Selective nuclei accumulation of ruthenium(II) complex enantiomers that target G-quadruplex DNA

Shining New Light on Biological Systems: Luminescent Transition Metal Complexes for Bioimaging and Biosensing Applications

Luminescence imaging is a powerful and versatile technique for investigating cell physiology and pathology in living systems, making significant contributions to life science research and clinical diagnosis. In recent years, luminescent transition metal complexes have gained significant attention for diagnostic and therapeutic applications due to their unique photophysical and photochemical properties. In this Review, we provide a comprehensive overview of the recent development of luminescent transition metal complexes for bioimaging and biosensing applications, with a focus on transition metal centers with a d6, d8, and d10 electronic configuration. We elucidate the structure-property relationships of luminescent transition metal complexes, exploring how their structural characteristics can be manipulated to control their biological behavior such as cellular uptake, localization, biocompatibility, pharmacokinetics, and biodistribution. Furthermore, we introduce the various design strategies that leverage the interesting photophysical properties of luminescent transition metal complexes for a wide variety of biological applications, including autofluorescence-free imaging, multimodal imaging, organelle imaging, biological sensing, microenvironment monitoring, bioorthogonal labeling, bacterial imaging, and cell viability assessment. Finally, we provide insights into the challenges and perspectives of luminescent transition metal complexes for bioimaging and biosensing applications, as well as their use in disease diagnosis and treatment evaluation.

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.

Interactions of ruthenium(II) polypyridyl complexes with human telomeric DNA

Eight [Ru(bpy)2L]2+ and three [Ru(phen)2L]2+complexes (where bpy = 2,2'-bipyridine and phen = 1,10-phenanthroline are ancillary ligands, and L = a polypyridyl experimental ligand) were investigated for their G-quadruplex binding abilities. Fluorescence resonance energy transfer melting assays were used to screen these complexes for their ability to selectively stabilize human telomeric DNA variant, Tel22. The best G-quadruplex stabilizers were further characterized for their binding properties (binding constant and stoichiometry) using UV-vis, fluorescence spectroscopy, and mass spectrometry. The ligands' ability to alter the structure of Tel22 was determined via circular dichroism and PAGE studies. We identified me2allox as the experimental ligand capable of conferring excellent stabilizing ability and good selectivity to polypyridyl Ru(II) complexes. Replacing bpy by phen did not significantly impact interactions with Tel22, suggesting that binding involves mostly the experimental ligand. However, using a particular ancillary ligand can help fine-tune G-quadruplex-binding properties of Ru(II) complexes. Finally, the fluorescence "light switch" behavior of all Ru(II) complexes in the presence of Tel22 G-quadruplex was explored. All Ru(II) complexes displayed "light switch" properties, especially [Ru(bpy)2(diamino)]2+, [Ru(bpy)2(dppz)]2+, and [Ru(bpy)2(aap)]2+. Current work sheds light on how Ru(II) polypyridyl complexes interact with human telomeric DNA with possible application in cancer therapy or G-quadruplex sensing.

Ruthenium(II) Polypyridyl Complexes and Their Use as Probes and Photoreactive Agents for G-quadruplexes Labelling

Due to their optical and electrochemical properties, ruthenium(II) polypyridyl complexes have been used in a wide array of applications. Since the discovery of the light-switch ON effect of [Ru(bpy)2dppz]2+ when interacting with DNA, the design of new Ru(II) complexes as light-up probes for specific regions of DNA has been intensively explored. Amongst them, G-quadruplexes (G4s) are of particular interest. These structures formed by guanine-rich parts of DNA and RNA may be associated with a wide range of biological events. However, locating them and understanding their implications in biological pathways has proven challenging. Elegant approaches to tackle this challenge relies on the use of photoprobes capable of marking, reversibly or irreversibly, these G4s. Indeed, Ru(II) complexes containing ancillary π-deficient TAP ligands can create a covalently linked adduct with G4s after a photoinduced electron transfer from a guanine residue to the excited complex. Through careful design of the ligands, high selectivity of interaction with G4 structures can be achieved. This allows the creation of specific Ru(II) light-up probes and photoreactive agents for G4 labelling, which is at the core of this review composed of an introduction dedicated to a brief description of G-quadruplex structures and two main sections. The first one will provide a general picture of ligands and metal complexes interacting with G4s. The second one will focus on an exhaustive and comprehensive overview of the interactions and (photo)reactions of Ru(II) complexes with G4s.

Ru(ii), Ir(iii), Re(i) and Rh(iii) based complexes as next generation anticancer metallopharmaceuticals

Several anticancer drugs such as cisplatin, and its analogues, epirubicin, and doxorubicin are well known for their anticancer activity but the therapeutic value of these drugs comes with certain side effects and they cannot distinguish between normal and cancer cells. Thus, a major challenge for researchers around the world is to develop an anticancer drug with the least toxicity and more target specificity. With the successful reporting of NAMI-A and KP1019, a new path has emerged in the anticancer field. Recently, several Ru(ii) complexes have been reported for their anticancer activity due to their enhanced cellular uptake and selectivity towards cancer cells. Apart from the Ru(ii) complexes, a large amount of research has been carried out with Ir(iii), Re(i), and Rh(iii) based complexes, which exhibited promising anticancer activity. The present review reports various Ru(ii), Ir(iii), Re(i), and Rh(iii) based complexes for their anticancer activity based on their cytotoxicity profiles, biological targets and mechanism of action.

Quadruplex Ligands in Cancer Therapy

Nucleic acids can adopt alternative secondary conformations including four-stranded structures known as quadruplexes. To date, quadruplexes have been demonstrated to exist both in human chromatin DNA and RNA. In particular, quadruplexes are found in guanine-rich sequences constituting G-quadruplexes, and in cytosine-rich sequences forming i-Motifs as a counterpart. Quadruplexes are associated with key biological processes ranging from transcription and translation of several oncogenes and tumor suppressors to telomeres maintenance and genome instability. In this context, quadruplexes have prompted investigations on their possible role in cancer biology and the evaluation of small-molecule ligands as potential therapeutic agents. This review aims to provide an updated close-up view of the literature on quadruplex ligands in cancer therapy, by grouping together ligands for DNA and RNA G-quadruplexes and DNA i-Motifs.

Ultrafast excited state dynamics and light-switching of [Ru(phen)2(dppz)]2+ in G-quadruplex DNA

The triplet metal to ligand charge transfer (³MLCT) luminescence of ruthenium (II) polypyridyl complexes offers attractive imaging properties, specifically towards the development of sensitive and structure-specific DNA probes. However, rapidly-deactivating dark state formation may compete with ³MLCT luminescence depending on different DNA structures. In this work, by combining femtosecond and nanosecond pump-probe spectroscopy, the ³MLCT relaxation dynamics of [Ru(phen)₂(dppz)]²⁺ (phen = 1,10-phenanthroline, dppz = dipyridophenazine) in two iconic G-quadruplexes has been scrutinized. The binding modes of stacking of dppz ligand on the terminal G-quartet fully and partially are clearly identified based on the biexponential decay dynamics of the ³MLCT luminescence at 620 nm. Interestingly, the inhibited dark state channel in ds-DNA is open in G-quadruplex, featuring an ultrafast picosecond depopulation process from ³MLCT to a dark state. The dark state formation rates are found to be sensitive to the content of water molecules in local G-quadruplex structures, indicating different patterns of bound water. The unique excited state dynamics of [Ru(phen)₂(dppz)]²⁺ in G-quadruplex is deciphered, providing mechanistic basis for the rational design of photoactive ruthenium metal complexes in biological applications.

Two novel fan-shaped trinuclear Pt(ii) complexes act as G-quadruplex binders and telomerase inhibitors

Two new trinuclear Pt(ii) complexes {[Pt(dien)]3(tib)}(NO3)6 (1) and {[Pt(dpa)]3(tib)}(NO3)6 (2) (dien: diethylenetriamine, dpa: bis-(2-pyridylmethyl)amine, tib: 1,3,5-tris(1H-imidazol-1-yl)benzene) have been designed, synthesized, characterized and applied to a series of biochemical studies. We found that both of the Pt(ii) complexes exhibited much better selectivity for human telomeric G-quadruplex sequence than promoter G-quadruplexes (c-kit, c-myc, and bcl2) or duplex DNA. Both complexes displayed comparative stability and affinity towards human telomeric G-quadruplex by the studies from surface plasmon resonance, fluorescence resonance energy transfer and polymerase chain reaction stop assays. The circular dichroism indicated that both complexes could induce and stabilize anti-parallel G-quadruplex structures. Molecule docking presented that Pt(ii) complex intercalated into the large groove of human telomeric G-quadruplex (PDB ID: 143D). Furthermore, telomeric repeat amplification protocol assays quantitatively evaluated the inhibition of telomerase activity caused by the Pt(ii) complexes. The obtained IC50 values of 6.41 ± 0.042 μM and 2.67 ± 0.035 μM for 1 and 2, respectively, exhibited strong telomerase inhibitions. All results suggest that such fan-shaped trinuclear Pt(ii) complexes are effective and selective G-quadruplex binders, as well as strong telomerase inhibitors. This study provides insight into the development of human telomeric G-quadruplex targeted anticancer drugs based on the metal complex.

Enhancement Effect of Zn-Arsenazo III Complex for G-quadruplex DNA Stability of Proto-oncogene Promoter Telomeres

Background:

Controlling the structure of proto-oncogene telomeres is very important in antitumor therapy. There are relationships between G-quadruplex DNA and the growth of tumor cell.

Methods:

In this study, spectroscopic, cyclic voltammetry and viscosity methods were employed to investigate the interaction between Zn-Arsenazo Ⅲ complex and G-quadruplex DNA by using 4S Green Plus Nucleic Acid Stain as a spectral probe in PBS buffer. The binding ratios were n Arsenazo Ⅲ : n Zn(Ⅱ) = 5:1 for Zn-Arsenazo Ⅲ complex and n Zn- Arsenazo Ⅲ : n G-quadruplex DNA = 8:1 for Zn-Arsenazo Ⅲ-G-quadruplex DNA. The bonding constants (Kθ 298.15K=4.44x105 L·mol-1, Kθ 308.15K= 1.00x105 L·mol-1, Kθ 318.15K= 1.04x106 L·mol-1) were obtained by double reciprocal method at different temperatures, Which was found that the interaction between Zn-Arsenazo Ⅲ complex and Gquadruplex DNA was driven by enthalpy. Furthermore, the research further confirmed that the interaction mode between Zn-Arsenazo Ⅲ complex and G-quadruplex DNA was a mixed binding which involved intercalation and non-intercalation interaction.

Results and Conclusion:

Together these findings also have corroborated the application of stabilizing ligands and intervening with their function for target G-quadruplexes in a cellular context.

Synthesis and biological properties of tetranuclear ruthenium complexes containing the bis[4(4′-methyl-2,2′-bipyridyl)]-1,7-heptane ligand

The non-linear polypyridylruthenium(ii) complex (Rubb7-TNL) exhibited good antimicrobial activity, but surprisingly was also highly active against cancer cells. The results suggestRubb7-TNLmay have potential as a new anticancer agent.

Comparative investigation of binding interactions with three steroidal derivatives of d(GGGT)4 G-quadruplex aptamer

Steroidal derivatives have attracted tremendous attentions in biological and biomedical areas, due to their variety biological activities. The investigation of structural influences helps in understanding their biological activities. The interactions of steroidal derivatives with DNA may play important roles in biological activities, however only a few investigations were reported on this issue. Herein, the structural influences of three steroidal derivatives were investigated based on their binding interactions with d(GGGT)₄ G-quadruplex aptamer by spectroscopic approaches, nuclear magnetic resonance (NMR), electrochemical methods, and molecular modeling techniques. Three compounds were found to selectively bind with parallel G-quadruplex aptamer to form three complexes through end-stacking binding modes. Three compounds stabilized the G-quadruplex structure of the aptamer at different levels, which enhanced the biological activity of this aptamer to some extent. The space steric hindrance was responsible for differences in the binding interactions between d(GGGT)₄ G-quadruplex aptamer and three compounds. These results provide new information for the molecular understanding of binding interactions of steroidal derivatives with DNA and the strategy for research of structural influences.

Photochemically active DNA-intercalating ruthenium and related complexes - insights by combining crystallography and transient spectroscopy

Recent research on the study of the interaction of ruthenium polypyridyl compounds and defined sequence nucleic acids is reviewed. Particular emphasis is paid to complexes [Ru(LL)2(Int)]2+ containing potentially intercalating ligands (Int) such as dipyridophenazine (dppz), which are known to display light-switching or photo-oxidising behaviour, depending on the nature of the ancillary ligands. X-ray crystallography has made a key contribution to our understanding, and the first complete survey of structural results is presented. These include sequence, enantiomeric, substituent and structural specificities. The use of ultrafast transient spectroscopic methods to probe the ultrafast processes for complexes such as [Ru(TAP)2(dppz)]2+ and [Ru(phen)2(dppz)]2+ when bound to mixed sequence oligonucleotides are reviewed with particular attention being paid to the complementary advantages of transient (visible) absorption and time-resolved (mid) infra-red techniques to probe spectral changes in the metal complex and in the nucleic acid. The observed photophysical properties are considered in light of the structural information obtained from X-ray crystallography. In solution, metal complexes can be expected to bind at more than one DNA step, so that a perfect correlation of the photophysical properties and factors such as the orientation or penetration of the ligand into the intercalation pocket should not be expected. This difficulty can be obviated by carrying out TRIR studies in the crystals. Dppz complexes also undergo insertion, especially with mismatched sequences. Future areas for study such as those involving non-canonical forms of DNA, such as G-quadruplexes or i-motifs are also briefly considered.

Combining a Ru(II) "Building Block" and Rapid Screening Approach to Identify DNA Structure-Selective "Light Switch" Compounds

A chemically reactive Ru(II) "building block", able to undergo condensation reactions with substituted diamines, was utilized to create a small library of luminescent "light switch" dipyrido-[3,2-a:2',3'-c] phenazine (dppz) complexes. The impact of substituent identity, position, and the number of substituents on the light switch effect was investigated. An unbiased, parallel screening approach was used to evaluate the selectivity of the compounds for a variety of different biomolecules, including protein, nucleosides, single stranded DNA, duplex DNA, triplex DNA, and G-quadruplex DNA. Combining these two approaches allowed for the identification of hit molecules that showed different selectivities for biologically relevant DNA structures, particularly triplex and quadruplex DNA.

Targeting human telomeric and c-myc G-quadruplexes with alkynylplatinum(II) terpyridine complexes under molecular crowding conditions

The interactions between alkynylplatinum(II) terpyridine complexes 1-3 and the G-quadruplex DNA, including c-myc and telomeric quadruplex DNA, are investigated both in dilute solution and under molecular crowding conditions. The UV-vis absorption spectroscopy, circular dichroism and molecular docking studies suggest that 1-3 associate with telomeric and c-myc G-quadruplexes via groove binding, and electrostatic interactions. Experimental studies indicate that under molecular crowding conditions (in the presence of 40wt% PEG 200), 1-2 show weak affinity for c-myc, while 3 still displays high affinity and selectivity for c-myc. On the other hand, 1-3 act as efficient and selective ligand for telomeric quadruplex DNA under molecular crowding conditions. The complex 3 exhibits excellent cytotoxicity against A549, K562 and SGC-7901, with IC₅₀ values that are 35.0-fold, 10.0-fold, and 12.1-fold lower than the values of cisplatin under the same conditions, respectively.

Photophysical, G-quadruplex DNA binding and cytotoxic properties of terpyridine complexes with a naphthalimide ligand

The complex3inhibits A549 cells selectively over non-cancerous NIH3T3 cells, which may correlate with its selective G-quadruplex binding and nuclear location.

Synthesis, crystal structure, cytotoxicity and action mechanism of Zn(ii) and Mn(ii) complexes with 4-([2,2′:6′,2′′-terpyridin]-4′-yl)-N,N-diethylaniline as a ligand

Two metallo-complexes inhibited telomerase by interacting with c-myc G4-DNA and induced cell cycle arrest at the S phase.

Synthesis of selenium nanoparticles with mesoporous silica drug-carrier shell for programmed responsive tumor targeted synergistic therapy

Exposure of folate by de-coating in a tumor microenvironment enhanced the in situ targeting. The integrated nanoplatform provides a promising way to programmed responsive tumor targeted synergistic therapy.