An 111In-labelled bis-ruthenium(ii) dipyridophenazine theranostic complex: mismatch DNA binding and selective radiotoxicity towards MMR-deficient cancer cells

Selenium-containing metallodrug overcomes cervical cancer radioresistance through physical-chemical dual sensitization

Radiotherapy is an important treatment for cervical cancer, but the efficacy of radiotherapy is often reduced in clinical practice owing to high frequency and high dose radiation leading to radiotherapy resistance. The development of efficient and low-toxicity radiotherapy sensitizers to reduce radiation dose is an effective strategy. Therefore, based on the existing radiotherapy sensitizers responding to radiophysical sensitization radiotherapy, we propose to design radiotherapy sensitizers with enzyme-mimicking and dual physical-chemical sensitization properties. In this work, we constructed Ru-Se complexes with cytochrome P450 enzyme-mimicking properties. On the one hand, the high concentration of ROS in tumor cells, along with the complexes, catalyzed the oxidation of intracellular active substances, breaking the redox balance of the cells and chemically sensitizing radiotherapy; on the other hand, the high atomic numbers of ruthenium and selenium responded to X-rays and physically sensitized radiotherapy. Experimental results demonstrated that the Ru-Se complexes can efficiently mimic cytochrome P450 enzyme activity and simultaneously respond to radiation dual sensitization radiotherapy, causing the expression of intracellular DNA damage response proteins. Thus, inhibition of repair protein expression overcomes radiotherapy resistance. This work provides a new idea for the development of efficient radiation sensitizers in the future.

Recognition of mismatched sites in double-stranded DNA by a pair of partially noncomplementary peptide nucleic acids

We have successfully achieved efficient recognition of mismatched sites in double-stranded DNA through the formation of an invasion complex by using partially noncomplementary peptide nucleic acids (PNAs). Owing to mismatches between 2 PNAs used for invasion, the undesired PNA/PNA duplex, which inhibits invasion complex formation, was destabilized. This approach overcame an inherent challenge in PNA invasion, in particular, undesired PNA/PNA duplex formation resulting from PNA complementarity, thereby enhancing overall invasion efficiency.

Cyrene™ as a green alternative to N,N'-dimethylformamide (DMF) in the synthesis of MLCT-emissive ruthenium(II) polypyridyl complexes for biological applications

Ruthenium(II) polypyridyl complexes (RPCs) that emit from triplet metal-to-ligand charge transfer (MLCT) states find a wide variety of uses ranging from luminophores to potential anti-cancer or anti-bacterial therapeutics. Herein we describe a greener, microwave-assisted synthetic pathway for the preparation of homoleptic [Ru(N^N)3]2+ and bis-heteroleptic [Ru(N^N)2(N'^N')]2+ type complexes. This employs the bio-renewable solvent Cyrene™, dihydrolevoglucosenone, as a green alternative to N,N'-dimethylformamide (DMF) in the synthesis of Ru(N^N)2Cl2 intermediate complexes, obtaining comparable yields for N^N = 2,2'-bipyridine, 1,10-phenanthroline and methylated derivatives. Employing these intermediates, a range of RPCs were prepared and we verify that the ubiquitous luminophore [Ru(bpy)3]2+ (bpy = 2,2'-bipyridine) can be prepared by this two-step green pathway where it is virtually indistinguishable from a commercial reference. Furthermore, the novel complexes [Ru(bpy)2(10,11-dmdppz)]2+ (10,11-dmdppz = 10,11-dimethyl-dipyridophenazine) and [Ru(5,5'-dmbpy)2(10,11-dmdppz)]2+ (5,5'-dmbpy = 5,5'-dimethyl-bpy) intercalate duplex DNA with high affinity (DNA binding constants, Kb = 5.7 × 107 and 1.0 × 107 M-1, respectively) and function as plasma membrane and nuclear DNA dyes for confocal and STED microscopies courtesy of their long-lived MLCT luminescence.

Strategies for the Nuclear Delivery of Metal Complexes to Cancer Cells

The nucleus is an essential organelle for the function of cells. It holds most of the genetic material and plays a crucial role in the regulation of cell growth and proliferation. Since many antitumoral therapies target nucleic acids to induce cell death, tumor-specific nuclear drug delivery could potentiate therapeutic effects and prevent potential off-target side effects on healthy tissue. Due to their great structural variety, good biocompatibility, and unique physico-chemical properties, organometallic complexes and other metal-based compounds have sparked great interest as promising anticancer agents. In this review, strategies for specific nuclear delivery of metal complexes are summarized and discussed to highlight crucial parameters to consider for the design of new metal complexes as anticancer drug candidates. Moreover, the existing opportunities and challenges of tumor-specific, nucleus-targeting metal complexes are emphasized to outline some new perspectives and help in the design of new cancer treatments.

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

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.

Indium(III)/2-benzoylpyridine chemistry: interesting indium(III) bromide-assisted transformations of the ligand

Reactions of 2-benzoylpyridine, (py)(ph)CO, with InX₃ (X = Cl, Br) in EtOH at room temperature have been studied. The InCl₃/(py)(ph)CO system has provided access to complex [InCl₃{(py)(ph)CO}(EtOH)]·{(py)(ph)CO} (1) and the byproduct {(pyH)(ph)CO}Cl (2). The reaction of InBr₃ with (py)(ph)CO has led to a mixture of (L)[InBr₄{(py)(ph)CO}] (3) and [In₂Br₄{(py)(ph)CH(O)}₂(EtOH)₂] (4), where L⁺ is the 9-oxo-indolo[1,2-a]pyridinium cation and (py)(ph)CH(O)^- is the anion of (pyridin-2-yl)methanol. Based on solubility and crystallisation time differences between the two components of the mixture, complex 4 was isolated in pure form, i.e. free from 3. The formations of the counterion L⁺ and the coordinated (py)(ph)CH(O)^- anion represent clearly InBr₃-promoted/assisted transformations. Reaction mechanisms have been proposed for the formation of 2, 3 and 4. Complex 4 could also be isolated by the reaction of InBr₃ and pre-formed (py)(ph)CH(OH) in EtOH. The solid-state structures of 1, 3 and 4 were determined by single-crystal X-ray crystallography, while the identity of the salt 2 was confirmed by microanalyses and a variety of spectroscopic techniques, including ESI-MS spectra. In the indium(III) complexes, the metal ions are 6-coordinate with a distorted octahedral geometry. The halogeno groups (Cl^-, Br^-) in the three complexes are terminal. The (py)(ph)CO molecule behaves as a N,O-bidentate (1.11) ligand in 1 and 3. A terminal EtOH ligand completes the coordination sphere of In^III in 1. The alkoxo oxygen atoms of the two 2.21 (py)(ph)CH(O)^- ligands doubly bridge the In^III centers in 4 creating a {InIII2(μ-OR)₂}⁴⁺ core; a nitrogen atom of one reduced organic ligand, two bromo ions and one terminal EtOH molecule complete the 6-coordination at each metal centre. Complexes 1, 3 and 4 were characterised by IR and Raman spectroscopies, and the data were discussed in terms of their known solid-state structures. Molar conductivity data and ¹H NMR spectra were used in an attempt to probe the behaviour of the complexes in DMSO. The to-date observed metal ion-assisted/promoted transformations of (py)(ph)CO are also discussed.

DNA-Templated Modulation in the Photophysical Properties of a Fluorescent Molecular Rotor Auramine O by Varying the DNA Composition

This work delineates an integrative approach combining spectroscopic and computational studies to decipher the association-induced fluorescence properties of a fluorescent molecular rotor, viz., auramine O (AuO), after interacting with 20-mer duplex DNA having diverse well-matched base pairs. While exploring the scarcely explored sequence-dependent interaction mechanism of AuO and DNA, we observed that DNA could act as a conducive scaffold to the formation of AuO dimer through noncovalent interactions at lower molecular density. The photophysical properties of AuO depend on the nucleotide compositions as described from sequence-dependent shifting in the emission and absorption maxima. Furthermore, we explored such DNA base pair-dependent fluorescence spectral characteristics of AuO toward discriminating the thermodynamically most stable single nucleotide mismatch in a 20-mer sequence. Our results are interesting and could be useful in developing analogues with further enhanced emission properties toward mismatched DNA sequences.

Metal-Based G-Quadruplex Binders for Cancer Theranostics

The ability of fluorescent small molecules, such as metal complexes, to selectively recognize G-quadruplex (G4) structures has opened a route to develop new probes for the visualization of these DNA structures in cells. The main goal of this review is to update the most recent research efforts towards the development of novel cancer theranostic agents using this type of metal-based probes that specifically recognize G4 structures. This encompassed a comprehensive overview of the most significant progress in the field, namely based on complexes with Cu, Pt, and Ru that are among the most studied metals to obtain this class of molecules. It is also discussed the potential interest of obtaining G4-binders with medical radiometals (e.g., 99mTc, 111In, 64Cu, 195mPt) suitable for diagnostic and/or therapeutic applications within nuclear medicine modalities, in order to enable their theranostic potential.

Structural insights into the recognition of DNA defects by small molecules

Studies on the binding interaction of small molecules and nucleic acids have been explored for their biological applications. With excellent photophysical/chemical properties, numerous metal complexes have been studied as structural probes for nucleic acids. The recognition of DNA defects is of high importance due to their association with various types of cancers. Small molecules that target DNA defects in a specific and selective manner offer a new avenue for developing novel drugs and diagnostic tools. Transition metal complexes have been studied as probes for abasic sites and DNA/RNA mismatches. By changing the ligand structure or metal center, the probing efficiency of the metal complexes varies towards the defects. In this perspective, we have discussed mainly the structural requirement of metal complexes as probes for abasic sites, mismatches, and covalent DNA adducts, followed by the challenges and future directions.