Tuning Polyamidoamine Design To Increase Uptake and Efficacy of Ruthenium Complexes for Photodynamic Therapy

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.

Encapsulation of Ru(II) Polypyridine Complexes for Tumor-Targeted Anticancer Therapy

Ru(II) polypyridine complexes have attracted much attention as anticancer agents because of their unique photophysical, photochemical, and biological properties. Despite their promising therapeutic profile, the vast majority of compounds are associated with poor water solubility and poor cancer selectivity. Among the different strategies employed to overcome these pharmacological limitations, many research efforts have been devoted to the physical or covalent encapsulation of the Ru(II) polypyridine complexes into nanoparticles. This article highlights recent developments in the design, preparation, and physicochemical properties of Ru(II) polypyridine complex-loaded nanoparticles for their potential application in anticancer therapy.

Cyclometalated Ru(II)-NHC complexes with phenanthroline ligands induce apoptosis mediated by mitochondria and endoplasmic reticulum stress in cancer cells

The exploration of ruthenium complexes as anticancer drugs has been the focus of intense investigation. In this study, we synthesized and characterized four C,N-cyclometalated ruthenium(II) complexes (Ru1-Ru4) coordinated with pyridine-functionalized N-heterocyclic carbene (NHC) and auxiliary ligands (e.g., acetonitrile, 1,10-phenanthroline, 3,4,7,8-tetramethyl-1,10-phenanthroline, and 4,7-diphenyl-1,10-phenanthroline). X-ray diffraction analysis showed that all of the four cycloruthenated complexes are hexa-coordinated in a typical octahedral geometry. In vitro cytotoxic studies revealed that cyclometalated Ru-NHC complexes Ru3 and Ru4 had stronger anticancer activity than their corresponding Ru-NHC precursor Ru1 and the clinically used cisplatin. For HeLa cells, Ru3 and Ru4 exhibited potent cytotoxicity with the IC₅₀ value of 4.31 ± 0.42 μM and 3.14 ± 0.23 μM, respectively, which was approximately three times lower than that of cisplatin. More interestingly, Ru3 and Ru4 not only effectively inhibited the proliferation of HeLa cells, but also exhibited potential anti-migration activity. In the scratch wound healing assay, Ru3 and Ru4 treatment significantly reduced the wound healing rate of HUVEC cells. Mechanistic studies showed that Ru3 and Ru4 caused a dual action mode of mitochondrial membrane depolarization and endoplasmic reticulum stress and finally induced apoptosis of HeLa cells.

Characterization of a Ruthenium(II) Complex in Singlet Oxygen-Mediated Photoelectrochemical Sensing

A water-soluble ruthenium(II) complex (L), capable of producing singlet oxygen (¹O₂) when irradiated with visible light, was used to modify the surface of an indium-tin oxide (ITO) electrode decorated with a nanostructured layer of TiO₂ (TiO₂/ITO). Singlet oxygen triggers the appearance of a cathodic photocurrent when the electrode is illuminated and biased at a proper reduction potential value. The L/TiO₂/ITO electrode was first characterized with cyclic voltammetry, impedance spectroscopy, NMR, and Raman spectroscopy. The rate constant of singlet oxygen production was evaluated by spectrophotometric measurements. Taking advantage of the oxidative process initiated by ¹O₂, the analysis of phenolic compounds was accomplished. Particularly, the ¹O₂-driven oxidation of hydroquinone (HQ) produced quinone moieties, which could be reduced back at the electrode surface, biased at -0.3 V vs Ag/AgCl. Such a light-actuated redox cycle produced a photocurrent dependent on the concentration of HQ in solution, exhibiting a limit of detection (LOD) of 0.3 μmol dm^-3. The L/TiO₂/ITO platform was also evaluated for the analysis of p-aminophenol, a commonly used reagent in affinity sensing based on alkaline phosphatase.

Factors that influence singlet oxygen formation vs. ligand substitution for light-activated ruthenium anticancer compounds

This review focuses on light-activated ruthenium anticancer compounds and the factors that influence which pathway is favored. Photodynamic therapy (PDT) is favored by π expansion and the presence of low-lying triplet excited states (e.g. ³MLCT, ³IL). Photoactivated chemotherapy (PACT) refers to light-driven ligand dissociation to give a toxic metal complex or a toxic ligand upon photo substitution. This process is driven by steric bulk near the metal center and weak metal-ligand bonds to create a low-energy ³MC state with antibonding character. With protic dihydroxybipyridine ligands, ligand charge can play a key role in these processes, with a more electron-rich deprotonated ligand favoring PDT and an electron-poor protonated ligand favoring PACT in several cases.

Nanosized T1 MRI Contrast Agent Based on a Polyamidoamine as Multidentate Gd Ligand

A linear polyamidoamine (PAA) named BAC-EDDS, containing metal chelating repeat units composed of two tert-amines and four carboxylic groups, has been prepared by the aza-Michael polyaddition of ethylendiaminodisuccinic (EDDS) with 2,2-bis(acrylamido)acetic acid (BAC). It was characterized by size exclusion chromatography (SEC), FTIR, UV–Vis and NMR spectroscopies. The pK_a values of the ionizable groups of the repeat unit were estimated by potentiometric titration, using a purposely synthesized molecular ligand (Agly-EDDS) mimicking the structure of the BAC-EDDS repeat unit. Dynamic light scattering (DLS) and ζ-potential analyses revealed the propensity of BAC-EDDS to form stable nanoaggregates with a diameter of approximately 150 nm at pH 5 and a net negative charge at physiological pH, in line with an isoelectric point <2. BAC-EDDS stably chelated Gd (III) ions with a molar ratio of 0.5:1 Gd (III)/repeat unit. The stability constant of the molecular model Gd-Agly-EDDS (log K = 17.43) was determined as well, by simulating the potentiometric titration through the use of Hyperquad software. In order to comprehend the efficiency of Gd-BAC-EDDS in contrasting magnetic resonance images, the nuclear longitudinal (r₁) and transverse (r₂) relaxivities as a function of the externally applied static magnetic field were investigated and compared to the ones of commercial contrast agents. Furthermore, a model derived from the Solomon–Bloembergen–Morgan theory for the field dependence of the NMR relaxivity curves was applied and allowed us to evaluate the rotational correlation time of the complex (τ = 0.66 ns). This relatively high value is due to the dimensions of Gd-BAC-EDDS, and the associated rotational motion causes a peak in the longitudinal relaxivity at ca. 75 MHz, which is close to the frequencies used in clinics. The good performances of Gd-BAC-EDDS as a contrast agent were also confirmed through in vitro magnetic resonance imaging experiments with a 0.2 T magnetic field.

Ru(II) Polypyridine Complex-Functionalized Mesoporous Silica Nanoparticles as Photosensitizers for Cancer Targeted Photodynamic Therapy

Cancer is the leading cause of death in the developed world. In the last few decades, photodynamic therapy (PDT) has augmented the number of medical techniques to treat this disease in the clinics. As the pharmacological active species to kill cancer cells are only generated upon light irradiation, PDT is associated with an intrinsic first level of selectivity. However, since PDT agents also accumulate in the surrounding, healthy tissue and since it is practically very challenging to only expose the tumor site to light, some side effects can be observed. Consequently, there is a need for a selective drug delivery system, which would give a second level of selectivity. In this work, a dual tumor targeting approach is presented based on mesoporous silica nanoparticles, which act by the enhanced permeability and retention effect, and the conjugation to folic acid, which acts as a targeting moiety for folate receptor-overexpressed cancer cells. The conjugates were found to be nontoxic in noncancerous human normal lung fibroblast cells while showing a phototoxic effect upon irradiation at 480 or 540 nm in the low nanomolar range in folate receptor overexpressing cancerous human ovarian carcinoma cells, demonstrating their potential for cancer targeted treatment.

Polymeric Encapsulation of a Ru(II)-Based Photosensitizer for Folate-Targeted Photodynamic Therapy of Drug Resistant Cancers

The currently used photodynamic therapy (PDT) photosensitizers (PSs) are generally associated with a poor cancer cell selectivity, which is responsible for some undesirable side effects. To overcome these problems, there is an urgent need for a selective drug delivery system for PDT PSs. Herein, the encapsulation of a promising Ru(II) polypyridine complex in a polymer with terminal folate groups to form nanoparticles is presented. While the Ru(II) complex itself has a cytotoxic effect in the dark, the encapsulation is able to overcome this drawback. Upon light exposure, the nanoparticles were found to be highly phototoxic in 2D monolayer cells as well as 3D multicellular tumor spheroids upon 480 or 595 nm irradiation. Importantly, the nanoparticles demonstrated a high selectivity for cancerous cells over noncancerous cells and were found to be active in drug resistant cancer cells lines, indicating that they are able to overcome drug resistances.

Incorporation of Ru(II) Polypyridyl Complexes into Nanomaterials for Cancer Therapy and Diagnosis

Ru(II) polypyridyl complexes are compounds of great interest in cancer therapy due to their unique photophysical, photochemical, and biological properties. For effective treatment, they must be able to penetrate tumor cells effectively and selectively. The development of nanoscale carriers capable of delivering Ru(II) polypyridyl complexes has the potential to passively or selectively enhance their cellular uptake in tumor cells. Many different strategies have been explored to incorporate Ru(II) polypyridyl complexes into a variety of nanosized constructs, ranging from organic to inorganic materials. Herein, recent developments in nanomaterials loaded with Ru(II) polypyridyl complexes are highlighted. Their rational design, preparation, and physicochemical properties are described, and their potential applications in cancer therapy are eventually discussed.

Light-Triggered Trafficking to the Cell Nucleus of a Cationic Polyamidoamine Functionalized with Ruthenium Complexes

Strategies for endosomal escape and access to the cell nucleus are highly sought for nanocarriers to deliver their load efficiently following endocytosis. In this work, we have studied the uptake and intracellular trafficking of a polycationic polyamidoamine (PAA) endowed with a luminescent Ru complex, Ru-PhenAN, that shows unique trafficking to the cell nucleus. Live cell imaging confirmed the capacity of this polymer to access the nucleus, excluding artifacts due to cell fixation, and clarified that the mechanism of escape is light-triggered and relies on the presence of the Ru complexes and their capacity to absorb light and act as photosensitizers for singlet oxygen production. These results open up the possibility to use PAA-ruthenium complexes for targeted light-triggered delivery of genetic material or drugs to the cytosol and nucleus.