Nanostructured Phthalocyanine Assemblies with Efficient Synergistic Effect of Type I Photoreaction and Photothermal Action to Overcome Tumor Hypoxia in Photodynamic Therapy

Smart self-assembly of a multifunctional theranostic nanozyme for self-enhanced precise chemo/chemodynamic therapy

The use of hypoxia-activated prodrugs to treat breast cancer is a promising therapeutic strategy, but limited by inconsistent hypoxia states in whole tumors. Herein, we developed a theranostic nanozyme using Mn2+-driven self-assembly of fluorenylmethyloxycarbonyl-protected cysteine (Fmoc-Cys) as a multifunctional carrier for the first time, and co-encapsulated with tirapazamine (TPZ) and glucose oxidase (GOX). The prepared nanozyme is sensitive to excess glutathione (GSH) and achieves efficient self-enhanced chemo/chemodynamic therapy (CDT) thanks to the synergistic effect among the multiple components. The encapsulated GOX could consume oxygen, which promoted the activation of TPZ in normoxic tumor regions, and generate excessive H2O2, which enhanced the CDT effect of Mn2+. Meanwhile, the release of Mn2+ was ideal for T1 magnetic resonance imaging (MRI), and the fluctuations of sO2 could be monitored by photoacoustic imaging (PAI). Therefore, this work presents a smart self-assembly nanozyme capable of dual-modality imaging and self-enhanced combined therapy.

ROS-catalytic self-amplifying benzothiophenazine-based photosensitive conjugates for photodynamic-immuno therapy

Activatable photosensitizer (aPS)-mediated photodynamic therapy (PDT) holds great potential towards precision cancer treatment, but which generally suffers from low therapeutic outcomes due to the low activation efficiency of aPS and the low phototherapeutic effect of single PDT. In this study, we present a newly aPS designing strategy based on benzothiophenazine (BP) for fabrication of the robust small-molecule photosensitizer conjugates (SMPCs). Specifically, after systematically studying the photosensitizing mechanism of BP, a fully caged pro-photosensitizing platform (BP-Cl) was established, based on which we can introduced various amine molecules to create a series of reactive oxygen species (ROS)-catalytic self-amplifying SMPCs. As a proof of concept, we synthesized a SMPC (BP-Mel) by employing the chemotherapeutic melphalan to BP-Cl. Upon triggered by endogenous ROS, BP-Mel can achieve self-amplified activation under infrared illumination to efficiently produce the active BP for type I PDT, and along with the release of melphalan to induce immunogenic cell death in breast cancer cells. BP-Mel was encapsulated with resiquimod (R848) to form the nanoagonist (BMR), where BP-Mel induces localized tumor damage and immunogenic cell death and the TLR7/8 agonist R848 potently stimulates dendritic cell maturation and enhances tumor-specific T cell responses. BMR-mediated combination therapy induces powerful tumor suppression and immunotherapeutic cascade in EMT6-tumor-bearing mice. This study presents a scalable strategy for the customization of activatable photosensitive conjugates, exemplifying precise and efficient PDT.

Engineering a Near-Infrared D-A-A-D BODIPY Dimer for ROS Generation and Photothermal Conversion in Multimodal Synergistic Phototherapy

To address the limitations of traditional single-mode phototherapy, this study developed a novel, symmetrical D-A-A-D structured BODIPY dimer (P-P) via a facile "one-pot" oxidative homocoupling reaction, with triphenylamine as the electron donor (D), BODIPY as the electron acceptor (A), and butadiyne as the conjugated bridge. Compared to its D-A monomer counterpart (P), P-P displayed a red-shifted absorption spectrum (465-725 nm), enhanced charge separation, an extended triplet excited-state lifetime (165 μs vs 104 μs), and significantly improved type I, type II, and total reactive oxygen species (ROS) generation, along with superior photothermal conversion efficiency. These properties enable P-P to achieve multimodal phototherapy with enhanced therapeutic efficacy. As a result, P-P demonstrated efficient cellular uptake, high phototoxicity (with an IC50 of 15.2 μM), and minimal dark toxicity in tumor cells. This work offers a promising strategy for developing high-performance phototherapeutic agents, paving the way for advancing multimodal synergistic phototherapy in clinical applications.

Bacteria-visualizing nano-bactericide with anti-inflammation and wound healing properties for in situ NIR phototherapeutic strategies

Anti-infection and wound healing are critical to the survival of patients with skin burns or postoperative infections, and there is an urgent clinical demand for drugs that combine anti-inflammatory and tissue recovery functions, especially new drugs that can overcome the inherent drug resistance of bacteria to conventional antibiotics. In this work, a phototherapeutic bactericide SiPc-CMCS was constructed by covalently grafting silicon phthalocyanine onto natural carboxymethyl chitosan. SiPc-CMCS ingeniously exhibited combined effects of photodynamic and photothermal therapies with wound healing effects for synergistic anti-inflammation and wound recovery, without the constraints of dosage and drug resistance. Two ROS, namely, O2˙- and 1O2, which belong to type I and type II photodynamic pathways, respectively, were observed, and SiPc-CMCS exhibited a photothermal conversion efficiency of η = 26.80%. In vitro and in vivo studies showed effective NIR photodynamic-photothermal antibacterial effect of SiPc-CMCS against both Gram-positive and Gram-negative bacteria. Furthermore, it realized in situ wound healing and fluorescence bacteria visualizing capability. These data prove that SiPc-CMCS is a potential bacteria-readout-guided NIR phototherapeutic bactericide, which is effective against both aerobic and anaerobic bacterial infections, and it possesses excellent wound-healing capability for treating skin burns and postoperative infections.

Photoacoustic contrast agents: a review focusing on image-guided therapy

Photoacoustic (PA) imaging is a burgeoning imaging modality that has a broad range of applications in the early diagnosis of cancer, detection of various diseases, and relevant scientific research. It is a non-invasive imaging modality that relies on the absorption coefficient of the imaging tissue and the injected PA-imaging contrast agent. Nevertheless, PA imaging exhibits weak imaging depth due to its exponentially decaying signal intensity with increasing tissue depth. To improve the depth and heighten the contrast of imaging, a series of PA contrast agents has been developed based on nanomaterials. In this review, we present a comprehensive overview of recent advancements in contrast agents for photoacoustic (PA) imaging, encompassing the emergence of first near-infrared region (NIR-I, 700-950 nm) PA contrast agents, second near-infrared region (NIR-II, 1000-1700 nm) PA contrast agents, and ratiometric PA contrast agents. Subsequently, the latest advances in PA image-guided cancer therapy were introduced, such as photothermal therapy (PTT), photodynamic therapy (PDT), sonodynamic therapy (SDT), and PTT-based synergistic therapy. Finally, the prospects of PA contrast agents and their biomedical applications were also discussed. This review provides a systematic summary of the development and utilization of the cutting-edge photoacoustic agents, which may inspire fresh thinking in the fabrication and application aspects of imaging agents.

Semiconducting Open-Shell Radicals for Precise Tumor Activatable Phototheranostics

Semiconducting open-shell radicals (SORs) have promising potential for the development of phototheranostic agents, enabling tumor bioimaging and boosting tumorous reactive oxygen species (ROS). Herein, a new class of semiconducting perylene diimide (PDI), designated as PDI(Br)n with various numbers of bromine (Br) atoms modified on PDI's bay/ortho positions is reported. PDI(Br)n is demonstrated to transform into a radical anion, [PDI(Br)n]•-, in a reducing solution, with a typical g-value of 2.0022. Specifically, [PDI(Br)4/6]•- is generated in the weakly reductive tumor-mimicking solution and exhibits high stability in air. Quantum chemical kinetic simulation and ultrafast femtosecond transient absorption spectroscopy indicate that [PDI(Br)6]•- has a low π-π stacking energy (0.35 eV), a fast electron transfer rate (192.4 ps) and energy gap of PDI(Br)6 (ΔES1, T1 = 1.307 eV, ΔES1, T2 = 0.324 eV) respectively, which together result in excited-state charge transfer characters. The PDI(Br)6 nanoparticle radicals, [PDI(Br)6] NPs•-, specifically enable chemodynamic and type-I photodynamic ROS generation in tumors, including superoxide and hydroxyl radicals, which elicit immunogenic cell death effect. Also, [PDI(Br)6] NPs•- facilitate activatable bioimaging-guided therapy due to their photoacoustic signal at 808 nm and NIR-II emission at 1115 nm. The work paves the way for the design of SORs for precise cancer theranostics.

Fast Imaging of Mitochondria and Efficient Generation of Singlet Oxygen by Red Fluorescent BODIPY Photosensitizers

The biomedical applications of BODIPY fluorophores are limited by challenges such as short-wavelength emission, high hydrophobicity, and poor selectivity. To address these issues, two water-soluble red-emitting BODIPY derivatives, namely, PSPyBDP and I-PSPyBDP, were synthesized by conjugating pyridine units to the BODIPY core, followed by the ring-opening reactions with 1,3-propanesulfonate. Notably, PSPyBDP showed fast mitochondrial imaging capability (∼5 min), indicating its potential as an alternative to mitochondria tracker. I-PSPyBDP, with the heavy-atom effect, could effectively produce singlet oxygen (1O2) under irradiation at 660 nm in a short time (∼1 min) with a 1O2 quantum yield of 0.89. Cytotoxicity assays revealed that the BODIPY derivatives exhibited phototoxicity to HeLa cells while maintaining low dark toxicity. Interestingly, they had low toxicity against normal COS-7 cells. Confocal imaging and flow cytometry confirmed that the BODIPY derivatives could increase intracellular reactive oxygen species (ROS), reduce mitochondrial membrane potential, and induce apoptosis upon irradiation. These findings suggest their promising application in photodynamic therapy (PDT) for tumors.

Highly Emissive Platinum(II) Metallacage in the Near-Infrared Region for Synergistic Chemo-Photodynamic Therapy

Highly emissive metallacages that generate reactive oxygen species (ROS) are important to synergistic cancer therapy, but it is still challenging to balance the emission and phototheranostic properties. Herein, a metallacage of DTPABT-Mc is prepared. It is observed that emission in the near-infrared region from 600 to 1000 nm with a high photoluminescence quantum yield value of 7.92% in solids is recorded for DTPABT-Mc. In addition, the ability to produce both type I and type II ROS under light irradiation is also observed, leading to potential application in photodynamic therapy (PDT) and chemotherapy. After that, 4T1@DTPABT-Mc-NPs, covering DTPABT-Mc nanoparticles with 4T1 cell membranes, are prepared to enhance their tumor-targeting ability. This finally results in effective therapeutic performance in vivo, effectively inhibiting tumor growth. These results suggest that DTPABT-Mc-NPs exhibit excellent synergistic therapeutic effects by combining PDT and chemotherapy, providing new ideas to design agents for diagnosis and therapy in the future.

A Hypoxia-Triggered Bioreduction of Hydrophilic Type I Photosensitizer for Switchable In Vivo Photoacoustic Imaging and High-Specificity Cancer Phototherapy

Considering that hypoxia is strongly connected with tumor proliferation, metastasis, invasion, and drug resistance, it is of significant implication for alleviating the effects of hypoxia in tumor treatment. The negligible oxygen-dependent nature of type I photosensitizers (PSs) has made them appropriate candidates for the treatment of hypoxic tumors. However, the lack of effective molecular design approaches, the phototoxicity of PSs to normal tissue before and after treatment, and the drawbacks of poor hydrophilicity severely hinder the development of PSs in hypoxic tumor therapy. Thus, developing a hydrophilic PS with good hypoxia resistance and minimal side effects is an urgent but challenging problem. Herein, we present a nanotheranostic (NanoPcN8O) based on the self-assembly of a hydrophilic phthalocyanine derivative (PcN8O), a hypoxia-responsive bioreductive phototherapeutic agent suitable for activatable photoacoustic (PA) imaging and tumor therapy. Hypoxic regions in various tumors exhibit strong reductive capability, and only in such conditions did NanoPcN8O feature multiple N-oxide groups that could be bioreduced to yield the product NanoPcN8 with abundant electron-rich tertiary amine groups, which switches on the type I photodynamic and photothermal effects, facilitating the generation of type I reactive oxygen species (ROS) and heat. Better still, NanoPcN8O achieved hypoxia-induced selective PA imaging in a preclinical model. Based on these merits, the hypoxia-induced switchable type I photodynamic therapy (PDT) and photothermal therapy (PTT) strategies demonstrated remarkable phototherapeutic efficiency with high biosafety. This delicate design is anticipated to offer a novel and safe strategy to overcome hypoxia resistance in phototherapeutics.

Albumin Modulated Homodimer as an Efficient Photosensitizer for Long-Term Imaging-Guided Tumor Therapy Directed with Sunlight Irradiation

The reactive oxygen species (ROS) amplification caused by inevitable plasma albumin encapsulation is still a challenge to circumvent the systemic adverse effects in the photodynamic therapy (PDT) process. Herein, a disulfide bond linked homodimer, Cy1280, which is modulated by albumin to accurately balance the fluorescence and ROS generation and exhibit a weak fluorescence and sealed PDT effect during blood circulation, is exploited. Cy1280 can be specifically internalized and dispersed at the tumor site via Organic Anion Transporter Proteins (OATPs) and thiol-disulfide exchange mediated synergistic uptake and activated after mild sunlight irradiation (100 ± 5 Klx) to sensitize neighboring oxygen in cellular mitochondria to execute direct protein dysfunction effect. The dynamic covalent chemistry (DCC) facilitates prolonged and sustained retention in tumors (>336 h) and demonstrates the efficacy of imaging-guided solid-tumor therapy in tumor-bearing BALB/C mice. This study resolves the inevitable stubborn impotent tumor penetration caused by bulky-sized nanoparticles and high interstitial pressure of tumor with synergistic uptake manner, the long-term circulation and sealed PDT manipulated with albumin also improve the whole body phototoxic symptom. The advantageous feature of Cy1280 provides a promising candidate for overcoming the off-target phototoxicity and inadequate accumulation challenges in clinical translation with photosensitizers (PSs).

Albumins constrainting the conformation of mitochondria-targeted photosensitizers for tumor-specific photodynamic therapy

Tumor ablation Preclinical organelle-targeted phototherapies have effectively achieved tumor photoablation for regenerative biomedical applications in cancer therapies. However, engineering effective phototherapy drugs with precise tumor-localization targeting and organelle direction remains challenging. Herein, we report a albumins constrainting mitochondrial-targeted photosensitizer nanoparticles (PSs@BSAs) for tumor-specific photodynamic therapy. X-ray crystallography elucidates the two-stage assembly mechanism of PSs@BSAs. Femtosecond transient absorption spectroscopy and quantum mechanical calculations reveal the implications of conformational dynamics at the excited state. PSs@BSAs can efficiently disable mitochondrial activity, and further disrupt tumor angiogenesis based on the photodynamic effect. This triggers a metabolic and oxidative stress crisis to facilitate photoablation of solid tumor and antitumor metastasis. The study fully elucidates the interdisciplinary issues of chemistry, physics, and biological interfaces, thereby opening new horizons to inspire the engineering of organelle-targeted tumor-specific photosensitizers for biomedical applications.

Regio-isomerization Optimization Strategy for Photosensitizers: Achieving Ultrahigh Type I Reactive Oxygen Species Generation to Enhance Cancer Photoimmunotherapy

Phototherapy, renowned for its noninvasiveness, is widely employed in tumor treatment. However, the tumor microenvironment is usually hypoxic, with insufficient reactive oxygen species (ROS) production, severely limiting its application. Herein, we introduce a regio-isomerization optimization strategy and have synthesized four regio-isomeric photosensitizers featuring a donor-acceptor (D-A) configuration by tactically varying the linkage sites between D and A. Among them, TAF-3 with excellent photostability has an ultrahigh type I ROS production efficiency (4.79 times that of methylene blue) and a photothermal conversion efficiency of 41.7%. TAF-3 improves the conjugation degree; produces an appropriate intramolecular charge transfer effect, which enhances its optical properties and phototherapeutic efficiency; and promotes a stronger immune cell death effect, reducing postoperative melanoma recurrence by 60%. Overall, the optical attributes of D-A type photosensitizers can be tailored through the precision modulation of regio-isomerization, offering a promising avenue for the advancement of clinical photosensitizers suitable for phototherapy.

Near-Infrared Chemiluminophore Switches Photodynamic Processes via Protein Complexation for Biomarker-Activatable Cancer Therapy

Despite the potential in cancer therapy, phototheranostic agents often face two challenges: limited diagnostic sensitivity due to tissue autofluorescence and suboptimal therapeutic efficacy due to the Type-II photodynamic process with the heavy oxygen reliance. In contrast, chemiluminescent theranostic agents without the requirement of real-time light excitation can address the issue of tissue autofluorescence, which however have been rarely reported for photodynamic therapy (PDT), not to mention less oxygen-dependent Type-I PDT. In this work, we synthesize near-infrared (NIR) chemiluminophores with the specific binding towards human serum albumin (HSA) to form chemiluminophore-protein complex for cancer detection and photodynamic therapy. Interestingly, after the complexation with HSA, the chemiluminescence (CL) intensities of chemiluminophores are enhanced by over 10-fold; meanwhile, the photodynamic process switches from Type-II (singlet-oxygen-generation dominated) to Type-I (superoxide anion and hydroxyl radical dominated), while the previously reported activated chemiluminophore with non-specific HSA binding can't switch photodynamic process. Based on the optimal chemiluminophore, a nitroreductase-activatable CL probe-protein complex is synthesized, which specially turns on its CL and Type-I PDT in hypoxic tumors for precision therapy. Thus, this study provides a complexation strategy to improve phototheranostic performance of chemiluminophores.

Nitric Oxide-Producing Multiple Functional Nanoparticle Remodeling Tumor Microenvironment for Synergistic Photodynamic Immunotherapy against Hypoxic Tumor

The treatment of pancreatic cancer faces significant challenges due to connective tissue hyperplasia and severe hypoxia. Unlike oxygen-dependent Type II photosensitizers, Type I photosensitizers can produce a substantial amount of reactive oxygen species, even under hypoxic conditions, making them more suitable for photodynamic therapy of pancreatic cancer. However, the dense extracellular matrix of pancreatic cancer limits the penetration efficiency of photosensitizers, and the presence of immunosuppressive cells in the tumor microenvironment reduces the therapeutic effect. To address these challenges, we designed the photoimmunotherapeutic M1@PAP nanoparticles composed of Type I photosensitizer and anti-PD-L1 siRNA (siPD-L1), which was encapsulated into M1 macrophage membrane vesicles. In this system, pyropheophorbide-a (PPA) was covalently conjugated to poly-l-arginine (Arg9). Notably, it was capable of generating sufficient superoxide anions under hypoxic conditions, thereby functioning as a Type I photosensitizer. Furthermore, Arg9 acted as a nitric oxide (NO) donor, enhancing the penetration efficiency of the nanophotosensitizer by inhibiting cancer-associated fibroblast (CAF) activation and decomposing the tumor extracellular matrix. Additionally, M1 macrophage membrane vesicles provided active targeting capabilities and reeducated immunosuppressed M2 macrophages. The reversal of immunosuppressive microenvironment further promoted the efficacy of anti-PD-L1 siRNA immunotherapy, showing great potential in synergistic photodynamic immunotherapy against hypoxic pancreatic tumor.

Using a stable radical as an "electron donor" to develop a radical photosensitizer for efficient type-I photodynamic therapy

Among type I photosensitizers, stable organic radicals are superior candidate molecules for hypoxia-overcoming photodynamic therapy. However, their wide applications are limited by complicated preparation processes and poor stabilities. Herein, a nitroxide radical was simply synthesized by introducing a commercially available "TEMPO" moiety. The radical exhibits efficient type-I ROS generation and appreciable photo-cytotoxicity under hypoxia, which open up a new avenue for the exploration of a novel and efficient type-I photosensitizer.

The Current Advances in Design Strategy (Indirect Strategy and Direct Strategy) for Type-I Photosensitizers

Type-I photosensitizers (PSs) are among the most potential candidates for photodynamic therapy (PDT), as their low dependence on oxygen endow them with many advantages for treating hypoxic tumor. However, most of the reported type-I PSs have a contingency of molecular design, because electron transfer (ET) reaction is more difficult to achieve than energy transfer (EET) process. Therefore, it is urgent to understand molecular design mechanisms for type-I PSs. In this review, the two ways to achieve the type-I PSs, i.e., inhibiting EET process (type-II) or enhancing ET process (type-I), are detailly explained. In response, the current design strategies of type-I PSs are summarized from two perspectives: indirect strategy (inhibiting EET process: reducing the energy of the lowest triplet excited state (T1) to lower than the energy required for the excitation energy transfer to produce singlet oxygen) and direct strategy (enhancing ET process: promoting the ET efficiency of PSs to generate superoxide radicals). The construction of direct strategy can be realized by forming an electron-rich microenvironment, providing an electron-deficient intermediate transmitter, and introducing an enhanced electron transfer capacity primitive.

Effective One-for-All Phototheranostic Agent for Hypoxia-Tolerant NIR-II Fluorescent/PA Image-Guided Phototherapy

Near-infrared (NIR)-triggered type-I photosensitizers are crucial to address the constraints of hypoxic tumor microenvironments in phototherapy; however, significant challenges remain. By selecting an electron-deficient unit, a matched energy gap in the upper-level state is instrumental in boosting the efficiency of intersystem crossing for the type-I electron transfer process. 2-Cyanothiazole, an electron acceptor, is covalently linked with N, N-diphenyl-4-(thiophen-2-yl)aniline to yield a multifunctional photosensitizer (TTNH) that exhibits intrinsic NIR absorbance and compatible T2 energy levels, facilitating both radiative and nonradiative transitions. The prepared nanoparticles (TTNH NPs) assembled from TTNH are activated by an 808 nm laser and generated the O2•- for hypoxia-tolerant type-I photodynamic therapy under both normoxia and hypoxic conditions. TTNH NPs emitted NIR-II fluorescence with an impressive NIR-II fluorescence quantum yield of 2.08%. With a high photothermal conversion efficiency of 51.8% under 808 nm laser stimulation, TTNH NPs exhibit photothermal therapy performance, accompanied by enhanced photoacoustic imaging capability owing to their strong NIR absorption. These characteristics make TTNH an effective NIR-wavelength-triggered phototheranostic agent that outperforms NIR-II fluorescence/photoacoustic dual-model imaging-guided type-I photodynamic therapy/photothermal therapy against hypoxic tumors. This results provide valuable insight for developing high-performance NIR-II-emissive superoxide radical phototheranostic agents.

Dually fluorinated unimolecular micelles for stable oxygen-carrying and enhanced photosensitive efficiency to boost photodynamic therapy against hypoxic tumors

Tumor hypoxia is one of key challenges in deep tumor photodynamic therapy (PDT), and how to fix this issue is attracting ongoing concerns worldwide. This work demonstrates dually fluorinated unimolecular micelles with desirable and stable oxygen-carrying capacity, high cellular penetration, and integrative type I & II PDT for deep hypoxic tumors. Dually fluorinated star copolymers with fluorinated phthalocyanines as the core are prepared through photoinitiated electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization under irradiation with NIR LED light at room temperature, followed by assembly into unimolecular micelles. Perfluorocarbons (PFCs) are also introduced into the star polymers during the polymerization to further enhance and stabilize oxygen-carrying capacity, which is slightly affected by concentration-induced size transformation. PFCs assist unimolecular micelles with repelling mucin adsorption, which results in superior cellular uptake within 1 h and high effective accumulation rates in tumors of CT26 tumor-bearing mice within 24 h after systemic administration, and showing effective anti-tumor effects under the irradiation of NIR LED light. This work provides a new type of nano-photosensitizers for highly efficient hypoxic PDT. STATEMENT OF SIGNIFICANCE: One of the major challenges in improving the efficiency of photodynamic therapy (PDT) for deep tumors is how to address tumor hypoxia, which is receiving continued attention worldwide. However, most of the reported oxygen carriers combine with photosensitizers by physical means and the carriers have the risk of dissociating easily, which is not conducive to long-term and efficient PDT, resulting in poor therapeutic effect. This work demonstrates dually fluorinated unimolecular micelles with desirable and stable oxygen-carrying capacity, high cellular penetration, and integrative type I & II PDT for enhanced deep hypoxic tumors, overcoming the key challenges of tumor hypoxia and low photosensitizer efficiency.

The Photodynamic Agent Designed by Involvement of Hydrogen Atom Transfer for Enhancing Photodynamic Therapy

Although Type-I photodynamic therapy has attracted increasingly growing interest due to its reduced dependence on oxygen, the design of effective Type-I photosensitizers remains a challenge. In this work, we report a design strategy for Type-I photosensitizers by the involvement of hydrogen atom transfer (HAT). As a proof of concept, a HAT-involved Type-I PS, which simultaneously generates superoxide and carbon-centered radicals under light-irradiation, was synthesized. This photosensitizer is comprised of a fluorene-substituted BODIPY unit as an electron acceptor covalently linked with a triphenylamine moiety as an electron donor. Under light-irradiation, photo-induced intramolecular electron transfer occurs to generate the BODIPY anion radical and triphenylamine cation radical. The former transfers electrons to oxygen to generate O2 -⋅, while the latter loses a proton to produce a benzyl carbon-centered radical which is well characterized. The resulting carbon-centered radicals efficiently oxidize NADH by HAT reaction. This photosensitizer demonstrates remarkable photocytotoxicity even under hypoxic conditions, along with outstanding in vivo antitumor efficacy in mouse models bearing HeLa tumors. This work offers a novel strategy for the design of Type-I photosensitizers by involvement of HAT.

Phthalocyanine aggregates as semiconductor-like photocatalysts for hypoxic-tumor photodynamic immunotherapy

Photodynamic immunotherapy (PIT) has emerged as a promising approach for efficient eradication of primary tumors and inhibition of tumor metastasis. However, most of photosensitizers (PSs) for PIT exhibit notable oxygen dependence. Herein, a concept emphasizing on transition from molecular PSs into semiconductor-like photocatalysts is proposed, which converts the PSs from type II photoreaction to efficient type I photoreaction. Detailed mechanism studies reveal that the nanostructured phthalocyanine aggregate (NanoNMe) generates radical ion pairs through a photoinduced symmetry breaking charge separation process, achieving charge separation through a self-substrate approach and leading to exceptional photocatalytic charge transfer activity. Additionally, a reformed phthalocyanine aggregate (NanoNMO) is fabricated to improve the stability in physiological environments. NanoNMO showcases significant photocytotoxicities under both normoxic and hypoxic conditions and exhibits remarkable tumor targeting ability. Notably, the NanoNMO-based photodynamic therapy and PD-1 checkpoint inhibitor-based immunotherapy synergistically triggers the infiltration of cytotoxic T lymphocytes into the tumor sites of female mice, leading to the effective inhibition of breast tumor growth.

Molecular acceptor engineering to precisely design a NIR type I photosensitizer for efficient PDT-based synergistic therapy

Molecular design plays a crucial role in regulating the photophysical properties and photodynamic therapy (PDT) performance of photosensitizers (PSs); however, realizing PDT-based synergistic therapy based on sole PSs is still rarely reported. Herein, three near-infrared red type I PSs (named TP1, TP2, and TP3) were synthesized by adjusting their electron acceptors. The results demonstrated that these PSs exhibited aggregation-enhanced reactive oxygen species (ROS) generation efficiency and cyano groups on PSs can reduce ROS generation in solution while achieving efficient PDT-based synergistic therapy in cells via glutathione depletion.

Potent Covalent Organic Framework Nanophotosensitizers with Staggered Type I/II Motifs for Photodynamic Immunotherapy of Hypoxic Tumors

Photodynamic therapy (PDT) using oxygen-dependent type II photosensitizers is frequently limited by the hypoxic microenvironment of solid tumors. Type I photosensitizers show oxygen-independent reactive oxygen species (ROS) generation upon light irradiation but still face the challenges of aggregation-caused quenching (ACQ) and low efficiency to produce ROS. Herein, we first prepare an efficient type I photosensitizer from a perylene derivative via intramolecular donor-acceptor binding and sulfur substitution, which significantly enhance intersystem crossing between singlet and triplet states and electron transfer capability. After reaction with a type II photosensitizer, the covalent organic framework (COF) nanophotosensitizer is formed with alternated type I and II photosensitizer motifs in the same layer and staggered AB stacking between layers to avoid ACQ. The nanophotosensitizer exhibits high-efficiency generation of singlet oxygen (1O2) and superoxide anion radicals (O2•-) via type I and II mechanism under normoxia upon exposure to light irradiation. Under hypoxia, massive O2•- can be produced continuously. The potent ROS generation capability results in efficient cellular apoptosis and immunogenic cell death (ICD) efficiently. After combination with immune checkpoint inhibitors, tumor immunosuppressive microenvironment is reversed, which effectively ablates bulky hypoxic primary tumors and suppresses metastases via photodynamic immunotherapy. The COF nanophotosensitizers with staggered type I and II photosensitizer motifs represent a promising strategy to boost photodynamic immunotherapy of hypoxic tumors.

Molecular Design of Phthalocyanine-Based Drug Coassembly with Tailored Function

Coassemblies with tailored functions, such as drug loading, tissue targeting and releasing, therapeutic and/or imaging purposes, and so on, have been widely studied and applied in biomedicine. De novo design of these coassemblies hinges on an integrated approach involving synergy between various design strategies, ranging from structure screening of combinations of "phthalocyanine-chemotherapeutic drug" molecules for molecular scaffolds, exploration of related fabrication principles to verification of intended activity of specific designs. Here, we propose an integrated approach combining computation and experiments to design from scratch coassembled nanoparticles. This nanocoassembly, termed NanoPC here, consists of phthalocyanine-based scaffolds hosting chemotherapeutic drugs, aimed at hypersensitive chemotherapy guided by photoimaging for targeting tumors. Our design starts from the selection of phthalocyanine derivatives that are not aggregation-prone, followed by computational screening of coassembled molecules covering various categories of chemotherapy drugs. To facilitate an efficient and accurate assessment of coassembly capabilities, we utilize small systems as surrogates to enable free-energy calculations at all-atom levels facilitated with enhanced sampling and statistical mechanics for efficient and accurate evaluation of coassembly ability. The final top NanoPC candidate, comprised of phthalocyanine PcL and cytarabine (CYT), can greatly increase the fluorescence intensity ratio of tumor/liver by 21.5 times and achieve higher antitumor efficiency in a pH-dependent manner. Therefore, the designing approach proposed here has a potential pattern, which can provide ideas and references for the design and development of coassembled nanodrugs with tailored functions and applications in biomedicine.

A tumor-pH-responsive phthalocyanine as activatable type I photosensitizer for improved photodynamic immunotherapy

The development of a simple drug formulation capable of achieving both activatable type I photoreaction and tumor-responsive release of immunomodulator is crucial for advancing photodynamic immunotherapy (PDIT). Herein, we present a nanostructured photosensitizer (NP5) that is activated by the acidic tumor microenvironment to produce type I reactive oxygen species (ROS) under light irradiation and release the immunomodulator demethylcantharidin (DMC) for PDIT. The NP5 is formed by self-assembly of a versatile phthalocyanine molecule which is composed of DMC and phthalocyanine linked via a pH-responsive amide bond. NP5 produces minimal ROS under light irradiation at the condition of pH 7.4. However, NP5 can release DMC at the condition of pH 6.5 and concurrently trigger type I photoreactions. The results of in vivo experiments indicate that NP5-mediated PDIT induce the increase of cytotoxic T lymphocytes and decrease of regulatory T lymphocytes, which can effectively inhibit the bilateral tumor growth. This work is anticipated to serve as a reference for the development of innovative agents for precise PDIT of hypoxic tumors.

Synthesis of heavy-atom-free thienoisoindigo dye as near-infrared photosensitizer for type I photodynamic therapy and photoacoustic imaging

Thienoisoindigo (TIIG) has been extensively employed as promising building block of near-infrared (NIR) dyes and organic semiconductor materials. Herein, heavy-atom-free TIIG-based NIR dye TIIGTPA is reported as photosensitizer for combinational photodynamic and photothermal therapy and photoacoustic imaging (PAI). By introducing two methoxy-substituted triphenylamines as the rotors and electron donors at the periphery sites of the electron-deficient TIIG core, dye TIIGTPA featuring Donor-Acceptor-Donor (D-AD) structure is constructed with intensive NIR absorption. Through co-assembly with amphipathic F-127, water-soluble TIIGTPA NPs were prepared with good superoxide anion radical (O2-•) production and high photothermal conversion efficiency (PCE) of 59.0 % under 730 nm photoirradiation. Additionally, the excellent photothermal effect enabled a superior photoacoustic response for tumor blood vessel visualization through PAI. All results indicated the favorable potential of TIIGTPA NPs for PAI-mediated combinational phototherapy.

Tracking Microenvironmental Response on Self-Assembled Phthalocyanine Systems - Adaptive and Non-Adaptive Antibacterial Photosensitization

Self-assembly has proven to be one of the effective methods for the formation of nanoscale therapeutics without the need to use nanodelivery systems. Such minimal models of supramolecular systems formed from amphiphilic photosensitizers (PS) have recently emerged as a new class of photoactive systems, providing unique and in some cases superior activities. Although the mechanism of photogenerated reactive oxygen species (ROS) in such systems is studied and to a certain extent understood, there are very limited studies investigating the influence of intricate environmental factors, including those occurring in the cellular environment, on the self-assembly and thus the activity of the system. Understanding the optimal conditions for the formation of active PS aggregates is an important area of research in the field of photodynamic therapy (PDT), as it is directly linked to the optimal treatment dose. In this study, we describe the synthesis, self-assembly properties, photophysical characterization, and photobiological efficacy of structurally closely related low-symmetry phthalocyanine derivatives. Studying the decay behavior of the PS fluorescence lifetime in the presence of molecular crowders and different bacterial strains, we found that certain derivatives exhibited adaptive behavior and change in activity, while others demonstrated non-adaptive characteristics.

A Renal Clearable Nano-Assembly with Förster Resonance Energy Transfer Amplified Superoxide Radical and Heat Generation to Overcome Hypoxia Resistance in Phototherapeutics

Given that type I photosensitizers (PSs) possess a good hypoxic tolerance, developing an innovative tactic to construct type I PSs is crucially important, but remains a challenge. Herein, we present a smart molecular design strategy based on the Förster resonance energy transfer (FRET) mechanism to develop a type I photodynamic therapy (PDT) agent with an encouraging amplification effect for accurate hypoxic tumor therapy. Of note, benefiting from the FRET effect, the obtained nanostructured type I PDT agent (NanoPcSZ) with boosted light-harvesting ability not only amplifies superoxide radical (O2 •-) production but also promotes heat generation upon near-infrared light irradiation. These features facilitate NanoPcSZ to realize excellent phototherapeutic response under both normal and hypoxic environments. As a result, both in vitro and in vivo experiments achieved a remarkable improvement in therapeutic efficacy via the combined effect of photothermal action and type I photoreaction. Notably, NanoPcSZ can be eliminated from organs (including the liver, lung, spleen, and kidney) apart from the tumor site and excreted through urine within 24 h of its systemic administration. In this way, the potential biotoxicity of drug accumulation can be avoided and the biosafety can be further enhanced.

Reversible pH-switchable NIR-II nano-photosensitizer for precise imaging and photodynamic therapy of tumors

Photodynamic therapy (PDT) has attracted widespread attention from researchers as an emerging cancer treatment method. There have been many reports on various types of NIR-II photosensitizers for imaging and treatment of tumor sites. However, there are few reports on the development of NIR-II organic small molecule photosensitizers that have intelligent response to the tumor microenvironment, precise imaging, real-time treatment, and high biocompatibility. In this work, we developed a series of NIR-II photosensitizers (RBTs) with near-infrared excitation, good photostability, and large Stokes shift. Among them, RBT-Br exhibited higher reactive oxygen species (ROS) generation efficiency due to the introduction of halogen heavy atoms to enhance intersystem crossing (ISC). It is noteworthy that RBT-Br can generate singlet oxygen (1O2) and superoxide anion radicals (•O2-) simultaneously under 730 nm laser. Subsequently, we used molecular engineering technology to construct three pH-responsive NIR-II photosensitizers (RBT-pHs) by utilizing the closure of the lactam ring, among which RBT-pH-1 (pKa = 6.78) is able to be directionally activated under the stimulation of tumor micro-acid environment, with its fluorescence emission window reaching 933 nm. Subsequently, RBT-pH-1 NPs encapsulated in DSPE-mPEG5k were applied for PDT treatment of mouse tumors. The results showed that RBT-pH-1 NPs were activated by the acidic tumor microenvironment and generated ROS under laser excitation, exhibiting precise tumor imaging and significant tumor growth inhibition. We look forward to these multifunctional NIR-II organic small molecule photosensitizers providing a more efficient approach for clinical treatment of tumors. STATEMENT OF SIGNIFICANCE: A reversible pH-switchable NIR-II nano-photosensitizer RBT-pH-1 NPs (pKa = 6.76) is developed for precise imaging and PDT therapy of mouse tumors, which can be effectively used for targeted enrichment and activation of tumor micro-acid environments. The results show that this NIR-II photosensitizer generates ROS through tumor micro-acid environment stimulation and laser triggering, showing precise tumor imaging guidance and significant tumor growth inhibition.

Tannic Acid-Based Self-Assembling Nanocarriers with Antiphotobleaching and Controlled Releasing Properties for Collaborative Near-Infrared Photothermal/Photodynamic Therapy

Near-infrared (NIR) organic materials have been widely developed for tumor phototherapy due to their deep tumor penetration, good biodegradability, and high photothermal conversion (PCE). However, most of the NIR organic dyes are easily destroyed by photooxidation due to their big and long conjugated structures, such as cyanine dyes. Under light irradiation, the reactive oxygen species (ROS) produced by these NIR dyes can easily break their conjugated skeleton, resulting in a dramatic decrease in phototherapeutic efficiency. Herein, an NIR organic dye cyanine dye (CyS) and a photosensitizer methylene blue (MB) were chosen to prepare nanocarrier CMTNPs by facile self-assembling with a natural antioxidant, tannic acid (TA). TA can greatly enhance the stability of NIR cyanine dyes by scavenging ROS. Furthermore, CMTNPs have a character of pH/thermal dual response, allowing for controlled release of MB in the slightly acidic tumor environment during photothermal therapy. The released MB can turn on both fluorescence and photodynamic therapy effects. In vitro and in vivo experiments demonstrated the remarkable tumor ablation ability of CMTNPs. Thus, our study provided an antiphotobleaching and controlled release photosensitizer strategy through the introduction of antioxidant TA into the nanocarrier for efficient collaborative photothermal/photodynamic therapy.

Tumor oxygen microenvironment-tailored electron transfer-type photosensitizers for precise cancer therapy

The oxygen level in a tumor typically exhibits complex characteristics, ranging from mild hypoxia to moderate and even severe hypoxia. This poses significant challenges for the efficacy of photodynamic therapy, where oxygen is an essential element. Herein, we propose a novel therapeutic strategy and develop a series of lipid droplet-targeting photosensitive dyes (Ser-TPAs), i.e., in situ synergistic activation of two different electron transfer-type reactions. Based on this strategy, Ser-TPAs can synergistically generate O2˙- and nitrogen radicals regardless of the oxygen content, which results in a sustained high concentration of strongly oxidizing substances in the lipid droplets of cancer cells. As such, Ser-TPAs exhibited inhibitory activity against tumor growth in vivo, resulting in a significant reduction in tumor volume (V experimental group : V control group ≈ 0.07). This strategy offers a conceptual framework for the design of innovative photosensitive dyes that are suitable for cancer therapy in complex oxygen environments.

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

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

A perylene diimide probe for NIR-II fluorescence imaging guided photothermal and type I/type II photodynamic synergistic therapy

Phototherapy has garnered significant attention in the past decade. Photothermal and photodynamic synergistic therapy combined with NIR fluorescence imaging has been one of the most attractive treatment options because of the deep tissue penetration, high selectivity and excellent therapeutic effect. Benefiting from the superb photometrics and ease of modification, perylene diimide (PDI) and its derivatives have been employed as sensing probes and therapeutic agents in the biological and biomedical research fields, and exhibiting excellent potential. Herein, we reported the development of a novel organic small-molecule phototherapeutic agent, PDI-TN. The absorption of PDI-TN extends into the NIR region, which provides feasibility for NIR phototherapy. PDI-TN overcomes the traditional Aggregation-Caused Quenching (ACQ) effect and exhibits typical characteristics of Aggregation-Induced Emission (AIE). Subsequently, PDI-TN NPs were obtained by using an amphiphilic triblock copolymer F127 to encapsulate PDI-TN. Interestingly, the PDI-TN NPs not only exhibit satisfactory photothermal effects, but also can generate O2•- and 1O2 through type I and type II pathways, respectively. Additionally, the PDI-TN NPs emit strong fluorescence in the NIR-II region, and show outstanding therapeutic potential for in vivo NIR-II fluorescence imaging. To our knowledge, PDI-TN is the first PDI derivative used for NIR-II fluorescence imaging-guided photodynamic and photothermal synergistic therapy, which suggests excellent potential for future biological/biomedical applications.

NIR-Absorbing Tetraphenylethene-Containing bisBODIPY Nanoplatforms Demonstrate Effective Lysosome-Targeting and Combinational Phototherapy

Photosensitizer-based phototherapies, including photodynamic therapy (PDT) and photothermal therapy (PTT), offer safe treatment modalities for tumor ablation with spatiotemporal precision. After photons are absorbed, PDT creates localized chemical damage by generating reactive oxygen species (ROS), while PTT induces localized thermal damage. However, PDT still faces hypoxic tumor challenges, while PTT encounters issues related to heat resistance and potential overheating. The combination of PDT and PTT shows great potential as an effective anticancer strategy. By targeting lysosomes with carefully designed phototherapeutic reagents for combined phototherapy, rapid dysfunction and cell death in cancer cells can be induced, showing promise for cancer treatment. Herein, two α-α-linked bisBODIPYs with tetraphenylethene (TPE) moieties are designed and synthesized. These TPE-substituted bisBODIPYs expand the absorption into NIR range (λmaxabs/λmaxem ∼ 740/810 nm) and confer aggregation-induced emission (AIE) activity (λmaxem ∼ 912 nm). Moreover, these bisBODIPYs self-assemble with surfactant F-127 into nanoparticles (NPs), which efficiently generate ROS (1O2 and •OH) in both solution and cellular environments and demonstrate superior photothermal conversion efficiencies (η ∼ 68.3%) along with exceptional photothermal stability. More importantly, these NPs showed lysosomal targeting and remarkable tumor ablation in cellular and murine models, indicating their potential in precision tumor therapy.

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.

Perphenazine modified pillar[5]arene based nano-assemblies for synergistic photothermal and photodynamic cancer therapy

Nano-assemblies based on perphenazine modified pillar[5]arene were constructed successfully for synergistic photothermal and photodynamic (I&II) cancer therapy.

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.

Macromolecular Nano-Assemblies for Enhancing the Effect of Oxygen-Dependent Photodynamic Therapy Against Hypoxic Tumors

In oxygen (O2)-dependent photodynamic therapy (PDT), photosensitizers absorb light energy, which is then transferred to ambient O2 and subsequently generates cytotoxic singlet oxygen (1O2). Therefore, the availability of O2 and the utilization efficiency of generated 1O2 are two significant factors that influence the effectiveness of PDT. However, tumor microenvironments (TMEs) characterized by hypoxia and limited utilization efficiency of 1O2 resulting from its short half-life and short diffusion distance significantly restrict the applicability of PDT for hypoxic tumors. To address these challenges, numerous macromolecular nano-assemblies (MNAs) have been designed to relieve hypoxia, utilize hypoxia or enhance the utilization efficiency of 1O2. Herein, we provide a comprehensive review on recent advancements achieved with MNAs in enhancing the effectiveness of O2-dependent PDT against hypoxic tumors.

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.

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.

Cationic Polythiophene as Gene Carrier and Sonosensitizer for Sonodynamic Synergic Gene Therapy of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most lethal and highly malignant tumors. Sonodynamic therapy (SDT) is a new cancer treatment method. One of its unique advantages lies in the treatment of deep tumors due to its excellent tissue penetration ability caused by ultrasound (US). However, most sonosensitizers suffer from weak sonodynamic activity and poor tumor-targeting ability. In addition, small interfering RNA (siRNA) is a promising anticancer drug, and the efficacy of siRNA-based gene therapy largely depends on the cell impermeability of the gene carrier. Here, we designed and synthesized a cationic polythiophene derivative (PT2) that can be used as a siRNA carrier for gene therapy. Moreover, PT2 could generate singlet oxygen (1O2) and hydroxyl radicals (O2•-) under US irradiation, which suggests that PT2 could be used for SDT. Our study discovered that NUDT1 promoted HCC proliferation and inhibited intracellular ROS production. Therefore, si-NUDT1 was designed and synthesized. NUDT1 silencing can inhibit the proliferation of tumor cells and increase the production of intracellular ROS to further improve the efficacy of SDT. Then, si-NUDT1 assembled with PT2 and DSPE-PEG-FA to prepare a novel tumor-targeting nanodrug (PT2-siRNA@PEG-FA) for synergic SDT and gene therapy of HCC.

Remote Control of Energy Transformation-Based Cancer Imaging and Therapy

Cancer treatment requires precise tumor-specific targeting at specific sites that allows for high-resolution diagnostic imaging and long-term patient-tailorable cancer therapy; while, minimizing side effects largely arising from non-targetability. This can be realized by harnessing exogenous remote stimuli, such as tissue-penetrative ultrasound, magnetic field, light, and radiation, that enable local activation for cancer imaging and therapy in deep tumors. A myriad of nanomedicines can be efficiently activated when the energy of such remote stimuli can be transformed into another type of energy. This review discusses the remote control of energy transformation for targetable, efficient, and long-term cancer imaging and therapy. Such ultrasonic, magnetic, photonic, radiative, and radioactive energy can be transformed into mechanical, thermal, chemical, and radiative energy to enable a variety of cancer imaging and treatment modalities. The current review article describes multimodal energy transformation where a serial cascade or multiple types of energy transformation occur. This review includes not only mechanical, chemical, hyperthermia, and radiation therapy but also emerging thermoelectric, pyroelectric, and piezoelectric therapies for cancer treatment. It also illustrates ultrasound, magnetic resonance, fluorescence, computed tomography, photoluminescence, and photoacoustic imaging-guided cancer therapies. It highlights afterglow imaging that can eliminate autofluorescence for sustained signal emission after the excitation.

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.

Photochemical and biological dual-effects enhance the inhibition of photosensitizers for tumour growth

Photosensitizers typically rely on a singular photochemical reaction to generate reactive oxygen species, which can then inhibit or eradicate lesions. However, photosensitizers often exhibit limited therapeutic efficiency due to their reliance on a single photochemical effect. Herein, we propose a new strategy that integrates the photochemical effect (type-I photochemical effect) with a biological effect (proton sponge effect). To test our strategy, we designed a series of photosensitizers (ZZ-sers) based on the naphthalimide molecule. ZZ-sers incorporate both a p-toluenesulfonyl moiety and weakly basic groups to activate the proton sponge effect while simultaneously strengthening the type-I photochemical effect, resulting in enhanced apoptosis and programmed cell death. Experiments confirmed near-complete eradication of the tumour burden after 14 days (Wlight/Wcontrol ≈ 0.18, W represents the tumour weight). These findings support the notion that the coupling of a type-I photochemical effect with a proton sponge effect can enhance the tumour inhibition by ZZ-sers, even if the basic molecular backbones of the photosensitizers exhibit nearly zero or minimal tumour inhibition ability. We anticipate that this strategy can be generalized to develop additional new photosensitizers with improved therapeutic efficacy while overcoming limitations associated with systems relying solely on single photochemical effects.

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.

Phthalocyanine-based probes in alleviating or evading tumour-hypoxia for enhanced photo- and/ sono-mediated therapeutic efficacies

This review discusses the possible methods for improving therapeutic efficacies of phthalocyanine (Pcs) -based therapeutic probes in photo- and sono-dynamic therapies under hypoxic conditions. Herein, the structural design strategies including varying the central metal, position substituents and the effects of adjuvant used in supplementing the therapeutics activities of Pcs or formation of NPs are discussed for cancer therapies in hypoxic conditions. Different mechanisms induced for cell death influenced by the compositions of the Pcs-probes are discussed. The focus mainly highlights the oxygen (O2) -dependent mechanisms including methods of supplementing tumour microenvironment O2-concentrations to promote PDT or SDT therapies. Alternatively, O2-independent mechanisms mainly used to evade hypoxia by stimulating anticancer processes that don't require O2 to initiate cell death, such as the Fenton reaction or thermal ablation effects.

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.

Suitable Isolation Side Chains: A Simple Strategy for Simultaneously Improving the Phototherapy Efficacy and Biodegradation Capacities of Conjugated Polymer Nanoparticles

Utilizing one molecule to realize combinational photodynamic and photothermal therapy upon single-wavelength laser excitation, which relies on a multifunctional phototherapy agent, is one of the most cutting-edge research directions in tumor therapy owing to the high efficacy achieved over a short course of treatment. Herein, a simple strategy of "suitable isolation side chains" is proposed to collectively improve the fluorescence intensity, reactive oxygen species production, photothermal conversion efficiency, and biodegradation capacity. Both in vitro and in vivo results reveal the practical value and huge potential of the designed biodegradable conjugated polymer PTD-C16 with suitable isolation side chains in fluorescence image-guided combinational photodynamic and photothermal therapy. These improvements are achieved through manipulation of aggregated states by only side chain modification without changing any conjugated structure, providing new insight into the design of biodegradable high-performance phototherapy agents.

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.