An Endoplasmic Reticulum Targeting Type I Photosensitizer for Effective Photodynamic Therapy against Hypoxic Tumor Cells

Organelle-targeted type I photodynamic therapy (PDT) shows great potential to overcome the hypoxic microenvironment in solid tumors. The endoplasmic reticulum (ER) is an indispensable organelle in cells with important biological functions. When the ER is damaged due to the production of reactive oxygen species (ROS), the accumulation of misfolded proteins will interfere with ER homeostasis, resulting in ER stress. Here, an ER-targeted benzophenothiazine-based photosensitizer NBS-ER was presented. ER targeting modification significantly reduced the dark toxicity and improved phototoxicity index (PI). NBS-ER could effectively produce O₂⁻⋅ with near-infrared irradiation, making its phototoxicity under hypoxia close to that under normoxia. Meanwhile, the photoinduced ROS triggered ER stress and induced apoptosis. In addition, NBS-ER possessed excellent photodynamic therapeutic effect in 4T1-tumor-bearing mice.     

Recent Progress in Boosted PDT Induced Immunogenic Cell Death for Tumor Immunotherapy

With the rapid development of materials science,photosensitive materials have been widely used in the field of immunogenic cell death(ICD),which was on account of the reactive oxygen species(ROS)generation by photosensitizer under light irradiation inducing cellular oxidative stress during the dying of cells.Considerable researches related to photodynamic therapy(PDT)induced ICD were conducted and exhibited brilliant performance in cancer immunotherapy.Herein,a variety of different strategies for PDT induced ICD have been summarized and discussed to provide researchers more inspiration for cancer immunotherapy.     

γ-Resorcyclic Acid-Based AIEgens for Illuminating Endoplasmic Reticulum**

Endoplasmic reticulum (ER) has emerged as one of the interesting sub-cellular organelles due to its role in myriads of biological phenomena. Subsequently, visualization of the structure-function and dynamics of ER remained a major challenge to understand its involvement in different diseased states including cancer. To illuminate the ER, herein we have designed and synthesized γ-resorcyclic acid-based small molecules, which showed remarkable aggregation-induced emission (AIE) property in water. This AIE property was originated from the dual intramolecular H-bonding leading to the self-assembled 2D aggregation confirmed by pH- and temperature-dependent fluorescence quenching studies as well as scanning electron microscopy. These small molecules illuminated the sub-cellular ER in HeLa cervical cancer cells as well as non-cancerous RPE-1 human retinal epithelial cells within 1 h. These novel small molecules have the potential to light up ER chemical biology in diseased states.     

Current Status of Endoplasmic Reticulum Stress in Type II Diabetes

The endoplasmic reticulum (ER) plays a multifunctional role in lipid biosynthesis, calcium storage, protein folding, and processing. Thus, maintaining ER homeostasis is essential for cellular functions. Several pathophysiological conditions and pharmacological agents are known to disrupt ER homeostasis, thereby, causing ER stress. The cells react to ER stress by initiating an adaptive signaling process called the unfolded protein response (UPR). However, the ER initiates death signaling pathways when ER stress persists. ER stress is linked to several diseases, such as cancer, obesity, and diabetes. Thus, its regulation can provide possible therapeutic targets for these. Current evidence suggests that chronic hyperglycemia and hyperlipidemia linked to type II diabetes disrupt ER homeostasis, thereby, resulting in irreversible UPR activation and cell death. Despite progress in understanding the pathophysiology of the UPR and ER stress, to date, the mechanisms of ER stress in relation to type II diabetes remain unclear. This review provides up-to-date information regarding the UPR, ER stress mechanisms, insulin dysfunction, oxidative stress, and the therapeutic potential of targeting specific ER stress pathways.     

Mitochondria‐Targeted Cancer Therapy Using a Light‐Up Probe with Aggregation‐Induced‐Emission Characteristics

Subcellular organelle‐specific reagents for simultaneous tumor targeting, imaging, and treatment are of enormous interest in cancer therapy. Herein, we present a mitochondria‐targeting probe (AIE‐mito‐TPP) by conjugating a triphenylphosphine (TPP) with a fluorogen which can undergo aggregation‐induced emission (AIE). Owing to the more negative mitochondrial membrane potential of cancer cells than normal cells, the AIE‐mito‐TPP probe can selectively accumulate in cancer‐cell mitochondria and light up its fluorescence. More importantly, the probe exhibits selective cytotoxicity for studied cancer cells over normal cells. The high potency of AIE‐mito‐TPP correlates with its strong ability to aggregate in mitochondria, which can efficiently decrease the mitochondria membrane potential and increase the level of intracellular reactive oxygen species (ROS) in cancer cells. The mitochondrial light‐up probe provides a unique strategy for potential image‐guided therapy of cancer cells.     

Aggregation-induced emission luminogen for specific identification of malignant tumour in vivo

Colorectal cancer(CRC) is still a major killer,mainly due to the lack of early detection biomarker with sensitivity/specificity.Conventional histopathology is the gold standard approach in practice,but there are still some issues(false diagnosis and long waiting period).Aggregation-induced emission(AIE) is a novel photophysical phenomenon which has been widely utilized for biological imaging in vitro,including malignant cells,showing remarkable imaging contrast and enhanced emission in high concentrated state.However,it is unclear if AIE dyes can identify malignant cells specifically in vivo.A great challenge for specific labeling of malignant cells is probably ascribed to the complex compositions in tumor tissues.Herein,an AIE dye-based mitochondria-targeted histological staining strategy was employed to localize cancer and the metastatic track in the fresh colorectal cancer.This novel approach holds great potential to revolutionize the clinical diagnosis and intervention for devastating malignancy.     

Light-Induced Self-Escape of Spherical Nucleic Acid from Endo/Lysosome for Efficient Non-Cationic Gene Delivery

Developing non-cationic gene carriers and achieving efficient endo/lysosome escape of functional nucleic acids in cytosol are two major challenges faced by the field of gene delivery. Herein, we demonstrate the concept of self-escape spherical nucleic acid (SNA) to achieve light controlled non-cationic gene delivery with sufficient endo/lysosome escape capacity. In this system, Bcl-2 antisense oligonucleotides (OSAs) were conjugated onto the surface of aggregation-induced emission (AIE) photosensitizer (PS) nanoparticles to form core–shell SNA. Once the SNAs were taken up by tumor cells, and upon light irradiation, the accumulative ¹O₂ produced by the AIE PSs ruptured the lysosome structure to promote OSA escape. Prominent in vitro and in vivo results revealed that the AIE-based core–shell SNA could downregulate the anti-apoptosis protein (Bcl-2) and induce tumor cell apoptosis without any transfection reagent.     

An aggregation-induced emission platform for efficient Golgi apparatus and endoplasmic reticulum specific imaging

As two important subcellular organelles in eukaryotic cells, the Golgi apparatus (GA) and endoplasmic reticulum (ER) have recently captivated much interest due to their considerable importance in many biofunctions and role as critical biomarkers for various diseases. The development of efficient GA- and ER-specific probes is of great significance, but remains an appealing yet significantly challenging task. Herein, we reported for the first time the construction of an aggregation-induced emission (AIE) platform for GA and ER fluorescent probes, termed as AIE-GA and AIE-ER, by facile synthesis and simple functionalization. Their excellent targeting specificity to GA or ER, remarkable photostability, high brightness, and low working concentration make AIE-GA and AIE-ER significantly impressive and superior to commercially available probes. Moreover, molecular docking calculations are performed to validate the targeting mechanism of the two AIE probes.

As two important subcellular organelles in eukaryotic cells, the Golgi apparatus (GA) and endoplasmic reticulum (ER) have recently captivated much interest due to their considerable importance in many biofunctions and role as critical biomarkers for various diseases.     

Image-guided combination chemotherapy and photodynamic therapy using a mitochondria-targeted molecular probe with aggregation-induced emission characteristics

Subcellular targeted cancer therapy and in situ monitoring of therapeutic effect are highly desirable for clinical applications. Herein, we report a series of probes by conjugating zero (TPECM-2Br), one (TPECM-1TPP) and two (TPECM-2TPP) triphenylphosphine (TPP) ligands to a fluorogen with aggregation-induced emission (AIE) characteristics. The probes are almost non-emissive as molecularly dissolved species, but they can light up in cell cytoplasm or mitochondria. TPECM-2TPP is found to be able to target mitochondria, depolarize mitochondria membrane potential and selectively exert potent chemo-cytotoxicity on cancer cells. Furthermore, it can efficiently generate singlet oxygen with strong photo-toxicity upon light illumination, which further enhances its anti-cancer effect. On the other hand, TPECM-1TPP can also target mitochondria and generate singlet oxygen to trigger cancer cell apoptosis, but it shows low cytotoxicity in dark. Meanwhile, TPECM-1TPP can report the cellular oxidative stress by visualizing the morphological changes of mitochondria. However, TPECM-2Br does not target mitochondria and shows no obvious anticancer effect either in dark or under light illumination. This study thus highlights the importance of molecular probe design, which yields a new generation of subcellular targeted molecular theranostic agents with multi-function, such as cancer cell imaging, chemotherapy, photodynamic therapy, and in situ monitoring of the therapeutic effect in one go.     

An AIE-Active Conjugated Polymer with High ROS-Generation Ability and Biocompatibility for Efficient Photodynamic Therapy of Bacterial Infections

New, biocompatible materials with favorable antibacterial activity are highly desirable. In this work, we develop a unique conjugated polymer featuring aggregation-induced emission (AIE) for reliable bacterial eradication. Thanks to the AIE and donor-π-acceptor structure, this polymer shows a high reactive oxygen species (ROS)-generation ability compared to a low-mass model compound and the common photosensitizer Chlorin E6. Moreover, the selective binding of pathogenic microorganisms over mammalian cells was found, demonstrating its biocompatibility. The effective growth inhibition of bacteria upon polymer treatment under light irradiation was validated in vitro and in vivo. Notably, the recovery from infection after treatment with our polymer is faster than that with cefalotin. Thus, this polymer holds great promise in fighting against bacteria-related infections in practical applications.     

Theranostic hyaluronic acid prodrug micelles with aggregation-induced emission characteristics for targeted drug delivery

Theranostic hyaluronic acid (HA) prodrug micelles with pH-responsive drug release and aggregation-induced emission (AIE) properties were prepared by chemical graft of biomimetic phosphorylcholine (PC), anticancer drug doxorubicin (DOX) and AIE fluorogen tetraphenylene (TPE) to the HA backbone. DOX was conjugated to the HA backbone by a hydrazone bond which can be hydrolyzed under acidic environment and result in pH-triggered smart release of DOX. The TPE units with typical AIE characteristics were applied for real time drug tracking in cancer cells. The HA-based prodrugs could self-assemble into micelles in aqueous solution as confirmed by the dynamic light scattering (DLS) and transmission electron microscopy (TEM). The intracellular distribution of HA prodrug micelles could be clearly observed by fluorescence microscopy based on the strong fluorescence of TPE. Moreover, after treated with the micelles, stronger fluorescence of TPE in CD44 overexpressed MDA-MB-231 cancer cells was observed, compared to the CD44 negative cell line, NIH3T3 cells, suggesting efficient cell uptake of HA prodrug micelles by receptor-mediated endocytosis. The cell viability results indicated that the prodrug micelles could inhibit the proliferation of the cancer cells effectively. Such pH-triggered theranostic drug delivery system with AIE features can provide a new platform for targeted and image-guided cancer therapy.     

An AIE‐Active Conjugated Polymer with High ROS‐Generation Ability and Biocompatibility for Efficient Photodynamic Therapy of Bacterial Infections

New, biocompatible materials with favorable antibacterial activity are highly desirable. In this work, we develop a unique conjugated polymer featuring aggregation‐induced emission (AIE) for reliable bacterial eradication. Thanks to the AIE and donor‐π‐acceptor structure, this polymer shows a high reactive oxygen species (ROS)‐generation ability compared to a low‐mass model compound and the common photosensitizer Chlorin E6. Moreover, the selective binding of pathogenic microorganisms over mammalian cells was found, demonstrating its biocompatibility. The effective growth inhibition of bacteria upon polymer treatment under light irradiation was validated in vitro and in vivo. Notably, the recovery from infection after treatment with our polymer is faster than that with cefalotin. Thus, this polymer holds great promise in fighting against bacteria‐related infections in practical applications.     

Induction of Immunogenic Cell Death by Chemotherapeutic Platinum Complexes

There is compelling evidence suggesting that the immune‐modulating effects of many conventional chemotherapeutics, including platinum‐based agents, play a crucial role in achieving clinical response. One way in which chemotherapeutics can engage a tumor‐specific immune response is by triggering an immunogenic mode of tumor cell death (ICD), which then acts as an “anticancer vaccine”. In spite of being a mainstay of chemotherapy, there has not been a systematic attempt to screen both existing and upcoming Pt agents for their ICD ability. A library of chemotherapeutically active Pt agents was evaluated in an in vitro phagocytosis assay, and no correlation between cytotoxicity and phagocytosis was observed. A Pt^II N‐heterocyclic carbene complex was found to display the characteristic hallmarks of a type II ICD inducer, namely focused oxidative endoplasmic reticulum (ER) stress, calreticulin exposure, and both HMGB1 and ATP release, and thus identified as the first small‐molecule immuno‐chemotherapeutic agent.     

A mononuclear copper(II) complex containing benzimidazole and pyridyl ligands: Synthesis,characterization, and antiproliferative activity against human cancer cells

Metal complexes are recently being hybridized with different moieties to discover new drugs due to their advantageous attributes. Among the metals, copper is a good one to synthesize a metal complex due to its being endogenous, redox and DNA cleavage potential, reported anti-cancer efficacies and selective permeability for cancer cells. In this study, first we synthesized a new copper (II) complex and determined its toxic doses on NIH/3T3 normal fibroblast cells, SPC212 mesothelioma and DU145 prostate cancer cells. Then, we ascertained anti-proliferative, apoptotic, morphological, oxidative and endoplasmic reticulum (ER) stress inducing effects of these newly synthesized compounds on DU145 prostate cancer cells. A novel Copper(II)/1-(4-(trifluoromethyl)benzyl)-1H-benzimidazole/2,2′-bipyridyl complex was synthesized and mainly characterized by single crystal X-ray diffraction analysis. Anti-proliferative effect of copper(II) complex was gauged by MTT. Oxidative and ER stress were evaluated by ELISA and Western blot. The morphological effect was examined by microscope analysis. Besides, immunocytochemistry of Bax, a pro-apoptotic protein and PCNA, a proliferation marker protein was performed. As a result, the inhibitory effect of newly synthesized substance was superior to the chemicals from which it was synthesized. Its IC₅₀s against DU145 were 37.0, 21.1 and 10.0 µM for 24, 48 and 72 h-treatments, respectively. Oxidative and ER stress increased after treatment. In microscopy, we observed apoptotic hallmarks like nuclear condensation, cellular shrinkage and membrane blebbings. In immunochemistry, increased Bax and decreased PCNA were apparent. Copper(II) complex with its relatively low IC₅₀ can also be tested on other cancer and normal cell lines.     

A Mitochondria-targeted AIEgen Labelled with 18F for Breast Cancer Cell Imaging and Therapy

A lack of efficient diagnostic tools for early and noninvasive diagnosis of breast cancer has restricted the clinical treatment effect. This problem might be addressed by the combination of aggregation-induced emission (AIE) fluorescence imaging and positron emission tomography (PET) with the dual advantages of high resolution and easy operation, and unlimited penetration and high sensitivity. Here, a mitochondria-targeted AIE luminogen (AIEgen) radiolabeled with ¹⁸F was developed through a two-step radiochemical reaction by virtue of a prosthetic group. The obtained ^18/19F-Bz-CP imaging probe was examined by in vitro cell uptake and cell proliferation inhibition in two breast cancer cell lines, showing that the probe can efficiently target and locate in the mitochondria through the analysis of fluorescence imaging and PET simultaneously. Additionally, the probe can induce cancer cell apoptosis with the half maximal inhibitory concentration (IC50) of 4.8 μM for MCF-7 cells and 7.2 μM for T47D cells, indicating its potential application for breast cancer therapy.     

Hydrazide–Hydrazone Small Molecules as AIEgens: Illuminating Mitochondria in Cancer Cells

Aggregation-induced-emission luminogens (AIEgens) have gained considerable attention as interesting tools for several biomedical applications, especially for bioimaging due to their brightness and photostability. Numerous AIEgens have been developed for lighting up the subcellular organelles to understand their forms and functions not only healthy but also unhealthy states, such as in cancer cells. However, there is lack of easily synthesizable, biocompatible small molecules for illuminating mitochondria (powerhouses) inside cells. To address this issue, an easy and short synthesis of new biocompatible hydrazide–hydrazone-based small molecules with remarkable aggregation-induced emission (AIE) properties is described. These small-molecule AIEgens showed hitherto unobserved AIE properties due to dual intramolecular H-bonding confirmed by theoretical calculation, pH- and temperature-dependent fluorescence and X-ray crystallographic studies. Confocal microscopy showed that these AIEgens were internalized into the HeLa cervical cancer cells without showing any cytotoxicity. One of the AIEgens was tagged with a triphenylphosphine (TPP) moiety, which successfully localized in the mitochondria of HeLa cells in a selective way compared to L929 noncancerous fibroblast cells. These unique hydrazide–hydrazone-based biocompatible AIEgens can serve as powerful tools to illuminate multiple subcellular organelles to elucidate their forms and functions in cancer cells for next-generation biomedical applications.     

Self-oxygenated co-assembled biomimetic nanoplatform for enhanced photodynamic therapy in hypoxic tumor

Photodynamic therapy (PDT) has shown great application potential in cancer treatment and the important manifestation of PDT in the inhibition of tumors is the activation of immunogenic cell death (ICD) effects. However, the strategy is limited in the innate hypoxic tumor microenvironment. There are two key elements for the realization of enhanced PDT: specific cellular uptake and release of the photosensitizer in the tumor, and a sufficient amount of oxygen to ensure photodynamic efficiency. Herein, self-oxygenated biomimetic nanoparticles (CS@M NPs) co-assembled by photosensitizer prodrug (Ce6-S-S-LA) and squalene (SQ) were engineered. In the treatment of triple negative breast cancer (TNBC), the oxygen carried by SQ can be converted to reactive oxygen species (ROS). Meanwhile, glutathione (GSH) consumption during transformation from Ce6-S-S-LA to chlorin e6 (Ce6) avoided the depletion of ROS. The co-assembled (CS NPs) were encapsulated by homologous tumor cell membrane to improve the tumor targeting. The results showed that the ICD effect of CS@M NPs was confirmed by the significant release of calreticulin (CRT) and high mobility group protein B1 (HMGB1), and it significantly activated the immune system by inhibiting the hypoxia inducible factor-1alpha (HIF-1α)-CD39-CD73-adenosine a2a receptor (A2AR) pathway, which not only promoted the maturation of dendritic cells (DC) and the presentation of tumor specific antigens, but also induced effective immune infiltration of tumors. Overall, the integrated nanoplatform implements the concept of multiple advantages of tumor targeting, reactive drug release, and synergistic photodynamic therapy-immunotherapy, which can achieve nearly 90% tumor suppression rate in orthotopic TNBC models.     

Revealing HOCl burst from endoplasmic reticulum in cisplatin-treated cells via a ratiometric fluorescent probe

The reactive oxygen species (ROS) are tightly associated with endoplasmic reticulum (ER) stress. Thus, the deep and visual insight of aberrant ROS fluctuations in the ER can help us better investigate the ER stress-associated pathology. In this work, a fluorescent probe ERC for HOCl detection in the ER based on phenothiazine-derived coumarin platform was developed. In the presence of HOCl, ERC exhibited an emission change from 609 nm to 503 nm within seconds. It also showed high sensitivity (0.44 μmol/L) and superb photostability. Significantly, ERC displayed low cytotoxicity, good cell membrane permeability, and appreciable ER-targetability. Ultimately, the probe was successfully utilized to image exogenous and endogenous HOCl in living cells and reveal the HOCl burst in cisplatin-treated cancer cells.     

Highly efficient and photostable photosensitizer based on BODIPY chromophore

Photosensitizers are reagents that produce reactive oxygen species upon light illumination and are commonly used to study oxidative stress or for photodynamic therapy. There are many available photosensitizers, but most have limitations, such as low photostability, structural instability, or a limited usable range of solvent conditions. Here, we describe a novel photosensitizer scaffold (2I-BDP) based on the unique characteristics of the BODIPY chromophore (i.e., high extinction coefficient, high photostability, and insensitivity to solvent environment). 2I-BDP shows stronger near-infrared singlet oxygen luminescence emission and higher photostability than the well-known photosensitizer, Rose Bengal. Unlike other photosensitizers, this scaffold is widely applicable under various conditions, including lipophilic and aqueous environments. HeLa cells loaded with 2I-BDP could be photosensitized by light illumination, demonstrating that 2I-BDP is potentially useful as a reagent for cell photosensitization, oxidative stress studies, or PDT.