discrimination in imaging as well as in solution. Crucially, unlike the constituent components of the probe, Ru-PDC3 is a powerful G4 disrupter. From circular dichroism (CD), a reduction of ellipticity of the G4 between 70 and 95% was observed depending on topology and in many cases was accompanied by an induced CD signal for the metal complex. The extent of change in ellipticity is amongst the largest reported for small-molecule ligand G4 binding. While a promising G4 probe, without modification, the complex is fully water-soluble and readily permeable to live cells.

Phototoxicity of Tridentate Ru(II) Polypyridyl Complex with Expanded Bite Angles toward Mammalian Cells and Multicellular Tumor Spheroids

“…Most reported metal complex peptide conjugates, certainly all reported to date by our group, undergo cell uptake by endocytosis or active transport, where the uptake was observed to switch off at 4 °C, indicating an energy-dependent pathway. 23 , 29 , 63 , 64 By contrast here, all three compounds remained strongly cell permeable at 4 °C and imaging following 1 h incubation confirmed, uniquely in our experience, that the mechanism of uptake is energy independent. This accounts for the rapid uptake by live cells.…”

“…Consequently, they tend to be less efficient singlet oxygen sensitizers than metal porphyrins, for example, whose PS efficiency is well established . But, Ru­(II) complexes owing to their synthetic versatility, can be tailored to offer the aforementioned advantages of lower dark cytotoxicity and cell targeting. , Means to promote singlet oxygen sensitization in such complexes include increasing the triplet character of the excited state, e.g., through mixing 3 LC states with the 3 MLCT state, by reducing singlet–triplet mixing of the 3 MLCT state or by enhancing the 3 MLCT lifetime. The latter is accomplished by manipulation of the relative energy of the triplet metal-centered state whose thermal population, likely to be promoted in the warm cellular environment, increases non-radiative decay.…”

Iridium(iii)-based minor groove binding complexes as DNA photocleavage agents

“…27,59,[100][101][102][103] Given that such studies have included transition metal complexes as binding substrates, 25,104 and previous work within the Thomas group has identified Ru II complexes that bind to quadruplex-folded human telomere sequence (HTS) with high affinities, 21,22,105,106 analogous experiments were carried out with 1 and 2. These were of particular interest as a very recent report from the Keyes group 107 has shown that a Ru II -complex containing a ligand derived from phen-DC3 108 a high-affinity quadruplex-binding substrate 109 that has some structural similarities to qtpyactually disrupts quadruplex structures. The addition of HTS to solutions of 1 and 2 also resulted in quenching, Fig.…”

G-Quadruplexes in Human Telomere: Structures, Properties, and Applications

“…Many fluorescent probes to detect DNA G-quadruplexes have been reported, and employed to image living cells [ 51 , 52 , 53 , 54 , 55 , 56 , 57 ]. In 2015, naturally occurring alkaloid epiberberine was found to emit fluorescence upon the binding with DNA G-quadruplex [ 58 ].…”