Self-assembly of a ruthenium-based cGAS-STING photoactivator for carrier-free cancer immunotherapy.

The cGAS (cyclic GMP-AMP synthase)-STING (stimulator of interferon genes) pathway promotes antitumor immune responses by sensing cytosolic DNA fragments leaked from nucleus and mitochondria. Herein, we designed a highly charged ruthenium photosensitizer (Ru1) with a ß-carboline alkaloid derivative as the ligand for photo-activating of the cGAS-STING pathway. Due to the formation of multiple non-covalent intermolecular interactions, Ru1 can self-assemble into carrier-free nanoparticles (NPs). By incorporating the triphenylphosphine substituents, Ru1 can target and photo-damage mitochondrial DNA (mtDNA) to cause the cytoplasmic DNA leakage to activate the cGAS-STING pathway. Finally, Ru1 NPs show potent antitumor effects and elicit intense immune responses in vivo. In conclusion, we report the first self-assembling mtDNA-targeted photosensitizer, which can effectively activate the cGAS-STING pathway, thus providing innovations for the design of new photo-immunotherapeutic agents.

Activation of the cGAS-STING pathway by a mitochondrial DNA-targeted emissive rhodium(iii) metallointercalator.

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon (STING) pathway is a key mediator of innate immunity involved in cancer development and treatment. The roles of mitochondrial DNA (mtDNA) in cancer immunotherapy have gradually emerged. Herein, we report a highly emissive rhodium(iii) complex (Rh-Mito) as the mtDNA intercalator. Rh-Mito can specifically bind to mtDNA to cause the cytoplasmic release of mtDNA fragments to activate the cGAS-STING pathway. Moreover, Rh-Mito activates the mitochondrial retrograde signaling by disturbing the key metabolites involved in epigenetic modifications, which alters the nuclear genome methylation landscape to influence the expression of genes related to immune signaling pathways. Finally, we demonstrate that ferritin-encapsulated Rh-Mito elicits potent anticancer activities and evokes intense immune responses in vivo by intravenous injection. Overall, we report for the first time that small molecules targeting mtDNA can activate the cGAS-STING pathway, which gives insights into the development of biomacromolecule-targeted immunotherapeutic agents.

Metals and inorganic molecules in regulating protein and nucleic acid phase separation.

The realization that liquid-liquid phase separation (LLPS) underlies the formation of membraneless compartments in cells has motivated efforts to modulate the condensation process of biomolecules. Increasing evidence shows that metals and inorganic molecules abundantly distributed in cells play important roles in the regulation of biomolecular condensation. Herein, we briefly reviewed the background of biomacromolecular phase separation and summarized the recent research progress on the roles of metals and inorganic molecules in regulating protein and nucleic acid phase separation in vitro and in cells.

Pt(IV)-Deferasirox Prodrug Combats DNA Damage Repair by Regulating RNA N6-Methyladenosine Methylation.

DNA damage repair is considered to be an important mechanism of cisplatin resistance, and the roles of iron homeostasis in action mechanisms of cisplatin have not been studied yet. Herein, a Pt(IV) prodrug (DFX-Pt) integrating cisplatin and the clinical oral iron-chelating agent deferasirox (DFX) is found to be highly active toward cisplatin-insensitive triple-negative breast cancer cells both in vitro and in vivo. RNA-sequencing shows that DFX-Pt can downregulate genes related to the double-strand break (DSB) damage pathway significantly. DFX-Pt can reduce cellular free iron, regulate the expression of the RNA demethylase, and elevate the levels of RNA N6-methyladenosine (m6A), which degrades the DSB-related genes in an m6A-dependent manner. In all, we first reveal the roles of RNA modification in mechanisms of combating DNA damage repair and show that the combination of iron homeostasis intervention may bring new treatment regimens for cisplatin resistance.

Self-Amplifying Iridium(III) Photosensitizer for Ferroptosis-Mediated Immunotherapy Against Transferrin Receptor-Overexpressing Cancer.

Photoimmunotherapy is attractive for cancer treatment due to its spatial controllability and sustained responses. This work presents a ferrocene-containing Ir(III) photosensitizer (IrFc1) that can bind with transferrin and be transported into triple-negative breast cancer (TNBC) cells via a transferrin receptor-mediated pathway. When the ferrocene in IrFc1 is oxidized by reactive oxygen species, its capability to photosensitize both type I (electron transfer) and type II (energy transfer) pathways is activated through a self-amplifying process. Upon irradiation, IrFc1 induces the generation of lipid oxidation to cause ferroptosis in TNBC cells, which promotes immunogenic cell death (ICD) under both normoxia and hypoxia. In vivo, IrFc1 treatment elicits a CD8+ T-cell response, which activates ICD in TNBC resulting in enhanced anticancer immunity. In summary, this work reports a small molecule-based photosensitizer with enhanced cancer immunotherapeutic properties by eliciting ferroptosis through a self-amplifying process.

Ru(II)-modified TiO2 nanoparticles for hypoxia-adaptive photo-immunotherapy of oral squamous cell carcinoma.

The alternations in the hypoxic and immune microenvironment are closely related to the therapeutic effect and prognosis of oral squamous cell carcinoma (OSCC). Herein, a new nanocomposite, TiO2@Ru@siRNA is constructed from a ruthenium-based photosensitizer (Ru) modified-TiO2 nanoparticles (NPs) loaded with siRNA of hypoxia-inducible factor-1α (HIF-1α). Under visible light irradiation, TiO2@Ru@siRNA can elicit both Type I and Type II photodynamic effects, which causes lysosomal damage, HIF-1α gene silencing, and OSCC cell elimination efficiently. As a consequence of hypoxia relief and pyroptosis induction, TiO2@Ru@siRNA reshapes the immune microenvironment by downregulation of key immunosuppressive factors, upregulation of immune cytokines, and activation of CD4+ and CD8+ T lymphocytes. Furthermore, patient-derived xenograft (PDX) and rat oral experimental carcinogenesis models prove that TiO2@Ru@siRNA-mediated photodynamic therapy significantly inhibits the tumor growth and progression, and markedly enhances cancer immunity. In all, this study presents an effective hypoxia-adaptive photo-immunotherapeutic nanosystem with great potential for OSCC prevention and treatment.

Real-time tracking of ER turnover during ERLAD by a rhenium complex via lifetime imaging.

Endoplasmic reticulum (ER) degradation by autophagy (ER-phagy) is a recently revealed selective autophagy pathway that plays important roles in organelle turnover and protein degradation, but the biological functions of ER-phagy are largely unknown. Here, we present an ER-targeting Re(I) tricarbonyl complex (Re-ERLAD) that can accumulate in the ER, induce ER-to-lysosome-associated degradation (ERLAD) upon visible light irradiation, and label ER buds and track their morphological alterations during ER-phagy. The emission of Re-ERLAD is sensitive to viscosity, which is a key parameter reflecting the amount of unfolded protein in the ER. Quantitative detection using two-photon fluorescence lifetime imaging microscopy shows that ER viscosity initially increases and then decreases during ERLAD, which reveals that ERLAD is a pathway for alleviating ER stress caused by unfolded proteins. In conclusion, our work presents the first specific photoinducer and tracker of ERLAD, which can be used in studying the regulatory mechanism and function of this process.

Simultaneous Photoactivation of cGAS-STING Pathway and Pyroptosis by Platinum(II) Triphenylamine Complexes for Cancer Immunotherapy.

Activation of the cyclic GMP-AMP synthase-stimulator of the interferon gene (cGAS-STING) pathway is a potent anticancer immunotherapeutic strategy, and the induction of pyroptosis is a feasible way to stimulate the anticancer immune responses. Herein, two PtII complexes (Pt1 and Pt2) were designed as photoactivators of the cGAS-STING pathway. In response to light irradiation, Pt1 and Pt2 could damage mitochondrial/nuclear DNA and the nuclear envelope to activate the cGAS-STING pathway, and concurrently induce pyroptosis in cancer cells, which evoked an intense anticancer immune response in vitro and in vivo. Overall, we present the first photoactivator of the cGAS-STING pathway, which may provide an innovative design strategy for anticancer immunotherapy.

Photodegradation of carbonic anhydrase IX via a binding-enhanced ruthenium-based photosensitizer.

Carbonic anhydrase IX (CAIX) is overexpressed in many cancer types. Herein, a CAIX targeting and binding-enhanced ruthenium-based photodegrader, Ru-dppz-CAi, is constructed by conjugating the photosensitizer with the inhibiting group via a rotatable moiety. The binding of Ru-dppz-CAi and CAIX leads to significant enhancement in the emission and photosensitizing properties. Ru-dppz-CAi can photodegrade CAIX both in vitro and in living cells, which significantly inhibits its catalytic activity. The protein photodegradation method may provide new strategies for the development of tools for protein functional studies.

Rising Interest in the Development of Metal Complexes in Cancer Immunotherapy.

Metal complexes have shown great potential in cancer immunotherapy. This review briefly introduces the basic concepts and strategies of cancer immunotherapy and summarizes the recent discoveries on the immune effects of traditional platinum-based anticancer compounds. In addition, we also outline the latest research progresses on metal complexes for cancer immunotherapy focusing on platinum, ruthenium, iridium, rhenium and copper complexes. Finally, the research perspectives and unsolved problems on the applications of metallo-anticancer agents in cancer immunotherapy are purposed.

A Nuclear-Targeted AIE Photosensitizer for Enzyme Inhibition and Photosensitization in Cancer Cell Ablation.

The nucleus is considered the ideal target for anti-tumor therapy because DNA and some enzymes in the nucleus are the main causes of cell canceration and malignant proliferation. However, nuclear target drugs with good biosafety and high efficiency in cancer treatment are rare. Herein, a nuclear-targeted material MeTPAE with aggregation-induced emission (AIE) characteristics was developed based on a triphenylamine structure skeleton. MeTPAE can not only interact with histone deacetylases (HDACs) to inhibit cell proliferation but also damage telomere and nucleic acids precisely through photodynamic treatment (PDT). The cocktail strategy of MeTPAE caused obvious cell cycle arrest and showed excellent PDT anti-tumor activity, which offered new opportunities for the effective treatment of malignant tumors.

Ferroptosis-Enhanced Cancer Immunity by a Ferrocene-Appended Iridium(III) Diphosphine Complex.

Ferroptosis is a programmed cell death pathway discovered in recent years, and ferroptosis-inducing agents have great potential as new antitumor candidates. Here, we report a IrIII complex (Ir1) containing a ferrocene-modified diphosphine ligand that localizes in lysosomes. Under the acidic environments of lysosomes, Ir1 can effectively catalyze Fenton-like reaction, produce hydroxyl radicals, induce lipid peroxidation, down-regulate glutathione peroxidase 4, and result in ferroptosis. RNA sequencing analysis shows that Ir1 can significantly affect pathways related to ferroptosis and cancer immunity. Accordingly, Ir1 can induce immunogenic cells death and suppress tumor growth in vitro, regulate T cell activity and immune microenvironments in vivo. In conclusion, we show the potential of small molecules with ferroptosis-inducing capabilities for effective cancer immunotherapy.

Inhibition of Aß peptide aggregation by ruthenium(II) polypyridyl complexes through copper chelation.

Alzheimer's disease (AD) is known as a complex multifactorial syndrome and both metal chelators and amyloid ß peptide (Aß) inhibitors show promise against AD. Herein, four small hybrid compounds have been designed and synthesized utilizing 8-hydroxyquinoline, pyridine or imidazole as chelators and benzimidazole as the recognition moiety for AD treatment. These conjugates can capture Cu2+ from Aß and become dimers upon Cu2+ coordination and show high efficiency for both Cu2+ elimination and Aß assembly inhibition. Besides, these designed complexes can inhibit the production of Aß-induced reactive oxygen species (ROS), protect mitochondria from damage, and improve the survival rate of neuron cells. Our work provides a new strategy to combine hydrophobic interaction and metal ion chelation to design amyloid inhibitors.

A Continuous Add-On Probe Reveals the Nonlinear Enlargement of Mitochondria in Light-Activated Oncosis.

Oncosis, depending on DNA damage and mitochondrial swelling, is an important approach for treating cancer and other diseases. However, little is known about the behavior of mitochondria during oncosis, due to the lack of probes for in situ visual illumination of the mitochondrial membrane and mtDNA. Herein, a mitochondrial lipid and mtDNA dual-labeled probe, MitoMN, and a continuous add-on assay, are designed to image the dynamic process of mitochondria in conditions that are unobservable with current mitochondrial probes. Meanwhile, the MitoMN can induce oncosis in a light-activated manner, which results in the enlargement of mitochondria and the death of cancer cells. Using structured illumination microscopy (SIM), MitoMN-stained mitochondria with a dual-color response reveals, for the first time, how swelled mitochondria interacts and fuses with each other for a nonlinear enlargement to accelerate oncosis into an irreversible stage. With this sign of irreversible oncosis revealed by MitoMN, oncosis can be segregated into three stages, including before oncosis, initial oncosis, and accelerated oncosis.

Induction and Monitoring of DNA Phase Separation in Living Cells by a Light-Switching Ruthenium Complex.

Phase separation of DNA is involved in chromatin packing for the regulation of gene transcription. Visualization and manipulation of DNA phase separation in living cells present great challenges. Herein, we present a Ru(II) complex (Ru1) with high DNA binding affinity and DNA "light-switch" behavior that can induce and monitor DNA phase separation both in vitro and in living cells. Molecular dynamics simulations indicate that the two phen-PPh3 ligands with positively charged lipophilic triphenylphosphine substituents and flexible long alkyl chains in Ru1 play essential roles in the formation of multivalent binding forces between DNA molecules to induce DNA phase separation. Importantly, the unique environmental sensitive emission property of Ru1 enables direct visualization of the dynamic process of DNA phase separation in living cells by two-photon phosphorescent lifetime imaging. Moreover, Ru1 can change the gene expression pattern by modulating chromatin accessibility as demonstrated by integrating RNA-sequencing and transposase-accessible chromatin with high-throughput sequencing. In all, we present here the first small-molecule-based tracer and modulator of DNA phase separation in living cells and elucidate its impact on the chromatin state and transcriptome.

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.

Mitochondria-targeted cyclometalated rhodium(III) complexes: synthesis, characterization and anticancer research.

Over the past few decades, the landscape of inorganic medicinal chemistry has been dominated by investigations on platinum or ruthenium, while the research based on other metal centers such as rhodium has been relatively insufficient. In this work, a series of cyclometalated rhodium(iii) complexes with imidazo[4,5-f][1,10]phenanthroline containing different aromatic rings were synthesized and characterized. Notably, all the complexes displayed stronger anticancer activity against various cancer cells compared with cisplatin. A mechanism study revealed that the rhodium complexes accumulated in the mitochondria, elevated the levels of mitochondrial reactive oxygen species (ROS) and released cytochrome c, indicating severe mitochondrial damage during the anticancer activity. Further studies illustrated that the rhodium complexes caused cell cycle arrest at the G2/M phase, upregulated the expression of p53 and reduced the ratio of B-cell lymphoma-2 (Bcl-2)/Bcl-2-associated x (Bax), which ultimately resulted in cellular apoptosis. Overall, through mitochondrial pathways, these Rh(iii) complexes could induce cellular apoptosis to a larger extent than cisplatin and should be paid close attention as promising chemotherapeutic drugs in anticancer research.

Quantitative tracking of endoplasmic reticulum viscosity during ferroptosis by an iridium complex via TPPLM.

Herein, we report a neutral iridium complex, [Ir(4-(2-pyridinyl)benzaldehyde)2(acetylacetone)] (Ir-ER), with viscosity-responsive phosphorescent emission intensity and lifetime. Quantitative measurement by two-photon phosphorescent lifetime imaging shows that the viscosity of ER increases significantly in the process of erastin-induced ferroptosis. Our work provides an effective strategy for quantitative measurement of the micro-environmental alternations of subcellular organelles during a specific cell death process.

A Polarity-Sensitive Ratiometric Fluorescence Probe for Monitoring Changes in Lipid Droplets and Nucleus during Ferroptosis.

Ferroptosis regulates cell death through reactive oxygen species (ROS)-associated lipid peroxide accumulation, which is expected to affect the structure and polarity of lipid droplets (LDs), but with no clear evidence. Herein, we report the first example of an LD/nucleus dual-targeted ratiometric fluorescent probe, CQPP, for monitoring polarity changes in the cellular microenvironment. Due to the donor-acceptor structure of CQPP, it offers ratiometric fluorescence emission and fluorescence lifetime signals that reflect polarity variations. Using nucleus imaging as a reference, CQPP was applied to report the increase in LD polarity and the homogenization of polarity between LDs and cytoplasm in the ferroptosis model. This LD/nucleus dual-targeted fluorescent probe shows the great potential of using fluorescence imaging to study ferroptosis and ferroptosis-related diseases.

Mitochondrial targeted rhodium(III) complexes: Synthesis, characterized and antitumor mechanism investigation.

Recently, rhodium complexes have received intensive attentions due to their tunable chemical and biological properties as well as attractive antitumor activity. In this work, two imidazole triphenylamino rhodium complexes [Rh(ppy)2L1]PF6 (Rh1) and [Rh(ppy)2L2]PF6 (Rh2) (ppy = 2-phenylpyridine, L1 = 4-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)-N,N-diphenylaniline, L2 = N-(4-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)phenyl)-4-methyl-N-(p-tolyl)aniline) have been synthesized and characterized. Both complexes display stronger anticancer activity against a various of cancer cells than cisplatin and they can effectively localize to mitochondria. Further mechanism studies show that Rh1 induce caspase-dependent apoptosis through mitochondrial damage, down-regulate the expression of B-cell lymphoma-2 (Bcl-2)/Bcl2-associated x (Bax) and reactive oxygen species (ROS) elevation. Our work provides a strategy for the construction of highly effective anticancer agents targeting mitochondrial metabolism through rational modification of rhodium complexes.