Thiol “Click” Chromene Ring Opening and Subsequent Cascade Nucleophilic Cyclization NIR Fluorescence Imaging Reveal High Levels of Thiol in Drug-Resistant Cells

A mitochondria-targeted colorimetric and NIR ratiometric fluorescent probe for biothiols with large Stokes shift based on thiol-chromene click reaction

In this study, a carbazole-based mitochondria-targeted colorimetric and NIR ratiometric fluorescent probe 1 for biothiols based on the thiol-chromene click reaction was subtly designed and synthesized. Upon interaction with biothiols (Cys, Hcy and GSH), the absorption of 1 shifted from 496 nm to 388 nm, while its fluorescence spectrum shifted from 650 nm to 530 nm. These transformations were accompanied by a visible color change from pink to colorless under visible light and from red to green when observed under a 365 nm UV lamp, which can be attributed to the click reaction of biothiols with the α,β-unsaturated ketone of the chromene moiety, subsequent pyran ring-opening and phenol formation as well as 1,6-elimination of a p-hydroxybenzyl moiety yielding 2. These advancements in 1 have allowed us to ratiometrically detect biothiols with high sensitivity (LODs of 97 nM, 94 nM and 93 nM for Cys, GSH and Hcy, respectively), a large Stokes shift (154 nm) and excellent selectivity. In addition, 1 can target mitochondria and image the fluctuation of intracellular biothiols through fluorescence ratiometry. Furthermore, the novel design strategy of modifying chromene to the N atom of quinoline was proposed for the first time.

Mitochondria-Targeted NIR Ratiometric and Colorimetric Fluorescent Probe for Biothiols Based on a Thiol-Chromene Click Reaction

In this work, a mitochondria-targeted NIR ratiometric and colorimetric fluorescent probe 1 was tactfully designed and synthesized by a novel design strategy of modifying chromene to pyridine for the first time. 1 exhibited a maximum absorption peak at 508 nm and a maximum fluorescence emission peak at 650 nm. Under the stimulus of biothiols (cysteine (Cys), homocysteine (Hcy), and glutathione (GSH)), the maximum absorption and fluorescence emission peaks of 1 blue-shifted to 448 and 541 nm, respectively, along with color changes from red to yellow under visible light and from red to green under a 365 nm ultraviolet (UV) lamp, which can be ascribed to the click reaction of biothiols with the α,β-unsaturated ketone of the chromene moiety with pyran ring-opening, phenol formation, and 1,6-elimination of the p-hydroxybenzyl moiety. 1 detected biothiols (Cys, GSH, and Hcy) with high sensitivity (LODs of 29, 23, and 16 nM for Cys, GSH, and Hcy, respectively), excellent selectivity, and fast response. Moreover, 1 can target mitochondria and image the fluctuation of intracellular biothiols by dual-emission channels.

Thiol-chromene click reaction-triggered mitochondria-targeted ratiometric fluorescent probe for intracellular biothiol imaging

Chromene as the efficient biothiol recognition site was widely used to develop fluorescent probes based on thiol-chromene click reaction. However, chromene-based fluorescent probes with the both properties of ratiometric measurement and mitochondria-targeted function have not been reported and remain challenging. In this paper, we skillfully designed and synthesized the first mitochondria-targeted ratiometric fluorescent probe (Probe 1) for biothiols based on chromene. Upon addition of biothiols (Cys, Hcy, and GSH), the absorption and fluorescence spectra of Probe 1 changed from 490 to 426 nm and from 567 to 498 nm respectively, accompanied by color changes from orange to pale yellow under natural light and from orange to blue under a 365-nm UV lamp, which can be attributed to the click reaction of biothiols with α,β-unsaturated ketone of chromene moiety, subsequent pyran ring-opening, and phenol formation as well as 1,6-elimination of p-hydroxybenzyl moiety. Probe 1 not only exhibited high sensitivity (LODs of 149 nM, 133 nM, and 116 nM for Cys, GSH, and Hcy respectively), rapid response, and excellent selectivity for biothiols (Cys, Hcy, and GSH), but also could target in mitochondria and ratiometrically image the fluctuation of intracellular biothiols. Moreover, the novel design strategy of modifying chromene to the N atom of pyridine was proposed for the first time.

Glutathione-responsive Aggregation-induced Emission Photosensitizers for Enhanced Photodynamic Therapy of Lung Cancer

Lung cancer, a highly prevalent and lethal form of cancer, is often associated with oxidative stress. Photodynamic therapy (PDT) has emerged as a promising alternative therapeutic tool in cancer treatments, but its efficacy is closely correlated to the photosensitizers generating reactive oxygen species (ROS) and the antioxidant capacity of tumor cells. In particular, glutathione (GSH) can reduce the ROS and thus compromise PDT efficacy. In this study, a GSH-responsive near-infrared photosensitizer (TBPPN) based on aggregation-induced emission for real-time monitoring of GSH levels and enhanced PDT for lung cancer treatment is developed. The strategic design of TBPPN, consisting of a donor-acceptor structure and incorporation of dinitrobenzene, enables dual functionality by not only the fluorescence being activated by GSH but also depleting GSH to enhance the cytotoxic effect of PDT. TBPPN demonstrates synergistic PDT efficacy in vitro against A549 lung cancer cells by specifically targeting different cellular compartments and depleting intracellular GSH. In vivo studies further confirm that TBPPN can effectively inhibit tumor growth in a mouse model with lung cancer, highlighting its potential as an integrated agent for the diagnosis and treatment of lung cancer. This approach enhances the effectiveness of PDT for lung cancer and deserves further exploration of its potential for clinical application.

A thiol-triggered croconaine-chromene integration to induce ferroptosis and photothermal synergistic efficient tumor ablation

Theranostic probes, combining diagnostic and treatment capabilities, have emerged as promising tools in tumor precision medicine. However, existing probes with constant fluorescence and photothermal activity can result in low signal-to-background ratios and phototoxicity. In this study, we introduced CM-Croc, a novel probe comprised of chromene and croconaine, selectively triggered by thiol. CM-Croc exhibited turn-on fluorescence and released croconaine for photothermal therapy. The croconaine moiety possesses high photothermal conversion efficiency up to 55%. Besides, it demonstrated potent activity against various cancer cell lines at low micromolar concentrations, including drug-resistant variants, through enhanced photothermal therapy combined with the ferroptosis effect. What's more, CM-Croc was proved to inhibit the activity of GPX4 to induce ferroptosis. Finally, CM-Croc was demonstrated to be the first croconaine-derived SOP, which targeted tumors and significantly inhibited tumor growth in vivo following intravenous administration with irradiation. This study showed CM-Croc's potential for enhancing tumor precision medicine.

Glutathione-triggered prodrugs: Design strategies, potential applications, and perspectives

The burgeoning prodrug strategy offers a promising avenue toward improving the efficacy and specificity of cytotoxic drugs. Elevated intracellular levels of glutathione (GSH) have been regarded as a hallmark of tumor cells and characteristic feature of the tumor microenvironment. Considering the pivotal involvement of elevated GSH in the tumorigenic process, a diverse repertoire of GSH-triggered prodrugs has been developed for cancer therapy, facilitating the attenuation of deleterious side effects associated with conventional chemotherapeutic agents and/or the attainment of more efficacious therapeutic outcomes. These prodrug formulations encompass a spectrum of architectures, spanning from small molecules to polymer-based and organic-inorganic nanomaterial constructs. Although the GSH-triggered prodrugs have been gaining increasing interests, a comprehensive review of the advancements made in the field is still lacking. To fill the existing lacuna, this review undertakes a retrospective analysis of noteworthy research endeavors, based on a categorization of these molecules by their diverse recognition units (i.e., disulfides, diselenides, Michael acceptors, and sulfonamides/sulfonates). This review also focuses on explaining the distinct benefits of employing various chemical architecture strategies in the design of these prodrug agents. Furthermore, we highlight the potential for synergistic functionality by incorporating multiple-targeting conjugates, theranostic entities, and combinational treatment modalities, all of which rely on the GSH-triggering. Overall, an extensive overview of the emerging field is presented in this review, highlighting the obstacles and opportunities that lie ahead. Our overarching goal is to furnish methodological guidance for the development of more efficacious GSH-triggered prodrugs in the future. By assessing the pros and cons of current GSH-triggered prodrugs, we expect that this review will be a handful reference for prodrug design, and would provide a guidance for improving the properties of prodrugs and discovering novel trigger scaffolds for constructing GSH-triggered prodrugs.

Thiol-Chromene "Click" Reaction-Activated Chemiluminescent Probe for Thiol Detection In Vitro and In Vivo

Biothiols are biomolecules found in a higher content in cancer cells compared to normal cells, marking them useful cancer biomarkers. Chemiluminescence is widely used in biological imaging due to its excellent sensitivity and signal-to-noise ratio (SNR). In this study, we designed and prepared a chemiluminescent probe that is activated by a thiol-chromene "click" nucleophilic reaction. This probe is initially chemiluminescent but turned off and releases extremely strong chemiluminescence in the presence of thiols. It has high selectivity to thiol compared with other analytes. Real-time imaging of mice tumor sites showed significant chemiluminescence after the probe was injected, and the chemiluminescence of osteosarcoma tissues was also significantly stronger than that in adjacent tissues. We conclude that this chemiluminescent probe has potential to detect thiol, diagnose cancer, especially in its early stages, and aid in the development of related cancer drugs.

Recent Progress in the Rational Design of Biothiol-Responsive Fluorescent Probes

Biothiols such as cysteine, homocysteine, and glutathione play significant roles in important biological activities, and their abnormal concentrations have been found to be closely associated with certain diseases, making their detection a critical task. To this end, fluorescent probes have become increasingly popular due to their numerous advantages, including easy handling, desirable spatiotemporal resolution, high sensitivity, fast response, and favorable biocompatibility. As a result, intensive research has been conducted to create fluorescent probes for the detection and imaging of biothiols. This brief review summarizes recent advances in the field of biothiol-responsive fluorescent probes, with an emphasis on rational probe design, including the reaction mechanism, discriminating detection, reversible detection, and specific detection. Furthermore, the challenges and prospects of fluorescence probes for biothiols are also outlined.

A simple lysosome-targeted fluorescent probe based on flavonoid for detection of cysteine in living cells

Cysteine (Cys) is one of the most important biothiols that plays a crucial role in many physiological and pathological processes, and therefore it is of great importance to detect and analyze Cys in subcellular environments, such as in lysosomes. However, only a few fluorescent probes were reported to be capable of detecting Cys in lysosomes selectively. In this wok, we designed and developed a simple, accessible flavone-based fluorescent probe LFA for detecting Cys in lysosomes. Morpholine was employed as the targeting unit for lysosome, and acrylate group was chosen as the Cys-response unit. The probe was easily prepared by a two-step procedure and displayed large Stokes shift, high sensitivity, turn-on response toward Cys over homocysteine (Hcy), glutathione (GSH), and other amino acids. With low cytotoxicity and good cell permeability, the probe could be successfully applied for fluorescence imaging of Cys in living cells. Furthermore, colocalization experiment revealed that lysosomal-targetable ability of LFA was significant. These results indicated that such simple fluorescent probe could provide a promising tool for detection of lysosomal Cys in living biological systems.

Recent development of small-molecule fluorescent probes based on phenothiazine and its derivates

Fluorescence probes, as analytical tools with the ability to perform rapid and sensitive detection of target analytes, have made outstanding contributions to environmental analysis and bioassays. Considering the expanding developments in these areas, fluorophores play a key role in the de-sign of fluorescence probes. Compared to classical fluorophores, phenothiazines with elec-tron-rich characteristics have been widely applied to construct electron donor-acceptor dyes, which exhibit outstanding performance in both fluorimetric and colorimetric analysis. In addition, these probes also exhibit the pronounced ability in both solution and solid-state, achieving portable detection for environmental analysis. In this review, we summarize recent advances in the performance of phenothiazine-based fluorescent probes for detecting various analytes, especially in cations, anions, ROS/RSS, enzyme and other small molecules. The general design rules, response mechanisms and practical applications of the probes are analyzed, followed by a discussion of exiting challenges and future research perspectives. It is hoped that this review will provide a few strategies for the development of phenothiazine-based fluorescent probes.

Thiocarbonyl photosensitizer, a feasible way to eliminate the photosensitizer residues in photodynamic therapy

Photodynamic therapy (PDT) has been successfully applied in clinical treatment several years. However, after finished treatment process the residual photosensitizer will spread throughout body, which forces patients stay in the dark room to avoid exposure in sunlight several weeks. Therefore, develop degradable photosensitizer could effectively eliminate this inconvenience. In the past, researchers have developed degradable photosensitizers based on supramolecular structure. In this study, we achieved the same effect in small molecule level. Three thiocarbonyl photosensitizers (PS) have high photogenerated ¹O₂ quantum yield and can be photodegraded by laser irradiation within 15 min. And due to its high phototoxicity and low toxicity, thiocarbonyl PS still maintains its high phototoxicity. Especially, mitochondrial targeting PS 1a has better properties than many BODIPY or cyanine heavy-atom-free photosensitizers. It only needs 1 μM to reduce HeLa cell activity to 30%. Finally the thiocarbonyl PS provided a convenient way to solve the PS residue problem without sacrificing PDT efficiency.

Unique assemble of carbonylpyridinium and chromene reveal mitochondrial thiol starvation under ferroptosis and novel ferroptosis inducer

To reveal the delicate function of mitochondrial, precise detection tools in spatiotemporal manner remains highly desirable. However, current probes with positive charge warheads for targeting mitochondria diffuse out of the...

AND-Logic Strategy for Accurate Analysis of Alzheimer's Disease via Fluorescent Probe Lighted Up by Two Specific Biomarkers

Alzheimer's disease (AD) has become a global threat to the elderly health with a short survival time after diagnosis. Due to the asymptomatic stage during the early development, patients are usually diagnosed at the middle or late stage. Therefore, an efficient tool for AD early diagnosis deserves considerable attention, which could make a significant contribution to the treatment intervention. A fluorescent probe has been widely applied for detecting and visualizing species of interest in vitro and in vivo, and the proper reaction between the probe and analytes is responsible for the fluorescence change to provide a lighting-on or ratiometric responsive pattern with satisfactory sensing behavior. In this work, we report the first attempt to build up an AND-logic probe P2 for AD accuracy diagnosis taking butyrylcholinesterase (BChE) and reactive oxygen species (ROSs) as dual targets. Upon the co-stimulation by these two factors through enzymatic hydrolysis and redox reaction, the NIR emission could be readily turned on. This AND sensing pattern avoided the false-positive response effectively, and other diseases sharing one biomarker could hardly induce a NIR fluorescence response. The sensing assay has also been confirmed to be feasible in vitro and in vivo with good sensibility and selectivity. It is worth mentioning that the probe structure has been optimized in terms of the linkage length. This study shows that probe P2 with a connecting arm of medium length (one methylene, n = 1) has superior sensing performance, promising to provide a reference for the relative structure design.