Integration of TADF Photosensitizer as “Electron Pump” and BSA as “Electron Reservoir” for Boosting Type I Photodynamic Therapy

Efficient hydroxyl radical generation of an activatable phthalocyanine photosensitizer: oligomer higher than monomer and nanoaggregate

It remains a challenge to develop a single-component organic photosensitizer that efficiently produces hydroxyl radicals (˙OH) without oxygen involvement, especially while maintaining tumor-targeting capability. Herein, we propose an intelligent molecular design strategy whereby a tumor-targeted phthalocyanine is initially ˙OH-free and can be activated by overexpressed β-nicotinamide adenine dinucleotide sodium salt hydrate (NAD(P)H) in hypoxic tumors to efficiently produce ˙OH under light irradiation. Furthermore, the oligomer models based on the phthalocyanine molecules were constructed by a supramolecular regulation strategy, which were in an intermediate state between monomer and nanoaggregate, to achieve enhanced ˙OH generation. The level of NAD(P)H in cancer cells can be exhausted through two pathways, including spontaneous redox and the photocatalytic redox of phthalocyanines. As a result, the in vivo and in vitro assays illustrated that the oligomeric phthalocyanine containing N-O units (OligPcNOB) can specifically target cancer cells and tumor tissue with overexpressing biotin receptors. OligPcNOB exhibited significant photocytotoxicity even in an extremely low oxygen environment and successfully inhibited tumor progression.

Self-assembly-integrated tumor targeting and electron transfer programming towards boosting tumor type I photodynamic therapy

Type I photodynamic therapy (PDT) is attracting increasing interest as an effective solution to the poor prognosis of patients with hypoxic tumors. The development of functional type I photosensitizers is limited by a lack of feasible strategies to systematically modulate electron transfer (ET) in photosensitization. Herein, we present an easily accessible approach for the preparation of nanophotosensitizers with self-assembly-integrated tumor-targeting and ET programming towards boosting tumor type I PDT. Specifically, a dual functional amphiphile PS-02 was designed with a ligand (6-NS) that had the ability to not only target tumor cell marker carbonic anhydrase IX (CAIX) but also regulate the ET process for type I PDT. The amphiphile PS-02 tended to self-assemble into PS-02 nanoparticles (NPs), which exhibited a local "ET-cage effect" due to the electron-deficient nature of 6-NS. It is noteworthy that when PS-02 NPs selectively targeted the tumor cells, the CAIX binding enabled the uncaging of the inhibited ET process owing to the electron-rich characteristic of CAIX. Therefore, PS-02 NPs integrated tumor targeting and CAIX activation towards boosting type I PDT. As a proof of concept, the improved PDT performance of PS-02 NPs was demonstrated with tumor cells under hypoxic conditions and solid tumor tissue in mouse in vivo experiments. This work provides a practical paradigm to develop versatile type I PDT nano-photosensitizers by simply manipulating ET and easy self-assembling.

Recent Progress in Thermally Activated Delayed Fluorescence Photosensitizers for Photodynamic Therapy

Photodynamic therapy (PDT) is a rapidly growing discipline that is expected to become an encouraging noninvasive therapeutic strategy for cancer treatment. In the PDT process, an efficient intersystem crossing (ISC) process for photosensitizers from the singlet excited state (S1) to the triplet excited state (T1) is critical for the formation of cytotoxic reactive oxygen species and improvement of PDT performance. Thermally activated delayed fluorescence (TADF) molecules featuring an extremely small singlet-triplet energy gap and an efficient ISC process represent an enormous breakthrough for the PDT process. Consequently, the development of advanced TADF photosensitizers has become increasingly crucial and pressing. The most recent developments in TADF photosensitizers aimed at enhancing PDT efficiency for bio-applications are presented in this review. TADF photosensitizers with water dispersibility, targeting ability, activatable ability, and two-photon excitation properties are highlighted. Furthermore, the future challenges and perspectives of TADF photosensitizers in PDT are proposed.

An NIR Type I Photosensitizer Based on a Cyclometalated Ir(III)-Rhodamine Complex for a Photodynamic Antibacterial Effect toward Both Gram-Positive and Gram-Negative Bacteria

Type I photosensitizers offer an advantage in photodynamic therapy (PDT) due to their diminished reliance on oxygen levels, thus circumventing the challenge of hypoxia commonly encountered in PDT. In this study, we present the synthesis and comprehensive characterization of a novel type I photosensitizer derived from a cyclometalated Ir(III)-rhodamine complex. Remarkably, the complex exhibits a shift in absorption and fluorescence, transitioning from "off" to "on" states in aprotic and protic solvents, respectively, contrary to initial expectations. Upon exposure to light, the complex demonstrates the effective generation of O2- and ·OH radicals via the type I mechanism. Additionally, it exhibits notable photodynamic antibacterial activity against both Gram-positive and Gram-negative bacteria, demonstrated through in vitro and in vivo experiments. This research offers valuable insights for the development of novel type I photosensitizers.

Electron-Withdrawing Substituents Enhance the Type I PDT and NIR-II Fluorescence of BODIPY J Aggregates for Bioimaging and Cancer Therapy

Organic dyes with simultaneously boosted near-infrared-II (NIR-II) fluorescence, type I photodynamic therapy (PDT), and photothermal therapy (PTT) in the aggregate state are still elusive due to the unclear structure-function relationship. Herein, electron-withdrawing substituents are introduced at the 5-indolyl positions of BODIPY dyes to form tight J-aggregates for enhanced NIR-II fluorescence and type I PDT/PTT. The introduction of an electron-rich julolidine group at the meso position and an electron-withdrawing substituent (-F) at the indolyl moiety can enhance intermolecular charge transfer and the hydrogen bonding effect, contributing to the efficient generation of superoxide radicals in the aggregate state. The nanoparticles of BDP-F exhibit NIR-II fluorescence at 1000 nm, good superoxide radical generation ability, and a high photothermal conversion efficiency (50.9%), which enabled NIR-II fluorescence-guided vasculature/tumor imaging and additive PDT/PTT. This work provides a strategy for constructing phototheranostic agents with enhanced NIR-II fluorescence and type I PDT/PTT for broad biomedical applications.

An Electron Donor-Acceptor Structured Rhenium(I) Complex Photo-Sensitizer Evokes Mutually Reinforcing "Closed-Loop" Ferroptosis and Immunotherapy

The hypoxic microenvironment of solid tumors severely lowers the efficacy of oxygen-dependent photodynamic therapy (PDT). The development of hypoxia-tolerant photosensitizers for PDT is an urgent requirement. In this study, a novel rhenium complex (Re-TTPY) to develop a "closed-loop" therapy based on PDT-induced ferroptosis and immune therapy is reported. Due to its electron donor-acceptor (D-A) structure, Re-TTPY undergoes energy transfer and electron transfer processes under 550 nm light irradiation and displays hypoxia-tolerant type I/II combined PDT capability, which can generate 1O2, O2 -, and ·OH simultaneously. Further, the reactive oxygen species (ROSs) leads to the depletion of 1,4-dihydronicotinamide adenine dinucleotide (NADH), glutathione peroxidase 4 (GPX4), and glutathione (GSH). As a result, ferroptosis occurs in cells, simultaneously triggers immunogenic cell death (ICD), and promotes the maturation of dendritic cells (DCs) and infiltration of T cells. The release of interferon-γ (IFN-γ) by CD8+ T cells downregulates the expression of GPX4, further enhancing the occurrence of ferroptosis, and thereby, forming a mutually reinforcing "closed-loop" therapeutic approach.

Thymoquinone as an electron transfer mediator to convert Type II photosensitizers to Type I photosensitizers

The development of Type I photosensitizers (PSs) is of great importance due to the inherent hypoxic intolerance of photodynamic therapy (PDT) in the hypoxic microenvironment. Compared to Type II PSs, Type I PSs are less reported due to the absence of a general molecular design strategy. Herein, we report that the combination of typical Type II PS and natural substrate carvacrol (CA) can significantly facilitate the Type I pathway to efficiently generate superoxide radical (O2-•). Detailed mechanism study suggests that CA is activated into thymoquinone (TQ) by local singlet oxygen generated from the PS upon light irradiation. With TQ as an efficient electron transfer mediator, it promotes the conversion of O2 to O2-• by PS via electron transfer-based Type I pathway. Notably, three classical Type II PSs are employed to demonstrate the universality of the proposed approach. The Type I PDT against S. aureus has been demonstrated under hypoxic conditions in vitro. Furthermore, this coupled photodynamic agent exhibits significant bactericidal activity with an antibacterial rate of 99.6% for the bacterial-infection female mice in the in vivo experiments. Here, we show a simple, effective, and universal method to endow traditional Type II PSs with hypoxic tolerance.

Membrane-anchoring selenophene viologens for antibacterial photodynamic therapy against periodontitis via restoring subgingival flora and alleviating inflammation

Antibacterial photodynamic therapy (aPDT) has emerged as a promising strategy for treating periodontitis. However, the weak binding of most photosensitizers to bacteria and the hypoxic environment of periodontal pockets severely hamper the therapeutic efficacy. Herein, two novel oxygen-independent photosensitizers are developed by introducing selenophene into viologens and modifying with hexane chains (HASeV) or quaternary ammonium chains (QASeV), which improve the adsorption to bacteria through anchoring to the negatively charged cell membrane. Notably, QASeV binds only to the bacterial surface of Porphyromonas gingivalis and Fusobacterium nucleatum due to electrostatic binding, but HASeV can insert into their membrane by strong hydrophobic interactions. Therefore, HASeV exhibits superior antimicrobial activity and more pronounced plaque biofilm disruption than QASeV when combined with light irradiation (MVL-210 photoreactor, 350-600 nm, 50 mW/cm2), and a better effect on reducing the diversity and restoring the structure of subgingival flora in periodontitis rat model was found through 16S rRNA gene sequencing analysis. The histological and Micro-CT analyses reveal that HASeV-based aPDT has a better therapeutic effect in reducing periodontal tissue inflammation and alveolar bone resorption. This work provides a new strategy for the development of viologen-based photosensitizers, which may be a favorable candidate for the aPDT against periodontitis.

A type I and type II chemical biology toolbox to overcome the hypoxic tumour microenvironment for photodynamic therapy

Photodynamic therapy (PDT) is a minimally invasive therapeutic modality employed for the treatment of various types of cancers, localized infections, and other diseases. Upon illumination, the photo-excited photosensitizer generates singlet oxygen and other reactive species, thereby inducing cytotoxicity in the target cells. The hypoxic tumour microenvironment (TME), however, poses a limitation on the supply of oxygen in tumour tissues. Moreover, under such conditions, tumour metastasis and drug resistance frequently occur, further compromising the efficacy of PDT in combating tumours. Traditionally, type I photosensitizers with lower oxygen consumption demonstrate significant potential in overcoming hypoxic environments and play a crucial role in determining the therapeutic efficacy of PDT because type I photosensitizers can generate highly cytotoxic free radicals. In comparison, type II photosensitizers exhibit high oxygen dependence. The rate of reactive oxygen species (ROS) generation in the type II process is significantly higher than that in the type I process. Thus, the efficiency and selectivity of PDT depend on the properties of the photosensitizer. Here, the recent development and application of type I and type II photosensitizers, mainly in the past year, are summarized. The design methods, electronic structures, photophysical properties, lipophilic properties, electric charge, and other molecular characteristics of these photosensitizers are discussed in detail. These modifications alter the microstructure of photosensitizers and directly impact the results of PDT. The main content of this paper will have a positive promoting and inspiring effect on the future development of PDT.

Unimolecular Chemiexcited Oxygenation of Pathogenic Amyloids

Pathogenic protein aggregates, called amyloids, are etiologically relevant to various diseases, including neurodegenerative Alzheimer disease. Catalytic photooxygenation of amyloids, such as amyloid-β (Aβ), reduces their toxicity; however, the requirement for light irradiation may limit its utility in large animals, including humans, due to the low tissue permeability of light. Here, we report that Cypridina luciferin analogs, dmCLA-Cl and dmCLA-Br, promoted selective oxygenation of amyloids through chemiexcitation without external light irradiation. Further structural optimization of dmCLA-Cl led to the identification of a derivative with a polar carboxylate functional group and low cellular toxicity: dmCLA-Cl-acid. dmCLA-Cl-acid promoted oxygenation of Aβ amyloid and reduced its cellular toxicity without photoirradiation. The chemiexcited oxygenation developed in this study may be an effective approach to neutralizing the toxicity of amyloids, which can accumulate deep inside the body, and treating amyloidosis.

Programmable Singlet Oxygen Battery for Automated Photodynamic Therapy Enabled by Pyridone-Pyridine Tautomer Engineering

The efficacy of photodynamic therapy is hindered by the hypoxic environment in tumors and limited light penetration depth. The singlet oxygen battery (SOB) has emerged as a promising solution, enabling oxygen- and light-independent 1O2 release. However, conventional SOB systems typically exhibit an "always-ON" 1O2 release, leading to potential 1O2 leakage before and after treatment. This not only compromises therapeutic outcomes but also raises substantial biosafety concerns. In this work, we introduce a programmable singlet oxygen battery, engineered to address all the issues discussed above. The concept is illustrated through the development of a tumor-microenvironment-responsive pyridone-pyridine switch, PyAce, which exists in two tautomeric forms: PyAce-0 (pyridine) and PyAce (pyridone) with different 1O2 storage half-lives. In its native state, PyAce remains in the pyridone form, capable of storing 1O2 (t1/2 = 18.5 h). Upon reaching the tumor microenvironment, PyAce is switched to the pyridine form, facilitating rapid and thorough 1O2 release (t1/2 = 16 min), followed by quenched 1O2 release post-therapy. This mechanism ensures suppressed 1O2 production pre- and post-therapy with selective and rapid 1O2 release at the tumor site, maximizing therapeutic efficacy while minimizing side effects. The achieved "OFF-ON-OFF" 1O2 therapy showed high spatiotemporal selectivity and was independent of the oxygen supply and light illumination.

A planar electronic acceptor motif contributing to NIR-II AIEgen with combined imaging and therapeutic applications

Designing molecules with donor-acceptor-donor (D-A-D) architecture plays an important role in obtaining second near-infrared region (NIR-II, 1000-1700 nm) fluorescent dyes for biomedical applications; however, this always comes with a challenge due to very limited electronic acceptors. On the other hand, to endow NIR-II fluorescent dyes with combined therapeutic applications, trivial molecular design is indispensable. Herein, we propose a pyrazine-based planar electronic acceptor with a strong electron affinity, which can be used to develop NIR-II fluorescent dyes. By structurally attaching two classical triphenylamine electronic donors to it, a basic D-A-D module, namely Py-NIR, can be generated. The planarity of the electronic acceptor is crucial to induce a distinct NIR-II emission peaking at ∼1100 nm. The unique construction of the electronic acceptor can cause a twisted and flexible molecular conformation by the repulsive effect between the donors, which is essential to the aggregation-induced emission (AIE) property. The tuned intramolecular motions and twisted D-A pair brought by the electronic acceptor can lead to a remarkable photothermal conversion with an efficiency of 56.1% and induce a type I photosensitization with a favorable hydroxyl radical (OH˙) formation. Note that no additional measures are adopted in the molecular design, providing an ideal platform to realize NIR-II fluorescent probes with synergetic functions based on such an acceptor. Besides, the nanoparticles of Py-NIR can exhibit excellent NIR-II fluorescence imaging towards orthotopic 4T1 breast tumors in living mice with a high sensitivity and contrast. Combined with photothermal imaging and photoacoustic imaging caused by the thermal effect, the imaging-guided photoablation of tumors can be well performed. Our work has created a new opportunity to develop NIR-II fluorescent probes for accelerating biomedical applications.

Manipulation of Nonradiative Process Based on the Aggregation Microenvironment to Customize Excited-State Energy Conversion

ConspectusNonradiative processes with the determined role in excited-state energy conversion, such as internal conversion (IC), vibrational relaxation (VR), intersystem crossing (ISC), and energy or electron transfer (ET or eT), have exerted a crucial effect on biological functions in nature. Inspired by these, nonradiative process manipulation has been extensively utilized to develop organic functional materials in the fields of energy and biomedicine. Therefore, comprehensive knowledge and effective manipulation of sophisticated nonradiative processes for achieving high-efficiency excited-state energy conversion are quintessential. So far, many strategies focused on molecular engineering have demonstrated tremendous potential in manipulating nonradiative processes to tailor excited-state energy conversion. Besides, molecular aggregation considerably affects nonradiative processes due to their ultrasensitivity, thus providing us with another essential approach to manipulating nonradiative processes, such as the famous aggregation-induced emission. However, the weak interactions established upon aggregation, namely, the aggregation microenvironment (AME), possess hierarchical, dynamic, and systemic characteristics and are extremely complicated to elucidate. Revealing the relationship between the AME and nonradiative process and employing it to customize excited-state energy conversion would greatly promote advanced materials in energy utilization, biomedicine, etc., but remain a huge challenge. Our group has devoted much effort to achieving this goal.In this Account, we focus on our recent developments in nonradiative process manipulation based on AME. First, we provide insight into the effect of the AME on nonradiative process in terms of its steric effect and electronic regulation, illustrating the possibility of nonradiative process manipulation through AME modulation. Second, the distinct enhanced steric effect is established by crystallization and heterogeneous polymerization to conduct crystallization-induced reversal from dark to bright excited states and dynamic hardening-triggered nonradiative process suppression for highly efficient luminescence. Meanwhile, promoting the ISC process and stabilizing the triplet state are also manipulated by the crystal and polymer matrix to induce room-temperature phosphorescence. Furthermore, the strategies employed to exploit nonradiative processes for photothermy and photosensitization are reviewed. For photothermal conversion, besides the weakened steric effect with promoted molecular motions, a new strategy involving the introduction of diradicals upon aggregation to narrow the energy band gap and enhance intermolecular interactions is put forward to facilitate IC and VR for high-efficiency photothermal conversion. For photosensitization, both the enhanced steric effect from the rigid matrix and the effective electronic regulation from the electron-rich microenvironment are demonstrated to facilitate ISC, ET, and eT for superior photosensitization. Finally, we explore the existing challenges and future directions of nonradiative process manipulation by AME modulation for customized excited-state energy conversion. We hope that this Account will be of wide interest to readers from different disciplines.

Mn-Based Artificial Mitochondrial Complex "VI" Acts as an Electron and Free Radical Conversion Factory to Suppress Macrophage Inflammatory Response

Disturbance in the mitochondrial electron transport chain (ETC) is a key factor in the emerging discovery of immune cell activation in inflammatory diseases, yet specific regulation of ETC homeostasis is extremely challenging. In this paper, a mitochondrial complex biomimetic nanozyme (MCBN), which plays the role of an artificial "VI" complex and acts as an electron and free radical conversion factory to regulate ETC homeostasis is creatively developed. MCBN is composed of bovine serum albumin (BSA), polyethylene glycol (PEG), and triphenylphosphine (TPP) hierarchically encapsulating MnO2 polycrystalline particles. It has nanoscale size and biological properties like natural complexes. In vivo and in vitro experiments confirm that MCBN can target the mitochondrial complexes of inflammatory macrophages, absorb excess electrons in ETC, and convert the electrons to decompose H2O2. By reducing the ROS and ATP bursts and converting existing free radicals, inhibiting NLRP3 inflammatory vesicle activation and NF-κB signaling pathway, MCBN effectively suppresses macrophage M1 activation and inflammatory factor secretion. It also demonstrates good inflammation control and significantly alleviates alveolar bone loss in a mouse model of ligation-induced periodontitis. This is the first nanozyme that mimics the mitochondrial complex and regulates ETC, demonstrating the potential application of MCBN in immune diseases.

Rational design of type-I photosensitizer molecules for mitochondrion-targeted photodynamic therapy

Photodynamic therapy (PDT) has emerged as a promising approach for tumor treatment. However, traditional type II PDT faces limitations due to its oxygen-dependent nature. Type-I photosensitizers (PSs) exhibit superiority over conventional type-II PSs owing to their diminished oxygen dependence. Nevertheless, designing effective type-I PSs remains a significant challenge. In this work, we provide a novel strategy to tune the PDT mechanism of an excited photosensitizer through aryl substituent engineering. Using S-rhodamine as the base structure, three PSs were synthesized by incorporating phenyl, furyl, or thienyl groups at the meso position. Interestingly, furyl- or thienyl-substituted S-rhodamine are type-I-dominated PSs that produce O2˙-, while phenyl S-rhodamine results in O2˙- and 1O2 through type-I and type-II mechanisms, respectively. Experimental analyses and theoretical calculations showed that the introduction of a five-membered heterocycle at the meso position promoted intersystem crossing (ISC) and electron transfer, facilitating the production of O2˙-. Furthermore, furyl- or thienyl-substituted S-rhodamine exhibited high phototoxicity at ultralow concentrations. Thienyl-substituted S-rhodamine showed promising PDT efficacy against hypoxic solid tumors. This innovative strategy provides an alternative approach to developing new type-I PSs without the necessity for creating entirely new skeletons.

Strategic Insertion of Heavy Atom to Tailor TADF OLED Material for the Development of Type I Photosensitizing Catalytic Red Emissive Assemblies

The work presented in the manuscript describes a simple strategy for transforming thermally activated delayed fluorescent organic light-emitting diodes (TADF OLEDs) compound 10-(dibenzo[a,c]phenazin-11-yl)-10H-phenoxazine (DPZ-PXZ) into type I photosensitizer 10-(dibenzo[a,c]phenazin-11-yl)-10H-phenothiazine (DPZ-PHZ) by strategically introducing sulfur atom in the photosensitizing core. The synthesized compound DPZ-PHZ exhibits aggregation-induced enhancement (AIE) and through-space charge transfer (TSCT) characteristics and generates red emissive assemblies in mixed aqueous media. The original compound DPZ-PXZ exhibits well-separated HOMO and LUMO levels and is reported to have highly efficient reverse intersystem crossing (RISC). In comparison, the incorporation of sulfur atom in the phenothiazine donor regulates the electronic communication between donor and acceptor units and promotes the intersystem crossing (ISC) in DPZ-PHZ molecules. Interestingly, compound DPZ-PHZ exhibits rapid activation of aerial oxygen for instant generation of superoxide radical anion. Backed by excellent type I photosensitizing activity, DPZ-PHZ assemblies have high catalytic potential for the synthesis of benzimidazoles, benzothiazoles and quinazolines derivatives under mild reaction conditions. The work presented in the manuscript provides an insight into the combination of heavy atom approach and TSCT for achieving adequate electronic communication between donor and acceptor units, balanced RISC/ISC, and stabilized-charge separated state for the development of efficient type I photosensitizing assemblies.

Deciphering Oxygen-Independent Augmented Photodynamic Oncotherapy by Facilitating the Separation of Electron-Hole Pairs

Developing Type-I photosensitizers provides an attractive approach to solve the dilemma of inadequate efficacy of photodynamic therapy (PDT) caused by the inherent oxygen consumption of traditional Type-II PDT and anoxic tumor microenvironment. The challenge for the exploration of Type-I PSs is to facilitate the electron transfer ability of photosensitization molecules for transforming oxygen or H2O to reactive oxygen species (ROS). Herein, we propose an electronic acceptor-triggered photoinduced electron transfer (a-PET) strategy promoting the separation of electron-hole pairs by marriage of two organic semiconducting molecules of a non-fullerene scaffold-based photosensitizer and a perylene diimide that significantly boost the Type-I PDT pathway to produce plentiful ROS, especially, inducing 3.5-fold and 2.5-fold amplification of hydroxyl (OH⋅) and superoxide (O2 -⋅) generation. Systematic mechanism exploration reveals that intermolecular electron transfer and intramolecular charge separation after photoirradiation generate a competent production of radical ion pairs that promote the Type-I PDT process by theoretical calculation and ultrafast femtosecond transient absorption (fs-TA) spectroscopy. By complementary tumor diagnosis with photoacoustic imaging and second near-infrared fluorescence imaging, this as-prepared nanoplatform exhibits fabulous photocytotoxicity in harsh hypoxic conditions and terrific cancer revoked abilities in living mice. We envision that this work will broaden the insight into high-efficiency Type-I PDT for cancer phototheranostics.

pH/GSH dual responsive nanosystem for nitric oxide generation enhanced type I photodynamic therapy

Tumor hypoxia diminishes the effectiveness of traditional type II photodynamic therapy (PDT) due to oxygen consumption. Type I PDT, which can operate independently of oxygen, is a viable option for treating hypoxic tumors. In this study, we have designed and synthesized JSK@PEG-IR820 NPs that are responsive to the tumor microenvironment (TME) to enhance type I PDT through glutathione (GSH) depletion. Our approach aims to expand the sources of therapeutic benefits by promoting the generation of superoxide radicals (O2-.) while minimizing their consumption. The diisopropyl group within PEG-IR820 serves a dual purpose: it functions as a pH sensor for the disassembly of the NPs to release JSK and enhances intermolecular electron transfer to IR820, facilitating efficient O2-. generation. Simultaneously, the release of JSK leads to GSH depletion, resulting in the generation of nitric oxide (NO). This, in turn, contributes to the formation of highly cytotoxic peroxynitrite (ONOO-.), thereby enhancing the therapeutic efficacy of these NPs. NIR-II fluorescence imaging guided therapy has achieved successful tumor eradication with the assistance of laser therapy.

Oxygen-independent organic photosensitizer with ultralow-power NIR photoexcitation for tumor-specific photodynamic therapy

Photodynamic therapy (PDT) is a promising cancer treatment but has limitations due to its dependence on oxygen and high-power-density photoexcitation. Here, we report polymer-based organic photosensitizers (PSs) through rational PS skeleton design and precise side-chain engineering to generate •O2- and •OH under oxygen-free conditions using ultralow-power 808 nm photoexcitation for tumor-specific photodynamic ablation. The designed organic PS skeletons can generate electron-hole pairs to sensitize H2O into •O2- and •OH under oxygen-free conditions with 808 nm photoexcitation, achieving NIR-photoexcited and oxygen-independent •O2- and •OH production. Further, compared with commonly used alkyl side chains, glycol oligomer as the PS side chain mitigates electron-hole recombination and offers more H2O molecules around the electron-hole pairs generated from the hydrophobic PS skeletons, which can yield 4-fold stronger •O2- and •OH production, thus allowing an ultralow-power photoexcitation to yield high PDT effect. Finally, the feasibility of developing activatable PSs for tumor-specific photodynamic therapy in female mice is further demonstrated under 808 nm irradiation with an ultralow-power of 15 mW cm-2. The study not only provides further insights into the PDT mechanism but also offers a general design guideline to develop an oxygen-independent organic PS using ultralow-power NIR photoexcitation for tumor-specific PDT.

Photo-Induced Disproportionation-Mediated Photodynamic Therapy: Simultaneous Oxidation of Tetrahydrobiopterin and Generation of Superoxide Radicals

We herein present an approach of photo-induced disproportionation for preparation of Type-I photodynamic agents. As a proof of concept, BODIPY-based photosensitizers were rationally designed and prepared. The photo-induced intermolecular electron transfer between homotypic chromophores leads to the disproportionation reaction, resulting in the formation of charged intermediates, cationic and anionic radicals. The cationic radicals efficiently oxidize the cellularimportant coenzyme, tetrahydrobiopterin (BH4 ), and the anionic radicals transfer electrons to oxygen to produce superoxide radicals (O2 - ⋅). One of our Type-I photodynamic agents not only self-assembles in water but also effectively targets the endoplasmic reticulum. It displayed excellent photocytotoxicity even in highly hypoxic environments (2 % O2 ), with a half-maximal inhibitory concentration (IC50 ) of 0.96 μM, and demonstrated outstanding antitumor efficacy in murine models bearing HeLa tumors.

Photoinduced Cuproptosis with Tumor-Specific for Metastasis-Inhibited Cancer Therapy

Cuproptosis is a novel form of regulated cell death which guarantees to increase the efficacy of existing anticancer treatments that employ traditional apoptotic therapeutics. However, reducing the amount of undesirable Cu ions released in normal tissue and maximizing Cu-induced cuproptosis therapeutic effects at tumor sites are the major challenges. In this study, exploiting the chemical properties of copper ionophores and the tumor microenvironment, a novel method is developed for controlling the valence of copper ions that cause photoinduced cuproptosis in tumor cells. CJS-Cu nanoparticles (NPs) can selectively induce cuproptosis after cascade reactions through H2 O2 -triggered Cu2+ release, photoirradiation-induced superoxide radical (∙O2 - ) generation, and reduction of Cu2+ to Cu+ by ∙O2 - . The generated reactive oxygen species can result in glutathione depletion and iron-sulfur cluster protein damage and further augmented cuproptosis. CJS-Cu NPs effectively suppressed tumor growth and downregulated the expression of metastasis-related proteins, contributing to the complete inhibition of lung metastasis. Ultimately, this study suggests novel avenues for the manipulation of cellular cuproptosis through photochemical reactions.

Design strategies for enhancing antitumor efficacy through tumor microenvironment exploitation using albumin-based nanosystems: A review

The tumor microenvironment (TME) is a complex and dynamic system that plays a crucial role in regulating cancer progression, treatment response, and the emergence of acquired resistance mechanisms. The TME is usually featured by severe hypoxia, low pH values, high hydrogen peroxide (H2O2) concentrations, and overproduction of glutathione (GSH). The current development of intelligent nanosystems that respond to TME has shown great potential to enhance the efficacy of cancer treatment. As one of the functional macromolecules explored in this field, albumin-based nanocarriers, known for their inherent biocompatibility, serves as a cornerstone for constructing diverse therapeutic platforms. In this paper, we present a comprehensive overview of the latest advancements in the design strategies of albumin nanosystems, aiming to enhance cancer therapy by harnessing various features of solid tumors, including tumor hypoxia, acidic pH, the condensed extracellular matrix (ECM) network, excessive GSH, high glucose levels, and tumor immune microenvironment. Furthermore, we highlight representative designs of albumin-based nanoplatforms by exploiting the TME that enhance a broad range of cancer therapies, such as chemotherapy, phototherapy, radiotherapy, immunotherapy, and other tumor therapies. Finally, we discuss the existing challenges and future prospects in direction of albumin-based nanosystems for the practical applications in advancing enhanced cancer treatments.

Suppressing ACQ of molecular photosensitizers by distorting the conjugated-plane for enhanced tumor photodynamic therapy

Non-AIE-type molecular photosensitizers (PSs) suffer from the aggregation-caused-quenching (ACQ) effect in an aqueous medium due to the strong hydrophobic and π-π interactions of their conjugated planes, which significantly hinders the enhancement of tumor photodynamic therapy (PDT). So far, some ionic PSs have been reported with good water-solubility, though the ACQ effect can still be induced in a biological environment rich in ions, leading to unsatisfactory in vivo delivery and fluorescence imaging performance. Hence, designing molecular PSs with outstanding anti-ACQ properties in water is highly desirable, but it remains a tough challenge for non-AIE-type fluorophores. Herein, we demonstrated a strategy for the design of porphyrin-type molecular PSs with remarkable solubility and anti-ACQ properties in an aqueous medium, which was assisted by quantum chemical simulations. It was found that cationic branched side chains can induce serious plane distortion in diphenyl porphyrin (DPP), which was not observed for tetraphenyl porphyrin (TPP) with the same side chains. Moreover, the hydrophilicity of the chain spacer is also crucial to the plane distortion for attaining the desired anti-ACQ properties. Compared to ACQ porphyrin, anti-ACQ porphyrin displayed type-I ROS generation in hypoxia and much higher tumor accumulation efficacy by blood circulation, leading to highly efficient in vivo PDT for hypoxic tumors. This study demonstrates the power of sidechain chemistry in tuning the configuration and aggregation behaviors of porphyrins in water, offering a new path to boost the performance of PSs to fulfill the increasing clinical demands on cancer theranostics.

B-embedded disulfide-bridged π-conjugated compounds: structures and optical tuning

Two novel B-embedded disulfide-bridged π-conjugated compounds (BS-CZ and BS-N) bearing different electron donor groups (phenyl carbazole and triphenylamine) have been prepared and show different optical mechanisms. The compound BS-CZ exhibits significant multiple resonance thermal activation delayed fluorescence (MR-TADF) properties with a small singlet-triplet energy gap (ΔEST = 0.16 eV) and a narrow half-peak full width (FWHM = 33 nm), while the compound BS-N shows traditional fluorescence luminescence (FL) characteristics with a larger ΔEST (0.28 eV) and FWHM (57 nm). Time-dependent density functional theory (TD-DFT) calculations show that the lowest excited singlet state (S1) of the compound BS-CZ exhibits local excited (LE) state characteristics, while the charge transfer (CT) state characteristics can be found in S1 of the compound BS-N. Considering good optical performance, the compound BS-CZ is used as an emitting layer of the organic light-emitting diode device and achieved saturated blue emission (473 nm) with a narrow FWHM (39 nm), and CIE color coordinates of (0.12, 0.21). This work provides an important strategy for the optical mechanism regulation and photoelectric applications of B-embedded disulfide-bridged π-conjugated molecules.

Reactive Reductive Species Participating Photodynamic Therapy for Cancer Treatment

Although the development of oxidative photodynamic therapy (O-PDT) based on reactive oxygen species (ROS) has led to great progress in cancer treatment, tumor hypoxia, cellular adaptation and intrinsic antioxidant defenses are still obstacles at this stage. Fortunately, with the discovery and development of reactive reductive species (RRS) in the PDT process, reductive PDT (R-PDT) is receiving increasing research interest. R-PDT with oxygen-independence is an effective reduction therapy that promises excellent therapeutic efficacy in extremely hypoxic or even anaerobic environments. In the concept, we introduce representative strategies to boost the type-I photosensitizing pathway, and then focus on the most recent R-PDT involving hydrogen radical (H⋅) and the single electron transfer (SET) process.

NIR-II Emissive Superoxide Radical Photogenerator for Photothermal/Photodynamic Therapy against Hypoxic Tumor

Due to the "Achilles' heels" of hypoxia, complicated location in solid tumor, small molecular photosensitizers with second near-infrared window (NIR-II) fluorescence, type-I photodynamic therapy (PDT), and photothermal therapy (PTT) have attracted great attention. However, these photosensitizers are still few but yet challenging. Herein, an "all in one" NIR-II acceptor-donor-acceptor fused-ring photosensitizer, Y6-Th, is presented for the in-depth diagnosis and efficient treatment of cancer. Benefiting from the strong intramolecular charge transfer, promoted highly efficient intersystem crossing, largely p-conjugated fused-ring structure, and reduced planarity, the fabricated nanoparticles (Y6-Th nanoparticles) can emit NIR-II fluorescence with the peak located at 1020 nm, exclusively generate O2•- for type-I PDT, and display excellent PTT performance under an 808 nm laser stimulation. These characteristics make Y6-Th a distinguished NIR-wavelength-triggered phototheranostic agent, which can effectively therapy the hypoxic tumor using NIR-II-fluorescence-guided type-I PDT/PTT. This work provides a valuable guideline for fabricating high-performing NIR-II emissive superoxide radical photogenerators.

Exploration of Thermally Activated Delayed Fluorescence (TADF)-Based Photoredox Catalyst To Establish the Mechanisms of Action for Photodynamic Therapy

The mechanisms of action (MoA) have been proposed to further reduce the O2 dependence of photodynamic therapy (PDT) significantly. However, the triplet states of traditional photosensitizers are relatively short and also are easily deactivated by the quenching of H2O or O2. This is not conducive for the electron transfer in the photocatalytic process and poses a great obstacle to establish the MoA. Therefore, we selected and synthesized a zirconium(IV) complex (Zr(MesPDPPh)2) reported by Milsmann to address this issue. The specific symmetric and intact geometry endowed Zr(MesPDPPh)2 NPs with long-lived triplet excited state (τ = 350 μs), desired sensitized ability, and improved anti-interfering performance on O2, which was matched with the requirements of photoredox catalyst significantly. The results showed that while PDT (I) and PDT (II) could be achieved simultaneously by leveraging Zr(MesPDPPh)2 NPs, it also could be served as a rare example of thermally activated delayed fluorescence (TADF)-based photoredox catalyst to implement the MoA of PDT. It involved the oxidation of NADH and the establishment of catalytic cycle collaborating by O2 and cytochrome c (cyt c) in normoxia and hypoxia, respectively. As a result, the oxygen-free PDT and tumor-growth inhibition was realized.

Type-I Photosensitizer-Triggered Controllable Carbon Monoxide Release for Effective Treatment of Staph Skin Infection

Staphylococcus aureus (S. aureus) infection is a major infectious skin disease that is highly resistant to conventional antibiotic treatment and host immune defense, leading to recurrence and exacerbation of bacterial infection. Herein, we developed a photoresponsive carbon monoxide (CO)-releasing nanocomposite by integrating anion-π+ type-I photosensitizer (OMeTBP) and organometallic complex (FeCO) for the treatment of planktonic S. aureus and biofilm-associated infections. After optimizing the molar ratio of FeCO and OMeTBP, the prepared nanoparticles, OMeTBP@FeCONPs, not only ensured sufficient loading of CO donors and efficient CO generation but also showed negligible free ROS leakage under light irradiation, which helped to avoid tissue damage caused by excessive ROS. Both in vitro and in vivo results demonstrated that OMeTBP@FeCONPs could effectively inhibit S. aureus methicillin-resistant S. aureus (MRSA), and bacterial biofilm. Our design has the potential to overcome the resistance of conventional antibiotic treatment and provide a more effective option for bacterial infections.

Metal-Organic Framework for Hypoxia/ROS/pH Triple-Responsive Cargo Release

Nanoparticulate antitumor photodynamic therapy (PDT) is suffering from a very short lifetime, limited diffusion distance of reactive oxygen species (ROS). Herein, a hypoxia/ROS/pH triple-responsive metal-organic framework (MOF) is designed to facilitate the on-demand release of photosensitizers and hence enhanced PDT efficacy. Tailored azo-containing imidazole ligand is coordinated with zinc to form MOF where photosensitizer (Chlorin e6/Ce6) is encapsulated. Azo can be reduced by overexpressed azoreductase in hypoxic tumor cells, resulting in depletion of glutathione (GSH) and thioredoxin (Trx) which are major antioxidants against ROS oxidative damage in PDT, resulting in rapid cargo release and additional efficacy amplification. The imidazole ionization causes a proton sponge effect to ensure the disintegration of the nanocarriers in acidic organelles, allowing the rapid release of Ce6 through lysosome escape. Under light irradiation, ROS produced by Ce6 may oxidize imidazole to urea, resulting in rapid cargo release. All of the triggers are expected to show interactive synergism. The pH- and hypoxia-responsiveness can improve the release rate of Ce6 for enhanced PDT therapy, whereas the consumption of oxygen by PDT may induce elevated hypoxia and hence in turn enhanced cargo release. This work highlights the role of triple-responsive nanocarriers for triggered photosensitizer release and improved antitumor PDT efficacy.

Tumor Stimulus-Activatable Pretheranostic Agent: One Key to Three Locks

The uncontrollable distribution of antitumor agents remains a large obstacle for specific and efficient cancer theranostics; thus, efficient construction of tumor-specific systems is highly desirable. In this work, a general design of tumor stimulus-activatable pretheranostic agents was put forward via a series of structures-tunable triphenylamine derivatives (TPA-2T-FSQ, TPA-2T-BSZ, and TPA-2T-ML) with phenothiazine, benzothiazine, and thiomorpholine as identifying groups of hypochlorite (HClO), respectively. Notably, the sulfur atom in phenothiazine of TPA-2T-FSQ was more easily oxidized to sulfoxide groups by HClO, transforming into an electron acceptor to form an excellent push-pull electronic system, which was beneficial to a large redshift of absorbance and emission wavelengths. Based on this, TPA-2T-FSQ resorted to a key of overexpressed HClO in the tumor to open "three locks", viz, NIR fluorescence, photothermal, and photoacoustic signals for multimodal diagnostic and treatment of the tumor. This study provided an elegant design to adopt tumor stimulus-triggerable pretheranostic for improving theranostic accuracy and efficiency, which was regarded as a promising candidate for precision medicine.

Iridium(III)-Based Infrared Two-Photon Photosensitizers: Systematic Regulation of Their Photodynamic Therapy Efficacy

Cyclometalated iridium(III) complexes are of significant importance in the field of antitumor photodynamic therapy (PDT), whether they exist as single molecules or are incorporated into nanomaterials. Nevertheless, a comprehensive examination of the relationship between their molecular structure and PDT effectiveness remains awaited. The influencing factors of two-photon excited PDT can be anticipated to be further multiplied, particularly in relation to intricate nonlinear optical properties. At present, a comprehensive body of research on this topic is lacking, and few discernible patterns have been identified. In this study, through systematic structure regulation, the nitro-substituted styryl group and 1-phenylisoquinoline ligand containing YQ2 was found to be the most potent infrared two-photon excitable photosensitizer in a 4 × 3 combination library of cyclometalated Ir(III) complexes. YQ2 could enter cells via an energy-dependent and caveolae-mediated pathway, bind specifically to mitochondria, produce 1O2 in response to 808 nm LPL irradiation, activate caspases, and induce apoptosis. In vitro, YQ2 displayed a remarkable phototherapy index for both malignant melanoma (>885) and non-small-cell lung cancer (>1234) based on these functions and was minimally deleterious to human normal liver and kidney cells. In in vivo antitumor phototherapy, YQ2 inhibited tumor growth by an impressive 85% and could be eliminated from the bodies of mice with a half-life as short as 43 h. This study has the potential to contribute significantly to the development of phototherapeutic drugs that are extremely effective in treating large, profoundly located solid tumors as well as the understanding of the structure-activity relationship of Ir(III)-based PSs in PDT.

Recent Advances in Nanomaterials-Based Targeted Drug Delivery for Preclinical Cancer Diagnosis and Therapeutics

Nano-oncology is a branch of biomedical research and engineering that focuses on using nanotechnology in cancer diagnosis and treatment. Nanomaterials are extensively employed in the field of oncology because of their minute size and ultra-specificity. A wide range of nanocarriers, such as dendrimers, micelles, PEGylated liposomes, and polymeric nanoparticles are used to facilitate the efficient transport of anti-cancer drugs at the target tumor site. Real-time labeling and monitoring of cancer cells using quantum dots is essential for determining the level of therapy needed for treatment. The drug is targeted to the tumor site either by passive or active means. Passive targeting makes use of the tumor microenvironment and enhanced permeability and retention effect, while active targeting involves the use of ligand-coated nanoparticles. Nanotechnology is being used to diagnose the early stage of cancer by detecting cancer-specific biomarkers using tumor imaging. The implication of nanotechnology in cancer therapy employs photoinduced nanosensitizers, reverse multidrug resistance, and enabling efficient delivery of CRISPR/Cas9 and RNA molecules for therapeutic applications. However, despite recent advancements in nano-oncology, there is a need to delve deeper into the domain of designing and applying nanoparticles for improved cancer diagnostics.

Recent advances in type I organic photosensitizers for efficient photodynamic therapy for overcoming tumor hypoxia

Photodynamic therapy (PDT) with an oxygen-dependent character is a noninvasive therapeutic method for cancer treatment. However, its clinical therapeutic effect is greatly restricted by tumor hypoxia. What's more, both PDT-mediated oxygen consumption and microvascular damage aggravate tumor hypoxia, thus, further impeding therapeutic outcomes. Compared to type II PDT with high oxygen dependence and high oxygen consumption, type I PDT with less oxygen consumption exhibits great potential to overcome the vicious hypoxic plight in solid tumors. Type I photosensitizers (PSs) are significantly important for determining the therapeutic efficacy of PDT, which performs an electron transfer photochemical reaction with the surrounding oxygen/substrates to generate highly cytotoxic free radicals such as superoxide radicals (˙O₂^-) as type I ROS. In particular, the primary precursor (˙O₂^-) would progressively undergo a superoxide dismutase (SOD)-mediated disproportionation reaction and a Haber-Weiss/Fenton reaction, yielding higher cytotoxic species (˙OH) with better anticancer effects. As a result, developing high-performance type I PSs to treat hypoxic tumors has become more and more important and urgent. Herein, the latest progress of organic type I PSs (such as AIE-active cationic/neutral PSs, cationic/neutral PSs, polymer-based PSs and supramolecular self-assembled PSs) for monotherapy or synergistic therapeutic modalities is summarized. The molecular design principles and strategies (donor-acceptor system, anion-π⁺ incorporation, polymerization and cationization) are highlighted. Furthermore, the future challenges and prospects of type I PSs in hypoxia-overcoming PDT are proposed.