Chemiluminescent Probe for the In Vitro and In Vivo Imaging of Cancers Over-Expressing NQO1

Catalytic NIR chemiluminescence sensor with enhanced persistence and intensity for in vivo imaging

Chemiluminescence (CL) is a self-illumination phenomenon that involves the emission of light from chemical reactions, and it provides favorable spatial and temporal information on biological processes. However, it is still a great challenge to construct effective CL sensors that equip strong CL intensity, long emission wavelength, and persistent luminescence for deep tissue imaging. Here, we report a liposome encapsulated polymer dots (Pdots)-based system using catalytic CL substrates (L-012) as energy donor and fluorescent polymers and dyes (NIR 695) as energy acceptors for efficient Near-infrared (NIR) CL in vivo imaging. Thanks to the modulation of paired donor and acceptor distance and the slow diffusion of biomarker by liposome, the Pdots show a NIR emission wavelength (λ em, max = 720 nm), long CL duration (>24 h), and a high chemiluminescence resonance energy transfer efficiency (46.5 %). Furthermore, the liposome encapsulated Pdots possess excellent biocompatibility, sensitive response to H2O2, and persistent whole-body NIR CL imaging in the drug-induced inflammation and the peritoneal metastatic tumor mouse model. In a word, this NIR-II CL nanoplatform with long-lasting emission and high spatial-temporal resolution will be a concise strategy in deep tissue imaging and clinical diagnostics.

Dual-Locked Fluorescent Probes Activated by Aminopeptidase N and the Tumor Redox Environment for High-Precision Imaging of Tumor Boundaries

Clear delineation of tumor margins is essential for accurate resection and decreased recurrence rate in the clinic. Fluorescence imaging is emerging as a promising alternative to traditional visual inspection by surgeons for intraoperative imaging. However, traditional probes lack accuracy in tumor diagnosis, making it difficult to depict tumor boundaries accurately. Herein, we proposed an offensive and defensive integration (ODI) strategy based on the "attack systems (invasive peptidase) and defense systems (reductive microenvironment)" of multi-dimensional tumor characteristics to design activatable fluorescent probes for imaging tumor boundaries precisely. Screened out from a series of ODI strategy-based probes, ANQ performed better than traditional probes based on tumor unilateral correlation by distinguishing between tumor cells and normal cells and minimizing false-positive signals from living metabolic organs. To further improve the signal-to-background ratio in vivo, derivatized FANQ, was prepared and successfully applied to distinguish orthotopic hepatocellular carcinoma tissues from adjacent tissues in mice models and clinical samples. This work highlights an innovative strategy to develop activatable probes for rapid diagnosis of tumors and high-precision imaging of tumor boundaries, providing more efficient tools for future clinical applications in intraoperative assisted resection.

A Self-Sustaining Near-Infrared Afterglow Chemiluminophore for High-Contrast Activatable Imaging

Afterglow imaging holds great promise for ultrasensitive bioimaging due to its elimination of autofluorescence. Self-sustaining afterglow molecules (SAMs), which enable all-in-one photon sensitization, chemical defect formation and afterglow generation, possess a simplified, reproducible, and efficient superiority over commonly used multi-component systems. However, there is a lack of SAMs, particularly those with much brighter near-infrared (NIR) emission and structural flexibility for building high-contrast activatable imaging probes. To address these issues, this study for the first time reports a methylene blue derivative-based self-sustaining afterglow agent (SAN-M) with brighter NIR afterglow chemiluminescence peaking at 710 nm. By leveraging the structural flexibility and tunability, an activatable nanoprobe (SAN-MO) is customized for simultaneously activatable fluoro-photoacoustic and afterglow imaging of peroxynitrite (ONOO- ), notably with a superior activation ratio of 4523 in the afterglow mode, which is at least an order of magnitude higher than other reported activatable afterglow systems. By virtue of the elimination of autofluorescence and ultrahigh activation contrast, SAN-MO enables early monitoring of the LPS-induced acute inflammatory response within 30 min upon LPS stimulation and precise image-guided resection of tiny metastatic tumors, which is unattainable for fluorescence imaging.

Enzymatic Activity Profiling Using an Ultrasensitive Array of Chemiluminescent Probes for Bacterial Classification and Characterization

Identification and characterization of bacterial species in clinical and industrial settings necessitate the use of diverse, labor-intensive, and time-consuming protocols as well as the utilization of expensive and high-maintenance equipment. Furthermore, while cutting-edge identification technologies such as mass spectrometry and PCR are highly effective in identifying bacterial pathogens, they fall short in providing additional information for identifying bacteria not present in the databases upon which these methods rely. In response to these challenges, we present a robust and general approach to bacterial identification based on their unique enzymatic activity profiles. This method delivers results within 90 min, utilizing an array of highly sensitive and enzyme-selective chemiluminescent probes. Leveraging our recently developed technology of chemiluminescent luminophores, which emit light under physiological conditions, we have crafted an array of probes designed to rapidly detect various bacterial enzymatic activities. The array includes probes for detecting resistance to the important and large class of β-lactam antibiotics. The analysis of chemiluminescent fingerprints from a diverse range of prominent bacterial pathogens unveiled distinct enzymatic activity profiles for each strain. The reported universally applicable identification procedure offers a highly sensitive and expeditious means to delineate bacterial enzymatic activity fingerprints. This opens new avenues for characterizing and identifying pathogens in research, clinical, and industrial applications.

A COX2-targeting cancer-specific fluorescent probe for hydrogen sulfide detection in living cells, Caenorhabditis elegans, and zebrafish

A novel cyclooxygenase-2 (COX-2) targeted H2S-activated cancer-specific fluorescent probe, namely, COX2-H2S, was designed and synthesized, with naphthalimide as the fluorophore and indomethacin as the targeting group. This H2S-sensing probe was developed to differentiate tumor cells from normal cells and was tested in living cells, Caenorhabditis elegans (C. elegans), and zebrafish. The probe could successfully be used for imaging endogenous and exogenous H2S in living cells, demonstrating high sensitivity and specificity and strong anti-interference. COX2-H2S had the ability to not only discern cancer cells from normal cells but also specifically recognize 9L/lacZ cells from other glioblastoma cells (U87-MG and LN229). It could also be successfully applied for the fluorescent live imaging of H2S in both C. elegans and zebrafish.

Molecularly generated light and its biomedical applications

Molecularly generated light, referred to here as "molecular light", mainly includes bioluminescence, chemiluminescence, and Cerenkov luminescence. Molecular light possesses unique dual features of being both a molecule and a source of light. Its molecular nature enables it to be delivered as molecules to regions deep within the body, overcoming the limitations of natural sunlight and physically generated light sources like lasers and LEDs. Simultaneously, its light properties make it valuable for applications such as imaging, photodynamic therapy, photo-oxidative therapy, and photobiomodulation. In this review article, we provide an updated overview of the diverse applications of molecular light and discuss the strengths and weaknesses of molecular light across various domains. Lastly, we present forward-looking perspectives on the potential of molecular light in the realms of molecular imaging, photobiological mechanisms, therapeutic applications, and photobiomodulation. While some of these perspectives may be considered bold and contentious, our intent is to inspire further innovations in the field of molecular light applications.

Spirostrain-Accelerated Chemiexcitation of Dioxetanes Yields Unprecedented Detection Sensitivity in Chemiluminescence Bioassays

Chemiluminescence is a fascinating phenomenon that involves the generation of light through chemical reactions. The light emission from adamantyl-phenoxy-1,2-dioxetanes can glow from minutes to hours depending on the specific substituent present on the dioxetane molecule. In order to improve the light emission properties produced by these chemiluminescent luminophores, it is necessary to induce the chemiexcitation rate to a flash mode, wherein the bulk of light is emitted instantly rather than slowly over time. We report the realization of this goal through the incorporation of spirostrain release into the decomposition of 1,2-dioxetane luminophores. DFT computational simulations provided support for the hypothesis that the spiro-cyclobutyl substituent accelerates chemiexcitation as compared to the unstrained adamantyl substituent. Spiro-linking of cyclobutane and oxetane units led to greater than 100-fold and 1000-fold emission enhancement, respectively. This accelerated chemiexcitation rate increases the detection sensitivity for known chemiluminescent probes to the highest signal-to-noise ratio documented to date. A turn-ON probe, containing a spiro-cyclobutyl unit, for detecting the enzyme β-galactosidase exhibited a limit of detection value that is 125-fold more sensitive than that for the previously described adamantyl analogue. This probe was also able to instantly detect and image β-gal activity with enhanced sensitivity in E. coli bacterial assays.

π-π Interaction-Induced Organic Long-wavelength Room-Temperature Phosphorescence for In Vivo Atherosclerotic Plaque Imaging

Room-temperature phosphorescent (RTP) materials have great potential for in vivo imaging because they can circumvent the autofluorescence of biological tissues. In this study, a class of organic-doped long-wavelength (≈600 nm) RTP materials with benzo[c][1,2,5] thiadiazole as a guest was constructed. Both host and guest molecules have simple structures and can be directly purchased commercially at a low cost. Owing to the long phosphorescence wavelength of the doping system, it exhibited good tissue penetration (10 mm). Notably, these RTP nanoparticles were successfully used to image atherosclerotic plaques, with a signal-to-background ratio (SBR) of 44.52. This study provides a new approach for constructing inexpensive red organic phosphorescent materials and a new method for imaging cardiovascular diseases using these materials.

Singlet Oxygen Detection by Chemiluminescence Probes in Living Cells

Singlet oxygen is a reactive oxygen species that causes oxidative damage to plant cells, but intriguingly it can also act as a signalling molecule to reprogram gene expression required to induce plant physiological/cellular responses. Singlet oxygen photosensitization in plants mainly occurs in chloroplasts after the molecular collision of ground-state molecular oxygen with triplet-excited-state chlorophyll. Singlet oxygen direct detection through phosphorescence emission in chloroplasts is a herculean task due to its extremely low luminescence quantum yield. Because of this, indirect alternative methods have been developed for its detection in biological systems, for example, by measuring the changes in the EPR signal or fluorescence intensity of singlet oxygen reaction-based probes. The singlet oxygen chemiluminescence (SOCL) is a chemiluminescence probe with high sensitivity and selectivity towards singlet oxygen and promising use to detect it in living cells without the inconvenience of low stability of the EPR signal of spin probes in the presence of redox compounds, spurious light scattering coming from the light source required for the excitation of fluorescence probes or the light emission of endogenous fluorescent molecules like chlorophyll in chloroplasts. The protocol presented in this chapter describes the first steps to characterizing singlet oxygen production within the biological system under study; this is accomplished through monitoring molecular oxygen consumption by SOCL using a Clark-type oxygen electrode and measuring the chemiluminescence generated by SOCL 1,2-dioxetane using a spectrofluorometer. For singlet oxygen detection within living cells, a version of SOCL with increased membrane permeability (SOCL-CPP) is described.

Cell-Specific Degradation of Histone Deacetylase Using Warhead-Caged Proteolysis Targeting Chimeras

Proteolysis targeting chimeras (PROTACs) have shifted the paradigm for drug development via target protein degradation. However, PROTACs may exhibit systemic toxicity to normal cells due to indiscriminate degradation and the utility of inhibitors as a warhead for protein targeting. Here, we propose a new strategy for developing activatable PROTACs for cell-specific degradation of histone deacetylase (HDAC) with minimal side effects via caging of the warhead. Molecular docking reveals that the hydroxyl group of the HDAC inhibitor is crucial for targeting. An enzyme-activatable PROTAC is designed by caging the hydroxyl group with the substrate for NAD(P)H: quinone oxidoreductase 1 (NQO1) overexpressed in cancer cells. We demonstrate that the caged PROTAC can be converted to its active form in response to NQO1. The enzyme-activatable PROTAC allows the efficient and specific degradation of HDAC6 and exerts antiproliferative activity in NQO1-positive cells. The generalizability of the design is further demonstrated by engineering a H2O2-responsive PROTAC for specific degradation of HDAC6 in cells with elevated H2O2. The strategy of caging the ligand for target proteins would afford a new dimension for developing activatable PROTACs with high specificity and minimal side effects.

Tumor Abnormality-Oriented Nanomedicine Design

Anticancer nanomedicines have been proven effective in mitigating the side effects of chemotherapeutic drugs. However, challenges remain in augmenting their therapeutic efficacy. Nanomedicines responsive to the pathological abnormalities in the tumor microenvironment (TME) are expected to overcome the biological limitations of conventional nanomedicines, enhance the therapeutic efficacies, and further reduce the side effects. This Review aims to quantitate the various pathological abnormalities in the TME, which may serve as unique endogenous stimuli for the design of stimuli-responsive nanomedicines, and to provide a broad and objective perspective on the current understanding of stimuli-responsive nanomedicines for cancer treatment. We dissect the typical transport process and barriers of cancer drug delivery, highlight the key design principles of stimuli-responsive nanomedicines designed to tackle the series of barriers in the typical drug delivery process, and discuss the "all-into-one" and "one-for-all" strategies for integrating the needed properties for nanomedicines. Ultimately, we provide insight into the challenges and future perspectives toward the clinical translation of stimuli-responsive nanomedicines.

Chemiluminescent duplex analysis using phenoxy-1,2-dioxetane luminophores with color modulation

Multiplex technology is an important emerging field, in diagnostic sciences, that enables the simultaneous detection of several analytes in a single sample. The light-emission spectrum of a chemiluminescent phenoxy-dioxetane luminophore can be accurately predicted by determining the fluorescence-emission spectrum of its corresponding benzoate species, which is generated during the chemiexcitation process. Based on this observation, we designed a library of chemiluminescent dioxetane luminophores with multicolor emission wavelengths. Two dioxetane luminophores that have different emission spectra, but similar quantum yield properties, were selected from the synthesized library for a duplex analysis. The selected dioxetane luminophores were equipped with two different enzymatic substrates to generate turn-ON chemiluminescent probes. This pair of probes exhibited a promising ability to act as a chemiluminescent duplex system for the simultaneous detection of two different enzymatic activities in a physiological solution. In addition, the pair of probes were also able to simultaneously detect the activities of the two enzymes in a bacterial assay, using a blue filter slit for one enzyme and a red filter slit for the other enzyme. As far as we know, this is the first successful demonstration of a chemiluminescent duplex system composed of two-color phenoxy-1,2-dioxetane luminophores. We believe that the library of dioxetanes presented here will be beneficial for developing chemiluminescence luminophores for multiplex analysis of enzymes and bioanalytes.

A Novel NQO1 Enzyme-Responsive Polyurethane Nanocarrier for Redox-Triggered Intracellular Drug Release

The design of nano-drug delivery vehicles responsive to tumor microenvironment stimuli has become a crucial aspect in developing cancer therapy in recent years. Among them, the enzyme-responsive nano-drug delivery system is particularly effective, as it utilizes tumor-specific and highly expressed enzymes as precise targets, leading to increased drug release at the target sites, reduced nonspecific release, and improved efficacy while minimizing toxic side effects on normal tissues. NAD(P)H:quinone oxidoreductase 1 (NQO1) is an important reductase associated with cancer and is overexpressed in some cancer cells, particularly in lung and breast cancer. Thus, the design of nanocarriers with high selectivity and responsiveness to NQO1 is of great significance for tumor diagnosis and treatment. It has been reported that under physiological conditions, NQO1 can specifically reduce the trimethyl-locked benzoquinone structure through a two-electron reduction, resulting in rapid lactonization via an enzymatic reaction. Based on this, a novel reduction-sensitive polyurethane (PEG-PTU-PEG) block copolymer was designed and synthesized by copolymerizing diisocyanate, a reduction-sensitive monomer (TMBQ), and poly(ethylene glycol). The successful synthesis of monomers and polymers was verified by nuclear magnetic resonance (¹H NMR) and gel permeation chromatography (GPC). Then, the PEG-PTU-PEG micelles were successfully prepared by self-assembly, and their reductive dissociation behavior in the presence of Na₂S₂O₄ was verified by dynamic light scattering (DLS), ¹H NMR, and GPC. Next, the model drug doxorubicin (DOX) was encapsulated into the hydrophobic core of this polyurethane micelles by microemulsion method. It was observed that the drug-loaded micelles could also achieve a redox response and rapidly release the encapsulated substances. In vitro cell experiments demonstrated that PEG-PTU-PEG micelles had good biocompatibility and a low hemolysis rate (<5%). Furthermore, in the presence of an NQO1 enzyme inhibitor (dicoumarol), lower drug release from micelles was observed in A549 and 4T1 cells by both fluorescence microscopy and flow cytometry assays, but not in NIH-3T3 control cells. Predictably, DOX-loaded micelles also showed lower cytotoxicity in 4T1 cells in the presence of NQO1 enzyme inhibitors. These results indicate that drug-loaded polyurethane micelles could accomplish specific drug release in the reducing environment in the presence of NQO1 enzymes. Therefore, this study provides a new option for the construction of polyurethane nanocarriers for precise targeting and reductive release, which could benefit the intracellular drug-specific release and precision therapy of tumors.

Fluorogenic Granzyme A Substrates Enable Real-Time Imaging of Adaptive Immune Cell Activity

Cytotoxic immune cells, including T lymphocytes (CTLs) and natural killer (NK) cells, are essential components of the host response against tumors. CTLs and NK cells secrete granzyme A (GzmA) upon recognition of cancer cells; however, there are very few tools that can detect physiological levels of active GzmA with high spatiotemporal resolution. Herein, we report the rational design of the near-infrared fluorogenic substrates for human GzmA and mouse GzmA. These activity-based probes display very high catalytic efficiency and selectivity over other granzymes, as shown in tissue lysates from wild-type and GzmA knock-out mice. Furthermore, we demonstrate that the probes can image how adaptive immune cells respond to antigen-driven recognition of cancer cells in real time.

Fluorogenic Granzyme A Substrates Enable Real-Time Imaging of Adaptive Immune Cell Activity

Cytotoxic immune cells, including T lymphocytes (CTLs) and natural killer (NK) cells, are essential components of the host response against tumors. CTLs and NK cells secrete granzyme A (GzmA) upon recognition of cancer cells; however, there are very few tools that can detect physiological levels of active GzmA with high spatiotemporal resolution. Herein, we report the rational design of the near-infrared fluorogenic substrates for human GzmA and mouse GzmA. These activity-based probes display very high catalytic efficiency and selectivity over other granzymes, as shown in tissue lysates from wild-type and GzmA knock-out mice. Furthermore, we demonstrate that the probes can image how adaptive immune cells respond to antigen-driven recognition of cancer cells in real time.

Dual Chemiexcitation by a Unique Dioxetane Scaffold Gated by an OR Logic Set of Triggers

Chemiexcitation of phenoxy-1,2-dioxetane chemiluminescent luminophores is initiated by electron transfer from a meta-positioned phenolate ion to the peroxide-dioxetane bond. Here we report the development of a unique 1,2-dioxetane chemiluminescent scaffold with chemiexcitation gated by an OR logic dual-set of triggering events. This scaffold is composed of meta-dihydroxyphenyl-1,2-dioxetane-adamantyl molecules, equipped with acrylic acid and chlorine substituents, that chemiexcitation under physiological conditions. A dual-mode chemiluminescent probe, armed with two different triggering substrates designed for activation by the enzymes β-galactosidase and alkaline phosphatase, was synthesized. The probe emitted intense light signals in the response to each enzyme, demonstrating its ability to serve as a single-component chemiluminescent sensor for dual-analyte detection. We also demonstrated the ability of the probe to detect β-galactosidase and phosphatase activities in bacteria. This is the first 1,2-dioxetane scaffold capable of responding to two different chemiexcitation events from two different positions on the same dioxetane molecule. We anticipate that the OR-gated mode of chemiexcitation, described herein, will find utility in the preparation of chemiluminescent probes with a dual-analyte detection/imaging mode.

A DNA origami nanostructure embedded with NQO1-activated prodrugs for precision drug delivery

A rectangle DNA origami nanostructure equipped with doxorubicin-derived prodrugs targeting a tumor cell-specific enzyme (NQO1) is constructed. Combining the high prodrug payload of DNA origami and NQO1-activated chemotherapy, this nanosystem presents therapeutic selectivity for NQO1-overexpressing MCF-7 cells over healthy L02 cells, offering a potent strategy for precision cancer therapy.

PROTAC Nanoplatform with Targeted Degradation of NAD(P)H:Quinone Oxidoreductase 1 to Enhance Reactive Oxygen Species-Mediated Apoptosis

Apoptosis mediated by reactive oxygen species (ROS) has emerged as a promising therapeutic strategy for tumors. However, the overexpression of NAD(P)H:quinone oxidoreductase 1 (NQO1) protein restricted ROS production through a negative feedback pathway in tumor cells, promoting tumor progression, and weakening the effect of drug therapy. Here, a PROTACs nanodrug delivery system (PN) was constructed to increase ROS generation by degrading the NQO1 protein. Specifically, a PROTAC (proteolytic targeting chimera) molecule DQ was designed and synthesized. Then DQ and withaferin A (WA, an inducer of ROS) were loaded into PNs. DQ degraded the overexpressed NQO1 protein in tumor cells through a protein ubiquitination degradation pathway, thereby weakening the antioxidant capacity of tumor cells. Meanwhile, the reduction of NQO1 could inhibit the negative feedback effect of ROS production, thus increasing ROS generation. It has been demonstrated that PNs can significantly increase ROS production and possess potent antitumor properties in vitro and in vivo. This nanoplatform may offer an alternative approach to treating tumors with NQO1 overexpression.

Fluorescence probes for lung carcinoma diagnosis and clinical application

This review provides an overview of the most recent developments in fluorescence probe technology for the accurate detection and clinical therapy of lung carcinoma.

β-Lactamase-Mediated Fragmentation: Historical Perspectives and Recent Advances in Diagnostics, Imaging, and Antibacterial Design

The discovery of β-lactam (BL) antibiotics in the early 20th century represented a remarkable advancement in human medicine, allowing for the widespread treatment of infectious diseases that had plagued humanity throughout history. Yet, this triumph was followed closely by the emergence of β-lactamase (BLase), a bacterial weapon to destroy BLs. BLase production is a primary mechanism of resistance to BL antibiotics, and the spread of new homologues with expanded hydrolytic activity represents a pressing threat to global health. Nonetheless, researchers have developed strategies that take advantage of this defense mechanism, exploiting BLase activity in the creation of probes, diagnostic tools, and even novel antibiotics selective for resistant organisms. Early discoveries in the 1960s and 1970s demonstrating that certain BLs expel a leaving group upon BLase cleavage have spawned an entire field dedicated to employing this selective release mechanism, termed BLase-mediated fragmentation. Chemical probes have been developed for imaging and studying BLase-expressing organisms in the laboratory and diagnosing BL-resistant infections in the clinic. Perhaps most promising, new antibiotics have been developed that use BLase-mediated fragmentation to selectively release cytotoxic chemical "warheads" at the site of infection, reducing off-target effects and allowing for the repurposing of putative antibiotics against resistant organisms. This Review will provide some historical background to the emergence of this field and highlight some exciting recent reports that demonstrate the promise of this unique release mechanism.

Cancer therapeutics based on diverse energy sources

Light-based phototherapy has been developed for cancer treatment owing to its non-invasiveness and spatiotemporal control. Despite the unique merits of phototherapy, one critical disadvantage of light is its limited penetration depth, which restricts its application in cancer treatment. Although many researchers have developed various strategies to deliver light into deep-seated tumors with two-photon and near-infrared light irradiation, phototherapy encounters the peculiar limitations of light. In addition, high oxygen dependency is another limitation of photodynamic therapy to treat hypoxic tumors. To overcome the drawbacks of conventional treatments, various energy sources have been developed for cancer treatment. Generally, most energy sources, such as ultrasound, chemiluminescence, radiation, microwave, electricity, and magnetic field, are relatively free from the restraint of penetration depth. Combining other strategies or therapies with other energy-source-based therapies improves the strength and compensates for the weakness. This tutorial review focuses on recent advances in the diverse energy sources utilized in cancer treatment and their future perspectives.

Small-Molecules as Chemiluminescent Probes to Detect Lipase Activity

The set-up of highly sensitive detection tools to evaluate lipase activity remains a central goal in different fields. In this context, we proposed new chemiluminescent 1,2-dioxetane luminophores, sharing an octanoyl triggerable group, to monitor lipase activity. We herein report the synthesis and both the evaluation of their luminescence emission profile and their enzyme-substrate specificity, generated by three different commercial lipases (Candida cylindracea, Pseudomonas fluorescens, and Mucor miehei) and one esterase (porcine liver esterase, PLE, as a literature control). Remarkably, the present study confirmed the applicability of these 1,2-dioxetane luminophores as (i) highly efficient, broad-range, chemiluminescent probes for the detection and the enzymatic activity evaluation of lipases and as (ii) promising candidates for the future development of both flash- and glow-type luminescence assays.

Immunosonodynamic Therapy Designed with Activatable Sonosensitizer and Immune Stimulant Imiquimod

Sonodynamic therapy (SDT) has garnered extensive attention as a noninvasive treatment for deep tumors. Furthermore, imiquimod (R837), an FDA-approved toll-like receptor 7 agonist, is commonly used in clinical settings as an immune adjuvant. We prepared an activatable sonodynamic sensitizer platform (MR) based on glutathione-sensitive disulfide bonds linking Leu-MB, the reduced form of methylene blue (MB), and R837 to achieve efficient combinatory SDT and immunotherapy for tumors without harming normal tissues. We also used the amphiphilic polymer C₁₈PMH-PEG to create self-assembled MB-R837-PEG (MRP) nanoparticles for immunosonodynamic therapy (iSDT). iSDT is a cancer treatment that combines activatable SDT and immunotherapy. Our iSDT demonstrated an excellent sonodynamic effect only at the tumor site, demonstrating high specificity in killing tumor cells when compared to SDT reported in the literature. The iSDT improves its tumor-killing effect by inducing an immune response, which is accomplished by secreted immune adjuvants in the tumor site. MRP was selectively activated by glutathione in the tumor microenvironment to release MB and R837, exhibiting excellent antitumor sonodynamic and immune responses. In addition, when combined with an α-PD-L1 antibody for immune checkpoint blockade, this therapy effectively inhibited tumor metastasis. Furthermore, mice treated with iSDT and α-PD-L1 antibody did not develop tumors even after tumor reinoculation, indicating that long-term immune memory was achieved. The concept of sonodynamic sensitizer preparation as a next-generation iSDT based on a noninvasive synergistic therapeutic modality applicable in the near future is presented in this study.

Ultrasound-Responsive Peptide Nanogels to Balance Conflicting Requirements for Deep Tumor Penetration and Prolonged Blood Circulation

A series of biological barriers need to be overcome for therapeutic nanocarriers accumulating at the tumor site and uptaken by cancer cells. One strategy is to construct switchable nanocarriers to meet the conflicting requirements for various physiology environments. In this work, besides widely studied endogenous stimuli-responsiveness, an exogenous ultrasound responsiveness was additionally embedded into nanocarriers to balance the conflicting needs of prolonged blood circulation and deep tumor penetration. Polylysine and Pluronic F127 were first coassembled and then cross-linked by genipin to form stable nanogel structure. Subsequently, ICAM-1 antibody was grafted onto the nanogel (designated as GenPLPF_T) for active tumor targeting. Upon external sonication, the F127 was shed from GenPLPF_T to induce swelling of nanogel with reduced stability and accelerated drug release. In detail, sonication leads to GenPLPF swelling from 329 to 516 nm, while its Young's modulus significantly decreased from 336.78 to 3.93 kPa. Through intravenous injection, relatively rigid GenPLPF_T was able to achieve a high level of accumulation at tumor site by active targeting and long-term blood circulation. Moreover, under sonication at the tumor site, GenPLPF_T became softer with enhanced deformability to achieve deep tumor penetration. In addition, in vivo studies revealed that GenPLPF_T was able to penetrate into the deep area of xenografted tumor with enhanced antitumor efficacy and reduced toxicity. Overall, this peptide nanogel with ultrasound-responsive stiffness demonstrates an effective approach to overcome a series of biological barriers for enhanced deep tumor therapy.

Enzyme-Activated, Chemiluminescent Siderophore-Dioxetane Probes Enable the Selective and Highly Sensitive Detection of Bacterial Pathogens

The sensitive detection of bacterial infections is a prerequisite for their successful treatment. The use of a chemiluminescent readout was so far hampered by an insufficient probe enrichment at the pathogens. We coupled siderophore moieties, that harness the unique iron transport system of bacteria, with enzyme‐activatable dioxetanes and obtained seven trifunctional probes with high signal‐to‐background ratios (S/B=426‐859). Conjugates with efficient iron transport capability into bacteria were identified through a growth recovery assay. All ESKAPE pathogens were labelled brightly by desferrioxamine conjugates, while catechols were weaker due to self‐quenching. Bacteria could also be detected inside lung epithelial cells. The best probe 8 detected 9.1×10³ CFU mL⁻¹ of S. aureus and 5.0×10⁴ CFU mL⁻¹ of P. aeruginosa, while the analogous fluorescent probe 10 was 205–305fold less sensitive. This qualifies siderophore dioxetane probes for the selective and sensitive detection of bacteria.

A bright chemiluminescence conjugated polymer-mesoporous silica nanoprobe for imaging of colonic tumors in vivo

Hypochlorite acid (ClO^-) is one of the major reactive oxygen species (ROS) in colon cancer, providing an effective target for colonic tumor in vivo imaging. For detection of ClO^- and tumor imaging, poly[(9,9-di(2-ethylhexyl)-9H-fluorene-2,7-vinylene)-co-(1-methoxy-4-(2-ethylhexyloxy)-2,5-phenylenevinylene)] (PFV-co-MEHPV, namely CP1) was encapsulated in mesoporous silica nanoparticles (MSNs) that were pre-modified with polyphenylenevinylene (PPV) via in situ polymerization to construct bright PPV@MSN-CP1 nanoparticles. The synthesized nanoparticles were size-stable and not cytotoxic as confirmed by FE-TEM, FE-SEM, and MTT assay. Hypochlorite oxidizes the vinylidene bond of CP1 through π²-π² cycloaddition to form PPV-dioxetane intermediates to generate photons. The CL quantum yield of PPV@MSN-CP1 was 16.7 times higher than that of Pluronic F-127 wrapped CP1. CL nanoparticles PPV@MSN-CP1 have good selectivity for hypochlorite detection among biological oxidants (mainly ROS). The linear range and the LOD of PPV@MSN@CP1 for ClO^- detection are 4-90 and 1.02 μM, respectively. Subsequently, we further coated PPV@MSN@CP1 with folic acid for tumor targeting by phospholipid wrapping. PPV@MSN-CP1@FA was successfully applied for in vivo imaging of endogenously produced ClO^- of tumor tissue in living animals.

Near-Infrared Afterglow Luminescence of Chlorin Nanoparticles for Ultrasensitive In Vivo Imaging

Afterglow imaging holds great potential for ultrasensitive biomedical imaging. As it detects photons after the cessation of real-time light excitation, autofluorescence can therefore be effectively eliminated. However, afterglow imaging is still in its infant stage due to the lack of afterglow agents with satisfactory lifetime, biocompatibility, and high luminescence brightness, particularly afterglow in the near-infrared region for in vivo applications. To address these issues, this study for the first time reports chlorin nanoparticles (Ch-NPs) emitting afterglow luminescence peaking at 680 nm with a half-life of up to 1.5 h, which is almost 1 order of magnitude longer than those of other reported organic afterglow probes. In-depth experimental and theoretical studies revealed that the brightness of the afterglow luminescence is strongly correlated with the singlet oxygen (¹O₂) capacity and the oxidizability of the chlorins. Benefitting from the ultralong half-life and the minimized imaging background, small metastatic tumor foci of 3 mm³ were successfully resected under the guidance of the afterglow luminescence generated upon a single shot of activation prior to the injection, which was impossible for conventional near-infrared fluorescence imaging due to tissue autofluorescence.

Selective detection of ozone in inflamed mice using a novel activatable chemiluminescent probe

We report here an activatable chemiluminescent probe CL-O₃ for the high-contrast imaging of O₃in vivo. CL-O₃ exhibited a high selectivity toward O₃ and was able to evaluate the degree of inflammation in mice by detecting endogenous O₃ levels in acute inflamed mice.

New horizons in the identification of circulating tumor cells (CTCs): An emerging paradigm shift in cytosensors

Circulating tumor cells (CTCs) are cancer cells that are shed from a primary tumor into the bloodstream and function as seeds for cancer metastasis at distant locations. Enrichment and identification methods of CTCs in the blood of patients plays an important role in diagnostic assessments and personalized treatments of cancer. However, the current traditional identification methods not only impact the viability of cells, but also cannot determine the type of cancer cells when the disease is unknown. Hence, new methods to identify CTCs are urgently needed. In this context, many advanced and safe technologies have emerged to distinguish between cancer cells and blood cells, and to distinguish specific types of cancer cells. In this review, at first we have briefly discussed recent advances in technologies related to the enrichment of CTCs, which lay a good foundation for the identification of CTCs. Next, we have summarized state-of-the-art technologies to confirm whether a given cell is indeed a tumor cell and determine the type of tumor cell. Finally, the challenges for application and potential directions of the current identification methods in clinical analysis of CTCs have been discussed.

Chemiluminescent Probes Based on 1,2-dioxetane Structures For Bioimaging

Chemiluminescent probes based on 1,2-dioxetane scaffold are one of the most sensitive imaging modalities for detecting disease-related biomarkers and can obtain more accurate biological information in cells and in vivo . Due to the elimination of external light excitation, the background autofluorescence problem in fluorescence technology can be effectively avoided, providing ultra-high sensitivity and signal-to-noise ratio for various applications. In this minireview, we highlight a comprehensive but concise overview of activatable 1,2-dioetxane-based chemiluminescent probes by reporting significant advances in accurate detection and bioimaging. The design principles and applications for reactive species, enzymes, and other disease-related biomarkers are systematically discussed and summarized. The challenges and potential prospects of chemiluminescent probes are also discussed to further promote the development of new chemiluminescence methods for biological analysis and diagnosis.

A bioluminescent probe for NQO1 overexpressing cancer cell imaging in vitro and in vivo

A bioluminescent probe NQO1-Luc toward NQO1 was constructed, which exhibits high selectivity and sensitivity toward NQO1 in vitro and adequate capability of distinguishing NQO1-overexpressing tumors in vivo.

From imines to amides via NHC-mediated oxidation

An efficient construction of amides through NHC-mediated oxidation of imines is described. This work has the advantages of wide scope, fast assembly and high yield, and can avoid the use of coupling agents, such as HATU, DCC, etc.

Convenient and Flexible Syntheses of gem-Dimethyl Carboxylic Triggers via Mono-Selective β-C(sp3)-H Arylation of Pivalic Acid with ortho-Substituted Aryl Iodides

This work presents a palladium(II)-catalyzed mono-selective C(sp3)-H arylation of pivalic acid for rapid construction of an important library of 3-aryl-2,2-dimethylpropanoic acids, especially those ortho-substituted-aryl compounds. The strategy greatly streamlines the...

Recent advances in self-immolative linkers and their applications in polymeric reporting systems

Interest in self-immolative chemistry has grown over the past decade with more research groups harnessing the versatility to control the release of a compound from a larger chemical entity, given...

Ultrasensitive chemiluminescent neuraminidase probe for rapid screening and identification of small-molecules with antiviral activity against influenza A virus in mammalian cells

Influenza A virus is the most virulent influenza subtype and is associated with large-scale global pandemics characterized by high levels of morbidity and mortality. Developing simple and sensitive molecular methods for detecting influenza viruses is critical. Neuraminidase, an exo-glycosidase displayed on the surface of influenza virions, is responsible for the release of the virions and their spread in the infected host. Here, we present a new phenoxy-dioxetane chemiluminescent probe (CLNA) that can directly detect neuraminidase activity. The probe exhibits an effective turn-on response upon reaction with neuraminidase and produces a strong emission signal at 515 nm with an extremely high signal-to-noise ratio. Comparison measurements of our new probe with previously reported analogous neuraminidase optical probes showed superior detection capability in terms of response time and sensitivity. Thus, as far as we know, our probe is the most sensitive neuraminidase probe known to date. The chemiluminescence turn-on response produced by our neuraminidase probe enables rapid screening for small molecules that inhibit viral replication through different mechanisms as validated directly in influenza A-infected mammalian cells using the known inhibitors oseltamivir and amantadine. We expect that our new chemiluminescent neuraminidase probe will prove useful for various applications requiring neuraminidase detection including drug discovery assays against various influenza virus strains in mammalian cells.

A new chemiluminescence neuraminidase probe enables rapid screening of small molecules that inhibit viral replication, directly in influenza A-infected mammalian cells.

Intracellular Enzyme-Responsive Profluorophore and Prodrug Nanoparticles for Tumor-Specific Imaging and Precise Chemotherapy

Responsive drug delivery systems possess great potential in disease diagnosis and treatment. Herein, we develop an activatable prodrug and fluorescence imaging material by engineering the endogenous NAD(P)H:quinone oxidoreductase-1 (NQO1) responsive linker. The as-prepared nanomaterials possess the NQO1-switched drug release and fluorescence enablement, which realizes the tumor-specific chemotherapy and imaging in living mice. The enzyme-sensitive prodrug nanoparticles exhibit selectively potent anticancer performance to NQO1-positive cancer and ignorable off-target toxicity. This work provides an alternative strategy for constructing smart prodrug nanoplatforms with precision, selectivity, and practicability for advanced cancer imaging and therapy.

Molecular Probes for Autofluorescence-Free Optical Imaging

Optical imaging is an indispensable tool in clinical diagnostics and fundamental biomedical research. Autofluorescence-free optical imaging, which eliminates real-time optical excitation to minimize background noise, enables clear visualization of biological architecture and physiopathological events deep within living subjects. Molecular probes especially developed for autofluorescence-free optical imaging have been proven to remarkably improve the imaging sensitivity, penetration depth, target specificity, and multiplexing capability. In this Review, we focus on the advancements of autofluorescence-free molecular probes through the lens of particular molecular or photophysical mechanisms that produce long-lasting luminescence after the cessation of light excitation. The versatile design strategies of these molecular probes are discussed along with a broad range of biological applications. Finally, challenges and perspectives are discussed to further advance the next-generation autofluorescence-free molecular probes for in vivo imaging and in vitro biosensors.

Synthesis and Evaluation of Ubiquitin-Dioxetane Conjugate as a Chemiluminescent Probe for Monitoring Deubiquitinase Activity

The removal of ubiquitin (Ub) from a modified protein or Ub chain is a process that occurs regularly by the ubiquitin–proteasome system. This process is known to be mediated by various deubiquitinating enzymes (DUBs) in order to control the protein’s half-life and its expression levels among many other signaling processes. Since the function of DUBs is also involved in numerous human diseases, such as cancer, there is an obvious need for an effective diagnostic probe that can monitor the activity of these enzymes. We have developed the first chemiluminescence probe for detection of DUBs activity. The probe was prepared by conjugation of the chemically synthesized C-terminally activated Ub(1-75) with a Gly-enolether precursor. Subsequent oxidation, under aqueous conditions, of the enolether conjuagate with singlet-oxygen furnished the dioxetane probe Ub-CL. This synthesis provides the first example of a dioxetane–luminophore protein conjugate. The probe’s ability to detect deubiquitinating activity was successfully validated with three different DUBs. In order to demonstrate the advantage of our new probe, comparison measurements for detection of DUB UCH-L3 activity were performed between the chemiluminescent probe Ub-CL and the well-known Ub-AMC probe. The obtained data showed significantly higher S/N, for probe Ub-CL (>93-fold) in comparison to that observed for Ub-AMC (1.5-fold). We anticipate that the successful design and synthesis of the turn-ON protein–dioxetane conjugate probe, demonstrated in this work, will provide the insight and motivation for preparation of other relevant protein–dioxetane conjugates.

Universal Access to Protease Chemiluminescent Probes through Solid-Phase Synthesis

Protease chemiluminescent probes exhibit extremely high detection sensitivity for monitoring activity of various proteolytic enzymes. However, their synthesis, performed in solution, involves multiple synthetic and purification steps, thereby generating a major limitation for rapid preparation of such probes with diverse substrate scope. To overcome this limitation, we developed a general solid-phase-synthetic approach to prepare chemiluminescent protease probes, by peptide elongation, performed on an immobilized chemiluminescent enol-ether precursor. The enol-ether precursor is immobilized on a 2-chlorotrityl-chloride resin through an acrylic acid substituent by an acid-labile ester linkage. Next, a stepwise elongation of the peptide is performed using standard Fmoc solid-phase peptide synthesis. After cleavage of the peptide-enol-ether precursor from the resin, by hexafluoro-iso-propanol, a simple oxidation of the enol-ether yields the final chemiluminescent dioxetane protease probe. To validate the applicability of the methodology, two chemiluminescent probes were efficiently prepared by solid-phase synthesis with dipeptidyl substrates designed for activation by aminopeptidase and cathepsin-B proteases. A more complex example was demonstrated by the synthesis of a chemiluminescent probe for detection of PSA, which includes a peptidyl substrate of six amino acids. We anticipate that the described methodology would be useful for rapid preparation of chemiluminescent protease probes with vast and diverse peptidyl substrates.

Chemiluminescent probe for the detection of inverse electron demand Diels-Alder reaction between tetrazine and trans-Cyclooctene

A chemiluminescent probe has been developed, consisting of phenoxy-dioxetane moiety covalently attached to trans-cyclooctene. The inverse electron demand Diels-Alder reaction with tetrazine produces a cycloaddition product which undergoes a series of spontaneous rearrangements resulting in emission of green light. The chemiluminescent probe can be applied to study bioconjugation chemistry with tetrazine-modified biomaterials, which have recently been shown to have great potential for anticancer drug delivery. This work describes in vitro studies, including NMR and spectroscopic investigation of chemiluminescence, which will pave way for future in vivo bioconjugation experiments.

Photoactivatable Red Chemiluminescent AIEgen Probe for In Vitro/Vivo Imaging Assay of Hydrazine

Here, we have developed a novel photoactivatable red chemiluminescent AIEgen probe (ACL), based on the combination of the red-emission AIEgen fluorophore (TPEDC) that shows excellent singlet oxygen (¹O₂)-generation ability and the precursor of Schaap's dioxetane (the linker connected to adamantane is the C═C bond) that can be modified to target various analytes, for in vitro and in vivo measurement of hydrazine. Prior to applying for sensing detection, the C═C bond connected to adamantane in ACL was first converted into dioxetane by irradiation to form the activated chemiluminescent AIEgen probe (ACLD). Then, the self-immolative reaction was triggered upon the deprotection of the acylated phenolic hydroxyl group in ACLD in the presence of hydrazine, resulting in the release of the high energy held in the 1,2-dioxetanes, and then, the chemiexcitation was triggered, thereby producing red chemiluminescence through the intramolecular chemiluminescence resonance energy transfer from Schaap's dioxetane to TPEDC. This chemiluminescent AIEgen probe was evaluated in a clean buffer environment as well as using living cells and mouse models.

NAD(P)H Quinone Oxidoreductase-1 in Organ and Tumor Tissues: Distinct Activity Levels Observed with a Benzo-rosol-Based Dual-Excitation and Dual-Emission Probe

NAD(P)H quinone oxidoreductase-1 (NQO1), a protective enzyme against cellular oxidative stress, is expressed abnormally high in solid tumors and thus recognized as a cancer biomarker. To develop a fluorescent NQO1 probe with practicality, we investigated benzo-rosol fluorophores linked with a known self-immolative quinone substrate. Four probe candidates exhibited ratiometric sensing behavior toward the enzyme, satisfying our orbital mismatch stratagem proposed before, under dual-excitation and dual-emission conditions that alleviate the spectral overlap issue commonly observed with the ratiometric probes based on intramolecular charge-transfer change. Among the candidates, two ester-linked compounds exhibited hydrolytic instability to water or an esterase, discouraging us to develop such ester-linked probes. One ether-linked, hydrolytically stable probe provided brighter cellular fluorescence than the other and thus was applied to ratiometric imaging of NQO1 in cells and tissues. We found that the enzyme activity levels are much different in organ tissues: stomach (56), kidney (22), colon (9.8), testis (7.8), bladder (5.6), lung (1.2), and muscle (1.0). Furthermore, a markedly high enzyme level (14.6-fold) was observed in a xenograft tumor tissue compared with that in a normal tissue, which suggests that such an NQO1 probe is promising for cancer diagnosis and for studying the enzyme-associated biology.

Tunable Methacrylamides for Covalent Ligand Directed Release Chemistry

Targeted covalent inhibitors are an important class of drugs and chemical probes. However, relatively few electrophiles meet the criteria for successful covalent inhibitor design. Here we describe α-substituted methacrylamides as a new class of electrophiles suitable for targeted covalent inhibitors. While typically α-substitutions inactivate acrylamides, we show that hetero α-substituted methacrylamides have higher thiol reactivity and undergo a conjugated addition-elimination reaction ultimately releasing the substituent. Their reactivity toward thiols is tunable and correlates with the pKa/pKb of the leaving group. In the context of the BTK inhibitor ibrutinib, these electrophiles showed lower intrinsic thiol reactivity than the unsubstituted ibrutinib acrylamide. This translated to comparable potency in protein labeling, in vitro kinase assays, and functional cellular assays, with improved selectivity. The conjugate addition-elimination reaction upon covalent binding to their target cysteine allows functionalizing α-substituted methacrylamides as turn-on probes. To demonstrate this, we prepared covalent ligand directed release (CoLDR) turn-on fluorescent probes for BTK, EGFR, and K-RasG12C. We further demonstrate a BTK CoLDR chemiluminescent probe that enabled a high-throughput screen for BTK inhibitors. Altogether we show that α-substituted methacrylamides represent a new and versatile addition to the toolbox of targeted covalent inhibitor design.

Fluorescent Probe for Monitoring Hydrogen Peroxide in COX-2-Positive Cancer Cells

Hydrogen peroxide (H₂O₂), an important marker for oxidative stress, plays a vital role in cellular biological functions. Overproduction of H₂O₂ causes oxidative damage to cellular functions and promotes cancer and other neurodegenerative diseases. Also, cyclooxygenase-2 (COX-2) enzyme is known to be expressed in several cancer types and exerts multifaceted roles in carcinogenesis and resistance to cancer treatment. Hence, it is important to monitor the H₂O₂ concentration changes in the COX-2-expressing cancer cells. Herein, we have developed a molecular fluorescent ratiometric H₂O₂-responsive probe (NPDIN) composed of indomethacin (COX-2 inhibitor) conjugated with 1,8-napthalimide boronate ester as fluorescent reporter through a chemical linker. The probe was capable of imaging the endogenous H₂O₂ in COX-2 overexpressing cancer cell lines (A549, LoVo, HT29, and Caco-2). Further studies revealed the critical role of the indomethacin moiety in the cellular uptake behavior of NPDIN in COX-2-overexpressing cancer cells. Collectively, our results demonstrated NPDIN as a COX-2-positive cancer-targeting sensitive ratiometric fluorescent probe (I₅₅₄/I₃₉₈) for H₂O₂ imaging and showed its promising biological applications in the future.

Molecular Design of d-Luciferin-Based Bioluminescence and 1,2-Dioxetane-Based Chemiluminescence Substrates for Altered Output Wavelength and Detecting Various Molecules

Optical imaging including fluorescence and luminescence is the most popular method for the in vivo imaging in mice. Luminescence imaging is considered to be superior to fluorescence imaging due to the lack of both autofluorescence and the scattering of excitation light. To date, various luciferin analogs and bioluminescence probes have been developed for deep tissue and molecular imaging. Recently, chemiluminescence probes have been developed based on a 1,2-dioxetane scaffold. In this review, the accumulated findings of numerous studies and the design strategies of bioluminescence and chemiluminescence imaging reagents are summarized.