A Mitochondria-Targeted Photosensitizer Showing Improved Photodynamic Therapy Effects Under Hypoxia

Mitochondria-targeted and near-infrared phosphorescent Ir(III) complexes for specific detection of Hg2+ and photodynamic therapy

S: Mercury ions (Hg2+) are highly toxic and prone to bioaccumulation, showing a strong attraction to proteins and enzymes that contain sulfur. Even minute quantities of Hg2+ can lead to severe health issues. Given that mitochondria are a primary target organelle of Hg2+, it is essential to create a probe that can accurately detect Hg2+ within intracellular mitochondria. In this study, we developed two innovative Ir(III) complex probes that emit near-infrared light. The crystal structure of Ir2 was determined using X-ray techniques, which reveals that Ir2 contains a pyridine group capable of recognizing Hg2+ and targeting mitochondria, allowing for the precise identification of Hg2+ both in vitro and within the mitochondria of living cells. Additionally, these two novel near-infrared phosphorescent Ir(III) complexes demonstrate significant capabilities in producing ROS including singlet oxygen, ·O2- and ·OH, which renders them effective photosensitizers under visible light exposure for photodynamic therapy (PDT). This research offers a promising approach for detecting Hg2+ in vitro and in the mitochondrial microenvironment of living cells, which have some implications for the future development of pertinent transition metal complexes for mitochondria-targeted photodynamic therapy in cancer cells.

A Mitochondrion-Targeted NIR-II Modulator for Synergistic Ferroptosis-Immunotherapy

Immune checkpoint inhibitors (ICIs) have limited clinical efficacy against gastric cancer (GC) due to the nonimmunogenic tumor microenvironment. Therefore, inducing immunogenic cell death (ICD) to reprogram the immunogenic landscape is essential. This study develops HD-FA nanoparticles by encapsulating a novel mitochondrion-targeted NIR-II modulator, HD, within DSPE-PEG-FA. HD-FA exhibits superior spatiotemporal resolution, robust tumor accumulation, and minimal adverse effects. Upon 808 nm laser irradiation, HD-FA generates reactive oxygen species, leading to ferroptosis and oxidative stress damage in GC cells by inhibiting the SLC7A11/GSH/GPX4 axis. HD-FA triggers ICD, resulting in antitumor activity not only in primary tumors but also in distant tumors. Moreover, HD-FA promotes dendritic cell maturation, increases the effector-memory T-cell frequency, and reduces the presence of myeloid-derived suppressor cells, thereby fostering enhanced antitumor immunity. This study presents the first report of a novel NIR-II modulator for GC immunogenic synergistic therapy with ICIs, marking significant advancements in the fight against GC.

Emerging magic bullet: subcellular organelle-targeted cancer therapy

The therapeutic efficacy of anticancer drugs heavily relies on their concentration and retention at the corresponding target site. Hence, merely increasing the cellular concentration of drugs is insufficient to achieve satisfactory therapeutic outcomes, especially for the drugs that target specific intracellular sites. This necessitates the implementation of more precise targeting strategies to overcome the limitations posed by diffusion distribution and nonspecific interactions within cells. Consequently, subcellular organelle-targeted cancer therapy, characterized by its exceptional precision, have emerged as a promising approach to eradicate cancer cells through the specific disruption of subcellular organelles. Owing to several advantages including minimized dosage and side effect, optimized efficacy, and reversal of multidrug resistance, subcellular organelle-targeted therapies have garnered significant research interest in recent years. In this review, we comprehensively summarize the distribution of drug targets, targeted delivery strategies at various levels, and sophisticated strategies for targeting specific subcellular organelles. Additionally, we highlight the significance of subcellular targeting in cancer therapy and present essential considerations for its clinical translation.

X-ray Induced Persistent Type I Photodynamic Therapy with Enhanced Hypoxia Tolerance and Chemoradiotherapy

The hypoxic tumor microenvironment (TME), inadequate penetration depth of Vis/NIR light, and lack of sustaining reactive oxygen species (ROS) production capability of photosensitizers pose significant obstacles to the widespread clinic applications of photodynamic therapy (PDT). Herein, we developed a "persistent type I X-PDT" platform to simultaneously overcome these three limitations. Such a nanoplatform could generate efficient ROS (•OH and O2•-) under X-ray irradiation in both normoxic and hypoxic environments. The ROS production persists in tumor cells for more than 4 h, even after the X-ray source is removed. Notably, the persistent type I X-PDT does not increase the levels of hypoxia-inducible factor-1 alpha (HIF-1α) and vascular endothelial growth factor (VEGF) in tumor cells both in vitro and in vivo. Moreover, to further enhance the radiotherapy efficacy in hypoxic conditions, a Pt (IV) prodrug was also introduced, which can be reduced to cisplatin selectively in tumor cells, functioning not only as a chemodrug but also as a radiosensitizer.

A Mitochondria-Targeted Iridium(iii) Phosphorescent Probe for Selective Detection of Hypochlorite in Living Cells

Hypochlorous acid(HClO)/hypochlorite ion (ClO-) is a highly reactive oxygen species (ROS) that play a crucial role in various biological processes. In this paper, a "turn-on" phosphorescent probe (Ir-TPP) for detecting ClO- in mitochondria was designed and synthesized. In solution, Ir-TPP is minimal emission due to rapid isomerization of C=N-OH as an efficient non-radiative decay process. When Ir-TPP was reacted with ClO- to form an oxidized carboxylate product, there is a significant enhancement both in absorbance and emission intensity, resulting in approximately 25-fold increase in phosphorescence signal. Furthermore, the probe demonstrates high selectivity towards other anions and ROS. It also exhibits specific targeting ability towards mitochondria with a co-staining coefficient of 94 % compared to commercial dyes, enabling "turn-on" detection of ClO- within mitochondria.

Organelle-Specific Thiochromenocarbazole Imide Derivative as a Heavy-Atom-Free Type I Photosensitizer for Biomolecule-Triggered Image-Guided Photodynamic Therapy

Modern photodynamic therapy (PDT) demands next-generation photosensitizers (PSs) that overcome heavy-atom dependency and enhance efficacy beyond traditional, highly oxygen-dependent type II mechanisms. We introduce herein TCI-NH, as a thiochromenocarbazole imide derivative designed for type I photodynamic action. Upon light activation, TCI-NH efficiently favors superoxide (O2•-) and PS-centered radical formation instead of singlet oxygen (1O2) generation. Its high luminescence efficiency and selective localization in both the endoplasmic reticulum and mitochondria enable precise, image-guided PDT. Notably, interactions with biomolecules, such as serum albumin or DNA, enhance TCI-NH's emission by up to 40-fold and amplify radical generation by up to 5-fold. With negligible dark toxicity, this results in ∼120 nM photocytotoxicity along with an impressive phototherapeutic index exceeding 200. Real-time live-cell imaging revealed rapid, light-triggered cytotoxicity characterized by apoptotic body formation and extensive cellular damage. With its small size, heavy-atom-free structure, exceptional, organelle specificity, and therapeutic efficacy, TCI-NH sets a new benchmark for anticancer type I PDT.

A Small-Molecule Drug for the Self-Checking of Mitophagy

Mitophagy, particularly in the context of drugs that disrupt mitochondrial membrane potential (MMP), represents a critical focus in pharmacology. However, the discovery and evaluation of MMP-disrupting drugs are often hampered using commercially available marker molecules that target similar or identical zones. These markers can significantly interfere with, obscure, or amplify the functional effects of MMP-targeting drugs, frequently leading to clinical failures. In response to this challenge, we propose a "one-two punch" drug design strategy that integrates both target-zone drug functionality and non-target zone biological reporting within a single small-molecule drug. We have developed a novel proof-of-concept mitophagy self-check drug (MitoSC) that exhibits dual-color and dual-localization properties. The functional component of this system is a variable MitoSC that disrupts mitochondrial membrane potential (MMP) homeostasis, thereby inducing mitophagy. Upon activation, this component transforms into a blue-fluorescent monomer (MitoSC-fun) specifically within the mitochondrial target zone. Concurrently, the biological reporting component is represented by a red-fluorescent monomer (MitoSC-rep) that localizes to lysosomes, the non-target zone. As mitophagy progresses, the fluorescent signals from MitoSC-rep (lysosomes) and MitoSC-fun (mitochondria) converge, enabling real-time monitoring of the mitophagic process. This strategy combines potent drug functionality with robust biological reporting, thereby minimizing interference and eliminating the complexities associated with external detection. Our findings underscore the potential of a single-molecule drug to exert target-zone specific actions while simultaneously providing non-target zone self-checking, offering a new perspective for drug design.

Ultra-pH-sensitive nanoplatform for precise tumor therapy

The emergence of precision cancer treatment has triggered a paradigm shift in the field of oncology, facilitating the implementation of more effective and personalized therapeutic approaches that enhance patient outcomes. The pH of the tumor microenvironment (TME) plays a pivotal role in both the initiation and progression of cancer, thus emerging as a promising focal point for precision cancer treatment. By specifically targeting the acidic conditions inherent to the tumor microenvironment, innovative therapeutic interventions have been proposed, exhibiting significant potential in augmenting treatment efficacy and ameliorating patient prognosis. The concept of ultra-pH-sensitive (UPS) nanoplatform was proposed several years ago, demonstrating exceptional pH sensitivity and an adjustable pH transition point. Subsequently, diverse UPS nanoplatforms have been actively explored for biomedical applications, enabling the loading of fluorophores, therapeutic drugs, and photosensitizers. This review aims to elucidate the design strategy and response mechanism of the UPS nanoplatform, with a specific emphasis on its applications in surgical therapy, immunotherapy, drug delivery, photodynamic therapy, and photothermal therapy. The potential and challenges of translating in the clinic on UPS nanoplatforms are finally explored. Thanks to its responsive and easily modifiable nature, the integration of multiple functional units within a UPS nanoplatform holds great promise for future advancements in tumor precision theranositcs.

Exploring the role and application of mitochondria in radiation therapy

Mitochondria are pivotal in cellular energy metabolism, the oxidative stress response and apoptosis. Recent research has focused on harnessing their functions to enhance the efficacy of radiation therapy (RT). This review focuses on the critical functions and applications of mitochondria in radiation therapy, including the targeting of mitochondrial metabolism and the modulation of mitochondria-mediated cell death and immune responses. While these strategies have demonstrated considerable potential in preclinical studies to improve radiotherapy outcomes, challenges remain, such as optimizing drug delivery systems, ensuring safety and overcoming resistance to therapy.

Advances in the Design of Photoactivatable Metallodrugs: Excited State Metallomics

Photoactivatable metal complexes offer the prospect of novel drugs with low side effects and new mechanisms of action to combat resistance to current therapy. We highlight recent progress in the design of platinum, ruthenium, iridium, gold and other transition metal complexes, especially for applications as anticancer and anti-infective agents. In particular, understanding excited state chemistry related to identification of the bioactive species (excited state metallomics/pharmacophores) is important. Photoactivatable metallodrugs are classified here as photocatalysts, photorelease agents and ligand-activated agents. Their activation wavelengths, cellular mechanisms of action, experimental and theoretical metallomics of excited states and photoproducts are discussed to explore new strategies for the design and investigation of photoactivatable metallodrugs. These photoactivatable metallodrugs have potential in clinical applications of Photodynamic Therapy (PDT), Photoactivated Chemotherapy (PACT) and Photothermal Therapy (PTT).

Triplet Electron Exchange in Carbon Nanodots-assisted Long-persistent near-infrared Chemiluminescence for Oncology Synergistic Imaging and Therapy

In classical photodynamic therapy, tumor cells are killed by the cytotoxic species via type-I/II photochemical reactions, seriously limited by the external photoexcitation and hypoxia. Herein, the electron transfer mechanism between fluorophores and peroxalate-H2O2 reaction is investigated and the singlet/triplet electron exchange is utilized to achieve long-persistent chemiluminescence imaging and synergistic type-I/II/III photodynamic therapy. As a proof-of-concept, the photosensitizers of carbon nanodots (CDs)-loaded chlorin e6 (CDs-Ce6) are designed and integrated with the peroxalate molecules, and the as-prepare polymer carbon nanodots (p-CDs) exhibit novel tumor microenvironment (TME)-responsive long-persistent near-infrared CL and photochemical reactions, evoking the in vivo imaging and synergistic dynamic therapy in tumor tissue. Mechanistically, the excess reactive oxygen species in TME can trigger the chemically initiated singlet/triplet electron exchange between the hydrophobic CDs-Ce6 and peroxalate-derived 1,2-dioxetanes and thus the excess excited singlet/triplet electron of the CDs-Ce6 can ensure the long-persistent near-infrared CL, type I/II photochemical production of hydroxyl radicals, superoxide radical and singlet oxygen, and type III photochemical damage of maladjusted biomacromolecules, enabling the long-persistent near-infrared biological imaging and enhanced cancer therapy. These results shed a new sight into the energy transfer mechanism in chemiluminescence and pave a new sight into the architecture of multifunctional theragnostic nanoplatforms.

Triphenylphosphine-modified cyclometalated iridiumIII complexes as mitochondria-targeting anticancer agents with enhanced selectivity

This study presents the development and evaluation of triphenylphosphine-modified cyclometalated iridiumIII complexes as selective anticancer agents targeting mitochondria. By leveraging the mitochondrial localization capability of the triphenylphosphine group, these complexes displayed promising cytotoxicity in the micromolar range (3.12-7.24 μM) against A549 and HeLa cancer cells, these complexes exhibit significantly higher activity compared to their unmodified counterparts lacking the triphenylphosphine moiety. Moreover, they demonstrate improved specificity for cancer cells over normal cells, achieving selectivity index in the range of 5.46-14.83. Mechanistic studies confirmed that these complexes selectively target mitochondria rather than DNA, as shown by confocal microscopy and flow cytometry, where they accumulate to induce mitochondrial dysfunction. This disruption leads to mitochondrial membrane depolarization (MMP), elevated reactive oxygen species (ROS) levels, and activation of intrinsic apoptosis pathways. Furthermore, the complexes induce cell cycle arrest at the G2/M phase and suppress the migration of A549 cells.

Dual-Emissive Iridium(III) Complex with Aggregation-Induced Emission: Mechanistic Insights into Electron Transfer for Enhanced Hypoxia Detection in 3D Tumor Models

Accurate oxygen detection and measurement of its concentration is vital in biological and industrial applications, necessitating highly sensitive and reliable sensors. Optical sensors, valued for their real-time monitoring, nondestructive analysis, and exceptional sensitivity, are particularly suited for precise oxygen measurements. Here, we report a dual-emissive iridium(III) complex, IrNPh2, featuring "aggregation-induced emission" (AIE) properties and used for sensitive oxygen sensing. IrNPh2 exhibits dual emissions at 450 and 515 nm, with 515 nm triplet-state emission demonstrating remarkable oxygen sensitivity due to its long-lived excited state (12.12 μs) and high quantum yield (68%). Stern-Volmer analysis reveals a notable quenching constant (Ksv = 12.44%-1) and an ultralow detection limit of 0.0397%, emphasizing its superior performance. The oxygen quenching mechanism is driven by electron transfer (ET), supported by computational studies showing the lowest-unoccupied molecular orbital (LUMO) alignment of IrNPh2 with the πg* orbitals of triplet oxygen, leading to superoxide radical (O2•-) formation. Electron paramagnetic resonance (EPR) studies further confirm this pathway. Biological evaluations using a three-dimensional (3D) U87-MG glioma spheroid model highlight the ability of IrNPh2 to detect hypoxic regions, with significant fluorescence enhancement under hypoxia and minimal cytotoxicity (>80% viability at 100 μM). With high sensitivity, low detection limits, and biocompatibility, IrNPh2 emerges as a promising candidate for oxygen sensing in environmental and biomedical applications, especially tumor hypoxia detection.

Targeting tumor microenvironment with photodynamic nanomedicine

Photodynamic therapy (PDT) is approved for the treatment of certain cancers and precancer lesions. While early Photosensitizers (PS) have found their way to the clinic, research in the last two decades has led to the development of third-generation PS, including photodynamic nanomedicine for improved tumor delivery and minimal systemic or phototoxicity. In terms of nanoparticle design for PDT, we are witnessing a shift from passive to active delivery for improved outcomes with reduced PS dosage. Tumor microenvironment (TME) comprises of a complex and dynamic landscape with myriad potential targets for photodynamic nanocarriers that are surface-modified with ligands. Herein, we review ways to improvise PDT by actively targeting nanoparticles (NPs) to intracellular organelles such as mitochondria or lysosomes and so forth, overcoming the limitations caused by PDT-induced hypoxia, disrupting the blood vascular networks in tumor tissues-vascular targeted PDT (VTP) and targeting immune cells for photoimmunotherapy. We propose that a synergistic outlook will help to address challenges such as deep-seated tumors, metastasis, or relapse and would lead to robust PDT response in patients.

Valence-Transforming O2-Depleting Nano-Assembly Enable In Situ Tumor Depositional Embolization

Abnormal metabolism and blood supply/O2 imbalance in tumor cells affect drug transport delivery and increase the difficulty of tumor treatment. Controlling tumor growth by inhibiting tumor cell metabolism and regulating progressive embolization in the tumor region provides an innovative basis for constructing tumor therapeutic models. A highly biocompatible and efficient O2-depleting agent has been investigated to enable in situ precipitation and embolization within the tumor microenvironment. In situ deformation embolizer, Fe-GA@CaCO3 nano-assembly (GA: gallic acid), can convert into the large granular size embolization components of Fe(III) precipitates and affluent Ca2+ within the tumor microenvironment. In situ progressive O2 depletion produces Fe(III) precipitates that embolize tumor regions, isolating O2 and nutrients by blocking supply. Meanwhile, affluent Ca2+ acts on the intracellular, causing mitochondrial dysfunction through calcium overload and contributing to irreversible tumor cell damage. Both internal and external routes work synergistically to produce precise functional inhibition of tumors from the inside out, simultaneously responding to both intracellular and the corresponding tumor regions, providing an innovative solution for anti-tumor therapy.

Recent progress of porphyrin metal-organic frameworks for combined photodynamic therapy and hypoxia-activated chemotherapy

Nanoscale metal-organic frameworks integrated with porphyrins (Por-nMOFs) have emerged as efficient nanoplatforms for photodynamic therapy (PDT), which relies on the conversion of molecular oxygen into cytotoxic singlet oxygen. However, the hypoxic microenvironment within tumors significantly limits the efficacy of PDT. To address this challenge, researchers have explored various strategies to either alter or exploit the hypoxic conditions in tumors. One such strategy involves leveraging the porous structure of Por-nMOFs to load hypoxia-activated prodrugs (HAPs) like tirapazamine (TPZ), thereby utilizing the tumor's intrinsic hypoxic environment to trigger a chemotherapeutic effect that synergizes with PDT. Advances in nanoscience have enabled the development of porphyrin-based nMOFs capable of simultaneously loading both porphyrin photosensitizers and TPZ, ensuring effective release within cancer cells under high-phosphate conditions. The subsequent activation of co-loaded TPZ, by the tumor's own hypoxic microenvironment, and that created during PDT, facilitates a combined PDT and chemotherapy approach. This method not only enhances the suppression of cancer cell proliferation but also improves control over tumor metastasis while mitigating the negative impact of hypoxia on singular Por-nMOFs in PDT. This review summarizes recent advances in Por-nMOFs research, focusing on the design strategies for enhancing water dispersibility, circulatory stability, and targeting specificity through post-synthetic modifications. Additionally, this review highlights the bioapplication of Por-nMOFs by integrating TPZ chemotherapy and other therapeutic modalities to combat hypoxic and metastatic malignancies. We anticipate that this review will inspire further research into Por-nMOFs and advance their application in biomedicine.

Multimodal Photodynamic Therapy by Inhibiting the Nrf2/ARE Signaling Pathway in Tumors

Photodynamic therapy (PDT) has been widely used in the clinical therapy of various tumors, especially superficial tumors. However, the tumor microenvironment presents hypoxia, as well as the inherent antioxidant system (e.g., Nrf2) of tumor cells limits the therapeutic outcomes. Herein, a cascade-responsive "oxidative stress amplifier" (named EZ@TD) is designed by encapsulating manganese-doped carbon dots acting as a photosensitizer and catalase (CAT)-like nanozyme within pH-sensitive ZIF-8 and Zn2+-activated DNAzyme for relieving hypoxia and efficient Nrf2 gene disruption to enhance PDT. It is demonstrated that EZ@TD synergistically inhibited tumor growth and activated the antitumor immune response by inhibiting the Nrf2/ARE signaling pathway in tumors. We provide a new paradigm for amplifying intracellular oxidative stress by interfering with various signaling pathways.

Leveraging the Photofunctions of Transition Metal Complexes for the Design of Innovative Phototherapeutics

Despite the advent of various medical interventions for cancer treatment, the disease continues to pose a formidable global health challenge, necessitating the development of new therapeutic approaches for more effective treatment outcomes. Photodynamic therapy (PDT), which utilizes light to activate a photosensitizer to produce cytotoxic reactive oxygen species (ROS) for eradicating cancer cells, has emerged as a promising approach for cancer treatment due to its high spatiotemporal precision and minimal invasiveness. However, the widespread clinical use of PDT faces several challenges, including the inefficient production of ROS in the hypoxic tumor microenvironment, the limited penetration depth of light in biological tissues, and the inadequate accumulation of photosensitizers at the tumor site. Over the past decade, there has been increasing interest in the utilization of photofunctional transition metal complexes as photosensitizers for PDT applications due to their intriguing photophysical and photochemical properties. This review provides an overview of the current design strategies used in the development of transition metal complexes as innovative phototherapeutics, aiming to address the limitations associated with PDT and achieve more effective treatment outcomes. The current challenges and future perspectives on the clinical translation of transition metal complexes are also discussed.

Iridium(III)-Incorporating Self-Healing Polysiloxanes as Materials for Light-Emitting Oxygen Sensors

Polymer-metal complexes (PMCs) based on poly(2,2'-bipyridine-4,4'-dicarboxamide-co-polydimethylsiloxanes) with cyclometalated di(2-phenylpyridinato-C2,N')iridium(III) fragments and cross-linked by Zn2+ (Zn[Ir]-BipyPDMSs) or Ir3+ (Ir[Ir]-BipyPDMSs) represent flexible, stretchable, phosphorescent, and self-healing molecular oxygen sensors. PMCs provide strong phosphorescence at λem = 595-605 nm. Zn[Ir]-BipyPDMS with PDMS chain length of Mn = 5000 has the highest quantum yield of 9.3% and is a molecular oxygen sensor at different O2 concentrations (0-100 vol%) compared to Ir[Ir]-BipyPDMSs. A Stern-Volmer constant is determined for Zn[Ir]-BipyPDMS as KSV = 0.014%-1, which is similar to the reported oxygen-sensitive iridium(III) complexes. All synthesized PMCs exhibit high elongation at break (up to 1100%) and self-healing efficiency (up to 99%).

Dissecting Exciton Dynamics in pH-Activatable Long-Wavelength Photosensitizers for Traceable Photodynamic Therapy

Tumor-specific activatable long-wavelength (LW) photosensitizers (PSs) show promise in overcoming the limitations of traditional photodynamic therapy (PDT), such as systemic phototoxicity and shallow tissue penetration. However, their insufficient LW light absorption and low singlet oxygen quantum yield (Φ 1O2) usually require high laser power density to produce thermal energy and synergistically enhance PDT. The strong photothermal radiation causing acute pain significantly reduces patient compliance and hinders the broader clinical application of LW PDT. Through the exciton dynamics dissection strategy, we have developed a series of pH-activatable cyanine-based LW PSs (LET-R, R = H, Cl, Br, I), among which the activated LET-I exhibits strong light absorption at 808 nm and a remarkable 3.2-fold enhancement in Φ 1O2 compared to indocyanine green. Transient spectroscopic analysis and theoretical calculations confirmed its significantly promoted intersystem crossing and simultaneously enhanced LW fluorescence emission characteristics. These features enable the activatable fluorescence and photoacoustic dual-modal imaging-escorted complete photodynamic eradication of tumors by the folic acid (FA)-modified LET-I probe (LET-I-FA), under the ultralow 808 nm laser power density (0.2 W cm-2) for irradiation, without the need for photothermal energy synergy. This research presents a novel strategy of dissecting exciton dynamics to screen activatable LW PSs for traceable PDT.

Targeting sub-cellular organelles for boosting precision photodynamic therapy

Among various cancer treatment methods, photodynamic therapy has received significant attention due to its non-invasiveness and high efficiency in inhibiting tumour growth. Recently, specific organelle targeting photosensitizers have received increasing interest due to their precise accumulation and ability to trigger organelle-mediated cell death signalling pathways, which greatly reduces the drug dosage, minimizes toxicity, avoids multidrug resistance, and prevents recurrence. In this review, recent advances and representative photosensitizers used in targeted photodynamic therapy on organelles, specifically including the endoplasmic reticulum, Golgi apparatus, mitochondria, nucleus, and lysosomes, have been comprehensively reviewed with a focus on organelle structure and organelle-mediated cell death signalling pathways. Furthermore, a perspective on future research and potential challenges in precision photodynamic therapy has been presented at the end.

Iridium(III) complexes as novel theranostic small molecules for medical diagnostics, precise imaging at a single cell level and targeted anticancer therapy

Medical applications of iridium (III) complexes include their use as state-of-the-art theranostic agents - molecules that combine therapeutic and diagnostic functions into a single entity. These complexes offer a promising avenue in medical diagnostics, precision imaging at single-cell resolution and targeted anticancer therapy due to their unique properties. In this review we report a short summary of their application in medical diagnostics, imaging at single-cell level and targeted anticancer therapy. The exceptional photophysical properties of Iridium (III) complexes, including their brightness and photostability, make them excellent candidates for bioimaging. They can be used to image cellular processes and the microenvironment within single cells with unprecedented clarity, aiding in the understanding of disease mechanisms at the molecular level. Moreover the iridium (III) complexes can be designed to selectively target cancer cells,. Upon targeting, these complexes can act as photosensitizers for photodynamic therapy (PDT), generating reactive oxygen species (ROS) upon light activation to induce cell death. The integration of diagnostic and therapeutic capabilities in Iridium (III) complexes offers the potential for a holistic approach to cancer treatment, enabling not only the precise eradication of cancer cells but also the real-time monitoring of treatment efficacy and disease progression. This aligns with the goals of personalized medicine, offering hope for more effective and less invasive cancer treatment strategies.

Metal-polyphenol self-assembled nanodots for NIR-II fluorescence imaging-guided chemodynamic/photodynamic therapy-amplified ferroptosis

The effectiveness of tumor treatment using reactive oxygen species as the primary therapeutic medium is hindered by limitations of tumor microenvironment (TME), such as intrinsic hypoxia in photodynamic therapy (PDT) and overproduction of reducing glutathione (GSH) in chemodynamic therapy (CDT). Herein, we fabricate metal-polyphenol self-assembled nanodots (Fe@BDP NDs) guided by second near-infrared (NIR-II) fluorescence imaging. The Fe@BDP NDs are designed for synergistic combination of type-I PDT and CDT-amplified ferroptosis. In a mildly acidic TME, Fe@BDP NDs demonstrate great Fenton activity, leading to the generation of highly toxic hydroxyl radicals from overproduced hydrogen peroxide in tumor cells. Furthermore, Fe@BDP NDs show favorable efficacy in type-I PDT, even in tolerating tumor hypoxia, generating active superoxide anion upon exposure to 808 nm laser irradiation. The significant efficiency in reactive oxygen species (ROS) products results in the oxidation of sensitive polyunsaturated fatty acids, accelerating lethal lipid peroxidation (LPO) bioprocess. Additionally, Fe@BDP NDs illustrate an outstanding capability for GSH depletion, causing the inactivation of glutathione peroxidase 4 and further promoting lethal LPO. The synergistic type-I photodynamic and chemodynamic cytotoxicity effectively trigger irreversible ferroptosis by disrupting the intracellular redox homeostasis. Moreover, Fe@BDP NDs demonstrate charming NIR-II fluorescence imaging capability and effectively accumulated at the tumor site, visualizing the distribution of Fe@BDP NDs and the treatment process. The chemo/photo-dynamic-amplified ferroptotic efficacy of Fe@BDP NDs was evidenced both in vitro and in vivo. This study presents a compelling approach to intensify ferroptosis via visualized CDT and PDT. STATEMENT OF SIGNIFICANCE: In this study, we detailed the fabrication of metal-polyphenol self-assembled nanodots (Fe@BDP NDs) guided by second near-infrared (NIR-II) fluorescence imaging, aiming to intensify ferroptosis via the synergistic combination of type-I PDT and CDT. In a mildly acidic TME, Fe@BDP NDs exhibited significant Fenton activity, resulting in the generation of highly toxic •OH from overproduced H2O2 in tumor cells. Fe@BDP NDs possessed a remarkable capability for GSH depletion, resulting in the inactivation of glutathione peroxidase 4 (GPX4) and further accelerating lethal LPO. This study presented a compelling approach to intensify ferroptosis via visualized CDT and PDT.

Pt(II) Bis(pyrrole-imine) complexes: Luminescent probes and cytotoxicity in MCF-7 cells†

Four Pt(II) bis(pyrrole-imine) Schiff base chelates (1-4) were synthesised by previously reported methods, through a condensation reaction, and the novel crystal structure of 2,2'-{propane-1,3-diylbis[nitrilo(E)methylylidene]}bis(pyrrol-1-ido)platinum(II) (1) was obtained. Pt(II) complexes 1-4 exhibited phosphorescence, with increased luminescence in anaerobic solvents or when bound to human serum albumin (HSA). One of the complexes shows a 15.6-fold increase in quantum yield when bound to HSA and could be used to detect HSA concentrations as low as 5 nM. Pt(II) complexes 1-3 was investigated as potential theranostic agents in MCF-7 breast cancer cells, but only complex 3 exhibited cytotoxicity when irradiated with UV light (λ355nmExcitation). Interestingly, the cytotoxicity of complex 1 was unresponsive to UV light irradiation. This indicates that only complex 3 can be considered a potential photosensitising agent.

Heavy-atom-free π-twisted photosensitizers for fluorescence bioimaging and photodynamic therapy

As the field of preclinical research on photosensitizers (PSs) for anticancer photodynamic therapy (PDT) continues to expand, a focused effort is underway to develop agents with innovative molecular structures that offer enhanced targeting, selectivity, activation, and imaging capabilities. In this context, we introduce two new heavy-atom-free PSs, DBXI and DBAI, characterized by a twisted π-conjugation framework. This innovative approach enhances the spin-orbit coupling (SOC) between the singlet excited state (S1) and the triplet state (T1), resulting in improved and efficient intersystem crossing (ISC). Both PSs are highly effective in producing reactive oxygen species (ROS), including singlet oxygen and/or superoxide species. Additionally, they also demonstrate remarkably strong fluorescence emission. Indeed, in addition to providing exceptional photocytotoxicity, this emissive feature, generally lacking in other reported structures, allows for the precise monitoring of the PSs' distribution within specific cellular organelles even at nanomolar concentrations. These findings underscore the dual functionality of these PSs, serving as both fluorescent imaging probes and light-activated therapeutic agents, emphasizing their potential as versatile and multifunctional tools in the field of PDT.

Optimization of a Modular Nanotransporter Design for Targeted Intracellular Delivery of Photosensitizer

Modular nanotransporters (MNTs) are drug delivery systems for targeted cancer treatment. As MNTs are composed of several modules, they offer the advantage of high specificity and biocompatibility in delivering drugs to the target compartment of cancer cells. The large carrier module brings together functioning MNT modules and serves as a platform for drug attachment. The development of smaller-sized MNTs via truncation of the carrier module appears advantageous in facilitating tissue penetration. In this study, two new MNTs with a truncated carrier module containing either an N-terminal (MNTN) or a C-terminal (MNTC) part were developed by genetic engineering. Both new MNTs demonstrated a high affinity for target receptors, as revealed by fluorescent-labeled ligand-competitive binding. The liposome leakage assay proved the endosomolytic activity of MNTs. Binding to the importin heterodimer of each truncated MNT was revealed by a thermophoresis assay, while only MNTN possessed binding to Keap1. Finally, the photodynamic efficacy of the photosensitizer attached to MNTN was significantly higher than when attached to either MNTC or the original MNTs. Thus, this work reveals that MNT's carrier module can be truncated without losing MNT functionality, favoring the N-terminal part of the carrier module due to its ability to bind Keap1.

Glutathione-Sensitive Photosensitizer-Drug Conjugates Target the Mitochondria to Overcome Multi-Drug Resistance in Cancer

Multi-drug resistance (MDR) is a major cause of cancer therapy failure. Photodynamic therapy (PDT) is a promising modality that can circumvent MDR and synergize with chemotherapies, based on the generation of reactive oxygen species (ROS) by photosensitizers. However, overproduction of glutathione (GSH) by cancer cells scavenges ROS and restricts the efficacy of PDT. Additionally, side effects on normal tissues are unavoidable after PDT treatment. Here, to develop organic systems that deliver effective anticancer PDT and chemotherapy simultaneously with very little side effects, three GSH-sensitive photosensitizer-drug conjugates (CyR-SS-L) are designed and synthesized. CyR-SS-L localized in the mitochondria then is cleaved into CyR-SG and SG-L parts by reacting with and consuming high levels of intracellular GSH. Notably, CyR-SG generates high levels of ROS in tumor cells instead of normal cells and be exploited for PDT and the SG-L part is used for chemotherapy. CyR-SS-L inhibits better MDR cancer tumor inhibitory activity than indocyanine green, a photosensitizer (PS) used for PDT in clinical applications. The results appear to be the first to show that CyR-SS-L may be used as an alternative PDT agent to be more effective against MDR cancers without obvious damaging normal cells by the combination of PDT, GSH depletion, and chemotherapy.

Constructing Heavy-Atom-Free Photosensitizers for Hypoxic Tumor Phototherapy Based on Donor-Excited Photoinduced Electron-Transfer-Driven Type-I and Type-II Mechanisms

The spin-orbit charge transfer intersystem crossing (SOCT-ISC) photophysical process has shown great potential for constructing heavy-atom-free photosensitizers (PSs) for photodynamic therapy (PDT) of tumors. However, for almost all such PSs reported to date, the SOCT-ISC is driven by the acceptor-excited photoinduced electron transfer (a-PeT). In this work, for the first time the donor-excited photoinduced electron transfer (d-PeT)-driven SOCT-ISC mechanism is utilized to construct the heavy-atom-free PSs for PDT of tumors by directly installing the electron-deficient N-alkylquinolinium unit (as an electron acceptor) into the meso-position of the near-infrared (NIR) distyryl Bodipy chromophore (as an electron donor). In the less polar environment, the PSs exist as the monomer and promote the production of singlet oxygen (1O2) (Type-II) relying on the d-PeT-driven population of the triplet excited state via SOCT-ISC, whereas in the aqueous environment, they exist as nanoaggregates and induce the generation of superoxides (O2-•) and hydroxyl radicals (HO•) (Type-I) via the d-PeT-driven formation of the delocalized charge-separated state. The PSs could rapidly be internalized into cancer cells and induce the simultaneous production of intracellular 1O2, O2-•, and HO• upon NIR light irradiation, endowing the PSs with superb photocytotoxicity with IC50 values up to submicromolar levels whether under normoxia or under hypoxia. Based on the PSs platform, a tumor-targetable PS is developed, and its abilities in killing cancer cells and in ablating tumors without damage to normal cells/tissues under NIR light irradiation are verified in vitro and in vivo. The study expands the design scope of PSs by introducing the d-PeT conception, thus being highly valuable for achieving novel PSs in the realm of tumor PDT.

Lysosome-targeted cyclometalated Ir(III) complexes as photosensitizers/photoredox catalysts for cancer therapy

A novel lysosome-targeted photosensitizer/photoredox catalyst based on cyclometalated Ir(III) complex IrL has been designed and synthesized, which exhibited excellent phosphorescence properties and the ability to generate single oxygen (1O2) and photocatalytically oxidize 1,4-dihydronicotinamide adenine dinucleotide (NADH) under light irradiation. Most importantly, the aforementioned activities are significantly enhanced due to protonation under acidic conditions, which makes them highly attractive in light-activated tumor therapy, especially for acidic lysosomes and tumor microenvironments. The photocytotoxicity of IrL and the mechanism of cell death have been investigated. Additionally, the tumor-killing ability of IrL under light irradiation was evaluated using a 4T1 tumor-bearing mouse model. This work provides a strategy for the development of lysosome-targeted photosensitizers/photoredox catalysts to overcome hypoxic tumors.

Synthesis, characterization and irradiation enhances anticancer activity of liposome-loaded iridium(III) complexes

Herein, we synthesized and characterized two novel iridium (III) complexes: [Ir(bzq)2(PPD)](PF6) (4a, with bzq = deprotonated benzo[h]quinoline and PPD = pteridino[6,7-f][1,10]phenanthroline-11,13-diamine) and [Ir(piq)2(PPD)](PF6) (4b, with piq = deprotonated 1-phenylisoquinoline). The anticancer efficacy of these complexes, 4a and 4b, was investigated using 3-(4,5-dimethylthiazole)-2,5-diphenltetraazolium bromide (MTT). Complex 4a exhibited no cytotoxic activity, while 4b demonstrated moderate efficacy against SGC-7901, A549, and HepG2 cancer cells. To enhance their anticancer potential, we explored two strategies: (I) light irradiation and (II) encapsulation of the complexes in liposomes, resulting in the formation of 4alip and 4blip. Both strategies significantly increased the ability of 4a, 4b to kill cancer cells. The cellular studies indicated that both the free complexes 4a, 4b and their liposomal forms 4alip and 4blip effectively inhibited cell proliferation. The cell cycle arrest analysis uncovered 4alip and 4blip arresting cell growth in the S period. Additionally, we investigated apoptosis and ferroptosis pathways, observing an increase in malondialdehyde (MDA) levels, a reduction of glutathione (GSH), a down-regulation of GPX4 (glutathione peroxidase) expression, and lipid peroxidation. The effects on mitochondrial membrane potential and intracellular Ca2+ concentrations were also examined, revealing that both light-activated and liposomal forms of 4alip and 4blip caused a decline in mitochondrial membrane potential and an enhancement in intracellular Ca2+ levels. In conclusion, these complexes and them encapsulated liposomes induce cell death through apoptosis and ferroptosis.

Anticancer activity of 8-hydroxyquinoline-triphenylphosphine rhodium(III) complexes targeting mitophagy pathways

Metallodrugs exhibiting distinct mechanisms of action compared with cisplatin hold promise for overcoming cisplatin resistance and improving the efficacy of anticancer drugs. In this study, a new series of rhodium (Rh)(III) complexes containing tris(triphenylphosphine)rhodium(I) chloride [(TPP)3RhCl] (TPP = triphenylphosphine, TPP=O = triphenylphosphine oxide) and 8-hydroxyquinoline derivatives (H-XR1-H-XR4), namely [Rh(XR1)2(TPP)Cl]·(TPP=O) (Yulin Normal University-1a [YNU-1a]), [Rh(XR2)2(TPP)Cl] (YNU-1b), [Rh(XR3)2(TPP)Cl] (YNU-1c), and [Rh(XR4)2(TPP)Cl] (YNU-1d), was synthesized and characterized via X-ray diffraction, mass spectrometry and IR. The cytotoxicity of the compounds YNU-1a-YNU-1d in Hep-G2 and HCC1806 human cancer cell lines and normal HL-7702 cell line was evaluated. YNU-1c exhibited cytotoxicity and selectivity in HCC1806 cells (IC50 = 0.13 ± 0.06 μM, selectivity factor (SF) = 384.6). The compounds YNU-1b and YNU-1c, which were selected for mechanistic studies, induced the activation of apoptotic pathways and mitophagy. In addition, these compounds released cytochrome c, cleaved caspase-3/pro-caspase-3 and downregulated the levels of mitochondrial respiratory chain complexes I/IV (M1 and M4) and ATP. The compound YNU-1c, which was selected for in vivo experiments, exhibited tumor growth inhibition (58.9 %). Importantly, hematoxylin and eosin staining and TUNEL revealed that HCC1806 tumor tissues exhibited significant apoptotic characteristics. YNU-1a-YNU-1d compounds are promising drug candidates that can be used to overcome cisplatin resistance.

Enhancing antitumor efficacy of NIR-I region zinc phthalocyanine@upconversion nanoparticle through lysosomal escape and mitochondria targeting

Accurately visualizing the intracellular trafficking of upconversion nanoparticles (UCNPs) loaded with phthalocyanines and achieving precise photodynamic therapy (PDT) using near-infrared (NIR) laser irradiation still present challenges. In this study, a novel NIR laser-triggered upconversion luminescence (UCL) imaging-guided nanoparticle called FA@TPA-NH-ZnPc@UCNPs (FTU) was developed for PDT. FTU consisted of UCNPs, folic acid (FA), and triphenylamino-phenylaniline zinc phthalocyanine (TPA-NH-ZnPc). Notably, TPA-NH-ZnPc showcases aggregation-induced emission (AIE) characteristic and NIR absorption properties at 741 nm, synthesized initially via molybdenum-catalyzed condensation reaction. The UCL emitted by FTU enable real-time visualization of their subcellular localization and intracellular trafficking within ovarian cancer HO-8910 cells. Fluorescence images revealed that FTU managed to escape from lysosomes due to the "proton sponge" effect of TPA-NH-ZnPc. The FA ligands on the surface of FTU further directed their transport and accumulation within mitochondria. When excited by a 980 nm laser, FTU exhibited UCL and activated TPA-NH-ZnPc, consequently generating cytotoxic singlet oxygen (1O2), disrupted mitochondrial function and induced apoptosis in cancer cells, which demonstrated great potential for tumor ablation.

Photodynamic Therapy Induced Mitochondrial Targeting Strategies for Cancer Treatment: Emerging Trends and Insights

The perpetuity of cancer prevalence at a global level calls for development of novel therapeutic approaches with improved targetability and reduced adverse effects. Conventional cancer treatments have a multitude of limitations such as nonselectivity, invasive nature, and severe adverse effects. Chemotherapy is also losing its efficacy because of the development of multidrug resistance in the majority of cancers. To address these issues, selective targeting-based approaches are being explored for an effective cancer treatment. Mitochondria, being the moderator of a majority of crucial cellular pathways like metabolism, apoptosis, and reactive oxygen species (ROS) homeostasis, are an effective targeting site. Mitochondria-targeted photodynamic therapy (PDT) has arisen as a potential approach in this endeavor. By designing photosensitizers (PSs) that preferentially accumulate in the mitochondria, PDT offers a localized technique to induce cytotoxicity in cancer cells. In this review, we intend to explore the crucial principles and challenges associated with mitochondria-targeted PDT, including variability in mitochondrial function, mitochondria-specific PSs, targeted nanocarrier-based monotherapy, and combination therapies. The hurdles faced by this emerging strategy with respect to safety, optimization, clinical translation, and scalability are also discussed. Nonetheless, mitochondria-targeted PDT exhibits a significant capacity in cancer treatment, especially in combination with other therapeutic modalities. With perpetual research and technological advancements, this treatment strategy is a great addition to the arsenal of cancer treatment options, providing better tumor targetability while reducing the damage to surrounding healthy tissues. This review emphasizes the current status of mitochondria-targeted PDT, limitations, and future prospects in its pursuit of safe and efficacious cancer therapy.

Verteporfin fluorescence in antineoplastic-treated pancreatic cancer cells found concentrated in mitochondria

BACKGROUND

Traditional treatments for pancreatic cancer (PC) are inadequate. Photodynamic therapy (PDT) is non-invasive, and proven safe to kill cancer cells, including PC. However, the mitochondrial concentration of the photosensitizer, such as verteporfin, is key.

AIM

To investigate the distribution of fluorescence of verteporfin in PC cells treated with antitumor drugs, post-PDT.

METHODS

Workable survival rates of PC cells (AsPC-1, BxPC-3) were determined with chemotherapy [doxorubicin (DOX) and gemcitabine (GEM)] and non-chemotherapy [sirolimus (SRL) and cetuximab (CTX)] drugs in vitro, with or without verteporfin, as measured via MTT, flow cytometry, and laser confocal microscopy. Reduced cell proliferation was associated with GEM that was more enduring compared with DOX. Confocal laser microscopy allowed observation of GEM- and verteporfin-treated PC cells co-stained with 4',6-diamidino-2-phenylindole and MitoTracker Green to differentiate living and dead cells and subcellular localization of verteporfin, respectively.

RESULTS

Cell survival significantly dropped upon exposure to either chemotherapy drug, but not to SRL or CTX. Both cell lines responded similarly to GEM. The intensity of fluorescence was associated with the concentration of verteporfin. Additional experiments using GEM showed that survival rates of the PC cells treated with 10 μmol/L verteporfin (but not less) were significantly lower relative to nil verteporfin. Living and dead stained cells treated with GEM were distinguishable. After GEM treatment, verteporfin was observed primarily in the mitochondria.

CONCLUSION

Verteporfin was observed in living cells. In GEM -treated human PC cells, verteporfin was particularly prevalent in the mitochondria. This study supports further study of PDT for the treatment of PC after neoadjuvant chemotherapy.

Coordination-induced and tunable layered rare-earth hydroxide-complex intercalated nanohybrid phosphorescent photosensitizer and therapy

Hydrotalcite intercalated nanohybrid has served as a vital phosphorescent photosensitizer owing to remarkable 1O2 quantum yield and high cell mortality performance. However, it is rather difficult for potential large or complex guest phosphors to directly intercalate into the hydrotalcite gallery. Hence, it is necessary to regulate the interlayer microenvironment of hydrotalcites firstly for outstanding photosensitive properties. Herein, two isomers, 5,5'BDA and 4,4'BDA, with distinctive dual coordinative features were selected to modify the layer microenvironment of the LGdH gallery and induce the introduction of prospective Gd(HPhN)3 phosphorescent complexes into hydrotalcite through two different coordination effects successively. A LGdH-BDA-Gd(HPhN)3 intercalated nanohybrid phosphorescent photosensitizer was successfully obtained. The results indicated that the more efficient improvement was observed from 5,5'BDA due to offering a more spacious and stable space. Specifically, LGdH-5,5'BDA-Gd(HPhN)3 showed significantly better room temperature phosphorescence properties than LGdH-4,4'BDA-Gd(HPhN)3, whose lifetime was nearly 15 times longer than the latter. Additionally, the LGdH-5,5'BDA-Gd(HPhN)3 system displayed superior singlet oxygen generation in vitro under 460 nm irradiation (the quantum yield Φ = 0.48) and outstanding photodynamic therapy performance in tumor cells. LGdH presented more remarkable enhancement performance on the RTP properties of the luminescent molecules. This work provides a novel platform for designing a high-performance hydrotalcite intercalated nanohybrid phosphorescent photosensitizer through coordination induction to regulate the layer microenvironment.

Combined Photosensitive Gene Therapy Effective Against Triple-Negative Breast Cancer in Mice Model

Introduction

Tumor hypoxia and invasion present significant challenges for the efficacy of photodynamic therapy (PDT) in triple-negative breast cancer (TNBC). This study developed a mitochondrial targeting strategy that combined PDT and gene therapy to promote each other and address the challenges.

Methods

The positively charged amphiphilic material triphenylphosphine-tocopherol polyethylene glycol succinate (TPP-TPGS, TPS) and the photosensitizer chloride e6 (Ce6) formed TPS@Ce6 nanoparticles (NPs) by hydrophobic interaction. They electrostatically condensed microRNA-34a (miR-34a) to form stable TPS@Ce6/miRNA NPs.

Results

Firstly, Ce6 disrupted the lysosomal membrane, followed by successful delivery of miR-34a by TPS@Ce6/miRNA NPs. Meanwhile, miR-34a reduced ROS depletion and further enhanced the effectiveness of PDT. Consequently, the mutual promotion between PDT and gene therapy led to enhanced anti-tumor effects. Furthermore, the TPS@Ce6/miRNA NPs promoted apoptosis by down-regulating Caspase-3 and inhibited tumor cell migration and invasion by down-regulating N-Cadherin. In addition, in vitro and in vivo experiments demonstrated that the TPS@Ce6/miRNA NPs achieved excellent anti-tumor effects. These findings highlighted the enhanced anticancer effects and reduced migration of tumor cells through the synergistic effects of PDT and gene therapy.

Conclusion

Taken together, the targeted co-delivery of Ce6 and miR-34a will facilitate the application of photodynamic and genic nanomedicine in the treatment of aggressive tumors, particularly TNBC.

Self-assembled porphyrin-peptide cages for photodynamic therapy

The development of photodynamic therapy requires access to smart photosensitizers which combine appropriate photophysical and biological properties. Interestingly, supramolecular and dynamic covalent chemistries have recently shown their ability to produce novel architectures and responsive systems through simple self-assembly approaches. Herein, we report the straightforward formation of porphyrin-peptide conjugates and cage compounds which feature on their surface chemical groups promoting cell uptake and specific organelle targeting. We show that they self-assemble, in aqueous media, into positively-charged nanoparticles which generate singlet oxygen upon green light irradiation, while also undergoing a chemically-controlled disassembly due to the presence of reversible covalent linkages. Finally, the biological evaluation in cells revealed that they act as effective photosensitizers and promote synergistic effects in combination with Doxorubicin.

Ir(III) Half-Sandwich Photosensitizers with a π-Expansive Ligand for Efficient Anticancer Photodynamic Therapy

One approach to reduce the side effects of chemotherapy in cancer treatment is photodynamic therapy (PDT), which allows spatiotemporal control of the cytotoxicity. We have used the strategy of coordinating π-expansive ligands to increase the excited state lifetimes of Ir(III) half-sandwich complexes in order to facilitate the generation of 1O2. We have obtained derivatives of formulas [Cp*Ir(C∧N)Cl] and [Cp*Ir(C∧N)L]BF4 with different degrees of π-expansion in the C∧N ligands. Complexes with the more π-expansive ligand are very effective photosensitizers with phototoxic indexes PI > 2000. Furthermore, PI values of 63 were achieved with red light. Time-dependent density functional theory (TD-DFT) calculations nicely explain the effect of the π-expansion. The complexes produce reactive oxygen species (ROS) at the cellular level, causing mitochondrial membrane depolarization, cleavage of DNA, nicotinamide adenine dinucleotide (NADH) oxidation, as well as lysosomal damage. Consequently, cell death by apoptosis and secondary necrosis is activated. Thus, we describe the first class of half-sandwich iridium cyclometalated complexes active in PDT.

Self-heating mitochondrion-induced free radical blast for immunogenic cell death stimulation and HCC immunotherapy

Hepatocellular carcinoma (HCC) is an immunosuppressive tumor associated with high mortality. Photothermal and photodynamic therapies have been applied to induce immunogenic cell death (ICD) in HCC, successfully eliciting immune responses but facing limitations in penetration depth in clinical trials. Here, intrinsic mitochondrial hyperthermia was used to trigger thermosensitive drug release. The mitochondria were further self-heated through 2,4-dinitrophenol uncoupling, dramatically promoting free radical initiation and inducing tumor ICD. The synthesized mitochondrial-targeting TPP-HA-TDV nanoparticles specifically generated free radicals in the mitochondria without external stimulation, and obviously enhanced the release of ICD markers, subsequently evoking immune responses. The results showed that mitochondrial hyperthermia could be an endogenous target for thermosensitive drug release. Furthermore, self-heating mitochondria-induced free radical blast could be an efficient therapeutic for deep-seated tumor therapy.

β-Galactosidase-Activated and Red Light-Induced RNA Modification Strategy for Prolonged NIR Fluorescence/PET Bimodality Imaging

Improving the retention of small-molecule-based therapeutic agents in tumors is crucial to achieve precise diagnosis and effective therapy of cancer. Herein, we propose a β-galactosidase (β-Gal)-activated and red light-induced RNA modification (GALIRM) strategy for prolonged tumor imaging. A β-Gal-activatable near-infrared (NIR) fluorescence (FL) and positron emission tomography (PET) bimodal probe 68Ga-NOTA-FCG consists of a triaaza triacetic acid chelator NOTA for 68Ga-labeling, a β-Gal-activated photosensitizer CyGal, and a singlet oxygen (1O2)-susceptible furan group for RNA modification. Studies have demonstrated that the probe emits an activated NIR FL signal upon cleavage by endogenous β-Gal overexpressed in the lysosomes, which is combined with the PET imaging signal of 68Ga allowing for highly sensitive imaging of ovarian cancer. Moreover, the capability of 68Ga-NOTA-FCG generating 1O2 under 690 nm illumination could be simultaneously unlocked, which can trigger the covalent cross-linking between furan and nucleotides of cytoplasmic RNAs. The formation of the probe-RNA conjugate can effectively prevent exocytosis and prolong retention of the probe in tumors. We thus believe that this GALIRM strategy may provide entirely new insights into long-term tumor imaging and efficient tumor treatment.

Metallaaromatic Complexes as Candidates for Future Molecular Materials and Electronic Devices: Recent Advancements

In recent years, the field of organometallic chemistry has made a great progress and diverse types of metallaaromatics have successively been reported. In those studies, incorporation of ligated osmium centers into metallaaromatic systems played a prominent role. The reviewed literature documents that certain metallaaromatics with unconventional photophysical properties, redox and electronic transport properties and magnetism, have potential to be widely used in diverse practical applications, with selected examples of amino acid and fluoride anion identification, photothermal effects, functional materials, photodynamic therapy (PDT) in biomedicine, single-molecule junction conductors, and electron-transport layer materials (ETLs) in solar cells.

Nanoscale Covalent Organic Framework with Staggered Stacking of Phthalocyanines for Mitochondria-Targeted Photodynamic Therapy

Phthalocyanine photosensitizers (PSs) have shown promise in fluorescence imaging and photodynamic therapy (PDT) of malignant tumors, but their practical application is limited by the aggregation-induced quenching (AIQ) and inherent photobleaching of PSs. Herein, we report the synthesis of a two-dimensional nanoscale covalent organic framework (nCOF) with staggered (AB) stacking of zinc-phthalocyanines (ZnPc), ZnPc-PI, for fluorescence imaging and mitochondria-targeted PDT. ZnPc-PI isolates and confines ZnPc PSs in the rigid nCOF to reduce AIQ, improve photostability, enhance cellular uptake, and increase the level of reactive oxygen species (ROS) generation via mitochondrial targeting. ZnPc-PI shows efficient tumor accumulation, which allowed precise tumor imaging and nanoparticle tracking. With high cellular uptake and tumor accumulation, intrinsic mitochondrial targeting, and enhanced ROS generation, ZnPc-PI exhibits potent PDT efficacy with >95% tumor growth inhibition on two murine colon cancer models without causing side effects.

Cyclometalated Ir(III) theranostic molecular probe enabled mitochondria targeted fluorescence-SERS-guided phototherapy in breast cancer cells

The increased energy demands inherent in cancer cells necessitate a dependence on mitochondrial assistance for their proliferation and metastatic activity. Herein, an innovative photo-medical approach has been attempted, specifically targeting mitochondria, the cellular powerhouses, to attain therapeutic benefit. This strategy facilitates the rapid and precise initiation of apoptosis, the programmed cell death process. In this goal, we have synthesized cyclometalated Iridium (III) molecular probes, denoted as Ir-CN and Ir-H, with a nitrile (CN) and a hydrogen-functionalized bipyridine as ancillary ligands, respectively. Ir-CN has shown superior photosensitizing properties and lower dark cytotoxicity compared to Ir-H in the breast cancer cell line MCF-7, positioning it as the preferred probe for photodynamic therapy (PDT). The synthesized Ir-CN induces alterations in mitochondrial membrane potential, disrupting the respiratory chain function, and generating reactive oxygen species that activate signaling pathways leading to cell death. The CN-conjugated bipyridine ligand in Ir-CN contributes to the intense red fluorescence and the positive charge on the central metal atom facilitates specific mitochondrial colocalization (colocalization coefficient of 0.90). Together with this, the Iridium metal, with strong spin-orbit coupling, efficiently generates singlet oxygen with a quantum yield of 0.79. Consequently, the cytotoxic singlet oxygen produced by Ir-CN upon laser exposure disrupts mitochondrial processes, arresting the electron transport chain and energy production, ultimately leading to programmed cell death. This mitochondrial imbalance and apoptotic induction were dually confirmed through various apoptotic assays including Annexin V staining and by mapping the molecular level changes through surface-enhanced Raman spectroscopy (SERS). Therefore, cyclometalated Ir-CN emerges as a promising molecular probe for cancer theranostics, inducing laser-assisted mitochondrial damage, as tracked through bimodal fluorescence and SERS.

Exploring a Mitochondria Targeting, Dinuclear Cyclometalated Iridium (III) Complex for Image-Guided Photodynamic Therapy in Triple-Negative Breast Cancer Cells

Photodynamic therapy (PDT) has emerged as an efficient and noninvasive treatment approach utilizing laser-triggered photosensitizers for combating cancer. Within this rapidly advancing field, iridium-based photosensitizers with their dual functionality as both imaging probes and PDT agents exhibit a potential for precise and targeted therapeutic interventions. However, most reported classes of Ir(III)-based photosensitizers comprise mononuclear iridium(III), with very few examples of dinuclear systems. Exploring the full potential of iridium-based dinuclear systems for PDT applications remains a challenge. Herein, we report a dinuclear Ir(III) complex (IRDI) along with a structurally similar monomer complex (IRMO) having 2-(2,4-difluorophenyl)pyridine and 4'-methyl-2,2'-bipyridine ligands. The comparative investigation of the mononuclear and dinuclear Ir(III) complexes showed similar absorption profiles, but the dinuclear derivative IRDI exhibited a higher photoluminescence quantum yield (Φp) of 0.70 compared to that of IRMO (Φp = 0.47). Further, IRDI showed a higher singlet oxygen generation quantum yield (Φs) of 0.49 compared to IRMO (Φs = 0.28), signifying the enhanced potential of the dinuclear derivative for image-guided photodynamic therapy. In vitro assessments indicate that IRDI shows efficient cellular uptake and significant photocytotoxicity in the triple-negative breast cancer cell line MDA-MB-231. In addition, the presence of a dual positive charge on the dinuclear system facilitates the inherent mitochondria-targeting ability without the need for a specific targeting group. Subcellular singlet oxygen generation by IRDI was confirmed using Si-DMA, and light-activated cellular apoptosis via ROS-mediated PDT was verified through various live-dead assays performed in the presence and absence of the singlet oxygen scavenger NaN3. Further, the mechanism of cell death was elucidated by an annexin V-FITC/PI flow cytometric assay and by investigating the cytochrome c release from mitochondria using Western blot analysis. Thus, the dinuclear complex designed to enhance spin-orbit coupling with minimal excitonic coupling represents a promising strategy for efficient image-guided PDT using iridium complexes.

Self-reported and self-facilitated theranostic oxygen nano-economizer for precise and hypoxia alleviation-potentiated photodynamic therapy

Photodynamic therapy (PDT) has been extensively investigated for cancer treatment by virtue of singlet oxygen-induced oxidative damage to tumors. Nevertheless, the therapeutic efficiency of PDT is still limited by the low singlet oxygen yield attributed to the improper irradiation duration and the tumor hypoxic microenvironment. To tackle these challenges, we elaborately design a theranostic oxygen nano-economizer to self-report the optimal irradiation duration and alleviate tumor hypoxia simultaneously, which is engineered by fluorescent 9,10-anthracenyl bis (benzoic acid) (DPA)-MOF, tetrakis (4-carboxyphenyl) porphyrin (TCPP), triphenyl phosphine (TPP) and redox-responsive lipid-PEG (DSPE-SS-PEG2k). Upon laser irradiation, the fluorescence of DPA-MOF could be quenched, thereby self-reporting the optimal irradiation duration for sufficient PDT. The decoration of DSPE-SS-PEG2k and TPP endows the theranostic oxygen nano-economizer with a tumor-specific response and mitochondrial targeting capability, respectively. Notably, singlet oxygen generated from TCPP reduces oxygen consumption by disrupting the entire oxidative phosphorylation (OXPHOS) pathway in the mitochondria of tumor cells, further improving the level of singlet oxygen in a self-facilitated manner for hypoxia alleviation-potentiated PDT. As expected, such a self-reported and self-facilitated theranostic oxygen nano-economizer exhibits potent antitumor activity in the 4T1 tumor-bearing mouse model. This study offers a theranostic paradigm for precise and hypoxia alleviation-potentiated cancer therapy.

Recent Advances in Mitochondria-Localized Luminescent Ruthenium(II) Metallodrugs as Anticancer Agents

Presently, the most effective way to transport drugs specifically to mitochondria inside the cells is of pharmacophoric interest, as mitochondria are recognized as one of the most important targets for new drug design in cancer diagnosis. To date, there are many reviews covering the photophysical, photochemical, and anticancer properties of ruthenium(II) based metallodrugs owing to their high interest in biological applications. There are, however, no reviews specifically covering the mitochondria-localized luminescent Ru(II) complexes and their subsequent mitochondria-mediated anticancer activities. Therefore, this review describes the physicochemical basis for the mitochondrial accumulation of ruthenium complexes, their synthetic strategies to localize and monitor the mitochondria in living cells, and their related underlying anticancer results. Finally, we review the related areas from previous works describing the mitochondria-localized ruthenium complexes for the treatment of cancer-related diseases. Along with this, we also deliberate the perspectives and future directions for emerging more bifunctional Ru(II) complexes that can target, image, and kill tumors more efficiently in comparison with the existing mitochondria-targeted cancer therapeutics.

Recent advances in the design of afterglow materials: mechanisms, structural regulation strategies and applications

Afterglow materials are attracting widespread attention owing to their distinctive and long-lived optical emission properties which create exciting opportunities in various fields. Recent research has led to the discovery of many new afterglow materials featuring high photoluminescence quantum yields (PLQY) and lifetimes of up to several hours under ambient conditions. Afterglow materials are typically categorized according to their luminescence mechanism, such as long-persistent luminescence (LPL), room temperature phosphorescence (RTP), or thermally activated delayed fluorescence (TADF). Through rational design and novel synthetic strategies to modulate spin-orbit coupling (SOC) and populate triplet exciton states (T1), luminophores with long lifetimes and bright afterglow characteristics can be realized. Initial research towards afterglow materials focused mainly on pure inorganic materials, many of which possessed inherent disadvantages such as metal toxicity or low energy emissions. In recent years, organic-inorganic hybrid afterglow materials (OIHAMs) have been developed with high PLQY and long lifetimes. These hybrid materials exploit the tunable structure and easy processing of organic molecules, as well as enhanced SOC and intersystem crossing (ISC) processes involving heavy atom dopants, to achieve excellent afterglow performance. In this review, we begin by briefly discussing the structure and composition of inorganic and organic-inorganic hybrid afterglow materials, including strategies for regulating their lifetime, PLQY and luminescence wavelength. The specific advantages of organic-inorganic hybrid afterglow materials, including low manufacturing costs, diverse molecular/electronic structures, tunable structures and optical properties, and compatibility with a variety of substrates, are emphasized. Subsequently, we discuss in detail the fundamental mechanisms used by afterglow materials, their classification, design principles, and end applications (including sensing, anticounterfeiting, and photoelectric devices, among others). Finally, existing challenges and promising future directions are discussed, laying a platform for the design of afterglow materials for specific applications.