Molecular Engineering to Boost AIE‐Active Free Radical Photogenerators and Enable High‐Performance Photodynamic Therapy under Hypoxia

The severe hypoxia in solid tumors and the vicious aggregation‐caused fluorescence quenching (ACQ) of conventional photosensitizers (PSs) have limited the application of fluorescence imaging‐guided photodynamic therapy (PDT), although this therapy has obvious advantages in terms of its precise spatial–temporal control and noninvasive character. PSs featuring type I reactive oxygen species (ROS) based on free radicals and novel aggregation‐induced emission (AIE) characteristics (AIE‐PSs) could offer valuable opportunities to resolve the above problems, but molecular engineering methods are rare in previous reports. Herein, a strategy is proposed for generating stronger intramolecular charge transfer in electron‐rich anion‐π⁺ AIE‐active luminogens (AIEgens) to help suppress nonradiative internal conversion and to promote radiative and intersystem crossing to boost free radical generation. Systematic and detailed experimental and theoretical calculations prove the proposal herein: the electron‐donating abilities are enhanced in collaborative donors, and the AIE‐PSs exhibit higher performance in near‐infrared fluorescence imaging‐guided cancer PDT in vitro/vivo. This work serves as an important reference for the design of AIE‐active free radical generators to overcome the ACQ and tumor hypoxia challenges in PDT.     

Hyaluronidase with pH‐responsive Dextran Modification as an Adjuvant Nanomedicine for Enhanced Photodynamic‐Immunotherapy of Cancer

The condensed tumor extracellular matrix (ECM) consisting of cross‐linked hyaluronic acid (HA) is one of key factors that results in the aberrant tumor microenvironment (TME) and the resistance to various types of therapies. Herein, hyaluronidase (HAase) is modified by a biocompatible polymer, dextran (DEX), via a pH‐responsive traceless linker. The formulated DEX‐HAase nanoparticles show enhanced enzyme stability, reduced immunogenicity, and prolonged blood half‐life after intravenous injection. With efficient tumor passive accumulation, DEX‐HAase within the acidic TME would be dissociated to release native HAase, which afterward triggers the breakdown of HA to loosen the ECM structure, subsequently leading to enhanced penetration of oxygen and other therapeutic agents. The largely relieved tumor hypoxia would promote the therapeutic effect of nanoparticle‐based photodynamic therapy (PDT), accompanied by the reverse of the immunosuppressive TME to boost cancer immunotherapy. Interestingly, the therapeutic responses achieved by the combination of PDT and anti‐programmed death‐ligand 1 (anti‐PD‐L1) checkpoint blockade therapy could be significantly enhanced by pretreatment with DEX‐HAase. In addition to destructing tumors with direct light exposure, a robust abscopal effect is achieved after such treatment, which is promising for tumor metastasis inhibition. The work presents a new type of adjuvant nanomedicine to assist photodynamic‐immunotherapy of cancer, by effective modulation of TME.     

Precise Molecular Engineering of Photosensitizers with Aggregation‐Induced Emission over 800 nm for Photodynamic Therapy

Owing to efficient singlet oxygen (¹O₂) generation in aggregate state, photosensitizers (PSs) with aggregation‐induced emission (AIE) have attracted much research interests in photodynamic therapy (PDT). In addition to high ¹O₂ generation efficiency, strong molar absorption in long‐wavelength range and near‐infrared (NIR) emission are also highly desirable, but difficult to achieve for AIE PSs since the twisted structures in AIE moieties usually lead to absorption and emission in short‐wavelength range. In this contribution, through acceptor engineering, a new AIE PS of TBT is designed to show aggregation‐induced NIR emission centered at 810 nm, broad absorption in the range between 300 and 700 nm with a large molar absorption coefficient and a high ¹O₂ generation efficiency under white light irradiation. Further, donor engineering by attaching two branched flexible chains to TBT yielded TBTC8 , which circumvented the strong intermolecular interactions of TBT in nanoparticles (NPs), yielding TBTC8 NPs with optimized overall performance in ¹O₂ generation, absorption, and emission. Subsequent PDT results in both in vitro and in vivo studies indicate that TBTC8 NPs are promising candidates in practical application.     

A Self‐Transformable pH‐Driven Membrane‐Anchoring Photosensitizer for Effective Photodynamic Therapy to Inhibit Tumor Growth and Metastasis

Poor tumor selectivity and short life span of reactive oxygen species (ROS) are two major challenges in photodynamic therapy (PDT). In this study, a self‐transformable pH‐driven membrane anchoring photosensitizer (pHMAPS) is used to realize tumor‐specific accumulation and in situ PDT on tumor cell membrane to maximize the therapeutic potency. It is found that pHMAPS was able to form α‐helix structure under acidic condition (pH 6.5 or 5.5), while remain random coil at normal pH of 7.4. This pH‐driven secondary structure switch enables the successful insertion of pHMAPS into membrane lipid bilayer, especially for cancerous cell membrane in the acidic tumor microenvironment. Under laser irradiation, cytotoxic ROS is generated in the immediate vicinity of cell membrane, resulting in superior cell killing effect in vitro and significant inhibition of tumor growth in vivo. Importantly, benefited from this membrane‐specific PDT, tumor growth‐induced hepatic, pulmonary, as well as osseous metastases of breast cancer cells are also retarded after PDT treatment. Thus, the membrane localized PDT by pHMAPS provides a simple but effective strategy to enhance the medical performance of photosensitizing agents in cancer therapy.     

Tumor-Activated Photosensitization and Size Transformation of Nanodrugs

Effective intratumoral distribution of anticancer agents with good tumor penetration is of practical importance for photo-chemotherapy. Herein, a metal-organic framework (MOF) assisted strategy is reported for smart delivery of aggregation-induced emission photosensitizer (AIE PS) and chemodrug for deep tumor penetration to realize effective image-guided photo-chemotherapy. A newly designed AIE PS is loaded inside an iron(III) carboxylate-based MOF, MIL-100, to produce PS@MIL-100, which is encapsulated by doxorubicin (Dox) conjugated poly(ethylene glycol) methyl ether (PEG) to yield Dox-PEG-PS@MIL nanoparticles (NPs) with a diameter of 120 nm. After Dox-PEG-PS@MIL NPs reached the tumor site, intratumoral H₂O₂ can cause the release of the loaded PS at the tumor surface for activatable photodynamic therapy (PDT). The Dox-PEG segment is simultaneously triggered to self-assemble into ultrasmall Dox NPs. Under light irradiation, PDT is activated at the tumor surface, synergistically enhancing the tumor penetration of Dox NPs along with their ultrasmall size. After endocytosis of Dox NPs, free Dox is released from Dox NPs under low pH to enter cell nuclei for effective chemotherapy. Accompanied by bright far-red/near-infrared emission from the PS, image-guided photo-chemotherapy with enhanced efficacy is achieved.     

Tumor Microenvironment‐Responsive Mesoporous MnO2‐Coated Upconversion Nanoplatform for Self‐Enhanced Tumor Theranostics

The insufficient blood flow and oxygen supply in solid tumor cause hypoxia, which leads to low sensitivity of tumorous cells and thus causing poor treatment outcome. Here, mesoporous manganese dioxide (mMnO₂) with ultrasensitive biodegradability in a tumor microenvironment (TME) is grown on upconversion photodynamic nanoparticles for not only TME‐enhanced bioimaging and drug release, but also for relieving tumor hypoxia, thereby markedly improving photodynamic therapy (PDT). In this nanoplatform, mesoporous silica coated upconversion nanoparticles (UCNPs@mSiO₂) with covalently loaded chlorin e6 are obtained as near‐infrared light mediated PDT agents, and then a mMnO₂ shell is grown via a facile ultrasonic way. Because of its unique mesoporous structure, the obtained nanoplatform postmodified with polyethylene glycol can load the chemotherapeutic drug of doxorubicin (DOX). When used for antitumor application, the mMnO₂ degrades rapidly within the TME, releasing Mn²⁺ ions, which couple with trimodal (upconversion luminescence, computed tomography (CT), and magnetic resonance imaging) imaging of UCNPs to perform a self‐enhanced imaging. Significantly, the degradation of mMnO₂ shell brings an efficient DOX release, and relieve tumor hypoxia by simultaneously inducing decomposition of tumor endogenous H₂O₂ and reduction of glutathione, thus achieving a highly potent chemo‐photodynamic therapy.     

Metal–Organic Framework as a Simple and General Inert Nanocarrier for Photosensitizers to Implement Activatable Photodynamic Therapy

There has been a surging interest in the synthesis of activatable photosensitizers (PSs) as they can be selectively activated with minimum nonspecific phototoxic damages for photodynamic therapy (PDT). Conventional strategies to realize activatable PSs are only applicable to a limited number of molecules. Herein, a simple and general strategy to yield activatable PSs by coupling MIL‐100 (Fe) (MIL: Materials Institute Lavoisier) with different kinds of PSs is presented. Specifically, when PSs are encapsulated into MIL‐100 (Fe), the photosensitization capability is suppressed due to their isolation from O₂. After the reaction between iron(III) in MIL‐100 (Fe) and H₂O₂ occurs, the framework of MIL‐100 (Fe) collapses and the encapsulated PSs regain contact with O₂, leading to activation of photosensitization. In addition, the decomposition of H₂O₂ can generate O₂ to relieve tumor hypoxia and enhance PDT effect. As O₂ is an indispensable factor for PDT, the activation strategy should be generally applicable to different PSs for activatable PDT.     

The AIE-Active Dual-Cationic Molecular Engineering: Synergistic Effect of Dark Toxicity and Phototoxicity for Anticancer Therapy

The development of anticancer therapy is significant to human health but remains a huge challenge. Photodynamic therapy (PDT), inducing the synergistic mitochondrial dysfunction in cancer cells is a promising approach but suffer from the low efficiency in hypoxic microenvironment and deep-seated tumors. Herein, to improve the outcomes of PDT for cancer treatment, a series of red fluorophores consisting of dual-cationic triphenylphosphonium-alkylated pyridinium and (substituted) triphenylamine are prepared as organelle-targeting antitumor photosensitizers (PSs) with aggregation-induced emission characteristics. These PSs can selectively accumulate at the mitochondria or lysosomes of cancer cells with both dark- and photo-cytotoxicity, making them possess excellent killing effect on cancer cells and efficient inhibition of tumor growth in living mice. This study brings about new insight into the development of powerful cancer treatment.     

An O2 Self‐Sufficient Biomimetic Nanoplatform for Highly Specific and Efficient Photodynamic Therapy

Conventional oxygen‐dependent photodynamic therapy (PDT) has faced severe challenges because of the non‐specificity of most available photosensitizers (PSs) and the hypoxic nature of tumor tissues. Here, an O₂ self‐sufficient cell‐like biomimetic nanoplatform (CAT‐PS‐ZIF@Mem) consisting of the cancer cell membrane (Mem) and a cytoskeleton‐like porous zeolitic imidazolate framework (ZIF‐8) with the embedded catalase (CAT) protein molecules and Al(III) phthalocyanine chloride tetrasulfonic acid (AlPcS₄, defined as PS) is developed. Because of the immunological response and homologous targeting abilities of the cancer cell membrane, CAT‐PS‐ZIF@Mem is selectively accumulated at the tumor site and taken up effectively by tumor cells after intravenous injection. After the intracellular H₂O₂ penetration into the framework, it is catalyzed by CAT to produce O₂ at the hypoxic tumor site, facilitating the generation of toxic ¹O₂ for highly effective PDT in vivo under near‐infrared irradiation. By integrating the immune escape, cell homologous recognition, and O₂ self‐sufficiency, this cell‐like biomimetic nanoplatform demonstrates highly specific and efficient PDT against hypoxic tumor cells with much reduced side‐effect on normal tissues.     

光动力疗法对荷瘤鼠杀伤作用的组织形态学实验研究

目的：探讨光动力疗法恶性肿瘤杀伤作用的机制。方法：应用光动力疗法对接种H22肝癌的40只昆明小鼠作肿瘤杀伤的对比实验研究。结果：通过组织形态学和抑瘤检测证实，光动力疗法能选择性杀伤癌细胞。结论：在治疗后24小时内就可以见到癌细胞出现空泡变性、核固缩、溶解、坏死，随着时间推移坏死更加明显。同时还证实这种光动力疗法对正常细胞和组织没有损伤。     

Tumor-Activated Prodrug with Synergistic Anti-Stemness Chemical and Photodynamic Therapies

Photodynamic therapy (PDT) has received extensive attention as a promising cancer treatment approach. Still, challenges to in vivo photodynamic therapy have existed for decades. First, the “always on” nature of conventional photosensitizers will cause damage to normal tissues thereby limiting the treatment efficiency of PDT. Second, the hypoxic TME protects cancer stem cells (CSCs) deeply harbored in the center of tumors from PDT administration, thus contributing to the recrudescence and metastasis of tumors. Herein, a ROS-triggered self-immolative therapeutic prodrug ( Mu-PS ) is reported, comprising of an activatable photosensitizer, an indomethacin (IMC) part, and a ROS-responsive trigger, for the anti-stemness chemical and photodynamic therapy of tumors. Intriguingly, Mu-PS can target the tumor and selectively release the photosensitizer and IMC upon the activation of TME-related ROS, generating massive phototoxic ¹O₂ to kill most non-CSCs tumor cells under the action of PDT and block the growth of CSCs by IMC, hence, it multiplies the therapeutic index. Noteworthy, the anti-stemness mechanism of IMC in tumors is confirmed and elucidated for the first time. Overall, this study introduces a self-immolatative prodrug for combined CSCs-involved chemical therapy and activatable PDT for tumors and provides a design paradigm of prodrug for the precise prognosis and treatment of tumors.     

Zwitterionic AIEgens: Rational Molecular Design for NIR-II Fluorescence Imaging-Guided Synergistic Phototherapy

Fluorescence imaging in the second near-infrared region (NIR-II) can penetrate tissue at centimeter depths and obtain high image fidelity. However, facile synthesis of small-molecule fluorescent photosensitizers for efficient NIR-II fluorescence imaging as well as photodynamic and photothermal combinatorial therapies is still a challenging task. Herein, a rational design and facile synthesis protocol are reported for a series of novel NIR-emissive zwitterionic luminogens with aggregation-induced emission (AIE) features for cancer phototheranostics. Consistent with the intrinsic features including long emission wavelength, effective reactive oxygen species generation, and excellent photothermal conversion efficiency (35.76%), in vitro and in vivo evaluation show that one of these presented AIE luminogens provides excellent performance in NIR-II fluorescence imaging-guided synergistic phototherapy against cancer.     

Molecular Engineering of Efficient Singlet Oxygen Generators with Near-Infrared AIE Features for Mitochondrial Targeted Photodynamic Therapy

Aggregation-caused fluorescence quenching with insufficient production of reactive oxygen species (ROS) has limited the application of photosensitizers (PSs) in fluorescence-imaging-guided photodynamic therapy (PDT). Aggregation-induced emission PSs (AIE-PSs) exhibit enhanced fluorescence intensity and a high efficiency of ROS generation in the aggregation state, which provides an opportunity to solve the above problems. Herein, a series of AIE-PSs are successfully designed and synthesized by adjusting the D–A intensity through molecular engineering. The photophysical properties and theoretical calculations prove that the synergistic effect of 3,4-ethylenedioxythiophene and quinolinium increases the intramolecular charge transfer effect (ICT) of the whole molecule and promotes the intersystem crossing (ISC) from the lowest excited singlet state (S₁) to the lowest triplet state (T₁). Among these AIE-PSs, the optimal AIE-PS (TPA-DT-Qy) exhibits the highest generation yield of ¹O₂ (5.3-fold of Rose Bengal). Further PDT experiments show that the TPA-DT-Qy has a highly efficient photodynamic ablation of breast cancer cells (MCF-7 and MDA-MB-231) under white light irradiation. Moreover, the photodynamic antibacterial study indicates that TPA-DT-Qy has the discrimination and excellent photodynamic inactivation of S. aureus. This work provides a feasible strategy for the molecular engineering of novel AIE-PSs to improve the development of fluorescence-imaging-guided PDT.     

A Bioactive Photosensitizer for Hypoxia-Tolerant Molecular Targeting-Photo-Immunotherapy of Malignant Tumor

Photosensitizers (PSs) with effective reactive oxygen species generation ability against hypoxia are of great potential for clinical treatment of malignant tumors. However, complex tumor microenvironment, such as antioxidative responses and immunosuppression, would ineluctably limit the efficiency of photodynamic therapy (PDT). Herein, a molecular-targeting photosensitizer QTANHOH is rationally designed for histone deacetylases (HDACs-targeting photo-immunotherapy application. The PS QTANHOH displays excellent type-I/II PDT performance, exhibiting significant phototoxicity toward cancer cells with half maximal inhibitory concentration (IC₅₀) less than 10 nm in both normoxia and hypoxia conditions under blue laser irradiation. Moreover, the bioactive compound could inhibit HDACs and activate the immune microenvironment to boost PDT efficacy on the immunocompetent BALB/c mice with breast cancer, leading to the eradication of solid tumor and inhibition of metastasis. Notably, the molecular-targeting photosensitizer introduces an alternative strategy to achieve superior phototherapy for cancer therapy.     

Red AIE Luminogens with Tunable Organelle Specific Anchoring for Live Cell Dynamic Super Resolution Imaging

Lysosomes and mitochondria play an important role in maintaining cell homeostasis. Visualizing the long-term activities of lysosomes and mitochondria on the nanometer scale in live cells is essential for further understanding their functions but remains challenging due to the limitations of existing fluorescent probes, such as aggregation-caused quenching (ACQ) effect, limited signal-to-noise ratio from fluorescence “always on” in the process of targeting organelle and poor photobleaching resistance. Herein, two efficient red-emitting aggregation-induced emission (AIE) luminogens are reported, which showed “off-on” fluorescence characteristic and specific lysosomes as well as mitochondria targeting capability. Owing to their AIE characteristics, a Stokes’ shift larger than 100 nm, good biocompatibility, and excellent photostability, the AIE luminogens have been successfully utilized for high fidelity imaging of lysosomes and mitochondria. By virtue of these two probes, stimulated emission depletion (STED) images of dynamic lysosomal fusion and mitochondrial fission with a high resolution of 65.6 nm are obtained. Furthermore, the interactions between lysosomes and mitochondria in the process of mitophagy are recorded. This study also provides practical guidance for designing specific organelle targeting probes to support live cell dynamic super-resolution imaging.     

Metal‐Organic Framework Nanoparticles in Photodynamic Therapy: Current Status and Perspectives

This feature article covers the recent applications of metal‐organic framework nanoparticles (MOF NPs) in photodynamic therapy (PDT) of cancer. It aims at giving the reader an overview about these two current research fields, i.e., MOF and PDT, and at highlighting the potential synergistic effect that could result from their association. After describing the general photophysics and photochemistry that underlie PDT, the relationship between photosensitizer (PS) properties and PDT requirements is discussed throughout the PSs historical development. This development reveals the advantages of using nanotechnology platforms for the creation of the ideal PS and leads us to define the fourth generation of PSs, which includes NPs built from the PS itself as porphysomes or PS‐based MOF NPs. Especially, the precise spatial control over the PS assembly into well‐defined MOF NPs, which keeps the PS in its monomeric form and prevents PS self‐quenching, appears as a notable feature to solve PS solubility and aggregation issues and therefore improves the PDT efficiency. Finally, we discuss the future perspectives of MOF NPs in PDT and shed light on how promising these nanomaterials are.     

Platinum-based photosensitizer with near-infrared aggregation-induced emission for synergistic photodynamic-chemo theranostics

Photodynamic therapy (PDT) is of great interest as an emerging paradigm towards cancer treatment, owing to its advantages of minimal invasiveness and low toxicity. In this work, we incorporated cisplatin into an AIE-based photosensitizer (BT) and achieved a highly efficient antitumor drug (BT-Pt). Possessing AIE characteristics, BT-Pt exhibited NIR fluorescence with large Stokes shift in cells, which can guide the location of the drug. More importantly, the ROS generation efficiency of BT-Pt has extremely been promoted with the fabrication of cisplatin, compared with BT. As a result, BT-Pt demonstrated favorable therapeutic efficacy with a half maximal inhibitory concentration (IC₅₀) value of 1.54 μM for HeLa cells upon white light irradiation, attributed to its synergetic PDT and chemotherapy. The design strategy of such platinated photosensitizer showed great potential in developing multifunctional anticancer drugs with combinatorial photodynamic–chemotherapy, especially when ablating cisplatin resistant cancer cells and hypoxic tumors.     

An Ultrasmall SnFe2O4 Nanozyme with Endogenous Oxygen Generation and Glutathione Depletion for Synergistic Cancer Therapy

The tumor microenvironment (TME) with the characteristics of severe hypoxia, overexpressed glutathione (GSH), and high levels of hydrogen peroxide (H₂O₂) dramatically limits the antitumor efficiency by monotherapy. Herein, a novel TME-modulated nanozyme employing tin ferrite (SnFe₂O₄, abbreviated as SFO) is presented for simultaneous photothermal therapy (PTT), photodynamic therapy (PDT), and chemodynamic therapy (CDT). The as-fabricated SFO nanozyme demonstrates both catalase-like and GSH peroxidase-like activities. In the TME, the activation of H₂O₂ leads to the generation of hydroxyl radicals (•OH) in situ for CDT and the consumption of GSH to relieve antioxidant capability of the tumors. Meanwhile, the nanozyme can catalyze H₂O₂ to generate oxygen to meliorate the tumor hypoxia, which is beneficial to achieve better PDT. Furthermore, the SFO nanozyme irradiated with 808 nm laser displays a prominent phototherapeutic effect on account of the enhanced photothermal conversion efficiency (η  = 42.3%) and highly toxic free radical production performance. This “all in one” nanozyme integrated with multiple treatment modalities, computed tomography, and magnetic resonance imaging properties, and persistent modulation of TME exhibits excellent tumor theranostic performance. This strategy may provide a new dimension for the design of other TME-based anticancer strategies.     

Modulation of Intracellular Oxygen Pressure by Dual‐Drug Nanoparticles to Enhance Photodynamic Therapy

Oxygen plays an essential role in the photodynamic therapy (PDT) of cancer. However, hypoxia inside tumors severely attenuates the therapeutic effect of PDT. To address this issue, a novel strategy is reported for cutting off the oxygen consumption pathway by using sub‐50 nm dual‐drug nanoparticles (NPs) to attenuate the hypoxia‐induced resistance to PDT and to enhance PDT efficiency. Specifically, dual‐drug NPs that encapsulate photosensitizer (PS) verteporfin (VER) and oxygen‐regulator atovaquone (ATO) with sub‐50 nm diameters can penetrate deep into the interior regions of tumors and effectively deliver dual‐drug into tumor tissues. Then, ATO released from NPs efficiently reduce in advance cellular oxygen consumption by inhibition of mitochondria respiratory chain and further heighten VER to generate greater amounts of ¹O₂ in hypoxic tumor. As a result, accompanied with the upregulated oxygen content in tumor cells and laser irradiation, the dual‐drug NPs exhibit powerful and overall antitumor PDT effects both in vitro and in vivo, and even tumor elimination. This study presents a potential appealing clinical strategy in photodynamic eradication of tumors.     

Facile Synthesis of Red/NIR AIE Luminogens with Simple Structures,Bright Emissions,and High Photostabilities,and Their Applications for Specific Imaging of Lipid Droplets and Image‐Guided Photodynamic Therapy

Red/near‐infrared (NIR) fluorescent molecules with aggregation‐induced emission (AIE) characteristics are of great interest in bioimaging and therapeutic applications. However, their complicated synthetic approaches remain the major barrier to implementing these applications. Herein, a one‐pot synthetic strategy to prepare a series of red/NIR‐emissive AIE luminogens (AIEgens) by fine‐tuning their molecular structures and substituents is reported. The obtained AIEgens possess simple structures, good solubilities, large Stokes shifts, and bright emissions, which enable their applications toward in vitro and in vivo imaging without any pre‐encapsulation or ‐modification steps. Excellent targeting specificities to lipid droplets (LDs), remarkable photostabilities, high brightness, and low working concentrations in cell imaging application make them remarkably impressive and superior to commercially available LD‐specific dyes. Interestingly, these AIEgens can efficiently generate reactive oxygen species upon visible light irradiation, endowing their effective application for photodynamic ablation of cancer cells. This study, thus, not only demonstrates a facile synthesis of red/NIR AIEgens for dual applications in simultaneous imaging and therapy, but also offers an ideal architecture for the construction of AIEgens with long emission wavelengths.