Controllable Coumarin-Based NIR Fluorophores: Selective Subcellular Imaging, Cell Membrane Potential Indication, and Enhanced Photodynamic Therapy

Coumarin-poly(2-oxazoline)s as synergetic and protein-undetected nanovectors for photodynamic therapy

Because of the difficult challenges of nanopharmaceutics, the development of a variety of nanovectors is still highly desired. Photodynamic therapy, which uses a photosensitizer to locally produce reactive oxygen species to kill the undesired cells, is a typical example for which encapsulation has been shown to be beneficial. The present work describes the use of coumarin-functionalized polymeric nanovectors based on the self-assembly of amphiphilic poly(2-oxazoline)s. Encapsulation of pheophorbide a, a known PDT photosensitizer, is shown to lead to an increased efficiency compared to the un-encapsulated version. Interestingly, the presence of coumarin both enhances the desired photocytotoxicity and enables the crosslinking of the vectors. Various nanovectors are examined, differing by their size, shape and hydrophilicity. Their behaviour in PDT protocols on HCT-116 cells monolayers is described, the influence of their crosslinking commented. Furthermore, the formation of a protein corona is assessed.

A dual organelle-targeting photosensitizer based on curcumin for enhanced photodynamic therapy

The efficiency of photodynamic therapy (PDT) is related to the subcellular localization of photosensitizers (PSs) because organelles are associated with many fundamental life-sustaining activities. In this work, we synthesized a PS (CN) based on curcumin (CUR) and obtained enhanced PDT efficiency by simultaneously targeting lipid droplets (LDs) and the endoplasmic reticulum (ER). Compared with CUR, CN with a D-π-A-π-D structure possessed stronger intramolecular charge transfer features, resulting in longer absorption and emission wavelengths. In cell imaging experiments of CN using a confocal laser scanning microscope, a bright green emission in LDs and a weak orange emission in the ER were simultaneously observed due to its sensitivity to polarity. Surprisingly, CN with low singlet oxygen yields (0.13) exhibited an excellent photodynamic effect. Further experimental results showed that the phototoxicity of CN resulted in apoptosis by destroying the ER and ferroptosis by oxidizing polyunsaturated fatty acids (PUFAs) in LDs. This work paves the way for developing more effective photosensitizers with superior dual-targeting specificity.

Molecular Engineering of Near-Infrared Fluorescent Probes for Cell Membrane Imaging

Cell membrane (CM) is a phospholipid bilayer that maintains integrity of a whole cell and relates to many physiological and pathological processes. Developing CM imaging tools is a feasible method for visualizing membrane-related events. In recent decades, small-molecular fluorescent probes in the near-infrared (NIR) region have been pursued extensively for CM staining to investigate its functions and related events. In this review, we summarize development of such probes from the aspect of design principles, CM-targeting mechanisms and biological applications. Moreover, at the end of this review, the challenges and future research directions in designing NIR CM-targeting probes are discussed. This review indicates that more efforts are required to design activatable NIR CM-targeting probes, easily prepared and biocompatible probes with long retention time regarding CM, super-resolution imaging probes for monitoring CM nanoscale organization and multifunctional probes with imaging and phototherapy effects.

Targeted implementation strategies of precise photodynamic therapy based on clinical and technical demands

With the development of materials science, photodynamic-based treatments have gradually entered clinics. Photodynamic therapy is ideal for cancer treatment due to its non-invasive and spatiotemporal properties and is the first to be widely promoted in clinical practice. However, the shortcomings resulting from the gap between technical and clinical demands, such as phototoxicity, low tissue permeability, and tissue hypoxia, limit its wide applications. This article reviews the available data regarding the pharmacological and clinical factors affecting the efficacy of photodynamic therapy, such as photosensitizers and oxygen supply, disease diagnosis, and other aspects of photodynamic therapy. In addition, the synergistic treatment of photodynamic therapy with surgery and nanotechnology is also discussed, which is expected to provide inspiration for the design of photodynamic therapy strategies.

An Ultrafast Fluorescent Probe for the Detection of Peroxynitrite in Living Cells

Peroxynitrite (ONOO−), a highly reactive nitrogen species, which plays a crucial role in numerous physiological and pathological processes of cell functionalization. The anomalous concentration of ONOO− may result in a range of diseases, such as arthritis, neurological disorders, and even cancer. Therefore, it is urgent to develop a simple and effective tool to monitor the fluctuation of ONOO− levels in biological systems. Herein, an ultrafast fluorescent probe (HND-ONOO) is proposed to detect ONOO−, which displays brilliant fluorescence in less than 30 s with a large Stokes shift. Furthermore, the probe exhibited the lower detection limit (48 nM) and satisfactory results in differentiating ONOO− from other related species. The probe that possesses good biocompatibility and low toxicity was employed to monitor the level of exogenous and endogenous ONOO− in living cells. Thus, the probe HND-ONOO could be served as a potential imaging tool to visualize intracellular ONOO− and understand the relationship between ONOO− and inflammation.

Fluorescence probe for selectively monitoring biothiols within cells and mouse depression diagnosis

As a global mental disorder, depression is associated with oxidative stress in the brain. Cysteine, a reductive biothiols, regulates the oxidative situation in many biological events including the stress that occurs in the tissues. Exploring the pathology and physiology of depression is still a challenge and always in an urgent need. Thus, developing a new method that could track Cys level without the interferes from other competing substances is of great importance. Herein, we developed a fluorescence probe that could selectively sensing Cys over other biothiols. Besides, we have demonstrated its desirable performance in cellular applications and mouse brain. This work provides a new method for Cys imaging and understanding pathogenesis of depression. We hope the work described here could be used as a potential chemical approach for the diagnosis of Cys associated diseases in clinical applications.

Antibacterial Theranostic Agents with Negligible Living Cell Invasiveness: AIE-Active Cationic Amphiphiles Regulated by Alkyl Chain Engineering

To address the threat of bacterial infection in the following post-antibiotic era, developing effective antibacterial approaches is of utmost urgency. Theranostic medicine integrating diagnosis and therapy is a promising protocol to fight against pathogenic bacteria. But numerous reported antibacterial theranostic materials are disclosed to be trapped in the excessive invasiveness to living mammal cells, leading to false positives and possible biosafety risks. Herein, a series of cationic pyridinium-substituted phosphindole oxide derivatives featuring aggregation-induced emission are designed, and alkyl chain engineering is conducted to finely tune their hydrophobicity and investigate their bioaffinity preference for living mammal cells and pathogenic bacteria. Most importantly, an efficient theranostic agent (PyBu-PIO) is acquired that is free from living cell invasiveness with negligible cytotoxicity and yet holds a good affinity for Gram-positive bacteria, including drug-resistant strains, with a superior inactivating effect. Externally applying PyBu-PIO onto Gram-positive bacteria-infected skin wounds can achieve creditable imaging effects and successfully accelerate the healing processes with reliable biosafety. This work proposes living cell invasiveness as a criterion for antibacterial theranostic materials and provides important enlightenment for the design of antibacterial theranostic materials.

A dual-responsive probe for the simultaneous monitoring of viscosity and peroxynitrite with different fluorescence signals in living cells

We developed a dual-responsive fluorescent probe MC-V-P for the simultaneous detection of ONOO^- and viscosity by different imaging channels. MC-V-P has high sensitivity and selectivity, and shows good stability at different pH levels. Notably, the probe has two independent fluorescence signals toward ONOO^- and viscosity changes at 580 nm and 740 nm, respectively. Cell imaging experiment results demonstrated that MC-V-P exhibits low cytotoxicity and could be used to monitor viscosity and ONOO^- in living HepG2 cells simultaneously.

New NIR spectroscopic probe with a large Stokes shift for Hg2+ and Ag+ detection and living cells imaging

A new near-infrared (NIR) probe based on a coumarinyl ligand (CL) was designed and synthesized. The probe CL can be used for simultaneous fluorescent turn-on and colorimetric detection of Hg²⁺ and Ag⁺ in ethanol/water medium. Colorless solution of probe CL changed to light yellow or dark yellow after addition of Hg²⁺ or Ag⁺ ions. Meanwhile the maximum absorption band shifted from 379 nm to 404 nm and the intensity increased enormously (for Hg²⁺) or moderately (for Ag⁺). Probe CL displayed an extraordinarily large Stokes shift of 316 nm and addition of Hg²⁺ or Ag⁺ to probe CL induced enhancement in the intensity of fluorescence emission at 695 nm by 15 or 8 fold. The detection limit of CL for Hg²⁺ and Ag⁺ ions is 0.83 and 8.8 μM, respectively. The applicable pH for sensing Hg²⁺ by probe CL is in a broad range of 2-12. Application of probe CL for in vitro U87MG cell imaging to detect Hg²⁺ ions was confirmed.

Liposome-Based Nanoencapsulation of a Mitochondria-Stapling Photosensitizer for Efficient Photodynamic Therapy

Mitochondria-targeting photodynamic therapy (PDT) can block mitochondrial function and trigger the inherent proapoptotic cascade signal of mitochondria, which has been considered to have the potential to amplify the efficiency of PDT. However, the dynamic change of mitochondrial membrane potential (MMP) makes most cationic photosensitizers easily fall off from the mitochondria, which greatly limits the efficiency of PDT. Here, we have developed a smart liposome encapsulation method based on a mitochondria-stapling photosensitizer for efficient theranostic photodynamic therapy. The stapling photosensitizer can be covalently bound inside mitochondria via two reaction sites without a falloff effect, regardless of the change of MMP. As a result, the liposome-based nanophotosensitizer showed a high efficiency of PDT (IC₅₀ = 0.98 μM) under 630 nm light. At the same time, the nanophotosensitizer had fluorescence imaging-guided ability to monitor abnormal mitochondrial morphology during PDT. Importantly, the results of mice experiments also showed that the liposome-based nanophotosensitizer possessed excellent antitumor PDT activity because the released photosensitizer can stay inside mitochondria during the whole process of PDT.

Monitoring thiophenols in both environmental water samples and bio-samples: A method based on a fluorescent probe with broad pH adaptation

Thiophenol, which is a highly toxic sulfhydryl compound widely used in chemical industry, is an environmental pollutant that threatens human health significantly. It is of great importance to detect highly toxic thiophenols in both environmental and biological system. Thus, the need to develop rapid response, selective and sensitive probes is urgent. In this study, a novel probe was presented for the detection of thiophenols based on an intramolecular charge transfer (ICT) mechanism. This probe exhibits rapid response, broad pH adaptation (2-10), highly selectivity, a large Stokes shift (131 nm) and 40-fold enhancement in fluorescence. Besides, this probe showed low toxicity towards human cell HEK293 and could be applied to detect thiophenol both in living cells, zebrafish and environmental water samples with good recovery (over 94%). All the results indicated that this probe could be a promising sensor for applications for thiophenol derivatives detection in both environmental and biological sciences.

Rhenium-guanidine complex as photosensitizer: trigger HeLa cell apoptosis through death receptor-mediated, mitochondria-mediated and cell cycle arrest pathways

During the last decades, growing evidence indicates that the photodynamic antitumor activity of transition metal complexes, and Re(I) compounds are potential candidates for photodynamic therapy (PDT). This study reports the synthesis, characterization, and anti-tumor activity of three new Re(I)-guadinium complexes. Cytotoxicity tests reveal that complex Re1 increased cytotoxicity by 145-fold from IC50 > 180 μM in the dark to 1.3 ± 0.7 μM following 10 min of light irradiation (425 nm) in HeLa cells. Further, the mechanism by which Re1 induces apoptosis in the presence or absence of light irradiation was investigated, and results indicate that cell death was caused through different pathways. Upon irradiation, Re1 first accumulates on the cell membrane and interacts with death receptors to activate the extrinsic death receptor-mediated signaling pathway, then is transported into the cell cytoplasm. Most of the intracellular Re1 locates within mitochondria, improving the ROS level, and decreasing MMP and ATP levels, and inducing the activation of caspase-9 and, thus, apoptosis. Subsequently, the residual Re1 can translocate into the cell nucleus, and activates the p53 pathway, causing cell-cycle arrest and eventually cell death.

A coumarin based fluorescent probe for NIR imaging guided photodynamic therapy against S. aureus-induced infection in mice models

A coumarin based and viscosity responsive fluorescent probe (HZAU800) was designed and synthesized. The probe, containing a strong electron-donating and rigid group on 7-position of coumarin, and a rhodamine derivative...

COUPY Coumarins as Novel Mitochondria-Targeted Photodynamic Therapy Anticancer Agents

Photodynamic therapy (PDT) for cancer treatment has drawn increased attention over the last decades. Herein, we introduce a novel family of low-molecular-weight coumarins as potential PDT anticancer tools. Through a systematic study with a library of 15 compounds, we have established a detailed structure-activity relationship rationale, which allowed the selection of three lead compounds exhibiting effective in vitro anticancer activities upon visible-light irradiation in both normoxia and hypoxia (phototherapeutic indexes up to 71) and minimal toxicity toward normal cells. Acting as excellent theranostic agents targeting mitochondria, the mechanism of action of the photosensitizers has been investigated in detail in HeLa cells. The generation of cytotoxic reactive oxygen species, which has been found to be a major contributor of the coumarins' phototoxicity, and the induction of apoptosis and/or autophagy have been identified as the cell death modes triggered after irradiation with low doses of visible light.

Recent Strategies to Develop Innovative Photosensitizers for Enhanced Photodynamic Therapy

This review presents a robust strategy to design photosensitizers (PSs) for various species. Photodynamic therapy (PDT) is a photochemical-based treatment approach that involves the use of light combined with a light-activated chemical, referred to as a PS. Attractively, PDT is one of the alternatives to conventional cancer treatment due to its noninvasive nature, high cure rates, and low side effects. PSs play an important factor in photoinduced reactive oxygen species (ROS) generation. Although the concept of photosensitizer-based photodynamic therapy has been widely adopted for clinical trials and bioimaging, until now, to our surprise, there has been no relevant review article on rational designs of organic PSs for PDT. Furthermore, most of published review articles in PDT focused on nanomaterials and nanotechnology based on traditional PSs. Therefore, this review aimed at reporting recent strategies to develop innovative organic photosensitizers for enhanced photodynamic therapy, with each example described in detail instead of providing only a general overview, as is typically done in previous reviews of PDT, to provide intuitive, vivid, and specific insights to the readers.

Real-time imaging mitochondrial viscosity dynamic during mitophagy mediated by photodynamic therapy

Photodynamic therapy has been generally developed and approved as a promising theranostic technique in recent years, which requires photosensitizers to bear high efficiency of reactive oxygen species production, precisely targeting ability and excellent biocompatibility. The real-time monitoring the microenvironments such as viscosity dynamic involved in mitophagy mediated by photodynamic therapy is significantly important to understand therapeutic process but barely reported. In this work, a pyridinium-functionalized triphenylamine derivative, (E)-4-(2-(4'-(diphenylamino)-[1,1'-biphenyl]-4-yl)vinyl)-1-methylpyridin-1-ium iodide (Mito-I), was exploited as photosensitizer for mitochondria-targeted photodynamic therapy and as fluorescent probe for imaging the mitochondrial viscosity dynamic during mitophagy simultaneously. The results indicated that the additional phenyl ring in Mito-I was beneficial to promote its efficiency of singlet oxygen production. The excellent capability of targeting mitochondria and singlet oxygen generation allowed Mito-I for the specifically mitochondria-targeted photodynamic therapy. Moreover, Mito-I displayed off-on fluorescence response to viscosity with high selectivity and sensitivity. The observed enhancement in fluorescence intensity of Mito-I revealed the increasingly mitochondrial viscosity during mitophagy mediated by the photodynamic therapy of Mito-I. As a result, this work presents a rare example to realize the mitochondria-targeting photodynamic therapy as well as the real-time monitoring viscosity dynamic during mitophagy, which is of great importance for the basic medical research involved in photodynamic therapy.

Mitochondria-Inspired Nanoparticles with Microenvironment-Adapting Capacities for On-Demand Drug Delivery after Ischemic Injury

Stimuli-responsive nanoparticles (NPs), so-called "smart" NPs, possess great potentials in drug delivery. Presently, the intelligence of smart NPs is mainly based on their chemical or physical changes to stimuli, which are usually "mechanical" and fundamentally different from biological intelligence. Inspired by mitochondria (MT), a biosmart nanoparticle with microenvironment targeting and self-adaptive capacity (MTSNP) was fabricated for ischemic tissue repair. The nanoparticles were designed as shell@circular DNA@shell@core. The double shells were like the two-layered membranes of MT, the melatonin-loaded cores corresponded to the MT matrix, and the circular DNA corresponded to MTDNA. In function, melatonin-loaded cores simulated the cell-protective mechanism of MT, which naturally synthesized melatonin to resist ischemia, while circular DNA was constructed to mimic the biological oxygen-sensing mechanism, synthesizing VEGF for vascularization according to oxygen level, like the ATP supply by MT according to microenvironment demand. At the acute stage of ischemia, melatonin was rapidly released from MTSNP to scavenge reactive oxygen species and activated melatonin receptor I on MT to prevent cytochrome c release, which would activate apoptosis. During the chronic stage, circular DNA could sense hypoxia and actively secrete VEGF for revascularization as a response. Importantly, circular DNA could also receive feedback of revascularization and shut down VEGF secretion as an adverse response. Then, the therapeutic potentials of the MTSNP were verified in myocardial ischemia by the multimodality of the methods. Such nanoparticles may represent a promising intelligent nanodrug system.

Beyond Antibiotics: Photo/Sonodynamic Approaches for Bacterial Theranostics

Rapid evolution and propagation of multidrug resistance among bacterial pathogens are outpacing the development of new antibiotics, but antimicrobial photodynamic therapy (aPDT) provides an excellent alternative. This treatment depends on the interaction between light and photoactivated sensitizer to generate reactive oxygen species (ROS), which are highly cytotoxic to induce apoptosis in virtually all microorganisms without resistance concern. When replacing light with low-frequency ultrasonic wave to activate sensitizer, a novel ultrasound-driven treatment emerges as antimicrobial sonodynamic therapy (aSDT). Recent advances in aPDT and aSDT reveal golden opportunities for the management of multidrug resistant bacterial infections, especially in the theranostic application where imaging diagnosis can be accomplished facilely with the inherent optical characteristics of sensitizers, and the generated ROS by aPDT/SDT cause broad-spectrum oxidative damage for sterilization. In this review, we systemically outline the mechanisms, targets, and current progress of aPDT/SDT for bacterial theranostic application. Furthermore, potential limitations and future perspectives are also highlighted.