Ruthenium(II) Polypyridyl Complexes as FRET Donors: Structure- and Sequence-Selective DNA-Binding and Anticancer Properties

Abstract

Ruthenium(II) polypyridyl complexes (RPCs) that emit from metal-to-ligand charge transfer (MLCT) states have been developed as DNA probes and are being examined as potential anticancer agents. Here, we report that MLCT-emissive RPCs that bind DNA undergo Förster resonance energy transfer (FRET) with Cy5.5-labeled DNA, forming mega-Stokes shift FRET pairs. Based on this discovery, we developed a simple and rapid FRET binding assay to examine DNA-binding interactions of RPCs with diverse photophysical properties, including non-“light switch” complexes [Ru(dppz)2(5,5′dmb)]2+ and [Ru(PIP)2(5,5′dmb)]2+ (dppz = dipyridophenazine, 5,5′dmb = 5,5′-dimethyl-2,2′-bipyridine, PIP = 2-phenyl-imidazo[4,5-f][1,10]phenanthroline). Binding affinities toward duplex, G-quadruplex, three-way junction, and mismatch DNA were determined, and derived FRET donor–acceptor proximities provide information on potential binding sites. Molecules characterized by this method demonstrate encouraging anticancer properties, including synergy with the PARP inhibitor Olaparib, and mechanistic studies indicate that [Ru(PIP)2(5,5′dmb)]2+ acts to block DNA replication fork progression.

Discovery of Ruthenium(II) Metallocompound and Olaparib Synergy for Cancer Combination Therapy

“…In a similar manner, by comparing IC 50 concentrations within the [Ru­(N^N) 2 (dmdppz)] 2+ sub-series, the order of cytotoxicity for each N^N ancillary ligand can be seen to be 4,4′dmb > 5,5′dmb ∼ bpy (5,5′dmb = 5,5′-dimethyl-2,2′bipyridine, 4,4′dmb = 4,4′-dimethyl-2,2′bipyridine). While cellular internalization was not examined in the present work, both of these findings would be in agreement with improved cellular uptake facilitated by increased ligand hydrophobicity, an established concept that has been reported in numerous other studies. ,,,− Along with the results of cell-free DNA binding studies, these findings also illustrate that methylated polypyridyl ligands can be employed to increase both DNA binding affinity and cytotoxicity of RPCs. It is also interesting to note that the most cytotoxic among these molecules 3 , 4 , and 7 showed an additive relationship with Olaparib rather than synergistic.…”

“…Numerous metallocompounds have been examined for their anticancer properties, where modulated chemical stability and metal- and/or ligand-based reactivities are cited as advantageous properties . The most successful have been the platinum drugs, including octahedral Pt­(IV) pro-drugs, while, more recently, substitutionally inert ruthenium­(II) polypyridyl complexes (RPCs) have become the subject of increasing interest as potential successors to these platinum systems. − The potential of RPCs within this area can be illustrated by work describing RPCs that intercalate between base pairs of DNA, “metallo-intercalators”, that are able to interfere with DNA replication or transcription with distinct mechanisms of action compared to existing DNA targeting agents such as cisplatin. − Specific examples include the organometallic complex [Ru­(bpy)­(phpy)­(dppz)] + (bpy = 2,2′bipyridine; phpy = 2-phenylpyridine; dppz = dipyrido­[3,2- a :2′,3′- c ]­phenazine), which disrupts the transcription factor NF-κB binding to DNA, resulting in low-micromolar half inhibitory IC 50 concentrations in numerous cancer cell lines and [Ru­(phen) 2 (tpphz)] 2+ (phen = 1,10-phenanthroline; tpphz = tetrapyridophenazine), which induces replication fork collapse and inhibits esophageal cancer cell proliferation through a combination of S-phase cell-cycle arrest and mitotic arrest . Notably, both complexes exhibit cytotoxicity comparable toor greater thancisplatin but with improved cancer selectivity.…”

Destabilizing Effect of Organo Ru(II) Salts on the Intermolecular Parallel CGG Repeat DNA Quadruplex Associated with Neurodegenerative/Neuromuscular Diseases

“…Thus, the Ru­(II) core is intact in solution. As a result, the Ru­(II) complex may either bind to the groove of the quadruplex or may stack in the middle of the quartets, as reported earlier. − Further, the ruthenium arene complexes do not destabilize the quadruplex through an exchange reaction between the ligand and the quadruplex base, as proposed earlier …”

Anticancer Potential of Dendritic Poly(aryl ether)-Substituted Polypyridyl Ligand-Based Ruthenium(II) Coordination Entities

“…In recent years, researchers have become interested in determining the binding sites of metallodrugs to biomolecules. There are several studies done on the DNA binding potential of Ru­(II) coordination entities; the extent of binding depends upon the constitution of ligands. − DNA binding can happen in two ways: the coordination entities can either bind by intercalation or groove binding. Hence, the molecular docking analysis was carried out to predict the binding energy and binding pockets.…”