Aggregation Effect on Multiperformance Improvement in Aryl-Armed Phenazine-Based Emitters

Stimuli-responsive nanotheranostic systems conjugated with AIEgens for advanced cancer bio-imaging and treatment

Aggregation-induced emission (AIE) is a unique phenomenon observed in various materials such as organic luminophores, carbon dots (CDs), organic-inorganic nanocomposites, fluorescent dye molecules, and nanoparticles (NPs). These AIE-active materials, or AIEgens, are ideal for balancing multifunctional phototheranostics and energy dissipation. AIE properties can manifest in organic fluorescent probes, rendering them effective for cancer treatment due to their ability to penetrate deeply and provide high therapeutic efficacy. This efficacy is attributed to their high photobleaching thresholds, ability to induce Stokes shifts, and capacity to activate fluorophores. Therefore, the development of innovative AIE-based materials for disease diagnosis and treatment, particularly for cancer, is both important and promising. Recent years have seen successful demonstrations of nanoparticles with AIE properties being used for photodynamic therapy (PDT) and multimodal imaging of tumor cells. These fluorophores have been shown to impact mitochondria and lysosomes, generate reactive oxygen species (ROS), activate the immune system, load and release drugs, and ultimately induce apoptosis in tumor cells. In this review, we examine previous studies on the manufacturing methods and effects of AIEgens on cancer cells, with a theranostic strategy of simultaneous treatment and imaging. We also investigate the factors affecting drug delivery on different cancer cells, including internal stimuli such as pH, ROS, enzymes, and external stimuli like near-infrared (NIR) light and ultrasound waves.

Dual-modal imaging-guided agent based on NIR-II aggregation-induced emission luminogens with balanced phototheranostic performance

Phototherapy has garnered considerable interest for its potential to revolutionize conventional cancer treatment. Organic materials with near-infrared II (NIR-II, 1000-1700 nm) fluorescence and photothermal effects are key for precise tumor diagnosis and treatment, yet optimizing their output for higher resolution and reduced photodamage remains a challenge. Herein, a multifunctional NIR-II photosensitizer (LSC) has been developed using the aggregation-induced emission (AIE) technology. The utilization of thieno[3,2-b]thiophene as an electron-rich and bulky donor/acceptor bridge has allowed for the elongation of conjugation length and distortion of the AIE main chain. This strategic modification effectively enhances the electron push-pull effect, endowing the LSC with a Stokes shift of over 400 nm and AIE characteristics. We have successfully built-up stable nanoparticles called FA-LSC NPs using a nano-precipitation method. These nanoparticles exhibit high NIR-II fluorescent brightness (ε × QY = 1064 M-1 cm-1) and photothermal conversion efficiency (41%). Furthermore, the biocompatible FA-LSC NPs demonstrate effective tumor accumulation and exceptional photothermal therapeutic efficacy both in vitro and in vivo. These nanoparticles were applied to fluorescence-photothermal dual-mode imaging-guided photothermal ablation in a HeLa tumor xenograft mouse model, resulting in favorable photothermal clearance outcomes.

A structure-guided strategy to design Golgi apparatus-targeted type-I/II aggregation-induced emission photosensitizers for efficient photodynamic therapy

The Golgi apparatus (GA) is a vital target for anticancer therapy due to its sensitivity against reactive oxygen species (ROS)-induced oxidative stress that could lead to cell death. In this study, we designed a series of aggregation-induced emission (AIE)-based photosensitizers (TPAPyTZ, TPAPyTC, TPAPyTM, and TPAPyTI) carrying different ROS with selective GA-targeted ability. The in vitro study showed that TPAPyTZ and TPAPyTC displayed strong AIE characteristics, robust type-I/II ROS production capabilities, specific GA-targeted, high photostability, and high imaging quality. The cell-uptake of TPAPyTZ was found primarily through an energy-dependent caveolae/raft-mediated endocytosis pathway. Remarkably, TPAPyTZ induced GA-oxidative stress, leading to GA fragmentation, downregulation of GM130 expression, and activation of mitochondria caspase-related apoptosis during photodynamic therapy (PDT). In vivo experiments revealed that TPAPyTZ significantly inhibited tumor proliferation under lower-intensity white light irradiation with minimal side effects. Overall, our work presents a promising strategy for designing AIEgens for fluorescence imaging-guided PDT. Additionally, it enriched the collection of GA-targeted leads for the development of cancer theranostics capable of visualizing dynamic changes in the GA during cancer cell apoptosis, which could potentially enable early diagnosis applications in the future. STATEMENT OF SIGNIFICANCE: AIE luminogens (AIEgens) are potent phototheranostic agents that can exhibit strong fluorescence emission and enhance ROS production in the aggregate states. In this study, through the precise design of photosensitizers with four different electron-acceptors, we constructed a series of potent AIEgens (TPAPyTZ, TPAPyTC, TPAPyTM, and TPAPyTI) with strong fluorescence intensity and ROS generation capacity. Among them, TPAPyTZ with an extended π-conjugation displayed the strongest ROS generation ability and anti-tumor activity, resulting in an 88 % reduction in tumor weight. Our studies revealed that the enhanced activity of TPAPyTZ may be due to its unique Golgi apparatus (GA)-targeted ability, which causes GA oxidative stress followed by effective cancer cell apoptosis. This unique GA-targeted feature of TPAPyTZ remains rare in the reported AIEgens, which mainly target organelles such as lysosome, mitochondria, and cell membrane. The successful design of a GA-targeted and potent AIEgen could enrich the collection of GA-targeted luminogens, providing a lead theranostic for the further development of fluorescence imaging-guided PDT, and serving as a tool to explore the potential mechanism and discover new GA-specific drug targets.

Regulating donor configuration to develop AIE-active type I photosensitizers for lipid droplet imaging and high-performance photodynamic therapy under hypoxia

Type I photodynamic therapy is considered to be a more promising cancer treatment than type II photodynamic therapy due to its non-oxygen-dependent characteristics. In this work, three D-A structure N,N'-dihydrophenazine (DHP)-based photosensitizers DP-CNPY, SMP-CNPY and DMP-CNPY were designed and synthesized by introducing different numbers of methyl groups in the backbone neighbor of DHP as the donor and combined with the typical strong electron acceptor 2-(pyridin-4-yl)acetonitrile. Among the three photosensitizers, SMP-CNPY with one methyl modification showed the best type I ROS (O2-˙, ˙OH) generation capacity and AIE performance. By encapsulation, SMP-CNPY was fabricated into nanoparticles, and SMP-CNPY NPs exhibited lipid droplet targeting ability with near-infrared (NIR) emission. Cell experiments have proved that SMP-CNPY NPs can effectively kill different kinds of cancer cells under normal oxygen conditions. Even under hypoxic and extreme hypoxic conditions, SMP-CNPY NPs can still produce ROS and kill cancer cells. This work holds significant potential in the field of type I AIE-active photosensitizers and provides a new strategy for overcoming the hypoxic dilemma in the malignant tumor microenvironment.

Exclusive and Switchable Superoxide Radical Generation by O2-Capture-Based Electron Transfer and Supramolecular Assembly

Type-I photosensitizers (PSs) can generate free radical anions with a broad diffusion range and powerful damage effect, rendering them highly desirable in various areas. However, it still remains a recognized challenge to develop pure Type-I PSs due to the inefficiency in producing oxygen radical anions through the collision of PSs with nearby substrates. In addition, regulating the generation of oxygen radical anions is also of great importance toward the control of photosensitizer (PS) activities on demand. Herein, a piperazine-based cationic Type-I PS (PPE-DPI) that exhibits efficient intersystem crossing and subsequently captures oxygen molecules through binding O2 to the lone pair of nitrogen in piperazine is reported. The close spatial vicinity between O2 and PPE-DPI strongly promotes the electron transfer reaction, ensuring the exclusive superoxide radical (O2 •-) generation via Type-I process. Particularly, PPE-DPI with cationic pyridine groups is able to associate with cucurbit[7]uril (CB[7]) through host-guest interactions. Thus, supramolecular assembly and disassembly are easily utilized to realize switchable O2 •- generation. This switchable Type-I PS is successfully employed in photodynamic antibacterial control.

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

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

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

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

Aza-dicyclopenta[a,g]naphthalenes: controllable seesaw-like emissive behavior and narrowband AIEgens

Molecular motions significantly influence the emissive behavior and properties of organic fluorescent molecules. However, achieving controllable emission remains a major challenge for fluorophores. In the case of aggregation-induced emission luminogens (AIEgens), the desired properties of aggregated emission and narrowband spectrum demand molecular motion patterns that inherently oppose each other. A nitrogen-containing dicyclopenta[a,g]naphthalene scaffold was discovered as a controllable luminogenic structure through a highly efficient one-step intermolecular cascade reaction. By carefully balancing molecular motions and introducing additional nitrogen atoms into the skeleton, pyrrole-conjugated dicyclopenta[a,g]naphthalenes with aggregation-caused quenching (ACQ) could be transformed into dual-state emission luminogens (DSEgens). This transformation was achieved by incorporating an additional weak H-bond "lock." Furthermore, the DSEgens could be converted into AIEgens with an exciting narrow full-width-at-half-maximum (FWHM, <50 nm) by methylation. This unprecedented discovery is attributed to the contribution of the weak H-bond "lock," which overcomes the limitations of broad band emission in AIEgens caused by restrictions of intramolecular motion. Specific organelle probes were developed by replacing the methyl group of the onium product with different positioning groups. This study emphasizes the delicate balance of molecular motions in controlling luminescence and demonstrates a successful approach to designing organic luminogens with controllable emission and narrowband AIEgens.

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

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

Synthesis and Characterization of Tetraphenylethene AIEgen-Based Push-Pull Chromophores for Photothermal Applications: Could the Cycloaddition-Retroelectrocyclization Click Reaction Make Any Molecule Photothermally Active?

Three new tetraphenylethene (TPE) push-pull chromophores exhibiting strong intramolecular charge transfer (ICT) are described. They were obtained via [2 + 2] cycloaddition-retroelectrocyclization (CA-RE) click reactions on an electron-rich alkyne-tetrafunctionalized TPE (TPE-alkyne) using both 1,1,2,2-tetracyanoethene (TCNE), 7,7,8,8-tetracyanoquinodimethane (TCNQ) and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F₄-TCNQ) as electron-deficient alkenes. Only the starting TPE-alkyne displayed significant AIE behavior, whereas for TPE-TCNE, a faint effect was observed, and for TPE-TCNQ and TPE-F₄-TCNQ, no fluorescence was observed in any conditions. The main ICT bands that dominate the UV-Visible absorption spectra underwent a pronounced red-shift beyond the near-infrared (NIR) region for TPE-F₄-TCNQ. Based on TD-DFT calculations, it was shown that the ICT character shown by the compounds exclusively originated from the clicked moieties independently of the nature of the central molecular platform. Photothermal (PT) studies conducted on both TPE-TCNQ and TPE-F4-TCNQ in the solid state revealed excellent properties, especially for TPE-F4-TCNQ. These results indicated that CA-RE reaction of TCNQ or F₄-TCNQ with donor-substituted are promising candidates for PT applications.