A Mitochondria-Targeted Nitric Oxide Probe for Multimodality Imaging of Macrophage Immune Responses.

Nitric oxide (NO) is a crucial signal molecule closely linked to the biological immune response, especially in macrophage polarization. When activated, macrophages enter a pro-inflammatory state and produce NO, a marker for the M1 phenotype. In contrast, the anti-inflammatory M2 phenotype does not produce NO. We developed a mitochondria-targeted two-photon iridium-based complex (Ir-ImNO) probe that can detect endogenous NO and monitor macrophages' different immune response states using various imaging techniques, such as one- and two-photon phosphorescence imaging and phosphorescence lifetime imaging. Ir-ImNO was used to monitor the immune activation of macrophages in mice. This technology aims to provide a clear and comprehensive visualization of macrophage immune responses.

A hetero-bimetallic Ru(II)-Ir(III) photosensitizer for effective cancer photodynamic therapy under hypoxia.

A hetero-bimetallic Ru(II)-Ir(III) photosensitizer was developed. Upon light exposure, contrary to the homogeneous Ru(II)-Ru(II) and Ir(III)-Ir(III) complexes that can only produce singlet oxygen, Ru(II)-Ir(III) can generate multiple reactive oxygen species and kill hypoxic tumors. This study presents the first example of a hetero-bimetallic type-I and type-II dual photosensitizer.

Apoferritin-Cu(II) Nanoparticles Induce Oncosis in Multidrug-Resistant Colon Cancer Cells.

Multidrug resistance (MDR) limits the application of clinical chemotherapeutic drugs. There is an urgent need to develop non-apoptosis-inducing agents that circumvent drug resistance. Herein, four therapeutic copper complexes encapsulated in natural nanocarrier apoferritin (AFt-Cu1-4) are reported. Although they are isomers, they exhibit significantly different organelle distributions and cell death mechanisms. AFt-Cu1 and AFt-Cu3 accumulate in the cytoplasm and induce autophagy, whereas AFt-Cu2 and AFt-Cu4 can quickly enter the nucleus and trigger oncosis. Excitedly, AFt-Cu2 and AFt-Cu4 show a strong tumor growth inhibition effect in mice models bearing multidrug-resistant colon xenograft via intravenous injection. To the best of the authors' knowledge, this is the first example of metal-based nucleus-targeted oncosis inducers overcoming multidrug resistance in vivo.

A Mitochondria-Localized Iridium(III) Complex for Simultaneous Two-Photon Phosphorescence Lifetime Imaging of Downstream Products N2O3 and ONOO- of Endogenous Nitric Oxide.

Nitric oxide (NO) serves as a ubiquitous and fundamental signaling molecule involved in intricate effects on both physiological and pathological processes. NO, biosynthesized by nitric oxide synthase (NOS) or generated from nitrite, can form nitrosation reagent N2O3 (4NO + O2 = 2N2O3) through its oxidation or quickly produce peroxynitrite anion ONOO- (NO + •O2- = ONOO-) by reacting with superoxide anion (•O2-). However, most of the existing luminescent probes for NO just focus on specificity and utilize only a single signal to distinguish products N2O3 or ONOO-. In most of the present work, they differentiate one product from another simply by fluorescence signal or fluorescence intensity, which is not enough to distinguish accurately the behavior of NO in living cells. Herein, a new mitochondria-targeted and two-photon near-infrared (NIR) phosphorescent iridium(III) complex, known as Ir-NBD, has been designed for accurate detection and simultaneous imaging of two downstream products of endogenous NO, i.e., N2O3 and ONOO-. Ir-NBD exhibits a rapid response to N2O3 and ONOO- in enhanced phosphorescence intensity, increased phosphorescence lifetime, and an exceptionally high two-photon cross-section, reaching values of 78 and 85 GM, respectively, after the reaction. Furthermore, we employed multiple imaging methods, phosphorescence intensity imaging, and phosphorescence lifetime imaging together to image even distinguish N2O3 and ONOO- by probe Ir-NBD. Thus, coupled with its excellent photometrics, Ir-NBD enabled the detection of the basal level of intracellular NO accurately by responding to N2O3 and ONOO- in the lipopolysaccharide-stimulated macrophage model in virtue of fluorescence signal and phosphorescence lifetime imaging, revealing precisely the endogenous mitochondrial NO distribution during inflammation in a cell environment.

Exosome camouflaged coordination-assembled Iridium(III) photosensitizers for apoptosis-autophagy-ferroptosis induced combination therapy against melanoma.

Melanoma represents the most fatal form of skin cancer due to its resistance mechanisms and high capacity for the development of metastases. Among other medicinal techniques, photodynamic therapy is receiving increasing attention. Despite promising results, the application of photodynamic therapy is inherently limited due to interference from melanin, poor tissue penetration of photosensitizers, low loading into drug delivery systems, and a lack of tumor selectivity. To overcome these limitations, herein, the coordination-driven assembly of Ir(III) complex photosensitizers with Fe(III) ions into nanopolymers for combined photodynamic therapy and chemodynamic therapy is reported. While remaining stable under physiological conditions, the nanopolymers dissociated in the tumor microenvironment. Upon exposure to light, the Ir(III) complexes produced singlet oxygen and superoxide anion radicals, inducing cell death by apoptosis and autophagy. The Fe(III) ions were reduced to Fe(II) upon depletion of glutathione and reduction of the GPX4 levels, triggering cell death by ferroptosis. To provide tumor selectivity, the nanopolymers were further camouflaged with exosomes. The generated nanoparticles were found to eradicate a melanoma tumor as well as inhibit the formation of metastases inside a mouse model.

In situ oxidative polymerization of platinum(iv) prodrugs in pore-confined spaces of CaCO3 nanoparticles for cancer chemoimmunotherapy.

Drug resistance and metastases are the leading causes of death in clinics. To overcome this limitation, there is an urgent need for new therapeutic agents and drug formulations that are able to therapeutically intervene by non-traditional mechanisms. Herein, the physical adsorption and oxidative polymerization of Pt(iv) prodrugs in pore-confined spaces of CaCO3 nanoparticles is presented, and the nanomaterial surface was coated with DSPE-PEG2000-Biotin to improve aqueous solubility and tumor targeting. While the nanoparticle scaffold remained stable in an aqueous solution, it quickly degraded into Ca2+ in the presence of acid and into cisplatin in the presence of GSH. The nanoparticles were found to interact in cisplatin-resistant non-small lung cancer cells by a multimodal mechanism of action involving mitochondrial Ca2+ overload, dual depletion of GSH, nuclear DNA platination, and amplification of ROS and lipid peroxide generation, resulting in triggering cell death by a combination of apoptosis, ferroptosis and immunogenic cell death in vitro and in vivo. This study could present a novel strategy for the treatment of drug-resistant and metastatic tumors and therefore overcome the limitations of currently used therapeutic agents in the clinics.

Recent progress in metal complexes functionalized nanomaterials for photodynamic therapy.

Metal complexes have shown promise as photosensitizers for cancer diagnosis and therapeutics. However, the vast majority of metal photosensitizers are not ideal and associated with several limitations including pharmacokinetic limitations, off-target toxicity, fast systemic clearance, poor membrane permeability, and hypoxic tumour microenvironments. Metal complex functionalized nanomaterials have the potential to construct multifunctional systems, which not only overcome the above defects of metal complexes but are also conducive to modulating the tumour microenvironment (TME) and employing combination therapies to boost photodynamic therapy (PDT) efficacy. In this review, we first introduce the current challenges of photodynamic therapy and summarize the recent research strategies (such as metal coordination bonds, self-assembly, π-π stacking, physisorption, and so on) used for preparing metal complexes functionalized nanomaterials in the application of PDT.

A mitochondria-localized iridium(iii) photosensitizer for two-photon photodynamic immunotherapy against melanoma.

Conventional photodynamic therapy mainly causes a therapeutic effect on the primary tumor through the localized generation of reactive oxygen species, while metastatic tumors remain poorly affected. Complementary immunotherapy is effective in eliminating small, non-localized tumors distributed across multiple organs. Here, we report the Ir(iii) complex Ir-pbt-Bpa as a highly potent immunogenic cell death inducing photosensitizer for two-photon photodynamic immunotherapy against melanoma. Ir-pbt-Bpa can produce singlet oxygen and superoxide anion radicals upon light irradiation, causing cell death by a combination of ferroptosis and immunogenic cell death. In a mouse model with two physically separated melanoma tumors, although only one of the primary tumors was irradiated, a strong tumor reduction of both tumors was observed. Upon irradiation, Ir-pbt-Bpa not only induced the immune response of CD8+ T cells and the depletion of regulatory T cells, but also caused an increase in the number of the effector memory T cells to achieve long-term anti-tumor immunity.

Recent Progress in Photodynamic Immunotherapy with Metal-Based Photosensitizers.

Cancer ranks as a leading cause of death. There is an urgent need to develop minimally invasive methods to eradicate tumors and prevent their recurrence. As a light-driven modality, photodynamic therapy takes advantage of high tumor selectivity and low normal tissue damage. However, it shows poor potential for preventing tumor recurrence. Immunotherapy is currently being used as an alternative treatment for the control of malignant diseases. Although immunotherapy can establish long-time immune memory and efficiently protects treated patients from cancer relapse, its clinical efficacy is limited by the minority of patients' responding rate. Recently, photodynamic immunotherapy, which utilizes photosensitizers as an immunotherapy trigger to exert synergistic effects of photodynamic therapy and tumor immunotherapy, has attracted considerable interest. Like all the newly proposed treatments, there is still room for improvement. In this mini review, the progress in photodynamic immunotherapy with metal-based photosensitizers is summarized. It is hoped that this review can give a broad update on photodynamic immunotherapy and inspire readers.

Chiral RuII -PtII Complexes Inducing Telomere Dysfunction against Cisplatin-Resistant Cancer Cells.

The application of G-quadruplex stabilizers presents a promising anticancer strategy. However, the molecular crowding conditions within cells diminish the potency of current G-quadruplex stabilizers. Herein, chiral RuII -PtII dinuclear complexes were developed as highly potent G-quadruplex stabilizers even under challenging molecular crowding conditions. The compounds were encapsulated with biotin-functionalized DNA cages to enhance sub-cellular localization and provide cancer selectivity. The nanoparticles were able to efficiently inhibit the endogenous activities of telomerase in cisplatin-resistant cancer cells and cause cell death by apoptosis. The nanomaterials demonstrated high antitumor activity towards cisplatin-resistant tumor cells as well as tumor-bearing mice. To the best of our knowledge, this study presents the first example of a RuII -PtII dinuclear complex as a G-quadruplex stabilizer with an anti-cancer effect towards drug-resistant tumors inside an animal model.

A Biodegradable Iridium(III) Coordination Polymer for Enhanced Two-Photon Photodynamic Therapy Using an Apoptosis-Ferroptosis Hybrid Pathway.

The clinical application of photodynamic therapy is hindered by the high glutathione concentration, poor cancer-targeting properties, poor drug loading into delivery systems, and an inefficient activation of the cell death machinery in cancer cells. To overcome these limitations, herein, the formulation of a promising IrIII complex into a biodegradable coordination polymer (IrS NPs) is presented. The nanoparticles were found to remain stable under physiological conditions but deplete glutathione and disintegrate into the monomeric metal complexes in the tumor microenvironment, causing an enhanced therapeutic effect. The nanoparticles were found to selectively accumulate in the mitochondria where these trigger cell death by hybrid apoptosis and ferroptosis pathways through the photoinduced production of singlet oxygen and superoxide anion radicals. This study presents the first example of a coordination polymer that can efficiently cause cancer cell death by apoptosis and ferroptosis upon irradiation, providing an innovative approach for cancer therapy.

Chiral rhodium(III)-azobenzene complexes as photoswitchable DNA molecular locks.

Chiral rhodium(III)-azobenzene complexes that are able to intercalate into DNA were developed. Upon light exposure, the azobenzene moiety of the metal complexes can photoisomerize from the trans-form to the cis-form, and strongly stabilize the DNA double-helix and modulate DNA transcription. This study presents the first example of metal-based photoswitchable DNA molecular locks.

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.

Cyclometalated Iridium(III) Complexes as Mitochondria-targeting Photosensitizers against Cisplatin-resistant Cells.

Four iridium (III) complexes Ir1-Ir4 were synthesized and characterized. Possessing high singlet oxygen production ability and specific mitochondria-localization, Ir1 was developed as a mitochondria-targeting photosensitizer. Ir1 exhibited strong phototoxicity against cancer cell line A549 and its corresponding cisplatin-resistant one A549R. In contrast, Ir1 showed low cytotoxicity toward normal cell HLF. This selectivity resulted from the different uptake amount. With 405 nm irradiation, Ir1 induced mitochondria-mediated cell death in A549R cells, achieving the overcome of drug-resistant.

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 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.

Autophagy-Dependent Apoptosis Induced by Apoferritin-Cu(II) Nanoparticles in Multidrug-Resistant Colon Cancer Cells.

Chemotherapy continues to be the most commonly applied strategy for cancer. Despite the impressive clinical success obtained with several drugs, increasing numbers of (multi)drug-resistant tumors are reported. To overcome this shortcoming, novel drug candidates and delivery systems are urgently needed. Herein, a therapeutic copper polypyridine complex encapsulated in natural nanocarrier apoferritin is reported. The generated nanoparticles showed higher cytotoxicity toward various (drug-resistant) cancer cell lines than noncancerous cells. The study of the mechanism revealed that the compound triggers cell autophagy-dependent apoptosis. Promisingly, upon injection of the nanodrug conjugate into the bloodstream of a mouse model bearing a multidrug-resistant colon tumor, a strong tumor growth inhibition effect was observed. To date, this is the first study describing the encapsulation of a copper complex in apoferritin that acts by autophagy-dependent apoptosis.

Iridium(iii) complexes as mitochondrial topoisomerase inhibitors against cisplatin-resistant cancer cells.

Herein, we developed the first metal-based mitochondrial topoisomerase inhibitors to achieve an effective therapeutic outcome for the therapy of cisplatin-resistant tumour cells.

Phosphorescent metal complexes as theranostic anticancer agents: combining imaging and therapy in a single molecule.

Phosphorescent metal complexes are a new kind of multifunctional antitumor compounds that can integrate imaging and antitumor functions in a single molecule. In this minireview, we summarize the recent research progress in this field, concentrating on the theranostic applications of phosphorescent iridium(iii), ruthenium(ii) and rhenium(i) complexes. The molecular design that affords these complexes with tumour- or subcellular organelle-targeting properties is elucidated. The potential of these complexes to induce and monitor the dynamic behavior of subcellular organelles and the changes in microenvironment during the process of therapy is demonstrated. Moreover, the potential and advantages of applying new technologies, such as super-resolution imaging and phosphorescence lifetime imaging, are also described. Finally, the challenges faced in the development of novel theranostic metallo-anticancer complexes for possible clinical translation are proposed.

Cancer cell membrane camouflaged iridium complexes functionalized black-titanium nanoparticles for hierarchical-targeted synergistic NIR-II photothermal and sonodynamic therapy.

The diagnosis and treatment of cancer is one of the biggest medical challenges of the century. Despite significant improvements, there remains an urgent need for novel anticancer procedures. Among the most promising approaches, increasing attention has been devoted towards photothermal and sonodynamic therapy in which sensitizers are activated upon light/ultrasound radiation to generate a cytotoxic effect. While these methods have undoubtedly shown a high therapeutic success, these techniques are intrinsically limited. Herein, the functionalization of black-titanium nanoparticle with iridium complexes and cancer cell membranes in a nanoplatform for hierarchical targeted synergistic photothermal and sonodynamic cancer imaging and therapy is proposed. The particles showed to generate efficiently heat upon irradiation and catalytically form reactive oxygen species upon ultrasound radiation. The nanoparticle formulation demonstrated to selectively localize in the mitochondria as well as to preferentially accumulate in cancerous over non-cancerous cells as well as in the tumor inside a mouse model, presenting a hierarchical targeting strategy. Upon synergistic irradiation at 1064 nm and ultrasound radiation, the nanoparticles were able to act as an imaging agent and identify the tumor site with high spatial resolution as well as act as a therapeutic agent and completely eradicate a tumor inside a mouse model.