Near-Infrared Light-Initiated Molecular Superoxide Radical Generator: Rejuvenating Photodynamic Therapy against Hypoxic Tumors

Recent advances in biomimetic nanodelivery systems for the treatment of glioblastoma

Glioblastoma remain one of the deadliest malignant tumors in the central nervous system, largely due to their aggressiveness, high degree of heterogeneity, and the protective barrier of the blood-brain barrier (BBB). Conventional therapies including surgery, chemotherapy and radiotherapy often fail to improve patient prognosis due to limited drug penetration and non-specific toxicity. We then present recent advances in biomimetic nanodelivery systems, focusing on cell membrane coatings, nanoenzymes, and exosome-based carriers. By mimicking endogenous biological functions, these systems demonstrate improved immune evasion, enhanced BBB traversal, and selective drug release within the tumor microenvironment. Nevertheless, we acknowledge unresolved bottlenecks related to large-scale production, stability, and the intricacies of regulatory compliance. Looking forward, we propose an interdisciplinary roadmap that combines materials engineering, cellular biology, and clinical expertise. Through this collaborative approach, this work aims to optimize biomimetic nanodelivery for glioma therapy and ultimately improve patient outcomes.

Hybrid membrane based biomimetic nanodrug with high-efficient melanoma-homing and NIR-II laser-amplified peroxynitrite boost properties for enhancing antitumor therapy via effective immunoactivation

Owing to the excellent stability, anticancer activity and immunogenicity, peroxynitrite (ONOO-) has been gained enormous interests in cancer therapy. Nevertheless, precise delivery and control release of ONOO- in tumors remains a big challenge. Herein, B16F10 cancer cell membrane/liposome hybrid membrane (CM-Lip) based biomimetic nanodrug with high-efficient tumor-homing and NIR-II laser controlled ONOO- boost properties was designed for melanoma treatment. Briefly, NIR-II molecule IR1061, NO donor BNN6 and β-lapachone (Lapa) were firstly encapsulated in the heat-responsive palmitoyl phosphatidylcholine/cholesterol liposome, followed by fusion with B16F10 cell membrane (CM) to obtain biomimetic CM-Lip@(IR/BNN6/Lapa). The hybrid membrane-based nanodrug displayed excellent biocompatibility and melanoma-targeting efficiency. Upon 1064 nm laser irradiation, the mild photothermal effect of CM-Lip@(IR/BNN6/Lapa) firstly triggered the release of NO and Lapa, which subsequently catalyzed the quinone oxidoreductase 1 (NQO1) overexpressed in tumors to produce O2•-, finally caused intraturmal ONOO- boost via cascade reaction. The boosted ONOO- could effectively inhibit melanoma by ways of triggering mitochondrion-mediated apoptotic pathway, upregulating 3-nitrotyrosine expression, inducing DNA damage and inhibiting DNA repair enzyme expression of poly (ADP-ribose) polymerase 1 (PARP-1). Moreover, ONOO- displayed excellent immunoactivation and immunomodulation activities by effectively inducing immunogenic tumor cell death, promoting dendritic cells maturation, increasing cytotoxic T lymphocytes expression and repolarizing M1-phenotype macrophages.

"From darkness to radiance": Light-induced type I and II ROS-mediated apoptosis for anticancer effects of dansylpiperazine-bearing squaraine dyes

Photodynamic therapy relies on the generation of cytotoxic effects triggered by the irradiation of a photosensitizer molecule, resulting in the production of reactive oxygen species at concentrations exceeding physiological levels. In this context, squaraine dyes, a prominent family of second-generation photosensitizers, have gained increasing attention for their remarkable properties, with their photobiological characteristics recently emerging as a key focus of in-depth research. Dansylpiperazine-bearing squaraine dyes exhibited strong absorption in the red visible spectral region, excellent photostability, and a predicted ability to interact with human serum albumin, potentially serving as a transport vehicle to target sites. Benzothiazole derivatives excelled in photodynamic activity, demonstrating 7- to 11-fold increased cytotoxicity upon irradiation against prostate adenocarcinoma PC-3 cells and tumor selectivity indices exceeding 10 when compared to normal NHDF cells. In contrast, the introduction of the dansylpiperazino group in indole-derived compounds unexpectedly declined their photodynamic activity. Concerning benzothiazole-based ones, multiple reactive oxygen species were shown to contribute to the photodynamic effects, with singlet oxygen playing a key role. Squaraine internalization was observed in various cytoplasmic organelles, including mitochondria, endoplasmic reticulum, and lysosomes, without clear evidence of preferential localization to any single organelle. Non-genotoxic in the dark, the squaraines induced cell death by apoptosis upon light activation, as evidenced by significant DNA fragmentation and increased caspase 3/7 activation, particularly for the dye with N-ethyl chains, at concentrations below 1.0 μM, underscoring their potency. Checkpoint arrests in G1 and G2/mitosis were observed for non-irradiated and irradiated conditions, respectively, highlighting the antiproliferative effects of these squaraine dyes.

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.

Smart Type I Squaraine Nano-Photosensitizer Combined with MnO2 for Tumor-Targeted and Ferroptosis-Induced Immunogenic Photodynamic Therapy

Most photosensitizers face enormous challenges in tumor hypoxia, the redox microenvironment, and low immune efficacies for reactive oxygen species (ROS). Herein, dye SQ-580 was constructed by coupling the electron-donating indole and thiophenazine-thiophene with the electron-withdrawing dicyanovinyl squaraine. It exhibited a high generation of •OH and O2•- by decreasing ΔES1T2 and acted as an excellent type I photosensitizer for conquering tumor hypoxia. The nanoplatform involving SQ-580, MnO2, and a targeting peptide CREKA was constructed and targeted breast tumor. In the tumor microenvironment, MnO2 reacted with high-expressed GSH and produced Mn2+, which catalyzed H2O2 to decompose into •OH and induced chemodynamic therapy (CDT). The reduction of GSH inhibited the consumption of SQ-580 and maintained its high photodynamic therapy (PDT) efficacy. GSH depletion and ROS resulted in cell ferroptosis. Under the synergy of ferroptosis and ROS, Mn2+ amplified immunogenic cell death (ICD). In the mouse models, SQ-580@MnO2 NPs showed NIRF/MR imaging-guided tumor targeting, effectively inhibited the growth of the primary and distant tumors, and amplified PDT and immune efficacies in the synergy of PDT, CDT, ferroptosis, and ICD. This study provides an effective strategy to design excellent type I photosensitizers and amplify the PDT and ICD efficacies utilizing valence metals and the tumor microenvironment.

Spin Manipulation Engineering of Photodynamic Intermediates: Magnetic Amplification of Oxyradicals Generation for Enhanced Antitumor Phototherapeutic Efficacy

Improving the photosensitization efficiency represents a critical challenge in photodynamic therapy (PDT) research. While cyanines exhibit potential as photosensitizers (PSs) due to their large extinction coefficients and excellent biocompatibility, the inherent limitations in intersystem crossing severely affect therapeutic efficacy. Herein, we proposed a bottom-up magnetically enhanced photodynamic therapy (magneto-PDT) paradigm employing fluorobenzene-substituted pentamethine cyanine as type-I reactive oxygen species generators. Based on the radical pair mechanism and magnetic field effect, the notable difference in g-factors (Δg) between PSs and oxyradicals enabled magnetically responsive amplification of Cy5-3,4,5-3F-mediated hydroxyl radical (•OH) and superoxide anion radical (O2•-) production, achieving maximum yield enhancements of 66.9 and 28.0% respectively at 500 mT. This magnetically augmented oxyradicals generation exhibited universal cytotoxicity superiority over conventional PDT protocols in various cancer cell models. Notably, the semi-inhibitory concentration (IC50) of murine mammary carcinoma 4T1 cells demonstrated a remarkable reduction under both normoxic and hypoxic conditions, with the most pronounced decrease observed in normoxia from 0.91 μM (PDT alone) to 0.38 μM (magneto-PDT). The significantly magneto-enhanced therapeutic performance effectively inhibited orthotopic tumor growth. This magneto-PDT paradigm established a novel strategy for manipulating spin-dependent photosensitization processes in biological applications.

Organelle-targeted small molecular photosensitizers for enhanced photodynamic therapy: a minireview for recent advances and potential applications

Photodynamic therapy (PDT) is a promising approach for cancer treatment that involves the use of photosensitizers to generate reactive oxygen species upon light irradiation, resulting in selective cytotoxicity. To enhance the efficiency of PDT, researchers have developed organelle-targeting photosensitizers that specifically accumulate in critical cellular organelles. This review provides a comprehensive overview of recent advancements in the development of organelle-targeting photosensitizers for PDT. Different organelles, including mitochondria, plasma membrane, lysosome, endoplasmic reticulum, lipid droplets, nucleus, and Golgi, have been targeted to improve the selectivity and effectiveness of PDT. Various strategies have been employed to design and synthesize these photosensitizers, optimizing their organelle-specific accumulation and photodynamic efficiency. This review discusses the principles and mechanisms underlying the design of organelle-targeting photosensitizers, along with their exceptional results achieved in preclinical studies. Furthermore, potential applications and challenges in the development of multi-organelles-targeting photosensitizers and the synergistic use of multiple photosensitizers targeting different organelles are highlighted. Overall, organelle-targeting photosensitizers offer a promising avenue for advancing the field of PDT and improving its clinical applicability.

Pyrazolo[1,5-a]pyrimidine-Based Type-I Photosensitizer as an Efficient Pyroptosis Inducer for Tumor Ablation

Pyroptosis is a proinflammatory and lytic programmed cell death form, which can promote cytotoxic T lymphocyte (CTL) maturation and tumor infiltration through the release of damage-associated molecular patterns (DAMPs). Therefore, the induction of pyroptosis by small molecules is a promising strategy to activate antitumor immunity. In this work, we report the design of a new class of pyrazolo[1,5-a]pyrimidine-based type-I photosensitizers (PSs) as efficient pyroptosis inducers for cancer photodynamic therapy (PDT). Among the compounds, ZS-3 exhibited the most excellent reactive oxygen species (ROS) generation ability and phototoxicity in vitro. It was found that ZS-3 induced cell pyroptosis through the caspase-3/gasdermin E (GSDME) pathway under light irradiation, characterized by bubble formation and damage-associated molecular pattern release. Furthermore, ZS-3 lipid nanoparticles significantly inhibited tumor growth and evoked antitumor immune responses in vivo.

Improved Orthogonality in Naphthalimide/Cyanine Dyad Boosts Superoxide Generation: a Tumor-Targeted Type-I Photosensitizer for Photodynamic Therapy of Tumor by Inducing Ferroptosis

It is highly desired to achieve Type-I photosensitizer (PS) to overcome the hypoxic limitation found in most clinically used PSs. Herein, a new heavy-atom-free Type-I PS T-BNCy5 is presented by incorporating a biotin-modified naphthalimide (NI) unit into the meso-position of a N-benzyl-functionalized, strongly photon-capturing pentamethine cyanine (Cy5) dye. Such molecular engineering induces a rigid orthogonal geometry between NI and Cy5 units by introducing an intramolecular sandwich-like π-π stacking assembly, which effectively promotes intersystem crossing (ISC) and greatly extends the triplet-state lifetime (τ = 389 µs), thereby markedly improving the superoxide (O2 •-)-generating ability. In vitro assays reveal that T-BNCy5 specifically accumulates in mitochondria, where it not only generates O2 •- under photoirradiation but also induces the burst of the most cytotoxic hydroxy radical (HO•) by a cascade of biochemical reactions, ultimately triggering cell ferroptosis with the IC50 value up to ≈0.45 µm whether under normoxia or hypoxia. In vivo assays manifest that, benefiting from its biotin unit, T-BNCy5 displays a strong tumor-targeting ability, and after a single PDT treatment, it can not only ablate the tumor almost completely but also be cleared from the body through biosafe urinary excretion, indicating its potential for future clinical translation.

NIR-II Photosensitizer-Based Nanoparticles Defunctionalizing Mitochondria to Overcome Tumor Self-Defense by Promoting Heat Shock Protein 40

Inherent self-defense pathways within malignant tumors include the action of heat shock proteins (HSPs) and often impede photothermal therapy efficacy. Interestingly, HSP40 inhibits glycolysis and disrupts mitochondrial function to overcome tumor self-defense mechanisms and exhibits a tumor-suppressive effect. Reactive oxygen species (ROS), especially hydroxyl radicals, generated by type-I photodynamic therapy inhibit adenosine triphosphate (ATP) production and lead to ATP-independent HSP40 overexpression during heat stress. However, the regulatory mechanisms linking heat and hydroxyl radicals to induce HSP40 expression remain unclear. Therefore, it is imperative to elucidate the underlying mechanism governing the induction of HSP40 expression during heat stress and explore its potential as a promising therapeutic strategy against tumor development. By strategically modifying the aza-BODIPY structure to precisely distribute the excited-state energy, we have demonstrated that HSP40 specific expression is correlated with the proportion of heat to hydroxyl radicals rather than their individual levels. This orchestrated NIR-II photosensitizer-based nanoparticles reduced tumor glycolysis and disrupted ATP production, driving cell apoptosis and amplifying the efficacy of photothermal therapy. Silencing and compensation of HSPs under heat and ROS stress represent a promising and effective strategy for overcoming tumor self-defense mechanisms in cancer therapy.

D-(+)-Biotinylated squaraine dyes: A journey from synthetic conception, photophysical and -chemical characterization, to the exploration of their photoantitumoral action mechanisms

Biotin is primarily taken up by cells through sodium-dependent multivitamin transporter, which is highly expressed in aggressive cancer cell lines, often at levels surpassing those of the folate receptor. This makes biotin an attractive ligand for tumor-targeted drug delivery. Building on this rationale, this study presents a series of six D-(+)-biotin-conjugated squaraine dyes derived from benzothiazole, indolenine, and benz[e]indole, with N-ethyl and N-hexyl chains. These compounds were thoroughly characterized in terms of their photophysical and photochemical properties, revealing strong absorption in the so-called "phototherapeutic window", notable fluorescence, especially the benzothiazole derivatives, aqueous stability, particularly the indolenine-based dyes, and moderate to high photostability. Computational studies further indicated a strong binding affinity to human serum albumin and avidin proteins. All dyes exhibited photodynamic activity, with indolenine derivatives showing remarkable tumor selectivity and benz[e]indole analogs evidencing superior photocytotoxicity. The most promising compounds preferentially accumulated in mitochondria, and both singlet oxygen and other reactive oxygen species were found to play a role in their photobiological effects. Additionally, they were non-genotoxic in the absence of irradiation, and apoptosis was the primary mechanism of cell death upon light activation. This was evidenced by preserved cytoplasmic membrane integrity, nuclear fragmentation, and caspase-3/7 activation, reinforcing the safety and potential of these compounds as phototherapeutic agents. Although cellular uptake via the sodium-dependent multivitamin transporter was not established, and diffusion is expected to be the predominant mechanism, the high predicted avidin-binding affinity of these dyes opens exciting new avenues for photodynamic therapy-combined strategies.

Recent Progress of Molecular Design in Organic Type I Photosensitizers

Photodynamic therapy (PDT) represents a high-efficient and non-invasive therapeutic modality for current and future tumor treatments, drawing extensive attention in the fields of antitumor drug and clinical phototherapy. In recent years, the photosensitizer (PS) market and PDT clinical applications have expanded to address various cancers and skin diseases. However, hypoxic environment within tumors poses a substantial challenge to the therapeutic capability of reactive oxygen species-dependent PDT. Consequently, researches have increasingly focus from the type II to type I PDT mechanism, which relies on radical production with less or no oxygen dependence. Despite significant progress in the development of type I PSs, a holistic understanding regarding the design principles for these molecules remains elusive. Specifically, electron transfer-mediated type I PDT are extensively studied in recent years but is insufficiently addressed in existing reviews. This review systematically summarizes recent advancements in the molecular design rationales of organic type I PSs, categorizing them into three key fundamental strategies: modulating PS charge distribution, singlet oxygen forbidden via low triplet excited state, and accelerating PS radical formation via inducing electron transfer. This review aims to offer valuable insights for the future type I PS design and the advancement of anti-hypoxia PDT.

Hepatoma Metastasis-Inhibiting Supramolecular Nanoglycocalyx for Enhanced Type I Photodynamic Therapy

Type I photodynamic therapy (PDT) is well demonstrated to have low oxygen dependency. However, fully suppressing the risk of hypoxia-induced tumor metastasis during PDT remains a great challenge. In this study, a tetra-lactosylated amphiphilic Aza-BODIPY glycocluster (TLBP) is reported that self-assembles into a supramolecular nanoglycocalyx on hepatoma cell membranes, serving as an artificial extracellular matrix (ECM) to inhibit hepatoma metastasis while facilitating efficient Type I PDT. Molecular engineering demonstrates that multi-glycosylation promotes the transition of nanostructures from disordered to ordered self-assembly by regulating intermolecular interactions. This modification enables the TLBP glycocalyx to exhibit significant intermolecular electron transfer, generating superoxide anion radicals (O2 -•) for Type I PDT. Moreover, the TLBP glycocalyx inhibits the PI3K-Akt signaling pathway by reducing Na+/K+-ATPase activity, leading to decreased migration and invasion of HepG2 cells. The synergistic antitumor effect of TLBP glycocalyx is further verified in a HepG2-bearing mouse model. This work innovatively utilizes glycosylation to regulate microelectronic properties and macroscopic nanoscale self-assembly characteristics, providing a novel concept for developing efficient synergistic anti-hepatoma strategies.

A NIR-II emissive sonosensitized biotuner for pyroptosis-enhanced sonodynamic therapy of hypoxic tumors

Pyroptosis is considered as a new way to effectively boost the immune response of tumors and inhibit tumor growth. Effective strategies to induce pyroptosis mainly rely on chemotherapeutic drugs and phototherapy, but their potential biotoxicity and phototoxicity limit their application in biomedicine. Herein, we designed a NIR-II emitting pyroptosis biotuner, Rd-TTPA, which induced pyroptosis under ultrasound irradiation to achieve pyroptosis-enhanced sonodynamic therapy (SDT) and immunogenic cell death (ICD) for tumors. Benefiting from its A-π-D1-D2 structure enhanced donor-acceptor interaction, Rd-TTPA can induce cell pyroptosis under both normoxia (21 % O2) and hypoxia (2 % O2) conditions by rapidly generating superoxide radicals (O2-•) upon ultrasound irradiation. The sonodynamic biotuner of pyroptosis overcomes the longstanding weakness of chemical drug and photosensitizer-based pyroptosis, such as drug resistance and limited penetration depth. In-depth studies demonstrated that Rd-TTPA can selectively target tumor cell mitochondria and possess excellent in vivo NIR-II fluorescence imaging capabilities. Administrating a tumor-bearing mouse model with Rd-TPPA, satisfying antitumor efficacy via pyroptosis-augmented SDT was achieved upon the guidance of NIR-II fluorescence imaging.

Oxygen tension regulating nanoformulation for the improved photodynamic therapy of hypoxic tumors

The clinical efficacy of photodynamic therapy (PDT) is hampered by the low oxygen tension highly prevalent in solid tumors. Hence, improving the oxygen tension by suppling hyperbaric oxygen (HBO), through oxygen delivery nanoarchitectures or by designing in situ oxygen-generating nanoenzymes is considered a robust approach for PDT that involves type II photosensitizers (PS). In this study, we successfully synthesized 4-arm chlorin-polylactide (CPLA) conjugates from meta-tetra-3-hydroxymethyl phenyl chlorin (m-THMPC) and D, L-lactide via ring opening polymerization (ROP), that could assemble into stable NPs, for the delivery of molecular oxygen into inner regions of hypoxic tumors (HTs). The monodispersed Air-CPLA-NPs prevented the PS, chlorin, from aggregation-induced quenching and loss of signal. Moreover, the Air-CPLA-NPs produced a marked level of intracellular ROS or 1O2 upon light irradiation (660 ± 10 nm, 20 J/cm2) which is indispensable for the prolonged and efficient PDT of HTs. The confocal laser scanning microscopy (CLSM) images revealed the gradual cellular internalization of Air-CPLA-NPs in hypoxic H1299 cells. It unveiled significant dose-dependent in vitro cytotoxicity towards normoxic and hypoxic H1299 cells. Furthermore, the in vivo anticancer study displayed the tumor growth inhibition (TGI) effect of Air-CPLA-NPs + PDT in normoxic and hypoxic xenograft mice models. Accordingly, the present architecture improved the PDT efficacy by overcoming the oxygen barrier in the inner tissues of HTs demonstrating the prospect of CPLA-NPs as an "oxygen shuttle" for the clinical PDT of solid tumors.

Fighting Cancer with Photodynamic Therapy and Nanotechnologies: Current Challenges and Future Directions

Photodynamic therapy (PDT) is an innovative treatment that has recently been approved for clinical use and holds promise for cancer patients. It offers several benefits, such as low systemic toxicity, minimal invasiveness, and the ability to stimulate antitumor immune responses. For certain types of cancer, it has shown positive results with few side effects. However, PDT still faces some challenges, including limited light penetration into deeper tumor tissues, uneven distribution of the photosensitizer (PS) that can also affect healthy cells, and the difficulties posed by the hypoxic tumor microenvironment (TME). In hypoxic conditions, PDT's effectiveness is reduced due to insufficient production of reactive oxygen species, which limits tumor destruction and can lead to relapse. This review highlights recent advances in photosensitizers and nanotechnologies that are being developed to improve PDT. It focuses on multifunctional nanoplatforms and nanoshuttles that have shown promise in preclinical studies, especially for treating solid tumors. One of the key areas of focus is the development of PSs that specifically target mitochondria to treat deep-seated malignant tumors. New mitochondria-targeting nano-PSs are designed with better water solubility and extended wavelength ranges, allowing them to target tumors more effectively, even in challenging, hypoxic environments. These advancements in PDT are opening new doors for cancer treatment, especially when combined with other therapeutic strategies. Moving forward, research should focus on optimizing PDT, creating more efficient drug delivery systems, and developing smarter PDT platforms. Ultimately, these efforts aim to make PDT a first-choice treatment option for cancer patients.

Ruthenium(II) Polypyridyl Complexes Containing COUBPY Ligands as Potent Photosensitizers for the Efficient Phototherapy of Hypoxic Tumors

Hypoxia, a hallmark of many solid tumors, is linked to increased cancer aggressiveness, metastasis, and resistance to conventional therapies, leading to poor patient outcomes. This challenges the efficiency of photodynamic therapy (PDT), which relies on the generation of cytotoxic reactive oxygen species (ROS) through the irradiation of a photosensitizer (PS), a process partially dependent on oxygen levels. In this work, we introduce a novel family of potent PSs based on ruthenium(II) polypyridyl complexes with 2,2'-bipyridyl ligands derived from COUPY coumarins, termed COUBPYs. Ru-COUBPY complexes exhibit outstanding in vitro cytotoxicity against CT-26 cancer cells when irradiated with light within the phototherapeutic window, achieving nanomolar potency in both normoxic and hypoxic conditions while remaining nontoxic in the dark, leading to impressive phototoxic indices (>30,000). Their ability to generate both Type I and Type II ROS underpins their exceptional PDT efficiency. The lead compound of this study, SCV49, shows a favorable in vivo pharmacokinetic profile, excellent toxicological tolerability, and potent tumor growth inhibition in mice bearing subcutaneous CT-26 tumors at doses as low as 3 mg/kg upon irradiation with deep-red light (660 nm). These results allow us to propose SCV49 as a strong candidate for further preclinical development, particularly for treating large hypoxic solid tumors.

Heterodimeric Photosensitizer as Radical Generators to Promoting Type I Photodynamic Conversion for Hypoxic Tumor Therapy

Photodynamic therapy (PDT) using traditional type II photosensitizers (PSs) has been limited in hypoxic tumors due to excessive oxygen consumption. The conversion from type II into a less oxygen-dependent type I PDT pathway has shown the potential to combat hypoxic tumors. Herein, the design of a heterodimeric PS, NBSSe, by conjugating a widely used type I PS NBS and a type II PS NBSe via molecular dimerization, achieving the aggregation-regulated efficient type I photodynamic conversion for the first time is reported. Electrochemistry characterizations and theoretical calculations elucidate that NBSSe tends to form a S+·/Se-· radical pair via intramolecular electron transfer in the co-excited NBSSe* aggregate, realizing 7.25-fold O2 -· generation compared to NBS and 80% suppression of 1O2 generation compared to NBSe. The enhanced O2 -· generation of NBSSe enables excellent anti-hypoxia PDT efficiency and inhibition of pulmonary metastasis. Additionally, the incorporation of electron-rich bovine serum albumin accelerates the recycling of cationic PS radical NBSSe+·, further boosting photostability and O2 -· generation. The resultant BSA@NBSSe nanoparticles demonstrate successful tumor-targeting PDT capability. This work provides an appealing avenue to convert ROS generation from the type II pathway to the type I pathway for efficient cancer phototherapy in hypoxia.

A One Stone Three Birds Paradigm of Photon-Driven Pyroptosis Dye for Amplifying Tumor Immunotherapy

Activating the pyroptosis pathway of tumor cells by photodynamic therapy (PDT) for immunogenic cell death (ICD) is considered a valid strategy in pursuit of antitumor immunotherapy, but it remains a huge challenge due to the lack of reliable design guidelines. Moreover, it is often overlooked that conventional PDT can exacerbate the development of tumor immunosuppressive microenvironment, which is apparently unfavorable to clinical immunotherapy. The endoplasmic reticulum's (ER) pivotal role in cellular homeostasis and its emerging link to pyroptosis have galvanized interest in ER-centric imaging and therapeutics. Herein, using the targeted group-assisted strategy (TAGS), an intriguing cyclooxygenase-2-targeted photodynamic conjugate, Indo-Cy, strategically created, which exploits the enzyme's overabundance in the tumoral ER, especially under proinflammatory hypoxic conditions. This conjugate, with its highly precise ER imaging, embodies a trifunctional strategy: i) innovating an electron transfer mechanism, converting the hemicyanine moiety into an oxygen-independent type I photosensitizer, thereby navigating around the hypoxia constraints of traditional PDT; ii) executing precise ER-targeted PDT, amplifying caspase-1/GSDMD-mediated pyroptosis for ICD; 3) attenuating immunosuppressive pathways by inhibiting cyclooxygenase-2 downstream factors, including HIF-1α, PGE2, and VEGF. Indo-Cy's multimodal approach potently induces in vivo tumor pyroptosis and bolsters antitumor immunity, underscoring cyclooxygenase-2-targeted dyes' potential as a versatile oncotherapeutics.

Electron Transfer Mediator Modulates Type II Porphyrin-Based Metal-Organic Framework Photosensitizers for Type I Photodynamic Therapy

Photodynamic therapy (PDT), a minimally invasive and effective local treatment, heavily depends on photosensitizer (PS) performance and oxygen availability. Despite the use of PS-based metal-organic frameworks (MOFs) to address the solubility and aggregation issues of PSs, the inherent hypoxic intolerance of mainstream Type II PDT remains challenging. Herein, we report an electron transfer strategy for the fabrication of hypoxia-tolerant Type I MOFs by encapsulating thymoquinone (TQ) into existing Type II MOFs. With TQ serving as an effective electron transfer mediator, it facilitates the electron transfer process from the MOF ligand PS to oxygen, establishing the Type I pathway and attenuating the original Type II pathway. Four representative porphyrin-based MOFs are synthesized to demonstrate the proposed strategy. Our findings reveal that TQ@MOF-1 nanoparticles (NPs) exhibit enhanced anticancer activity under hypoxic conditions and superior in vivo antitumor efficacy compared to parent MOF-1 NPs. This work offers an effective and universal strategy to modulate ROS generation in PS-based MOFs, endowing hypoxic tolerance with improved PDT performance against solid tumors.

Simultaneous production of singlet oxygen and superoxide anion by thiocarbonyl coumarin for photodynamic therapy

Photodynamic therapy (PDT) is a medical treatment that kills target cells through reactive oxygen species (ROS) generated by photosensitizers (PS) and surrounding oxygen under the stimulus of light. Despite of its popularity in cancer treatment, PDT relys on oxygen and therefore suffers from long response time and low efficiency under low-oxygen situations such as tumor hypoxia. Herein, to improve the usage of oxygen and increase ROS yield, we synthesized six potential PSs termed DC-O, DC-S, DC-BrO, DC-BrS, DC-IO, and DC-IS, by modifying coumarins with thiocarbonyl and bromine/iodine. We found that the thiocarbonyl group induces a significant bathochromic shift of the absorption spectra. In addition, the ROS production was significantly improved, likely because these PSs can simultaneously generate singlet oxygen (1O2) and superoxide anions (O2•-) through different pathways. Among these compounds, DC-BrS produces largest amount of ROS and exhibits strongest cytotoxicity towards cells, the survival rate of B16-F10 cells incubated with DC-BrS was only 20.7 % after irradiation at 460 nm for 10 min, indicating DC-BrS as a strong candidate for photodynamic therapy. Most importantly, this work provides an important direction for the design of PSs in the future.

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.

pH-Sensitive and Lysosome Targetable Photosensitizers Based on BODIPYs

Photodynamic therapy (PDT) is an effective and U.S. Food and Drug Administration (FDA) approved treatment for cancer and other diseases. Photosensitizer is one of the three key components that harvest the energy of light at a certain wavelength. Compared to the conventional fluorophores used as photosensitizers, boron dipyrromethene (BODIPY) derivatives have grown fast in recent years due to their low dark toxicity, versatile tunable sites, and easiness of being paired with other treatments. In this paper, two pH-sensitive BODIPY-based photosensitizers (BDC and BDBrC) were synthesized by adding carbazole moieties onto the BODIPY cores (BD and BDBr) through condensation reactions. BDBrC has two Br atoms at the BODIPY core that promote singlet oxygen generation and further red-shift the absorption maximum peak. Both compounds showed sensitivity toward pH change and generated more singlet oxygen under acidic conditions. The cellular uptake and cell imaging experiments showed that BDBrC can selectively target the lysosome organelle. The further dark cell viability and light cytotoxicity indicate the light triggered PDT treatment can be accomplished with BDBrC.

Nitric Oxide-Releasing Nanoscale Metal-Organic Layer Overcomes Hypoxia and Reactive Oxygen Species Diffusion Barriers to Enhance Cancer Radiotherapy

Hafnium (Hf)-based nanoscale metal-organic layers (MOLs) enhance radiotherapeutic effects of tissue-penetrating X-rays via a unique radiotherapy-radiodynamic therapy (RT-RDT) process through efficient generation of hydroxy radical (RT) and singlet oxygen (RDT). However, their radiotherapeutic efficacy is limited by hypoxia in deep-seated tumors and short half-lives of reactive oxygen species (ROS). Herein the conjugation of a nitric oxide (NO) donor, S-nitroso-N-acetyl-DL-penicillamine (SNAP), to the Hf12 secondary building units (SBUs) of Hf-5,5'-di-p-benzoatoporphyrin MOL is reported to afford SNAP/MOL for enhanced cancer radiotherapy. Under X-ray irradiation, SNAP/MOL efficiently generates superoxide anion (O2 -.) and releases nitric oxide (NO) in a spatio-temporally synchronized fashion. The released NO rapidly reacts with O2 -. to form long-lived and highly cytotoxic peroxynitrite which diffuses freely to the cell nucleus and efficiently causes DNA double-strand breaks. Meanwhile, the sustained release of NO from SNAP/MOL in the tumor microenvironment relieves tumor hypoxia to reduce radioresistance of tumor cells. Consequently, SNAP/MOL plus low-dose X-ray irradiation efficiently inhibits tumor growth and reduces metastasis in colorectal and triple-negative breast cancer models.

Tröger's Base as a Potential Bridge to Type-I Photosensitizers: Mechanism and Antitumor Applications

In contrast to Type-II photodynamic therapy (PDT), Type-I PDT with less oxygen consumption has shown great potential against tumor hypoxia. However, there are limited strategies available for designing Type-I photosensitizers (PSs). Herein, we present a promising strategy for synthesizing Type-I PSs (TBC-1-TBC-4) using Tröger's base (TB) framework. The TB framework can promote intersystem crossing efficiency and create an electron-rich environment, making it the most likely site for electron transfer to O2 to generate Type-I ROS. As anticipated, TBC-1-TBC-4 demonstrates Type-I ROS generation capability and their impressive visible light-harvesting ability significantly enhances this capability. Among them, TBC-1 demonstrates outstanding biocompatibility and PDT efficiency in vitro under both normoxia and hypoxia. Furthermore, TBC-1 effectively inhibits tumor growth in vivo, with negligible side effects. This is attributed to TBC-1's efficient generation of Type-I ROS and endoplasmic reticulum targeting ability. This study thus offers useful insights into developing Type-I PSs.

Rational Design of an Activatable Near-Infrared Fluorogenic Platform for In Vivo Orthotopic Tumor Imaging and Resection

Rational and effective design of a universal near-infrared (NIR) light-absorbed platform employed to prepare diverse activatable NIR fluorogenic probes for in vivo imaging and the imaging-guided tumor resection remains less exploited but highly meaningful. Herein, mandelic acid with a core structure of 4-hydroxylbenzyl alcohol to link recognition unit, a fluorophore and a quencher was employed to prepare activatable probes. We exemplified ester as carboxylesterase (CE)-recognized unit, ferrocene as quencher and phenothiazinium as NIR fluorophore to afford fluorogenic probes termed NBS-Fe-CE and NBS-C-Fe-CE. These probes enabled the conversion toward CE with significant fluorescence increases and successfully discriminate CE activity in cells. NIR light enhances the tumor penetration and enable imaging-guided orthotopic tumor resection. This specific case demonstrated that this platform can be effectively used to construct diverse NIR probes for imaging analytes in biological systems.

Acid-responsive singlet oxygen nanodepots

The singlet oxygen carrier addresses the challenges of traditional photodynamic therapy (PDT), which relies on the presence of oxygen within solid tumors and struggles with light penetration issues. However, the inability to control the release of singlet oxygen has hindered precise treatment applications. Here, we introduce an acid-responsive singlet oxygen nanodepot (aSOND) designed to overcome this limitation. The aSOND is synthesized using a responsive diblock copolymer system that includes a hydrophilic PEG block and a pH-responsive block with singlet oxygen loading sites. In neutral or alkaline environments, the aSOND releases singlet oxygen slowly, ensuring stability in blood circulation. In contrast, in acidic environments such as the tumor microenvironment or intracellular lysosomes, protonation of the tertiary amine group within the pH responsive block increases the hydration of the polymer, triggering a rapid release of singlet oxygen. This feature enables controlled, tumor-specific release of reactive oxygen species (ROS). The aSOND system effectively implements an "OFF-ON" singlet oxygen therapy, demonstrating high spatiotemporal selectivity and independence from both oxygen supply and external light, offering a promising approach for targeted cancer therapy.

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.

Glycosylated AIE-active Red Light-triggered Photocage with Precisely Tumor Targeting Capability for Synergistic Type I Photodynamic Therapy and CPT Chemotherapy

Photocaging is an emerging protocol for precisely manipulating spatial and temporal behaviors over biological activity. However, the red/near-infrared light-triggered photolysis process of current photocage is largely singlet oxygen (1O2)-dependent and lack of compatibility with other reactive oxygen species (ROS)-activated techniques, which has proven to be the major bottleneck in achieving efficient and precise treatment. Herein, we reported a lactosylated photocage BT-LRC by covalently incorporating camptothecin (CPT) into hybrid BODIPY-TPE fluorophore via the superoxide anion radical (O2 -⋅)-cleavable thioketal bond for type I photodynamic therapy (PDT) and anticancer drug release. Amphiphilic BT-LRC could be self-assembled into aggregation-induced emission (AIE)-active nanoparticles (BT-LRCs) owing to the regulation of carbohydrate-carbohydrate interactions (CCIs) among neighboring lactose units in the nanoaggregates. BT-LRCs could simultaneously generate abundant O2 -⋅ through the aggregation modulated by lactose interactions, and DNA-damaging agent CPT was subsequently and effectively released. Notably, the type I PDT and CPT chemotherapy collaboratively amplified the therapeutic efficacy in HepG2 cells and tumor-bearing mice. Furthermore, the inherent AIE property of BT-LRCs endowed the photocaged prodrug with superior bioimaging capability, which provided a powerful tool for real-time tracking and finely tuning the PDT and photoactivated drug release behavior in tumor therapy.

Self-Boosting Programmable Release of Multiple Therapeutic Agents by Activatable Heterodimeric Prodrug-Enzyme Assembly for Antitumor Therapy

Endogenous stimuli-responsive prodrugs, due to their disease lesion specificity and reduced systemic toxicity, have been widely explored for antitumor therapy. However, reactive oxygen species (ROS) as classical endogenous stimuli in the tumor microenvironment (TME) are not enough to achieve the expected drug release. Herein, a ROS-activatable heterodimeric prodrug-loaded enzyme assembly is developed for self-boosting programmable release of multiple therapeutic agents. The heterodimeric prodrug NBS-TK-PTX (namely NTP) is composed of 5-(ethylamino)-9-diethylaminobenzo[a]phenothiazinium chloride analog (NBS), paclitaxel (PTX) and ROS-responsive thioketal (TK) linker, which shows a strong binding affinity with glucose oxidase (GOx), thus obtaining NTP@GOx assembly. Notably, the enzymatic activity of GOx in NTP@GOx is inhibited by NTP. The programmable release is achieved by following steps: i) NTP@GOx is partially dissociated in acidic TME, thus releasing a small segment of NTP and GOx. Thereupon, the enzymatic activity of GOx is recovered; ii) GOx-triggered pH reduction further facilitates the dissociation of NTP@GOx, thus accelerating a large amount of NTP and GOx release; iii) The TK linker of prodrug NTP is cleaved by hydrogen peroxide generated by GOx catalysis, thus expediting the release of NBS for Type-I photodynamic therapy and PTX for chemotherapy, respectively. The NTP@GOx shows great potential for multimodal synergistic cancer therapy.

Two-pronged strategy: A mitochondria targeting AIE photosensitizer for hydrogen sulfide detection and type I and type II photodynamic therapy

Multifunctional type-I photosensitizers (PSs) for hydrogen sulfide (H2S) detection and photodynamic therapy (PDT) of hypoxia tumors exhibits attractive curative effect but remains a challenging task. Herein, a mitochondria targeted aggregation-induced emission (AIE) photosensitizer TSPy-SS-P was designed and synthesized, which could be used for H2S detection and simultaneously type I and type II PDT. TSPy-SS-P had excellent selectivity and anti-interference abilities for endogenous and exogenous H2S detection in tumor cells. TSPy-SS-P was able to distinguish tumor cells with high level of H2S from normal cells by fluorescence "turn off" response to H2S. In addition, TSPy-SS-P showed type Ⅰ and type Ⅱ reactive oxygen species (ROS) generation ability to effectively ablate hypoxic tumor cells. TSPy-SS-P showed mitochondria targeting capacity which could produce ROS in situ to disrupt mitochondria and promote cell apoptosis. In vivo PDT experiments showcased that TSPy-SS-P had excellent tumor retention capability, effective tumor ablation ability and good biocompatibility. This work provided a two-pronged strategy to design organelles targeted photosensitizers for H2S detection and effective PDT of tumors.

Unravelling the modes of phototoxicity of NIR absorbing chlorophyll derivative in cancer cells under normoxic and hypoxic conditions

The efficacy of photodynamic treatment (PDT) against deep-seated tumor is hindered by low penetration depth of light as well as hypoxic conditions which prevails in tumor. To overcome this limitation, Near-infrared (NIR) absorbing photosensitizers have been investigated actively. In the present study we evaluated the PDT efficacy of an NIR absorbing chlorophyll derivative 'Cycloimide Purpurin-18 (CIPp-18)' in Human Breast carcinoma (MCF-7) and cervical adenocarcinoma (Hela) cells under normoxic and hypoxic conditions. PDT with CIPp-18 (2.0 µM, 3 h) and NIR light (700 ± 25 nm, 0.36-1.4 J /cm2) induced potent phototoxicity in both the cell lines. Under hypoxic conditions, PDT induced ~ 32% and 42% phototoxicity at LD50 and LD70 light dose, respectively, which corresponds to phototoxic dose under normoxia. CIPp-18 in neat buffer (pH 7.4) showed generation of singlet oxygen (1O2) as well as superoxide (O2·-) radicals. Studies on ROS generation in cells using fluorescence probes and the effect of mechanistic probes of 1O2 (Sodium Azide, Histidine, D2O) and free radicals (DMSO, Mannitol, Cyanocobalamin, SOD-PEG) on phototoxicity show that 1O2 plays major role in phototoxicity under normoxia. Whereas, under hypoxic conditions, PDT led to no significant generation of ROS and phototoxicity remained unaffected by cyanocobalamin, a quencher of O2·-. Moreover, CIPp-18 showed localization in cell membrane and PDT led to more pronounced loss of membrane permeability in cells under hypoxia than for normoxia. These results demonstrate that CIPp-18 is suitable for PDT of cancer cells under hypoxia and also suggest that phototoxicity under hypoxia is mediated via ROS-independent contact-dependent mechanism.

Oxygen Effect on 0-30 eV Electron Damage to DNA Under Different Hydration Levels: Base and Clustered Lesions, Strand Breaks and Crosslinks

Studies on radiosensitization of biological damage by O2 began about a century ago and it remains one of the most significant subjects in radiobiology. It has been related to increased production of oxygen radicals and other reactive metabolites, but only recently to the action of the numerous low-energy electrons (LEEs: 0-30 eV) produced by ionizing radiation. We provide the first complete set of G-values (yields of specific products per energy deposited) for all conformational damages induced to plasmid DNA by LEEs (GLEE (O2)) and 1.5 keV X-rays (GX(O2)) under oxygen at atmospheric pressure. The experiments are performed in a chamber, under humidity levels ranging from 2.5 to 33 water molecules/base. Photoelectrons from 0 to 30 eV are produced by X-rays incident on a tantalum substrate covered with DNA. Damage yields are measured by electrophoresis as a function of X-ray fluence. The oxygen enhancement ratio GLEE(O2)/GLEE(N2), which lies around 2 for potentially lethal cluster lesions, is similar to that found with cells. The average ratio, GLEE(O2)/GX(O2), of 12 for cluster lesions and crosslinks strongly suggest that DNA damages that harm cells are much more likely to be created by LEEs than any other initial species generated by X-rays in the presence of O2.

A glycosylated AIE-active Fe(III) photosensitizer activated by the tumor microenvironment for synergistic type I photodynamic and chemodynamic therapy

Photodynamic therapy (PDT) and chemodynamic therapy (CDT) are both promising cancer treatments to inhibit tumor cells by generating highly cytotoxic reactive oxygen species (ROS). Herein, we report a novel tumor microenvironment (TME) stimulus-responsive water-soluble glycosylated photosensitizer (BT-TPE@Fe-Lac), which can serve as a high-efficiency antitumor agent by combining PDT and CDT, based on the coordination of Fe3+ with lactosyl bis(2-pyridylmethyl)amine and an AIE luminogen (benzothiazole-hydroxytetraphenylethene, BT-TPE). BT-TPE@Fe-Lac is stable under physiological conditions and selectively targets HepG2 cells via asialoglycoprotein receptor (ASGPR)-mediated endocytosis. It rapidly dissociates into AIE-active BT-TPE molecules and a lactosyl ferric(III) complex in the acidic lysosomes of cancer cells. Upon exposure to light, BT-TPE produces O2˙- radicals for type I PDT. The ferric(III) complex is reduced to an Fe(II) complex upon depletion of glutathione, which primes the breakdown of endogenous H2O2 within the tumor microenvironment, thus generating highly toxic ˙OH for enhanced CDT. Compared with the monotherapy of PDT or CDT, BT-TPE@Fe-Lac can significantly increase the intracellular ROS levels to induce more tumor cell death under low drug doses and hypoxia-dependent conditions. This strategy leverages the unique properties of the TME to optimize therapeutic outcomes, offering a promising approach for the TME-responsive nanoplatform in advanced cancer therapy.

PAD4 Inhibitor-Loaded Layered Double Hydroxide Nanosheets as a Multifunctional Nanoplatform for Photodynamic Therapy-Mediated Tumor Metastasis Treatment

Photodynamic therapy (PDT) is demonstrated to be effective in inducing antitumor immune responses for tumor metastasis treatment. However, tumor hypoxia, inferior tissue penetration of light, and low singlet oxygen (1O2) quantum yield significantly hamper the efficacy of PDT, thus weakening its immune function. Moreover, PDT-mediated neutrophil extracellular traps (NETs) formation can further reduce the therapeutic effectiveness. Herein, the use of defect-rich CoMo-layered double hydroxide (DR-CoMo-LDH) nanosheets as a carrier to load a typical peptidyl arginine deiminase 4 inhibitor, i.e., YW4-03, to construct a multifunctional nanoagent (403@DR-LDH) for PDT/immunotherapy, is reported. Specifically, 403@DR-LDH inherits excellent 1O2 generation activity under 1550 nm laser irradiation and improves the half-life of YW4-03. Meanwhile, 403@DR-LDH plus 1550 nm laser irradiation can stimulate immunogenic cell death to promote the maturation of dendric cells and activation/infiltration of T cells and significantly downregulate H3cit protein expression to inhibit NETs formation, synergistically promoting the antitumor metastasis effect. Taken together, 403@DR-LDH can kill cancer cells and inhibit tumor growth/metastasis under 1550 nm laser irradiation. Single-cell analysis indicates that 403@DR-LDH can regulate the ratio of immune cells and immune-related proteins to improve the tumor immune microenvironment, showing strong efficacy to inhibit the tumor growth, metastasis, and recurrence.

Building Block for Designing Bright Type I AIE-Active Photosensitizers with Deep/Near-infrared Red Fluorescence

Bright deep red/near-infrared red (DR/NIR) active type I photosensitizers (PSs) with generating superoxide anion and hydroxyl radical have been regarded as powerful functional materials to fight the "Achilles's heel" of hypoxia from solid tumor. But some problems have still existed, for example, lacking effective molecular designed strategy or typical building block to design precisely type I PSs. In addition, the relationship between fluorescent quantum efficiency and NIR fluorescent color is inconsistent according to energy gap rule. To overcome above mentioned problems, in this work, we propose a typical building block to design precisely type I PSs with DR/NIR fluorescence and high photoluminescent quantum yield at aggregation by combining molecular design of aggregation-induced emission and hybrid locally and charge transfer (HLCT) theory. The synthetic small molecular PSs just produce superoxide anion without any singlet oxygen production, which is ascribed to their lower T1 energy levels to suppress energy transfer from triplet state to oxygen. Two strategies of small molecular structural designing and polymeric nanoparticles modification are utilized to improve efficiency of type I ROS. More interestingly, original small molecular PSs is in capable to produce hydroxyl radical, once forming BSA encapsulated nanoparticles, obvious hydroxyl radical is appeared.

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.

The cyano positional isomerism strategy for constructing mitochondria-targeted AIEgens with type I reactive oxygen species generation capability

In this work, a series of cationic luminogens (designated as PSMP isomers) were developed based on the cyano positional isomerism strategy. The isomerism of the cyano substituent on the molecular skeleton can finely regulate the optical behaviour, the type of photoinduced reactive oxygen species (ROS), and mitochondria-targeted capability of isomers. Interestingly, PSMP-4, with the cyano group installed at an appropriate location, exhibits a special aggregation-induced emission effect and potent O2˙- generation efficacy through the type I photochemistry pathway. Notably, PSMP-4 can accumulate in mitochondria with high specificity. Taking advantage of its excellent photostability, PSMP-4 realizes in situ mitochondria imaging in a washing-free manner and sensitive response to the change of mitochondrial membrane potential. The integration of comprehensive photophysical properties and mitochondrial specificity enable PSMP-4 to successfully trigger the death of cancer cells through an efficient type I photodynamic therapy process both in vitro and in multicellular tumor spheroid models.

A simple hydrogen peroxide-activatable Bodipy for tumor imaging and type I/II photodynamic therapy

Tumor microenvironment-activatable photosensitizers have gained significant attention for cancer theranostics. Considering the hypoxic environment of solid tumors, activatable phototheranostic agents with type I PDT are desired to obtain improved cancer treatment efficiency. Herein, we report a simple, effective and multifunctional Bodipy photosensitizer for tumor imaging and type I/II photodynamic therapy. The photosensitizer featuring a methylphenylboronic acid pinacol ester group at the meso-position of Bodipy specifically responds to tumor-abundant H2O2. Its photophysical properties were characterized using steady-state and time-resolved transient optical spectroscopies. The fluorescence (ΦF = 0.09%) and singlet oxygen efficacy (ΦΔ = 10.2%) of the Bodipy units were suppressed in the caged dyads but significantly enhanced (ΦF = 0.72%, ΦΔ = 20.3%) upon H2O2 activation. Fluorescence emission spectroscopy and continuous wave electron paramagnetic resonance (EPR) spectroscopy confirmed that the Bodipy photosensitizer generates reactive oxygen species (ROS) via both electron transfer-mediated type I and energy transfer-mediated type II mechanisms. In vitro experiments demonstrated rapid internalization into tumor cells, enhanced brightness stimulated by tumor microenvironments, and tumor cell death (phototoxicity, IC50 = 0.5 μM). In vivo fluorescence imaging indicated preferential accumulation of this Bodipy photosensitizer in tumor sites, followed by decaging by tumor-abundant H2O2, further elevating the signal-to-background ratio (SBR) of imaging. Besides outstanding performance in tumor imaging, a prominent inhibition of tumor growth was observed. Given its simple molecular skeleton, this Bodipy photosensitizer is a competitive candidate for cancer theranostics.

A near-infrared superoxide generator based on a biocompatible indene-bearing heptamethine cyanine dye

One of the most significant limitations of photodynamic therapy is its reduced efficacy in hypoxic microenvironments, which are typical of the majority of tumors. This work demonstrates that indolenine heptamethine cyanines with different substituents in the polymethine chain and at the terminal heterocycles are effective superoxide generators that can be activated in the near-infrared range. The introduction of an indene moiety into the polymethine chain results in a significant enhancement in photostability compared to dyes with a cyclohexene moiety or an unsubstituted polymethine chain. A hydrophilic indene-bearing heptamethine cyanine dye is shown to be efficiently internalized by Vero E6 cells and to give bright intracellular fluorescence in the 700-850 nm range. Furthermore, the dye generates superoxide anion radicals and induces severe oxidative stress in cells upon activation in the near-infrared range (∼750 nm), ultimately resulting in cell death. The capacity of heptamethine cyanines to generate a superoxide anion radical may prove advantageous for enhancing the efficacy of photodynamic therapy under hypoxic conditions.

Molecular Engineering of Pure Superoxide Radical Photogenerator for Hypoxia-Tolerant Tumor Theranostics

Photodynamic therapy (PDT) is a promising cancer treatment, but limited oxygen supply in tumors (hypoxia) can hinder its effectiveness. This is because traditional PDT relies on Type-II reactions that require oxygen. Type-I photosensitizers (PSs) offer a promising approach to overcome the limitations of tumor photodynamic therapy (PDT) in hypoxic environments. To leverage the advantages of Type-I PDT, the design and evaluation of a series of Type-I PSs for developing pure Type-1 PSs, by incorporating benzene, thiophene, or bithiophene into the donor-acceptor molecular skeleton are reported. Among them, CTTI (with bithiophene) shows the best performance, generating the most superoxide radical (O2 •-) upon light irradiation. Importantly, CTTI exclusively produced superoxide radicals, avoiding the less effective Type-II pathway. This efficiency is due to CTTI's energy gap and low reduction potential, which favor electron transfer to oxygen for O2 •- generation. Finally, CTTI NPs are successfully fabricated by encapsulating CTTI into liposomes, and validated to be effective in killing tumor cells, even under hypoxic conditions, making them promising hypoxia-tolerant tumor phototheranostic agents in both in vitro and in vivo applications.

A Type I Photosensitizer-Polymersome Boosts Reactive Oxygen Species Generation by Forcing H-Aggregation for Amplifying STING Immunotherapy

Activation of the innate immune Stimulator of Interferon Genes (STING) pathway potentiates antitumor immunity. However, delivering STING agonists systemically to tumors presents a formidable challenge, and resistance to STING monotherapy has emerged in clinical trials with diminishing natural killer (NK) cell proliferation. Here, we encapsulated the STING agonist diABZI within polymersomes containing a Type I photosensitizer (NBS), creating a nanoagonist (PNBS/diABZI) for highly responsive tumor immunotherapy. This structure promoted H-aggregation and intersystem crossing of NBS, resulting in a ∼ 3-fold amplification in superoxide anion and singlet oxygen generation. The photodynamic therapy directly damaged hypoxia tumor cells and stimulated the proliferation of NK cells and cytotoxic T lymphocytes, thereby sensitizing STING immunotherapy. A single systemic intravenous administration of PNBS/diABZI eradicated orthotopic mammary tumors in murine models, achieving long-term antitumor immune memory to inhibit tumor recurrence and metastasis and significantly improving long-term tumor-free survival. This work provides a design rule for boosting reactive oxygen species production by promoting the intersystem crossing process, highlighting the potential of Type I photosensitizer-polymer vehicles for augmenting STING immunotherapy.

Multifunctional Molecular Hybrids Photoreleasing Nitric Oxide: Advantages, Pitfalls, and Opportunities

The multifaceted role nitric oxide (NO) plays in human physiology and pathophysiology has opened new scenarios in biomedicine by exploiting this free radical as an unconventional therapeutic against important diseases. The difficulties in handling gaseous NO and the strict dependence of the biological effects on its doses and location have made the light-activated NO precursors, namely NO photodonors (NOPDs), very appealing by virtue of their precise spatiotemporal control of NO delivery. The covalent integration of NOPDs and additional functional components within the same molecular skeleton through suitable linkers can lead to an intriguing class of multifunctional photoactivatable molecular hybrids. In this Perspective, we provide an overview of the recent advances in these molecular constructs, emphasizing those merging NO photorelease with targeting, fluorescent reporting, and phototherapeutic functionalities. We will highlight the rational design behind synthesizing these molecular hybrids and critically describe the advantages, drawbacks, and opportunities they offer in biomedical research.

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.

A novel photosensitizer based on hypocrellin B activated by cysteine over-expressed in cancer cells

L-Cysteine (Cys)-activatable photosensitizer 3 was designed and synthesized based on hypocrellin B (1). Cys is a novel tumor-associated biomarker. 3 exhibited negligible photosensitizing ability without Cys. However, when 1 was released from 3 by reaction with Cys, the photosensitizing activity was restored. Furthermore, 3 showed selective and effective photo-cytotoxicity against only cancer cells such as HeLa and A549 cells that highly express Cys when irradiated with 660 nm light, which is inside the phototherapeutic window.

Heavy-atom-free triplet benzothiophene-fused BODIPY derivatives for lipid droplet-specific biomaging and photodynamic therapy

The twist fusion of a benzothiophene group and the introduction of a 4-methyloxystyryl donor group to the BODIPY core resulted in large spin-orbit coupling values and smaller singlet-triplet energy gaps for the novel infrared absorbed photosensitizers named BSBDP. They show a high reactive oxygen species efficiency exceeding 69% and a fluorescence quantum yield of 23% and are successfully applied in imaging-guided photodynamic therapy in vitro and in vivo.

Fabrication of photo-induced molecular superoxide radical generator for highly efficient therapy against bacterial wound infection

The pressing need for highly efficient antibacterial strategies arises from the prevalence of microbial biofilm infections and the emergence of rapidly evolving antibiotic-resistant strains of pathogenic bacteria. Photodynamic therapy represents a highly efficient and compelling antibacterial approach, offering promising prospects for effective control of the development of bacterial resistance. However, the effectiveness of many photosensitizers is limited due to the reduced generation of reactive oxygen species (ROS) in hypoxic microenvironment, which commonly occur in pathological conditions such as inflammatory and bacteria-infected wounds. Herein, we designed and prepared two phenothiazine-derived photosensitizers (NB-1 and NB-2), which can effectively generate superoxide anion radicals (O2●-) through the type I process. Both photosensitizers demonstrate significant efficacy in vitro for the eradication of broad-spectrum bacteria. Moreover, NB-2 possesses distinct advantages including strong membrane binding and strong generation of O2●-, rendering it an exceptionally efficient antibacterial agent against mature biofilms. In addition, laser activated NB-2 could be applied to treat MRSA-infected wound in vivo, which offers new opportunities for potential practical applications.

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.

Exclusive generation of a superoxide radical by a porous aromatic framework for fast photocatalytic decontamination of mustard gas simulant in room air

Mustard gas and other chemical warfare agents (CWAs) are a global threat to public security, arising from unpredictable emergencies and chemical spill accidents. So far, photocatalysts such as metal clusters, polyoxometalates and porous solids have been exploited for oxidative degradation of mustard gas, commonly with 1O2 as reactive species. However, the production of 1O2 is oxygen-dependent and requires a high oxygen concentration to sustain the detoxication process. For safety and operation process considerations, it is always preferable to rapidly detoxify dangerous chemicals in the atmosphere of room air. In this work, a porous aromatic framework, PAF-68, was synthesized as a metal-free photocatalyst. In the presence of PAF-68, fast detoxication occurred in typical room air atmosphere. The half-life (t 1/2) for the complete conversion of mustard gas simulant to nontoxic product in room air was only 1.7 min, which is comparable to the performance in pure oxygen, surpassing that of any other porous photocatalysts. It was found that ˙O2 - rather than 1O2 is the predominant reactive species initiated by PAF-68 for mustard gas detoxication. Unlike the formation of 1O2 which prefers the environment of pure oxygen, generation of the ˙O2 - is an oxygen-independent process. It is suggested that amorphous PAFs possess low exciton binding energy and long decay lifetime, which facilitate the generation of ˙O2 -, and this offers a general design strategy to detoxifying chemical warfare agents under real-world conditions.

BF2-Bridged Azafulvene Dimer-Based 1064 nm Laser-Driven Superior Photothermal Agent for Deep-Seated Tumor Therapy

Small organic photothermal agents (PTAs) with absorption bands located in the second near-infrared (NIR-II, 1000-1700 nm) window are highly desirable for effectively combating deep-seated tumors. However, the rarely reported NIR-II absorbing PTAs still suffer from a low molar extinction coefficient (MEC, ϵ), inadequate chemostability and photostability, as well as the high light power density required during the therapeutic process. Herein, we developed a series of boron difluoride bridged azafulvene dimer acceptor-integrated small organic PTAs. The B-N coordination bonds in the π-conjugated azafulvene dimer backbone endow it the strong electron-withdrawing ability, facilitating the vigorous donor-acceptor-donor (D-A-D) structure PTAs with NIR-II absorption. Notably, the PTA namely OTTBF shows high MEC (7.21×104 M-1 cm-1), ultrahigh chemo- and photo-stability. After encapsulated into water-dispersible nanoparticles, OTTBF NPs can achieve remarkable photothermal conversion effect under 1064 nm irradiation with a light density as low as 0.7 W cm-2, which is the lowest reported NIR-II light power used in PTT process as we know. Furthermore, OTTBF NPs have been successfully applied for in vitro and in vivo deep-seated cancer treatments under 1064 nm laser. This study provides an insight into the future exploration of versatile D-A-D structured NIR-II absorption organic PTAs for biomedical applications.