Superoxide Radical Photogenerator with Amplification Effect: Surmounting the Achilles’ Heels of Photodynamic Oncotherapy

Photoimmunotherapy for cancer treatment based on organic small molecules: Recent strategies and future directions

Photodynamic therapy (PDT) is considered as a promising anticancer approach, owning to its high efficiency and spatiotemporal selectivity. Ample evidence indicated that PDT can trigger immunogenic cell death by releasing antigens that activate immune cells to promote anti-tumor immunity. Nevertheless, the inherent nature of tumors and their complex heterogeneity often limits the efficiency of PDT, which can be overcome with a novel strategy of photo-immunotherapy (PIT) strategy. By exploring the principles of PDT induction and ICD enhancement, combined with other therapies such as chemotherapy or immune checkpoint blockade, the tailored solutions can be designed to address specific challenges of drug resistance, hypoxic conditions, and tumor immunosuppressive microenvironments (TIMEs), which enables targeted enhancement of systemic immunity to address most distant and recurrent cancers. The present article summarizes the specific strategies of PIT and discusses recent existing limitations. More importantly, we anticipate that the perspectives presented herein will help address the clinical translation challenges associated with PIT.

Theoretical Investigation of Novel Nitrogen-Heterocyclic Iridium(III) Polypyridyl Complexes as Photosensitizers for Two-Photon Photodynamic Therapy

Two-photon photodynamic therapy (TP-PDT) has become a major cancer treatment due to its larger tissue penetration depth, good spatial selectivity, and less damage to normal cells. In this contribution, a series of novel photosensitizer molecules (Ir-2, Ir-2-1∼Ir-2-4) have been designed based on the experimentally demonstrated photosensitizer [Ir(ppy)2(osip)] (PF6) by fine tuning the π-conjugated structure and introducing different nitrogen-heterocyclic substituents. The electronic structures, one- and two-photon absorption spectra, triplet excited state lifetime, solvation-free energy, and photosensitizing performance were evaluated by means of density functional theory (DFT) and time-dependent density functional theory (TDDFT). The results suggested that the molecule Ir-2, incorporating thiophene as the π-connecting group, exhibits a higher probability of triplet state formation, enhanced two-photon absorption cross-section, and prolonged triplet state lifetime. Furthermore, the four designed nitrogen-heterocyclic complexes Ir-2-1∼Ir-2-4 demonstrate favorable photosensitizing properties, with two-photon absorption cross-sections reaching up to 110 GM and triplet excited state lifetimes exceeding 1000 μs for Ir-2-4.

In vivo targeted-imaging of mitochondrial acidification in an aristolochic acid I-induced nephrotoxicity mouse model by a fluorescent/photoacoustic bimodal probe

Aristolochic acid I (AAI), a natural compound in aristolochia type Chinese medicinal herb, is generally acknowledged to have nephrotoxicity, which may be associated with mitophagy. Mitophagy is a cellular process with important functions that drive AAI-induced renal injury. Mitochondrial pH is currently measured by fluorescent probes in cell culture, but existing probes do not allow for in situ imaging of AAI-induced mitophagy in vivo. We developed a ratiometric fluorescent/PA dual-modal probe with a silicon rhodamine fluorophore and a pH-sensitive hemicyanine dye covalently linked via a short chain to obtain a FRET type probe. The probe was used to measure AAI-mediated mitochondrial acidification in live cells and in vivo. The Förster resonance energy transfer (FRET)-mediated ratiometric and bimodal method can efficiently eliminate signal variability associated with the commonly used one-emission and single detection mode by ratiometric two channels of the donor and acceptor. The probe has good water-solubility and low molecular weight with two positively charged, facilitating its precise targeting into renal mitochondria, where the fluorescent/PA changes in response to mitochondrial acidification, enabling dynamic and semi-quantitative mapping of subtle changes in mitochondrial pH in AAI-induced nephrotoxicity mouse model for the first time. Also, the joint use of L-carnitine could mitigate the mitophagy in AAI-induced nephrotoxicity.

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.

Trapped in Cells: A Selective Accumulation Approach for Type-I Photodynamic Ablation of Cancer Stem-like Cells

Aldehyde dehydrogenase (ALDH) is an enzyme responsible for converting aldehyde functional groups into carboxylate metabolites. Elevated ALDH activity is a characteristic feature of cancer stem-like cells (CSCs). As a novel approach to target the CSC trait of overexpressing ALDH, we aimed to utilize ALDH activity for the selective accumulation of a photosensitizer in ALDHHigh CSCs. A novel ALDH substrate photosensitizer, SCHO, with thionylated coumarin and N-ethyl-4-(aminomethyl)benzaldehyde was developed to achieve this goal. Our study demonstrated the efficient metabolism of the aldehyde unit of SCHO into carboxylate, leading to its accumulation in ALDHHigh MDA-MB-231 cells. Importantly, we established the selectivity of SCHO as an ALDHHigh cell photosensitizer as it is not a substrate for ABC transporters. SCHO-based photodynamic therapy triggers apoptosis and pyroptosis in MDA-MB-231 cells and further reduces the characteristics of CSCs. Our study presents a novel strategy to target CSCs by exploiting their cellular metabolism to enhance photosensitizer accumulation, highlighting the potential of photodynamic therapy as a powerful tool for eliminating ALDHHigh CSCs.

Preparation of Composite Hydrogels Based on Cysteine-Silver Sol and Methylene Blue as Promising Systems for Anticancer Photodynamic Therapy

In this study, a novel supramolecular composite, "photogels", was synthesized by mixing of cysteine-silver sol (CSS) and methylene blue (MB). A complex of modern physico-chemical methods of analysis such as viscosimetry, UV spectroscopy, dynamic and electrophoretic light scattering, scanning electron microscopy and energy-dispersive X-ray spectroscopy showed that MB molecules are uniformly localized mainly in the space between fibers of the gel-network formed by CSS particles. Molecules of the dye also bind with the surface of CSS particles by non-covalent interactions. This fact is reflected in the appearance of a synergistic anticancer effect of gels against human squamous cell carcinoma even in the absence of light irradiation. A mild toxic influence of hydrogels was observed in normal keratinocyte cells. Photodynamic exposure significantly increased gel activity, and there remained a synergistic effect. The study of free-radical oxidation in cells has shown that gels are not only capable of generating reactive oxygen species, but also have other targets of action. Flow cytometric analysis allowed us to find out that obtained hydrogels caused cell cycle arrest both without irradiation and with light exposure. The obtained gels are of considerable interest both from the point of view of academics and applied science, for example, in the photodynamic therapy of superficial neoplasms.

Designing NIR AIEgens for lysosomes targeting and efficient photodynamic therapy of tumors

Cancer is the most severe health problem facing most people today. Photodynamic therapy (PDT) for tumors has attracted attention because of its non-invasive nature, negligible adverse reactions, and high spatiotemporal selectivity. Developing biocompatible photosensitizers that can target, guide, and efficiently kill cancer cells is desirable in PDT. Here, two amphiphilic organic compounds, PS-I and PSS-II, were synthesized based on the D-π-A structure with a positive charge. The two AIEgens exhibited near-infrared emission, large Stokes shift, high 1O2 and O2-∙ generation efficiency, good biocompatibility, and photostability. They were co-incubated with cancer cells and eventually accumulated to lysosomes by cell imaging experiments. In vitro and in vivo experiments demonstrated that PS-I and PSS-II could effectively kill cancer cells and sufficiently inhibit tumor growth under light irradiation. PS-I had a higher fluorescence quantum yield in the aggregated state, which made it better for bio-imaging in imaging-guided photodynamic therapy. In contrast, PSS-II with a longer conjugated structure had more ROS generation to kill tumor cells under illumination, and the tumor growth inhibition of mice reached 71.95% during the treatment. No observable injury or undesirable outcomes were detected in the vital organs of the mice within the treatment group, suggesting that PSS-II/PS-I had a promising future in efficient imaging-guided PDT for cancer.

Self-reporting photodynamic nanobody conjugate for precise and sustainable large-volume tumor treatment

Nanobodies (Nbs), the smallest antigen-binding fragments with high stability and affinity derived from the variable domain of naturally occurring heavy-chain-only antibodies in camelids, have been shown as an efficient way to improve the specificity to tumors for photodynamic therapy (PDT). Nonetheless, the rapid clearance of Nbs in vivo restricts the accumulation and retention of the photosensitizer at the tumor site causing insufficient therapeutic outcome, especially in large-volume tumors. Herein, we develop photodynamic conjugates, MNB-Pyra Nbs, through site-specific conjugation between 7D12 Nbs and type I photosensitizer MNB-Pyra (morpholine-modified nile blue structure connected to pyrazolinone) in a 1:2 ratio. The photosensitizers with long-term retention can be released at the tumor site by reactive oxygen species cleavage after illumination, accompanied with fluorescence recovery for self-reporting the occurrence of PDT. Ultimately, a single dose of MNB-Pyra Nbs demonstrate highly effective tumor suppression with high biosafety in the large-volume tumor models after three rounds of PDT. This nanobody conjugate provides a paradigm for the design of precise long-time retention photosensitizers and is expected to promote the development of PDT.

In situ self-assembled near-infrared phototherapeutic agent: unleashing hydrogen free radicals and coupling with NADPH oxidation

Investigation of electron transfer (ET) between photosensitizers (PSs) and adjacent substrates in hypoxic tumors is integral to highly efficient tumor therapy. Herein, the oxygen-independent ET pathway to generate hydrogen free radicals (H˙) was established by the in situ self-assembled phototherapeutic agent d-ST under near-infrared (NIR)-light irradiation, coupled with the oxidation of reduced coenzyme NADPH, which induced ferroptosis and effectively elevated the therapeutic performance in hypoxic tumors. The higher surface energy and longer exciton lifetimes of the fine crystalline d-ST nanofibers were conducive to improving ET efficiency. In hypoxic conditions, the excited d-ST can effectively transfer electrons to water to yield H˙, during which the overexpressed NADPH with rich electrons can power the electron flow to facilitate the generation of H˙, accompanied by NADP+ formation, disrupting cellular homeostasis and triggering ferroptosis. Tumor-bearing mouse models further showed that d-ST accomplished excellent phototherapy efficacy. This work sheds light onto the versatile electron pathways between PSs and biological substrates.

Recent advances for enhanced photodynamic therapy: from new mechanisms to innovative strategies

Photodynamic therapy (PDT) has been developed as a potential cancer treatment approach owing to its non-invasiveness, spatiotemporal control and limited side effects. Currently, great efforts have been made to improve the PDT effect in terms of safety and efficiency. In this review, we highlight recent advances in innovative strategies for enhanced PDT, including (1) the development of novel radicals, (2) design of activatable photosensitizers based on the TME and light, and (3) photocatalytic NADH oxidation to damage the mitochondrial electron transport chain. Additionally, the new mechanisms for PDT are also presented as an inspiration for the design of novel PSs. Finally, we discuss the current challenges and future prospects in the clinical practice of these innovative strategies. It is hoped that this review will provide a new angle for understanding the relationship between the intratumoural redox environment and PDT mechanisms, and new ideas for the future development of smart PDT systems.

Rod-Shaped Au@Ce Nano-Platforms for Enhancing Photodynamic Tumor Collaborative Therapy

Tumor photodynamic therapy (PDT) relies on intratumoral free radicals, while the limited oxygen source and the depletion of tissue oxygen may exacerbate the hypoxia. As the treatment progresses, there will eventually be a problem of insufficient free radicals. Here, it is found that Au@CeO2 nano-rods (Au@Ce NRs), assembled by gold nano-rods (Au NRs) and ceria nanoparticles (CeO2 NPs), can efficaciously absorb near-infrared light (NIR) to promote the release of oxygen and free radicals. Au@Ce NRs exhibit a higher proportion of Ce3+ (Ce2O3) after oxygen release, while Ce3+ is subsequently oxidized to Ce4+ (CeO2) by trace H2O2. Interestingly, Au@Ce NRs re-oxidized by trace H2O2 can re-releasing oxygen and free radicals again upon NIR treatment, achieving oxygenation/oxygen evolution, similar to charging/discharging. This loop maximizes the conversion of limited oxygen source into highly cytotoxic free radicals. As a result, when B16-F10 cells are treated by NIR/Au@Ce NRs, more tumor cells undergo apoptosis, consistent with the higher level of free radicals. Importantly, NIR/Au@Ce NRs successfully suppresses tumor growth and promotes the generation of epidermal collagen fibers in the transplanted tumor model. Therefore, the rod-shaped Au@Ce NRs provide an ideal platform for maximizing the utilization of intratumoral oxygen sources and improving the treatment of melanoma.

Totally Caged Type I Pro-Photosensitizer for Oxygen-Independent Synergistic Phototherapy of Hypoxic Tumors

Activatable type I photosensitizers are an effective way to overcome the insufficiency and imprecision of photodynamic therapy in the treatment of hypoxic tumors, however, the incompletely inhibited photoactivity of pro-photosensitizer and the limited oxidative phototoxicity of post-photosensitizer are major limitations. It is still a great challenge to address these issues using a single and facile design. Herein, a series of totally caged type I pro-photosensitizers (Pro-I-PSs) are rationally developed that are only activated in tumor hypoxic environment and combine two oxygen-independent therapeutic mechanisms under single-pulse laser irradiation to enhance the phototherapeutic efficacy. Specifically, five benzophenothiazine-based dyes modified with different nitroaromatic groups, BPN 1-5, are designed and explored as latent hypoxia-activatable Pro-I-PSs. By comparing their optical responses to nitroreductase (NTR), it is identified that the 2-methoxy-4-nitrophenyl decorated dye (BPN 2) is the optimal Pro-I-PSs, which can achieve NTR-activated background-free fluorescence/photoacoustic dual-modality tumor imaging. Furthermore, upon activation, BPN 2 can simultaneously produce an oxygen-independent photoacoustic cavitation effect and a photodynamic type I process at single-pulse laser irradiation. Detailed studies in vitro and in vivo indicated that BPN 2 can effectively induce cancer cell apoptosis through synergistic effects. This study provides promising potential for overcoming the pitfalls of hypoxic-tumor photodynamic therapy.

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.

Gram-negative bacteria recognition and photodynamic elimination by Zn-DPA based sensitizers

The abuse and overuse of antibiotics let drug-resistant bacteria emerges. Antibacterial photodynamic therapy (APDT) has shown outstanding merits to eliminate the drug-resistant bacteria via cytotoxic reactive oxygen species produced by irradiating photosensitizer. However, most of photosensitizers are not effective for Gram-negative bacteria elimination. Herein conjugates of NBS, a photosensitizer, linked with one (NBS-DPA-Zn) or two (NBS-2DPA-Zn) equivalents of zinc-dipicolylamine (Zn-DPA) have been designed to achieve the functional recognition of different bacteria. Due to the cationic character of NBS and metal transfer channel effect of Zn-DPA, NBS-DPA-Zn exhibited the first regent to distinguish P. aeruginosa from other Gram-negative bacteria. Whereas NBS-2DPA-Zn showed broad-spectrum antibacterial effect because the two arm of double Zn-DPA enhanced interactions with anionic membranes of bacteria, led the bacteria aggregation and thus provided the efficacy of APDT to bacteria and corresponding biofilm. In combination with a hydrogel of Pluronic, NBS-2DPA-Zn@gel shows promising clinical application in mixed bacterial diabetic mouse model infection. This might propose a new method that can realize functional identification and elimination of bacteria through intelligent regulation of Zn-DPA, and shows excellent potential for antibacterial application.

"Cicada Out of the Shell" Deep Penetration and Blockage of the HSP90 Pathway by ROS-Responsive Supramolecular Gels to Augment Trimodal Synergistic Therapy

Deep penetration and downregulation of heat shock protein (HSP) expression in multimodal synergistic therapy are promising approaches for curing cancer in clinical trials. However, free small-molecule drugs and most drug vehicles have a low delivery efficiency deep into the tumor owing to poor drug penetration and hypoxic conditions at the tumor site. In this study, the objective is to use reactive oxygen species (ROS)-responsive supramolecular gels co-loaded with the photosensitizer Zn(II) phthalocyanine tetrasulfonic acid (ZnPCS4) and functionalized tetrahedral DNA (TGSAs) (G@P/TGSAs) to enhance deep tissue and cell penetration and block the HSP90 pathway for chemo- photodynamic therapy (PDT) - photothermal therapy (PTT) trimodal synergistic therapy. The (G@P/TGSAs) are injected in situ into the tumor to release ZnPCS4 and TGSAs under high ROS concentrations originating from both the tumor and PDT. TGSAs penetrate deeply into tumor tissues and augment photothermal therapy by inhibiting the HSP90 pathway. Proteomics show that HSP-related proteins and molecular chaperones are inhibited/activated, inhibiting the HSP90 pathway. Simultaneously, the TGSA-regulated apoptotic pathway is activated. In vivo study demonstrates efficient tumor penetration and excellent trimodal synergistic therapy (45% tumor growth inhibition).

Switchable Site-Selective Benzanilide C(sp2)-H Bromination via Promoter Regulation

Regioselective benzanilide bromination that generates either regioisomer from the same starting material is desirable. Herein, we develop switchable site-selective C(sp2)-H bromination by promoter regulation. This protocol leads to regiodivergent brominated benzanilide starting from the single substrate via selection of promoters. The protocol demonstrates excellent regioselectivity and good tolerance of functional groups with high yields. The utility effectiveness of this method has been well exemplified in the late-stage modification of biologically important molecules.

Novel angiogenesis inhibitors with superoxide anion radical amplification effect: Surmounting the Achilles' heels of angiogenesis inhibitors and photosensitizers

Angiogenesis inhibitors and photosensitizers are pivotal in tumor clinical treatment, yet their utilization is constrained. Herein, eleven novel angiogenesis inhibitors were developed through hybridization strategy to overcome their clinical limitations. These title compounds boast excitation wavelengths within the "therapeutic window", enabling deep tissue penetration. Notably, they could generate superoxide anion radicals via the Type I mechanism, with compound 36 showed the strongest superoxide anion radical generating capacity. Biological evaluation demonstrated remarkable cellular activity of all the title compounds, even under hypoxic conditions. Among them, compound 36 stood out for its superior anti-proliferative activity in both normoxic and hypoxic environments, surpassing individual angiogenesis inhibitors and photosensitizers. Compound 36 induced cell apoptosis via superoxide anion radical generation, devoid of dark toxicity. Molecular docking revealed that the target-recognizing portion of compound 36 was able to insert into the ATP binding pocket of the target protein similar to sorafenib. Collectively, our results suggested that hybridization of angiogenesis inhibitors and photosensitizers was a potential strategy to address the limitations of their clinical use.

NIR-II Light-Driven Genetically Engineered Exosome Nanocatalysts for Efficient Phototherapy against Glioblastoma

Glioblastoma (GBM) poses a significant therapeutic challenge due to its invasive nature and limited drug penetration through the blood-brain barrier (BBB). In response, here we present an innovative biomimetic approach involving the development of genetically engineered exosome nanocatalysts (Mn@Bi2Se3@RGE-Exos) for efficient GBM therapy via improving the BBB penetration and enzyme-like catalytic activities. Interestingly, a photothermally activatable multiple enzyme-like reactivity is observed in such a nanosystem. Upon NIR-II light irradiation, Mn@Bi2Se3@RGE-Exos are capable of converting hydrogen peroxide into hydroxyl radicals, oxygen, and superoxide radicals, providing a peroxidase (POD), oxidase (OXD), and catalase (CAT)-like nanocatalytic cascade. This consequently leads to strong oxidative stresses to damage GBM cells. In vitro, in vivo, and proteomic analysis further reveal the potential of Mn@Bi2Se3@RGE-Exos for the disruption of cellular homeostasis, enhancement of immunological response, and the induction of cancer cell ferroptosis, showcasing a great promise in anticancer efficacy against GBM with a favorable biosafety profile. Overall, the success of this study provides a feasible strategy for future design and clinical study of stimuli-responsive nanocatalytic medicine, especially in the context of challenging brain cancers like GBM.

First-principles design of heavy-atom-free singlet oxygen photosensitizers for photodynamic therapy

In photodynamic therapy (PDT) treatment, heavy-atom-free photosensitizers (PSs) are a great source of singlet oxygen photosensitizer. Reactive oxygen species (ROS) are produced by an energy transfer from the lowest energy triplet excited state to the molecular oxygen of cancer cells. To clarify the photophysical characteristics in the excited states of a few experimentally identified thionated (>C=S) molecules and their oxygenated congeners (>C=O), a quantum chemical study is conducted. This study illustrates the properties of the excited states in oxygen congeners that render them unsuitable for PDT treatment. Concurrently, a hierarchy is presented based on the utility of the lowest-energy triplet excitons of thionated compounds. Their non-radiative decay rates are calculated for reverse-ISC and inter-system crossover (ISC) processes. In addition, the vibronic importance of C=O and C=S bonds is clarified by the computation of the Huang-Rhys factor, effective vibrational mode, and reorganization energy inside the Marcus-Levich-Jörtner system. ROS generation in thionated PSs exceeds their oxygen congeners as kf ≪ kISC, where radiative decay rate is designated as kf. As a result, the current work offers a calculated strategy for analyzing the effectiveness of thionated photosensitizers in PDT.

Molecular engineering to design a bright near-infrared red photosensitizer: cellular bioimaging and phototherapy

Near-infrared red (NIR) fluorescence imaging guide phototherapeutic therapy (PDT) has the advantages of deep tissue penetration, real-time monitoring of drug treatment and disease, little damage to normal tissue, low cytotoxicity and almost no side effects, and thus, it is attracting increasing research attention and is expected to show promising potential for clinical tumor treatment. The photosensitizer (PS), light source and oxygen are the three basic and important factors to construct PDT technology, and highly efficient PSs are still being passionately pursued because they determine the PDT efficiency. Ideal PSs should have properties such as good biocompatibility, deep tissue penetration, and highly efficient reactive oxygen species (ROS) generation despite the hypoxic environment. Therefore, pure organic type I PSs with NIR fluorescence have been receiving increasing attention due to their deep penetration and hypoxia resistance. However, reported NIR-active type I PSs usually require complex synthetic procedures, which presents a challenge for mass production. In this research work, based on the molecular design ideas of introducing the heavy atom effect and intramolecular charge transfer, we prepared three NIR-active type I PSs (TNZ, TNZBr, and TNZCHO) using a very simple method with one or two synthetic steps. Clear characterizations of photophysical properties, ROS performance tests, and fluorescent imaging of human umbilical vein endothelial (HUVE) cells and PDT treatment of HepG2 cells were carried out. The results revealed that the heavy atom and intramolecular charge transfer (ICT) effects could obviously enhance the ROS efficiency, and both PSs produce only type I ROS without any type II ROS (1O2) generation. The good NIR fluorescence brightness and type I ROS efficiency ensure satisfactory bioimaging and PDT outcomes. This research provides the possibility of preparing NIR-active type I PSs via mass production.

Mitochondria-Targeting Type-I Photodrug: Harnessing Caspase-3 Activity for Pyroptotic Oncotherapy

Precise control of cellular signaling events during programmed cell death is crucial yet challenging for cancer therapy. The modulation of signal transduction in cancer cells holds promise but is limited by the lack of efficient, biocompatible, and spatiotemporally controllable approaches. Here we report a photodynamic strategy that modulates both apoptotic and pyroptotic cell death by altering caspase-3 protein activity and the associated signaling crosstalk. This strategy employs a mitochondria-targeting, near-infrared activatable probe (termed M-TOP) that functions via a type-I photochemical mechanism. M-TOP is less dependent on oxygen and more effective in treating drug-resistant cancer cells, even under hypoxic conditions. Our study shows that higher doses of M-TOP induce pyroptotic cell death via the caspase-3/gasdermin-E pathway, whereas lower doses lead to apoptosis. This photodynamic method is effective across diverse gasdermin-E-expressing cancer cells. Moreover, the M-TOP mediated shift from apoptotic to pyroptotic modulation can evoke a controlled inflammatory response, leading to a robust yet balanced immune reaction. This effectively inhibits both distal tumor growth and postsurgical tumor recurrence. This work demonstrates the feasibility of modulating intracellular signaling through the rational design of photodynamic anticancer drugs.

Cyclic peptide conjugated photosensitizer for targeted phototheranostics of gram-negative bacterial infection

Antimicrobial photodynamic therapy (PDT) is a promising alternative to antibiotics for eradicating pathogenic bacterial infections. It holds advantage of not inducing antimicrobial resistance but is limited for the treatment of gram-negative bacterial infection due to the lack of photosensitizer (PS) capable of targeted permeating the outer membrane (OM) of gram-negative bacteria. To facilitate the targeted permeability of PS, cyclic polymyxin b nonapeptide that can specifically bind to the lipopolysaccharide on OM, is conjugated to an FDA approved PS chlorin e6 via variable linkers. Based on structure to activity study, C6pCe6 with aminohexanoic linker and P2pCe6 with amino-3, 6-dioxaoctanoic linker are identified to preferentially image gram-negative bacteria. These two conjugates also exhibit improved aqueous dispersity and enhanced ROS generation, consequently enabled their selective bactericidal activities against gram-negative bacteria upon 660 nm light irradiation. The effective photobactericidal ability of P2pCe6 is further validated on P. aeruginosa infected G. mellonella. Moreover, it is demonstrated to effectively treat the P. aeruginosa infection and accelerate the healing process at the wound site of mouse. Owing to the light irradiation triggered targeted imaging and enhanced bactericidal capacities, P2pCe6 hold great potential to serve as a potent PS for mediating the phototheranostics of gram-negative bacterial infection.

Nanomaterials-Induced Redox Imbalance: Challenged and Opportunities for Nanomaterials in Cancer Therapy

Cancer cells typically display redox imbalance compared with normal cells due to increased metabolic rate, accumulated mitochondrial dysfunction, elevated cell signaling, and accelerated peroxisomal activities. This redox imbalance may regulate gene expression, alter protein stability, and modulate existing cellular programs, resulting in inefficient treatment modalities. Therapeutic strategies targeting intra- or extracellular redox states of cancer cells at varying state of progression may trigger programmed cell death if exceeded a certain threshold, enabling therapeutic selectivity and overcoming cancer resistance to radiotherapy and chemotherapy. Nanotechnology provides new opportunities for modulating redox state in cancer cells due to their excellent designability and high reactivity. Various nanomaterials are widely researched to enhance highly reactive substances (free radicals) production, disrupt the endogenous antioxidant defense systems, or both. Here, the physiological features of redox imbalance in cancer cells are described and the challenges in modulating redox state in cancer cells are illustrated. Then, nanomaterials that regulate redox imbalance are classified and elaborated upon based on their ability to target redox regulations. Finally, the future perspectives in this field are proposed. It is hoped this review provides guidance for the design of nanomaterials-based approaches involving modulating intra- or extracellular redox states for cancer therapy, especially for cancers resistant to radiotherapy or chemotherapy, etc.

Type I photodynamic antimicrobial therapy: Principles, progress, and future perspectives

The emergence of drug-resistant bacteria has significantly diminished the efficacy of existing antibiotics in the treatment of bacterial infections. Consequently, the need for finding a strategy capable of effectively combating bacterial infections has become increasingly urgent. Photodynamic therapy (PDT) is considered one of the most promising emerging antibacterial strategies due to its non-invasiveness, low adverse effect, and the fact that it does not lead to the development of drug resistance. However, bacteria at the infection sites often exist in the form of biofilm instead of the planktonic form, resulting in a hypoxic microenvironment. This phenomenon compromises the treatment outcome of oxygen-dependent type-II PDT. Compared to type-II PDT, type-I PDT is not constrained by the oxygen concentration in the infected tissues. Therefore, in the treatment of bacterial infections, type-I PDT exhibits significant advantages over type-II PDT. In this review, we first introduce the fundamental principles of type-I PDT in details, including its physicochemical properties and how it generates reactive oxygen species (ROS). Next, we explore several specific antimicrobial mechanisms utilized by type-I PDT and summarize the recent applications of type-I PDT in antimicrobial treatment. Finally, the limitations and future development directions of type-I photosensitizers are discussed. STATEMENT OF SIGNIFICANCE: The misuse and overuse of antibiotics have accelerated the development of bacterial resistance. To achieve the effective eradication of resistant bacteria, pathfinders have devised various treatment strategies. Among these strategies, type I photodynamic therapy has garnered considerable attention owing to its non-oxygen dependence. The utilization of non-oxygen-dependent photodynamic therapy not only enables the effective elimination of drug-resistant bacteria but also facilitates the successful eradication of hypoxic biofilms, which exhibits promising prospects for treating biofilm-associated infections. Based on the current research status, we anticipate that the novel type I photodynamic therapy agent can surmount the biofilm barrier, enabling efficient treatment of hypoxic biofilm infections.

Theranostic Fluorescent Probes

The ability to gain spatiotemporal information, and in some cases achieve spatiotemporal control, in the context of drug delivery makes theranostic fluorescent probes an attractive and intensely investigated research topic. This interest is reflected in the steep rise in publications on the topic that have appeared over the past decade. Theranostic fluorescent probes, in their various incarnations, generally comprise a fluorophore linked to a masked drug, in which the drug is released as the result of certain stimuli, with both intrinsic and extrinsic stimuli being reported. This release is then signaled by the emergence of a fluorescent signal. Importantly, the use of appropriate fluorophores has enabled not only this emerging fluorescence as a spatiotemporal marker for drug delivery but also has provided modalities useful in photodynamic, photothermal, and sonodynamic therapeutic applications. In this review we highlight recent work on theranostic fluorescent probes with a particular focus on probes that are activated in tumor microenvironments. We also summarize efforts to develop probes for other applications, such as neurodegenerative diseases and antibacterials. This review celebrates the diversity of designs reported to date, from discrete small-molecule systems to nanomaterials. Our aim is to provide insights into the potential clinical impact of this still-emerging research direction.

Toward Type I/II ROS Generation Photoimmunotherapy by Molecular Engineering of Semiconducting Perylene Diimide

As prospective phototheranostic agents for cancer imaging and therapy, semiconducting organic molecule-based nanomedicines are developed. However, near-infrared (NIR) emission, and tunable type I (O2 • -) and type II (1O2) photoinduced reactive oxygen species (ROS) generation to boost cancer photoimmunotherapy remains a big challenge. Herein, a series of D-π-A structures, NIR absorbing perylene diimides (PDIs) with heavy atom bromide modification at the bay position of PDIs are prepared for investigating the optimal photoinduced type I/II ROS generation. The heavy atom effect has demonstrated a reduction of molecular ∆EST and promotion of the intersystem crossing processes of PDIs, enhancing the photodynamic therapy (PDT) efficacy. The modification of three bromides and one pyrrolidine at the bay position of PDI (TBDT) has demonstrated the best type I/II PDT performance by batch experiments and theoretical calculations. TBDT based nanoplatforms (TBDT NPs) enable type I/II PDT in the hypoxic tumor microenvironment as a strong immunogenic cell death (ICD) inducer. Moreover, TBDT NPs showing NIR emission allow in vivo bioimaging guided phototherapy of tumor. This work uses novel PDIs with adjustable type I/II ROS production to promote antitumor immune response and accomplish effective tumor eradication, consequently offering molecular guidelines for building high-efficiency ICD inducers.

A Self-Assembly-Induced Exciton Delocalization Strategy for Converting a Perylene Diimide Derivative from a Type-II to Type-I Photosensitizer

Type-I photosensitizers have shown advantages in addressing the shortcomings of traditional oxygen-dependent type-II photosensitizers for the photodynamic therapy (PDT) of hypoxic tumors. However, developing type-I photosensitizers is yet a huge challenge because the type-II energy transfer process is much faster than the type-I electron transfer process. Herein, from the fundamental point of view, an effective approach is proposed to improve the electron transfer efficiency of the photosensitizer by lowering the internal reorganization energy and exciton binding energy via self-assembly-induced exciton delocalization. An example proof is presented by the design of a perylene diimide (PDI)-based photosensitizer (PDIMp) that can generate singlet oxygen (1O2) via a type-II energy transfer process in the monomeric state, but induce the generation of superoxide anion (O2˙-) via a type-I electron transfer process in the aggregated state. Significantly, with the addition ofcucurbit[6]uril (CB[6]), the self-assembled PDIMp can convert back to the monomeric state via host-guest complexation and consequently recover the generation of 1O2. The biological evaluations reveal that supramolecular nanoparticles (PDIMp-NPs) derived from PDIMp show superior phototherapeutic performance via synergistic type-I PDT and mild photothermal therapy (PTT) against cancer under either normoxia or hypoxia conditions.

"Two-Stage Rocket-Propelled" Strategy Boosting Theranostic Efficacy with Mitochondria-Specific Type I-II Photosensitizers

Imaging-guided photodynamic therapy (PDT) holds great potential for tumor therapy. However, achieving the synergistic enhancement of the reactive oxygen species (ROS) generation efficiency and fluorescence emission of photosensitizers (PSs) remains a challenge, resulting in suboptimal image guidance and theranostic efficacy. The hypoxic tumor microenvironment also hinders the efficacy of PDT. Herein, we propose a "two-stage rocket-propelled" photosensitive system for tumor cell ablation. This system utilizes MitoS, a mitochondria-targeted PS, to ablate tumor cells. Importantly, MitoS can react with HClO to generate a more efficient PS, MitoSO, with a significantly improved fluorescence quantum yield. Both MitoS and MitoSO exhibit less O2-dependent type I ROS generation capability, inducing apoptosis and ferroptosis. In vivo PDT results confirm that this mitochondrial-specific type I-II cascade phototherapeutic strategy is a potent intervention for tumor downstaging. This study not only sheds light on the correlation between the PS structure and the ROS generation pathway but also proposes a novel and effective strategy for tumor downstaging intervention.

Lutetium texaphyrin: A photocatalyst that triggers pyroptosis via biomolecular photoredox catalysis

Photon-controlled pyroptosis activation (PhotoPyro) is a promising technique for cancer immunotherapy due to its noninvasive nature, precise control, and ease of operation. Here, we report that biomolecular photoredox catalysis in cells might be an important mechanism underlying PhotoPyro. Our findings reveal that the photocatalyst lutetium texaphyrin (MLu) facilitates rapid and direct photoredox oxidation of nicotinamide adenine dinucleotide, nicotinamide adenine dinucleotide phosphate, and various amino acids, thereby triggering pyroptosis through the caspase 3/GSDME pathway. This mechanism is distinct from the well-established role of MLu as a photodynamic therapy sensitizer in cells. Two analogs of MLu, bearing different coordinated central metal cations, were also explored as controls. The first control, gadolinium texaphyrin (MGd), is a weak photocatalyst but generates reactive oxygen species (ROS) efficiently. The second control, manganese texaphyrin (MMn), is ineffective as both a photocatalyst and a ROS generator. Neither MGd nor MMn was found to trigger pyroptosis under the conditions where MLu was active. Even in the presence of a ROS scavenger, treating MDA-MB-231 cells with MLu at concentrations as low as 50 nM still allows for pyroptosis photo-activation. The present findings highlight how biomolecular photoredox catalysis could contribute to pyroptosis activation by mechanisms largely independent of ROS.

Aggregation-induced emission photosensitizer microneedles for enhanced melanoma photodynamic therapy

The incidence and mortality rates of skin melanoma have been increasing annually. Photodynamic therapy (PDT) enables effective destruction of tumor cells while minimizing harm to normal cells. However, traditional photosensitizers (PSs) suffer from photobleaching, photodegradation and the aggregation-caused quenching (ACQ) effect, and it is challenging for light to reach the deep layers of the skin to maximize the efficacy of PSs. Herein, we developed dissolving microneedles (MNs) loaded with PSs of TPE-EPy@CB[7] through supramolecular assembly. The PSs effectively enhanced the type-I reactive oxygen species (ROS) generation capacity, with a concentration of 2 μM possessing nearly half of the tumor cell-killing ability under 10 min white light irradiation. The MNs were successfully pierced into the targeted site for precise drug delivery. Additionally, the conical structure of the MNs, as well as the lens-like structure after dissolution, facilitated the transmission of light in the subcutaneous tissue, achieving significant inhibition of tumor growth with a tumor suppression rate of 97.8% and no systemic toxicity or side effects in melanoma mice. The results demonstrated the potent melanoma inhibition and biosafety of this treatment approach, exhibiting a new and promising strategy to conquer malignant melanoma.

An ER-targeted, Viscosity-sensitive Hemicyanine Dye for the Diagnosis of Nonalcoholic Fatty Liver and Photodynamic Cancer Therapy by Activating Pyroptosis Pathway

The concept of molecular design, integrating diagnostic and therapeutic functions, aligns with the general trend of modern medical advancement. Herein, we rationally designed the smart molecule ER-ZS for endoplasmic reticulum (ER)-targeted diagnosis and treatment in cell and animal models by combining hemicyanine dyes with ER-targeted functional groups (p-toluenesulfonamide). Owing to its ability to target the ER with a highly specific response to viscosity, ER-ZS demonstrated substantial fluorescence turn-on only after binding to the ER, independent of other physiological environments. In addition, ER-ZS, being a small molecule, allows for the diagnosis of nonalcoholic fatty liver disease (NAFLD) via liver imaging based on high ER stress. Importantly, ER-ZS is a type I photosensitizer, producing O2 ⋅- and ⋅OH under light irradiation. Thus, after irradiating for a certain period, the photodynamic therapy inflicted severe oxidative damage to the ER of tumor cells in hypoxic (2 % O2 ) conditions and activated the unique pyroptosis pathway, demonstrating excellent antitumor capacity in xenograft tumor models. Hence, the proposed strategy will likely shed new light on integrating molecular optics for NAFLD diagnosis and cancer therapy.

A photo-degradable BODIPY-modified Ru(II) photosensitizer for safe and efficient PDT under both normoxic and hypoxic conditions

Photodynamic therapy (PDT) is promising for cancer treatment but still suffers from some limitations. For instance, PDT based on 1O2 generation (in a type-II mechanism) is heavily dependent on high oxygen concentrations and will be significantly depressed in hypoxic tumors. In addition, the residual photosensitizers after PDT treatment may cause severe side-effects under light irradiation. To solve these problems, herein a BODIPY (boron dipyrromethene)-modified Ru(II) complex [Ru(dip)2(tpy-BODIPY)]2+ (complex 1, dip = 4,7-diphenyl-1,10-phenanthroline, tpy = 2,2':6',2''-terpyridine) was designed and synthesized. Complex 1 exhibited both high singlet oxygen quantum yield (Φ = 0.7 in CH3CN) and excellent superoxide radical (O2˙-) generation, and thus demonstrated efficient PDT activity under both normoxic and hypoxic conditions. Moreover, complex 1 is photo-degradable in water, and greatly loses its ROS generation ability after PDT treatment. These novel properties of complex 1 make it promising for efficient PDT under both normoxic and hypoxic conditions with reduced side-effects.

A near-infrared aggregation-induced emission photosensitizer targeting mitochondria for depleting Cu2+ to trigger light-activated cancer cells oncosis

Abnormally high levels of copper in tumors stimulate malignant proliferation and migration of cancer cells, which proposes a formidable challenge for the thorough therapy of malignant tumors. In this work, we developed a reliable, mitochondria-targeted near-infrared aggregation-induced emission fluorescent probe, TTQ-Th, whose thiourea moiety specifically could recognize mitochondria even both upon loss of mitochondrial membrane potential or in fixated cells, and can capture copper overexpressed by tumor cells, leading to severe copper deficiency. In parallel, TTQ-Th can generate sufficient reactive oxygen species (ROS) upon photoexcitation, while copper deficiency inhibits expression of related copper-based enzymes, resulting in a decline in ATP production. Such energy deficiency, combined with reduced MMP and elevated oxidative stress can lead to critical cell oncosis. Both in vitro and intracellular experiments can illustrate that the elevated ROS has remarkable damage to tumor cells and contributes to the elimination of the primary tumor, while copper deficiency further hinder tumor cell migration and induces G0/G1 cell cycle arrest in a dose-dependent manner, which is an efficacious strategy for the treatment of malignant tumors.

Aryl-Modified Pentamethyl Cyanine Dyes at the C2' Position: A Tunable Platform for Activatable Photosensitizers

Pentamethyl cyanine dyes are promising fluorophores for fluorescence sensing and imaging. However, advanced biomedical applications require enhanced control of their excited-state properties. Herein, a synthetic approach for attaching aryl substituents at the C2' position of the thio-pentamethine cyanine (TCy5) dye structure is reported for the first time. C2'-aryl substitution enables the regulation of both the twisted intramolecular charge transfer (TICT) and photoinduced electron transfer (PET) mechanisms to be regulated in the excited state. Modulation of these mechanisms allows the design of a nitroreductase-activatable TCy5 fluorophore for hypoxic tumor photodynamic therapy and fluorescence imaging. These C2'-aryl TCy5 dyes provide a tunable platform for engineering cyanine dyes tailored to sophisticated biological applications, such as photodynamic therapy.

Metallopolymer strategy to explore hypoxic active narrow-bandgap photosensitizers for effective cancer photodynamic therapy

Practical photodynamic therapy calls for high-performance, less O2-dependent, long-wavelength-light-activated photosensitizers to suit the hypoxic tumor microenvironment. Iridium-based photosensitizers exhibit excellent photocatalytic performance, but the in vivo applications are hindered by conventional O2-dependent Type-II photochemistry and poor absorption. Here we show a general metallopolymerization strategy for engineering iridium complexes exhibiting Type-I photochemistry and enhancing absorption intensity in the blue to near-infrared region. Reactive oxygen species generation of metallopolymer Ir-P1, where the iridium atom is covalently coupled to the polymer backbone, is over 80 times higher than that of its mother polymer without iridium under 680 nm irradiation. This strategy also works effectively when the iridium atom is directly included (Ir-P2) in the polymer backbones, exhibiting wide generality. The metallopolymer nanoparticles exhibiting efficient O2•- generation are conjugated with integrin αvβ3 binding cRGD to achieve targeted photodynamic therapy.

Lipid Droplet Targeting Type I Photosensitizer for Ferroptosis via Lipid Peroxidation Accumulation

As an iron-dependent lipid peroxidation (LPO) mediated cell death pathway, ferroptosis offers promises for anti-tumor treatment. Photodynamic therapy (PDT) is an ideal way to generate reactive oxygen species (ROS) for LPO. However, the conventional PDT normally functions on subcellular organelles, such as endoplasmic reticulum, mitochondria, and lysosome, causing rapid cell death before triggering ferroptosis. Herein, the first lipid droplet (Ld)-targeting type I photosensitizer (PS) with enhanced superoxide anion (O2 -· ) production, termed MNBS, is reported. The newly designed PS selectively localizes at Ld in cells, and causes cellular LPO accumulation by generating sufficient O2 -· upon irradiation, and subsequently induces ferroptosis mediated chronical PDT, achieving high-efficient anti-tumor PDT in hypoxia and normoxia. Theoretical calculations and comprehensive characterizations indicate that the Ld targeting property and enhanced O2 -· generation of MNBS originate from the elevated H-aggregation tendency owing to dispersed molecular electrostatic distribution. Further in vivo studies using MNBS-encapsulated liposomes demonstrate the excellent anti-cancer efficacy as well as anti-metastatic activity. This study offers a paradigm of H-aggregation reinforced type I PS to achieve ferroptosis-mediated PDT.

Mitochondria-specific near-infrared photoactivation of peroxynitrite upconversion luminescent nanogenerator for precision cancer gas therapy

Gas therapy is emerging as a highly promising therapeutic strategy for cancer treatment. However, there are limitations, including the lack of targeted subcellular organelle accuracy and spatiotemporal release precision, associated with gas therapy. In this study, we developed a series of photoactivatable nitric oxide (NO) donors NRh-R-NO (R = Me, Et, Bn, iPr, and Ph) based on an N-nitrosated upconversion luminescent rhodamine scaffold. Under the irradiation of 808 nm light, only NRh-Ph-NO could effectively release NO and NRh-Ph with a significant turn-on frequency upconversion luminescence (FUCL) signal at 740 nm, ascribed to lower N-N bond dissociation energy. We also investigated the involved multistage near-infrared-controlled cascade release of gas therapy, including the NO released from NRh-Ph-NO along with one NRh-Ph molecule generation, the superoxide anion O2⋅- produced by the photodynamic therapy (PDT) effect of NRh-Ph, and highly toxic peroxynitrite anion (ONOO‒) generated from the co-existence of NO and O2⋅-. After mild nano-modification, the nanogenerator (NRh-Ph-NO NPs) empowered with superior biocompatibility could target mitochondria. Under an 808 nm laser irradiation, NRh-Ph-NO NPs could induce NO/ROS to generate RNS, causing a decrease in the mitochondrial membrane potential and initiating apoptosis by caspase-3 activation, which further induced tumor immunogenic cell death (ICD). In vivo therapeutic results of NRh-Ph-NO NPs showed augmented RNS-potentiated gas therapy, demonstrating excellent biocompatibility and effective tumor inhibition guided by real-time FUCL imaging. Collectively, this versatile strategy defines the targeted RNS-mediated cancer therapy.

Highly bright stable organic radicals encapsulated by amphiphilic polypeptide for efficient near-infrared phototheranostics

Stable organic radical molecules have received extensive attention due to their unique electronic structure and photophysical properties, and the highly fluorescent quantum efficiency has great appeal to bioimaging. However, still scarce reports on the application of them on the therapy of tumors, especially theranostics. Here, 3,6-dibromocarbazole modified tris (2,4,6-trichlorophenyl) methane radical (TB) has been synthesized with high NIR fluorescence quantum efficiency, and free radical nanoparticles (NPs) have been prepared using the precursor of the radical doping strategy. The free radical molecule TB and its precursor molecule HTB were mixed in proportion and encapsulated with an amphiphilic polypeptide (PEG-PAsp) to obtain the NPs. The 4% NPs can achieve a high fluorescence quantum efficiency (18.68%) in the NIR region. In addition, the NPs also have a good ability to produce reactive oxygen species (ROS) under either normoxia or hypoxia conditions, which makes it possible for photodynamic therapy (PDT). Interestingly, the NPs also show preferable photothermal ability (PCE = 42.39%) for photothermal therapy (PTT). Both in vitro and in vivo studies reveal that the as-prepared radical NPS show a NIR fluorescence imaging-guided synergistic PTT and type I/II PDT to tumors. It provides new strategies and new clues for the application of free radical molecules in the theranostics of tumors.

Dyads and Triads of Boron Difluoride Formazanate and Boron Difluoride Dipyrromethene Dyes

Dye-dye conjugates have attracted significant interest for their utility in applications such as bioimaging, theranostics, and light-harvesting. Many classes of organic dyes have been employed in this regard; however, building blocks don't typically extend beyond small chromophores. This can lead to minor changes to the optoelectronic properties of the original dye. The exploration of dye-dye structures is impeded by long synthetic routes, incompatible synthetic conditions, or a mismatch of the desired properties. Here, we present the first-of-their-kind dye-dye conjugates of boron difluoride complexes of formazanate and dipyrromethene ligands. These conjugates exhibit dual photoluminescence bands that reach the near-infrared spectral region and implicate anti-Kasha processes. Cyclic voltammetry experiments revealed the generation of polyanionic species that can reversibly tolerate the uptake of up to 6 electrons. Ultimately, we demonstrate that BF2 formazanates can serve as a synthetically accessible platform to build upon new classes of dye-dye conjugates.

Optimized strategies of ROS-based nanodynamic therapies for tumor theranostics

Reactive oxygen species (ROS) play a crucial role in regulating the metabolism of tumor growth, metastasis, death and other biological processes. ROS-based nanodynamic therapies (NDTs) are becoming attractive due to non-invasive, low side effects and tumor-specific advantages. NDTs have rapidly developed into numerous branches, such as photodynamic therapy, chemodynamic therapy, sonodynamic therapy and so on. However, the complexity of the tumor microenvironment and the limitations of existing sensitizers have greatly restricted the therapeutic effects of NDTs, which heavily rely on ROS levels. To address the limitations of NDTs, various strategies have been developed to increase ROS yield, which is an urgent aspect for the positive development of NDTs. In this review, the nanodynamic potentiation strategies in terms of unique properties and universalities of NDTs are comprehensively outlined. We mainly summarize the current dilemmas faced by each NDT and the respective solutions. Meanwhile, the NDTs universalities-based potentiation strategies and NDTs-based combined treatments are elaborated. Finally, we conclude with a discussion of the key issues and challenges faced in the development and clinical transformation of NDTs.

Self-Assembly Induced Photosensitization of Long-Tailed Heavy-Atom-Free BODIPY Derivatives for Photodynamic Therapy

Type I photosensitizers (PSs) are a promising approach for photodynamic therapy (PDT) since they can generate radicals that are tolerant to hypoxia. Thus, the development of highly efficient type I PSs is essential. Self-assembly is a promising strategy for developing novel PSs with desirable properties. Here, a simple and effective approach is developed to create heavy-atom-free PSs for PDT by self-assembling long-tailed boron dipyrromethene dyes (BODIPYs). The resulting aggregates BY-I16 and BY-I18 can efficiently convert their excited energy to the triplet state, producing reactive oxygen species that are essential for PDT. Furthermore, the aggregation and PDT performance can be regulated by adjusting the length of the tailed alkyl chains. As proof of concept, the efficacy of these heavy-atom-free PSs both in vitro and in vivo under both normoxic and hypoxic conditions is demonstrated.

Metal-Coordination-Mediated H-Aggregates of Cyanine Dyes for Effective Photothermal Therapy

Integration of cyanine dyes and metal ions into one nanoplatform via metal-coordination interactions is an effective strategy to build multimodality phototheranostics. The multifunctionalities of the formed nanoscale metal-organic particles (NMOPs) have been widely explored. However, the effect of metal-coordination interaction on the aggregation behavior of cyanine dyes is rarely reported. Herein, we reported the H-aggregation behavior of cyanine dye Cy-3COOH induced by different metal ions M (Fe2+ or Mn2+ ). Moreover, the extent of H-aggregates varied with different metal-coordination interactions. Upon NIR irradiation, H-aggregates of Cy-3COOH remarkably promoted photothermal conversion efficiency. Interestingly, we also find that H-aggregates of Cy-3COOH induced by metal ions can generate the reactive oxygen species (ROS) involving singlet oxygen (1 O2 ) and superoxide anion radical (O2 - ⋅) upon light irradiation. In addition, the ROS efficiency varies depending on the extent of H-aggregates. Additionally, the photoinduced ROS could disassemble aggregates and decompose cyanine dye Cy-3COOH, which limits the photothermal capability of Cy-3COOH/M NPs. Therefore, the photothermal performance of Cy-3COOH/M NPs could be manipulated by the degree of H-aggregation. This would provide a new insight to develop efficient phototheranostics NMOPs for cancer treatment.

A Cascade Strategy Boosting Hydroxyl Radical Generation with Aggregation-Induced Emission Photosensitizers-Albumin Complex for Photodynamic Therapy

Effective photodynamic therapy (PDT) requires photosensitizers (PSs) to massively generate type I reactive oxygen species (ROS) in a less oxygen-dependent manner in the hypoxia tumor microenvironment. Herein, we present a cascade strategy to boost type I ROS, especially hydroxyl radical (OH·-), generation with an aggregation-induced emission (AIE) photosensitizer-albumin complex for hypoxia-tolerant PDT. The cationic AIE PS TPAQ-Py-PF6 (TPA = triphenylamine, Q = anthraquinone, Py = pyridine) contains three important moieties to cooperatively enhance free radical generation: the AIE-active TPA unit ensures the effective triplet exciton generation in aggregate, the anthraquinone moiety possesses the redox cycling ability to promote electron transfer, while the cationic methylpyridinium cation further increases intramolecular charge transfer and electron separation processes. Inserting the cationic TPAQ-Py-PF6 into the hydrophobic domain of bovine serum albumin nanoparticles (BSA NPs) could greatly immobilize its molecular geometry to further increase triplet exciton generation, while the electron-rich microenvironment of BSA ultimately leads to OH·- generation. Both experimental and theoretical results confirm the effectiveness of our molecular cationization and BSA immobilization cascade strategy for enhancing OH·- generation. In vitro and in vivo experiments validate the excellent antitumor PDT performance of BSA NPs, superior to the conventional polymeric encapsulation approach. Such a multidimensional cascade strategy for specially boosting OH·- generation shall hold great potential in hypoxia-tolerant PDT and related antitumor applications.

Recent Progress of Copper-Based Nanomaterials in Tumor-Targeted Photothermal Therapy/Photodynamic Therapy

Nanotechnology, an emerging and promising therapeutic tool, may improve the effectiveness of phototherapy (PT) in antitumor therapy because of the development of nanomaterials (NMs) with light-absorbing properties. The tumor-targeted PTs, such as photothermal therapy (PTT) and photodynamic therapy (PDT), transform light energy into heat and produce reactive oxygen species (ROS) that accumulate at the tumor site. The increase in ROS levels induces oxidative stress (OS) during carcinogenesis and disease development. Because of the localized surface plasmon resonance (LSPR) feature of copper (Cu), a vital trace element in the human body, Cu-based NMs can exhibit good near-infrared (NIR) absorption and excellent photothermal properties. In the tumor microenvironment (TME), Cu2+ combines with H2O2 to produce O2 that is reduced to Cu1+ by glutathione (GSH), causing a Fenton-like reaction that reduces tumor hypoxia and simultaneously generates ROS to eliminate tumor cells in conjunction with PTT/PDT. Compared with other therapeutic modalities, PTT/PDT can precisely target tumor location to kill tumor cells. Moreover, multiple treatment modalities can be combined with PTT/PDT to treat a tumor using Cu-based NMs. Herein, we reviewed and briefly summarized the mechanisms of actions of tumor-targeted PTT/PDT and the role of Cu, generated from Cu-based NMs, in PTs. Furthermore, we described the Cu-based NMs used in PTT/PDT applications.

A S-substituted Nile Blue-derived bifunctional near-infrared fluorescent probe for in vivo carboxylesterase imaging-guided photodynamic therapy of hepatocellular carcinoma

The development of theranostic probes that integrate both diagnostic and therapeutic functions still remains an intractable challenge in precise cancer treatment. Herein, a novel bifunctional near-infrared (NIR) fluorescent probe (CEP1) for carboxylesterase (CE) imaging and photodynamic therapy (PDT) of hepatocellular carcinoma (HCC) has been firstly developed and successfully applied in vitro and in vivo. The probe was constructed by introducing carbamate as both the recognition unit and the fluorescence quenching unit into the fluorophore S-substituted Nile Blue (ENBS) via a self-eliminating spacer with substituted chloride. It can be activated by CE and hydrolyzed into fluorescent ENBS, which recover fluorescence at about 700 nm, and can generate superoxide radical anions under NIR irradiation. Additionally, the probe could effectively distinguish tumor cells from normal cells by CE imaging of live cells. Furthermore, it could achieve CE imaging in vivo and significantly inhibits tumor growth by imaging-guided PDT. Therefore, this study offers a promising and attractive platform for activatable imaging-guided PDT of HCC.

A GPX4-targeted photosensitizer to reverse hypoxia-induced inhibition of ferroptosis for non-small cell lung cancer therapy

Ferroptosis therapy is gradually becoming a new strategy for the treatment of non-small cell lung cancer (NSCLC) because of its active iron metabolism. Because the hypoxic microenvironment in NSCLC inhibits ferroptosis heavily, the therapeutic effect of some ferroptosis inducers is severely limited. To address this issue, this work describes a promising photosensitizer ENBS-ML210 and its application against hypoxia of NSCLC treatment based on type I photodynamic therapy and glutathione peroxidase 4 (GPX4)-targeted ferroptosis. ENBS-ML210 can promote lipid peroxidation and reduce GPX4 expression by generating superoxide anion radicals under 660 nm light irradiation, which reverses the hypoxia-induced resistance of ferroptosis and effectively kills H1299 tumor cells. Finally, the excellent synergistic antitumor effects are confirmed both in vitro and in vivo. We firmly believe that this method will provide a new direction for the clinical treatment of NSCLC in the future.

Highly Efficient Photosensitizers with Molecular Vibrational Torsion for Cancer Photodynamic Therapy

The development of highly effective photosensitizers (PSs) for photodynamic therapy remains a great challenge at present. Most PSs rely on the heavy-atom effect or the spin-orbit charge-transfer intersystem crossing (SOCT-ISC) effect to promote ISC, which brings about additional cytotoxicity, and the latter is susceptible to the interference of solvent environment. Herein, an immanent universal property named photoinduced molecular vibrational torsion (PVT)-enhanced spin-orbit coupling (PVT-SOC) in PSs has been first revealed. PVT is verified to be a widespread intrinsic property of quinoid cyanine (QCy) dyes that occurs on an extremely short time scale (10-10 s) and can be captured by transient spectra. The PVT property can provide reinforced SOC as the occurrence of ISC predicted by the El Sayed rules (1ππ*-3nπ*), which ensures efficient photosensitization ability for QCy dyes. Hence, QTCy7-Ac exhibited the highest singlet oxygen yield (13-fold higher than that of TCy7) and lossless fluorescence quantum yield (ΦF) under near-infrared (NIR) irradiation. The preeminent photochemical properties accompanied by high biosecurity enable it to effectively perform photoablation in solid tumors. The revelation of this property supplies a new route for constructing high-performance PSs for achieving enhanced cancer phototherapy.

Fluorescent dyes based on rhodamine derivatives for bioimaging and therapeutics: recent progress, challenges, and prospects

Since their inception, rhodamine dyes have been extensively applied in biotechnology as fluorescent markers or for the detection of biomolecules owing to their good optical physical properties. Accordingly, they have emerged as a powerful tool for the visualization of living systems. In addition to fluorescence bioimaging, the molecular design of rhodamine derivatives with disease therapeutic functions (e.g., cancer and bacterial infection) has recently attracted increased research attention, which is significantly important for the construction of molecular libraries for diagnostic and therapeutic integration. However, reviews focusing on integrated design strategies for rhodamine dye-based diagnosis and treatment and their wide application in disease treatment are extremely rare. In this review, first, a brief history of the development of rhodamine fluorescent dyes, the transformation of rhodamine fluorescent dyes from bioimaging to disease therapy, and the concept of optics-based diagnosis and treatment integration and its significance to human development are presented. Next, a systematic review of several excellent rhodamine-based derivatives for bioimaging, as well as for disease diagnosis and treatment, is presented. Finally, the challenges in practical integration of rhodamine-based diagnostic and treatment dyes and the future outlook of clinical translation are also discussed.

Selenium-Containing Type-I Organic Photosensitizers with Dual Reactive Oxygen Species of Superoxide and Hydroxyl Radicals as Switch-Hitter for Photodynamic Therapy

Organic type-I photosensitizers (PSs) which produce aggressive reactive oxygen species (ROS) with less oxygen-dependent exhibit attractive curative effect for photodynamic therapy (PDT), as they adapt better to hypoxia microenvironment in tumors. However, the reported type-I PSs are limited and its exacted mechanism of oxygen dependence is still unclear. Herein, new selenium-containing type-I PSs of Se6 and Se5 with benzoselenadiazole acceptor has been designed and possessed aggregation-induced emission characteristic. Benefited from double heavy-atom-effect of selenium and bromine, Se6 shows a smaller energy gap (ΔEST ) of 0.03 eV and improves ROS efficiency. Interestingly, type-I radicals of both long-lived superoxide anion (O2 •‾ ) and short-lived hydroxyl (• OH) are generated from them upon irradiation. This may provide a switch-hitter of dual-radical with complementary lifetimes for PDT. More importantly, simultaneous processes to produce • OH are revealed, including disproportionation of O2 •‾ and reaction between excited PS and water. Actually, Se6 displays superior in-vitro PDT performance to commercial chlorin e6 (Ce6), under normoxia or hypoxia. After intravenous injection, a significantly in-vivo PDT performance is demonstrated on Se6, where tumor growth inhibition rates of 99% is higher than Ce6. These findings offer new insights about both molecular design and mechanism study of type-I PSs.