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.

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 (λ_em =445 nm) and assembly-induced yellow emission (λ_em =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.

Recent progress in photosensitizers for overcoming the challenges of photodynamic therapy: from molecular design to application

Photodynamic therapy (PDT), a therapeutic mode involving light triggering, has been recognized as an attractive oncotherapy treatment. However, nonnegligible challenges remain for its further clinical use, including finite tumor suppression, poor tumor targeting, and limited therapeutic depth. The photosensitizer (PS), being the most important element of PDT, plays a decisive role in PDT treatment. This review summarizes recent progress made in the development of PSs for overcoming the above challenges. This progress has included PSs developed to display enhanced tolerance of the tumor microenvironment, improved tumor-specific selectivity, and feasibility of use in deep tissue. Based on their molecular photophysical properties and design directions, the PSs are classified by parent structures, which are discussed in detail from the molecular design to application. Finally, a brief summary of current strategies for designing PSs and future perspectives are also presented. We expect the information provided in this review to spur the further design of PSs and the clinical development of PDT-mediated cancer treatments.

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.

Necroptosis-inducing iridium(iii) complexes as regulators of cyclin-dependent kinases

Mitochondria-targeted Ir(iii) complexes induce necroptosis and downregulate certain cell cycle proteins to achieve cell cycle arrest and an anti-proliferation effect in drug-resistant lung cancer.

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

A lysosome-targeting and near-infrared absorbing Ru(ii)–BODIPY conjugate exhibits prominent tumor inhibitory efficiency in malignant melanoma A375 cells and in vivo experiments.

A mitochondrial-targeting iridium(iii) complex for H2O2-responsive and oxidative stress amplified two-photon photodynamic therapy

The mitochondrial-targeting iridium(iii) complex Ir–B(OH)2 is activated in the presence of endogenous H2O2 to release the two-photon photosensitizer Ir–OH and the GSH scavenger methylquinone for amplified two-photon photodynamic therapy.

Polymeric Encapsulation of a Ruthenium Polypyridine Complex for Tumor Targeted One- and Two-Photon Photodynamic Therapy

Photodynamic therapy is a medical technique, which is gaining increasing attention to treat various types of cancer. Among the investigated classes of photosensitizers (PSs), the use of Ru(II) polypyridine complexes is gaining momentum. However, the currently investigated compounds generally show poor cancer cell selectivity. As a consequence, high drug doses are needed, which can cause side effects. To overcome this limitation, there is a need for the development of a suitable drug delivery system to increase the amount of PS delivered to the tumor. Herein, we report the encapsulation of a promising Ru(II) polypyridyl complex into polymeric nanoparticles with terminal biotin groups. Thanks to this design, the particles showed much higher selectivity for cancer cells in comparison to noncancerous cells in a 2D monolayer and 3D multicellular tumor spheroid model. As a highlight, upon intravenous injection of an identical amount of the Ru(II) polypyridine complex of the nanoparticle formulation, an improved accumulation inside an adenocarcinomic human alveolar basal epithelial tumor of a mouse up to a factor of 8.7 compared to the Ru complex itself was determined. The nanoparticles were found to have a high phototoxic effect upon one-photon (500 nm) or two-photon (800 nm) excitation with eradication of adenocarcinomic human alveolar basal epithelial tumor inside a mouse model. Overall, this work describes, to the best of our knowledge, the first in vivo study demonstrating the cancer cell selectivity of a very promising Ru(II)-based PDT photosensitizer encapsulated into polymeric nanoparticles with terminal biotin groups.

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 (λ_ex =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 (IC₅₀ ^light =2.1 μm, IC₅₀ ^dark =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.

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.

An Ultrasmall RuO2 Nanozyme Exhibiting Multienzyme-like Activity for the Prevention of Acute Kidney Injury

Oxidative stress induced by reactive oxygen species (ROS) is one of the major pathological mechanisms of acute kidney injury (AKI). Inorganic nanomaterial-mediated antioxidant therapy is considered a promising method for the prevention of AKI; however, currently available antioxidants for AKI exhibit limited clinical efficacy due to the glomerular filtration threshold (∼6 nm). To address this issue, we developed ultrasmall RuO₂ nanoparticles (RuO₂NPs) (average size ≈ 2 nm). The NPs show excellent antioxidant activity and low biological toxicity. In addition, they can pass through the glomerulus to be excreted. These properties in combination make the ultrasmall RuO₂NPs promising as a nanozyme for the prevention of AKI. The NP catalytic properties mimic the activity of catalase, peroxidase, superoxide dismutase, and glutathione peroxidase. The nanozyme can be efficiently and rapidly absorbed by human embryonic kidney cells while significantly reducing ROS-induced apoptosis by eliminating excess ROS. After intravenous injection, the ultrasmall RuO₂NPs significantly inhibit the development of AKI in mice. In vivo toxicity experiments demonstrate the biosafety of the NPs after long-term preventing. The multienzyme-like activity and biocompatibility of the ultrasmall RuO₂NPs makes them of great interest for applications in the fields of biomedicine and biocatalysis.