Photodecaging of a Mitochondria-Localized Iridium(III) Endoperoxide Complex for Two-Photon Photoactivated Therapy under Hypoxia.

Despite the clinical success of photodynamic therapy (PDT), the application of this medical technique is intrinsically limited by the low oxygen concentrations found in cancer tumors, hampering the production of therapeutically necessary singlet oxygen (1O2). To overcome this limitation, we report on a novel mitochondria-localized iridium(III) endoperoxide prodrug (2-O-IrAn), which, upon two-photon irradiation in NIR, synergistically releases a highly cytotoxic iridium(III) complex (2-IrAn), singlet oxygen, and an alkoxy radical. 2-O-IrAn was found to be highly (photo-)toxic in hypoxic tumor cells and multicellular tumor spheroids (MCTS) in the nanomolar range. To provide cancer selectivity and improve the pharmacological properties of 2-O-IrAn, it was encapsulated into a biotin-functionalized polymer. The generated nanoparticles were found to nearly fully eradicate the tumor inside a mouse model within a single treatment. This study presents, to the best of our knowledge, the first example of an iridium(III)-based endoperoxide prodrug for synergistic photodynamic therapy/photoactivated chemotherapy, opening up new avenues for the treatment of hypoxic tumors.

Mitochondria-Targeting and Reversible Near-Infrared Emissive Iridium(III) Probe for in vivo ONOO-/GSH Redox Cycles Monitoring.

Peroxynitrite (ONOO-) and glutathione (GSH), two unique reactive species, play an essential regulating role in the oxidation and antioxidation in the living body and are closely associated with various physiological and pathological processes, like cancer, cardiovascular disorders, diabetes, inflammation, Alzheimer's disease, and hepatotoxicity. Thus, it is crucial to study mitochondria ONOO-/GSH redox cycles by an effective molecular tool. In this work, a mitochondria-targeting and redox-reversible near-infrared (NIR) phosphorescent iridium complex, Ir-diol, has been synthesized and used for the detection and imaging of a cellular redox state by visualizing endogenous ONOO-/GSH content. Ir-diol shows excellent photophysical properties, including NIR emission (the maximum emissive wavelength for 704 nm, approximately) and high phosphorescent quantum yield (Φ = 0.136) and exhibits high sensitivity and selectivity toward ONOO-/GSH redox cycles in aqueous solution and living cells. Therefore, these features, combined with low cytotoxicity and excellent cell permeability, enable probe Ir-diol to monitor the changes of the intracellular ONOO-/GSH level induced by drug both in vitro and in vivo.

An ER-Targeting Iridium(III) Complex That Induces Immunogenic Cell Death in Non-Small-Cell Lung Cancer.

Immunogenic cell death (ICD) is a vital component of therapeutically induced anti-tumor immunity. An iridium(III) complex (Ir1), containing an N,N-bis(2-chloroethyl)-azane derivate, as an endoplasmic reticulum-localized ICD inducer for non-small cell lung cancer (NSCLC) is reported. The characteristic discharge of damage-associated molecular patterns (DAMPs), that is, cell surface exposure of calreticulin (CRT), extracellular exclusion of high mobility group box 1 (HMGB1), and ATP, were generated by Ir1 in A549 lung cancer cells, accompanied by an increase in endoplasmic reticulum stress and reactive oxygen species (ROS). The vaccination of immunocompetent mice with Ir1-treated dying cells elicited an antitumor CD8+ T cell response and Foxp3+ T cell depletion, which eventually resulted in long-acting anti-tumor immunity by the activation of ICD in lung cancer cells. Ir1 is the first Ir-based complex that is capable of developing an immunomodulatory response by immunogenic cell death.

Supramolecular Assembly of An Organoplatinum(II) Complex with Ratiometric Dual Emission for Two-Photon Bioimaging.

The organoplatinum(II) complex [Pt(C^N^N)(Cl)] (C^N^N=5,6-diphenyl-2,2'-bipyridine, Pt1) can assemble into nanoaggregates via π-π stacking and complementary hydrogen bonds, rather than Pt-Pt interactions. Pt1 exhibits ratiometric dual emission, including rare blue emission (λem =445 nm) and assembly-induced yellow emission (λem =573 nm), under one- and two-photon excitation. Pt1 displays blue emission in cells with an intact membrane due to its low cellular uptake. In cells where the membrane is disrupted, uptake of the complex is increased and at higher concentrations yellow emission is observed. The ratio of yellow to blue emission shows a linear relationship to the loss of cell membrane integrity. Pt1 is, to our knowledge, the first example of an assembly-induced two-photon ratiometric dual emission organoplatinum complex. The excellent and unique characteristics of the complex enabled its use for the tracking of cell apoptosis, necrosis, and the inflammation process in zebrafish.

Lysosome-Targeting Iridium(III) Probe with Near-Infrared Emission for the Visualization of NO/O2•- Crosstalk via In Vivo Peroxynitrite Imaging.

Nitric oxide (NO) and superoxide anions (O2•-) are two noteworthy reactive species implicated in various physiological and pathological processes, such as ROS-induced lysosomal cell death. The interaction ("crosstalk") between them may form a new mediator peroxynitrite (ONOO-) which has implications for cancer, diabetes, Alzheimer's disease, and liver-damage. It is therefore essential to investigate lysosomal NO/O2•- crosstalk in vivo through ONOO--responsive molecular tools in order to fully comprehend the physiological and pathological mechanisms involved. In this study, a lysosome-targeting iridium(III) complex, Ir-NIR, has been investigated as a near-infrared (NIR) phosphorescent probe for visualizing NO/O2•- crosstalk by the phosphorescent detection of endogenous ONOO- levels in vivo. Ir-NIR exhibits a rapid (within 200 s), highly sensitive, and approximately 100-fold enhanced response to ONOO- in phosphorescence intensity. Thus, these characteristics, coupled with good cell permeability and low cytotoxicity, enable the probe to be used to detect intracellular ONOO- living organisms both in vitro and in vivo.

A Mitochondrion-Localized Two-Photon Photosensitizer Generating Carbon Radicals Against Hypoxic Tumors.

The efficacy of photodynamic therapy is typically reliant on the local concentration and diffusion of oxygen. Due to the hypoxic microenvironment found in solid tumors, oxygen-independent photosensitizers are in great demand for cancer therapy. We herein report an iridium(III) anthraquinone complex as a mitochondrion-localized carbon-radical initiator. Its emission is turned on under hypoxic conditions after reduction by reductase. Furthermore, its two-photon excitation properties (λex =730 nm) are highly desirable for imaging. Upon irradiation, the reduced form of the complex generates carbon radicals, leading to a loss of mitochondrial membrane potential and cell death (IC50light =2.1 µm, IC50dark =58.2 µm, PI=27.7). The efficacy of the complex as a PDT agent was also demonstrated under hypoxic conditions in vivo. To the best of our knowledge, it is the first metal-complex-based theranostic agent which can generate carbon radicals for oxygen-independent two-photon photodynamic therapy.

FerriIridium: A Lysosome-Targeting Iron(III)-Activated Iridium(III) Prodrug for Chemotherapy in Gastric Cancer Cells.

Reported is the FeIII -activated lysosome-targeting prodrug FerriIridium for gastric cancer theranostics. It contains a meta-imino catechol group that can selectively bond to, and be oxidized by, free FeIII inside the cell. Subsequent oxidative rearrangement releases FeII and hydrolyses the amine bond under acidic conditions, forming an aminobipyridyl Ir complex and 2-hydroxybenzoquinone. Thus, FeII catalyzes the Fenton reaction, transforming hydrogen peroxide into hydroxyl radicals, the benzoquinone compounds interfere with the respiratory chain, and conversion of the prodrug into the Ir complex leads to an increase in phosphorescence and toxicity. These properties, combined with the high FeIII content and acidity of cancer cells, make FerriIridium a selective and efficient theranostic agent (IC50 =9.22 µm for AGS cells vs. >200 µm for LO2 cells). FerriIridium is the first metal-based compound that has been developed for chemotherapy using FeIII to enhance both selectivity and potency.

Necroptosis Induced by Ruthenium(II) Complexes as Dual Catalytic Inhibitors of Topoisomerase I/II.

Inducing necroptosis in cancer cells is an effective approach to circumvent drug-resistance. Metal-based triggers have, however, rarely been reported. Ruthenium(II) complexes containing 1,1-(pyrazin-2-yl)pyreno[4,5-e][1,2,4]triazine were developed with a series of different ancillary ligands (Ru1-7). The combination of the main ligand with bipyridyl and phenylpyridyl ligands endows Ru7 with superior nucleus-targeting properties. As a rare dual catalytic inhibitor, Ru7 effectively inhibits the endogenous activities of topoisomerase (topo) I and II and kills cancer cells by necroptosis. The cell signaling pathway from topo inhibition to necroptosis was elucidated. Furthermore, Ru7 displays significant antitumor activity against drug-resistant cancer cells in vivo. To the best of our knowledge, Ru7 is the first Ru-based necroptosis-inducing chemotherapeutic agent.

Rational Design of Cyclometalated Iridium(III) Complexes for Three-Photon Phosphorescence Bioimaging.

Compared to 2PE (two-photon excitation) microscopy, 3PE microscopy has superior spatial resolution, deeper tissue penetration, and less defocused interference. The design of suitable agents with a large Stokes shift, good three-photon absorption (3PA), subcellular targeting, and fluorescence lifetime imaging (FLIM) properties, is challenging. Now, two IrIII complexes (3PAIr1 and 3PAIr2) were developed as efficient three-photon phosphorescence (3PP) agents. Calculations reveal that the introduction of a new group to the molecular scaffold confers a quadruple promotion in three-photon transition probability. Confocal and lifetime imaging of mitochondria using IrIII complexes as 3PP agents is shown. The complexes exhibit low working concentration (50 nm), fast uptake (5 min), and low threshold for three-photon excitation power (0.5 mW at 980 nm). The impressive tissue penetration depth (ca. 450 µm) allowed the 3D imaging and reconstruction of brain vasculature from a living specimen.

Bimodal Visualization of Endogenous Nitric Oxide in Lysosomes with a Two-Photon Iridium(III) Phosphorescent Probe.

Nitric oxide (NO) is a fundamental signaling molecule that shows complex effects on the catabolic autophagy process, which is closely linked with lysosomal function. In this study, a new lysosome-targeted, pH-independent, and two-photon phosphorescent iridium(III) complex, Ir-BPDA, has been investigated for endogenous NO detection and imaging. The rational design of the probe, as the addition of the morpholine moieties and the substitution of a benzyl group in the amino group in Ir-BPDA, facilitates its accumulation in lysosomes and makes the reaction product with NO, Ir-BPDA-NO, insusceptible in its phosphorescence intensity and lifetime against pH changes (pH 4-10), well suited for lysosomal NO detection (pH 4-6). Furthermore, Ir-BPDA exhibits a fast and 50-fold response to NO in phosphorescence intensity and a two-photon cross-section as high as 60 GM after the reaction, as well as a notably increased phosphorescence lifetime from 200.1 to 619.6 ns. Thus, accompanied by its photostability, Ir-BPDA enabled the detection of NO in the lipopolysaccharide-stimulated macrophages and zebrafish model, revealing the endogenous lysosomal NO distribution during inflammation in vivo by means of both TPM and PLIM imaging techniques.

Hydrothermal synthesis of tetragonal BaTiO3 nanotube arrays with high dielectric performance.

Tetragonal Barium titanate (BaTiO3) nanotube arrays have been prepared using the template-assisted hydrothermal method combined with an annealing process. The in-situ chemical conversion of TiO2 nanotube array templates ensured that BaTiO3 maintained the morphology of the nanotube architectures. Moreover, X-ray diffraction and Raman spectrum characterization were used to confirm that the BaTiO3 nanotube arrays had a tetragonal phase after the use of a simple annealing technique. Typical hysteresis loops showed their ferroelectricity, with the remanent polarization and coercive fields being 2.57 microC/cm2 and 2.52 kV/cm, respectively. The relative dielectric constant of the tetragonal BaTiO3 nanotube arrays reached up to 1000 and the dielectric loss was as low as 0.02 at 1 kHz at room temperature.

Cycloruthenated Self-Assembly with Metabolic Inhibition to Efficiently Overcome Multidrug Resistance in Cancers.

The synthesis and the evaluation of the efficacy of a cycloruthenated complex, RuZ, is reported, to overcome multi-drug resistance (MDR) in cancer cells. RuZ can self-assemble into nanoaggregates in the cell culture medium, resulting in a high intracellular concentration of RuZ in MDR cancer cells. The self-assembly significantly decreases oxygen consumption and inhibits glycolysis, which decreases cellular adenosine triphosphate (ATP) levels. The decrease in ATP levels and its low affinity for the ABCB1 and ABCG2 transporters (which mediate MDR) significantly increase the retention of RuZ by MDR cancer cells. Furthermore, RuZ increases cellular oxidative stress, inducing DNA damage, and, in combination with the aforementioned effects of RuZ, increases the apoptosis of cancer cells. Proteomic profiling analysis suggests that the RuZ primarily decreases the expression of proteins that mediate glycolysis and aerobic mitochondrial respiration and increases the expression of proteins involved in apoptosis. RuZ inhibits the proliferation of 35 cancer cell lines, of which 7 cell lines are resistant to clinical drugs. It is also active in doxorubicin-resistant MDA-MB-231/Adr mouse tumor xenografts. To the best of our knowledge, the results are the first to show that self-assembled cycloruthenated complexes are efficacious in inhibiting the growth of MDR cancer cells.

A mitochondrion-targeted BODIPY-Ir(III) conjugate as a photoinduced ROS generator for the oxidative destruction of triple-negative breast cancer cells.

Photodynamic therapy (PDT) provides an alternative option to root out localized triple-negative breast cancer (TNBC) and has been experiencing a surge of research interest over recent years. In this study, we put forward a paradigm of designing novel transition metal-based PSs with the following characteristics: favorable cell-permeability, significant light-harvesting ability and prominent ROS yield. A novel BODIPY-Ir(III) conjugate has been designed as a photoinduced ROS (1O2, ˙OH and ˙O2-) generator. BODIPY-Ir is highly photoactive in subduing cancer cells in the PDT regimen with PI values ranging from 172 to 519 and EC50 in the nanomolar regime. Among various cancerous cell lines, TNBC was especially sensitive to BODIPY-Ir-mediated PDT, with a stunning EC50 value of 4.32 nM (PI = 519) under a moderate flux of visible-light irradiation (500 nm, 10.5 mW cm-2). BODIPY-Ir mainly accumulates in mitochondria and induces cell apoptosis under irradiation. Furthermore, the nanomolar antiproliferative activity of BODIPY-Ir is retained under hypoxia (2.5% O2). This work sheds light on instilling the O2-independent type I mechanism and conferring a red-shift absorption to metal-based PSs which fundamentally facilitate the clinical translation of PSs.

Ruthenium(II) complexes as bioorthogonal two-photon photosensitizers for tumour-specific photodynamic therapy against triple-negative breast cancer cells.

Herein, we developed the first Ru(ii) complex-based bioorthogonal two-photon photosensitizers. Through bioorthogonal labelling, they realize effective tumour-specific photodynamic therapy against triple-negative breast cancer cells.

Rational design of a lysosome-targeting and near-infrared absorbing Ru(ii)-BODIPY conjugate for photodynamic therapy.

A Ru(ii)-BODIPY conjugate has been rationally designed and exhibits an intense absorption in the NIR region to boost lysosome-targeted PDT in vitro and in vivo. The advantages of Ru(ii) and BODIPY were successfully instilled into the conjugate to yield highly effective PDT efficacy against malignant melanoma A375 cells (PI = 3448) and A375 mice xenografts.

Ruthenium(II) complexes coordinated to graphitic carbon nitride: Oxygen self-sufficient photosensitizers which produce multiple ROS for photodynamic therapy in hypoxia.

The photodynamic therapy (PDT) of cancer is limited by tumor hypoxia as PDT efficiency depends on O2 concentration. A novel oxygen self-sufficient photosensitizer (Ru-g-C3N4) was therefore designed and synthesized via a facile one-pot method in order to overcome tumor hypoxia-induced PDT resistance. The photosensitizer is based on [Ru(bpy)2]2+ coordinated to g-C3N4 nanosheets by Ru-N bonding. Compared to pure g-C3N4, the resulting nanosheets exhibit increased water solubility, stronger visible light absorption, and enhanced biocompatibility. Once Ru-g-C3N4 is taken up by hypoxic tumor cells and exposed to visible light, the nanosheets not only catalyze the decomposition of H2O2 and H2O to generate O2, but also catalyze H2O2 and O2 concurrently to produce multiple ROS (•OH, •O2-, and 1O2). In addition, Ru-g-C3N4 affords luminescence imaging, while continuously generating O2 to alleviate hypoxia greatly improving PDT efficacy. To the best of our knowledge, this oxygen self-sufficient photosensitizer produced via grafting a metal complex onto g-C3N4 is the first of its type to be reported.

Nano-assembly of ruthenium(II) photosensitizers for endogenous glutathione depletion and enhanced two-photon photodynamic therapy.

Photodynamic therapy (PDT) is a promising noninvasive cancer treatment. PDT in the clinic faces several hurdles due to the unique tumor environment, a feature of which is high levels of glutathione (GSH). An excess amount of GSH consumes reactive oxygen species (ROS) generated by photosensitizers (PSs), reducing PDT efficiency. Herein, nano-photosensitizers (RuS1 NPs and RuS2 NPs) are reported. These consist of ruthenium complexes joined by disulfide bonds forming GSH sensitive polymer nanoparticles. The NPs achieve enhanced uptake compared to their constituent monomers. Inside cancer cells, high levels of GSH break the S-S bonds releasing PS molecules in the cell. The level of GSH is also then reduced leading to excellent PDT activity. Furthermore, RuS2 NPs functionalized with tumor targeting hyaluronic acid (HA@RuS2 NPs) assessed in vivo were highly effective with minimal side effects. To the best of our knowledge, RuS NPs are the first metal complex-based nano-assembled photosensitizers which exhibit enhanced specificity and consume endogenous GSH simultaneously, thus achieving excellent two-photon PDT efficiency in vitro and in vivo.

Boosting two-photon photodynamic therapy with mitochondria-targeting ruthenium-glucose conjugates.

Herein, we present a series of dual-targeted ruthenium-glucose conjugates that can function as two-photon absorption (TPA) PDT agents to effectively destroy tumors by preferentially targeting both tumor cells and mitochondria. The in vivo experiments revealed an excellent tumor inhibitory efficiency of the dual-targeted TPA PSs.

Correction: Mitochondria-targeted Ir@AuNRs as bifunctional therapeutic agents for hypoxia imaging and photothermal therapy.

Correction for 'Mitochondria-targeted Ir@AuNRs as bifunctional therapeutic agents for hypoxia imaging and photothermal therapy' by Libing Ke et al., Chem. Commun., 2019, 55, 10273-10276.

Correction: Fabrication of red blood cell membrane-camouflaged Cu2-xSe nanoparticles for phototherapy in the second near-infrared window.

Correction for 'Fabrication of red blood cell membrane-camouflaged Cu2-xSe nanoparticles for phototherapy in the second near-infrared window' by Zhou Liu et al., Chem. Commun., 2019, 55, 6523-6526.