A lysosome-targetable fluorescent probe for real-time imaging cysteine under oxidative stress in living cells

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.

Treatment evaluation of Rheumatoid arthritis by in situ fluorescence imaging of the Golgi cysteine

Rheumatoid arthritis (RA) is a long-term systemic inflammatory disease that causes severe joint pain. Golgi stress caused by redox imbalance significantly involves in acute and chronic inflammatory diseases, in which cysteine (Cys), as a representative reducing agent, may be an effective biomarker for RA. Hence, in order to achieve RA early detection and drugs evaluation, based on our previous work about innovative Golgi-targeting group, we established a phenylsulfonamide-modified fluorescence probe, Golgi-Cys, for the selective fluorescence imaging of Cys in Golgi apparatus in vivo. By application of Golgi-Cys, the Cys changes under Golgi stress in cells were elucidated. More importantly, we found that the probe can be effectively utilized for the RA detection and treatment evaluation in situ.

Mitochondria-targeted ruthenium(II) complexes for photodynamic therapy and GSH detection in living cells

Photodynamic therapy is an emerging tumor therapy that kills tumor cells by activating reactive oxygen species (ROS) produced by photosensitizers. Mitochondria, as an important organelle, are the main generator of cellular ROS. Therefore, the development of photosensitizers capable of targeting mitochondria could significantly enhance the efficacy of photodynamic therapy. In this study, two novel ruthenium(II) complexes, Ru-1 and Ru-2, were designed and synthesized, both of which were functionalized with α,β-unsaturated ketones for sensing of glutathione (GSH). The crystal structures of the two complexes were determined and they exhibited good recognition of GSH by off-on luminescence signals. The complex Ru-2 containing aromatic naphthalene can enter the cells and react with GSH to generate a strong luminescence signal that can be used to monitor intracellular GSH levels through imaging. Ru-2 also has an excellent mitochondrial localization ability with a Pearson's coefficient of 0.95, which demonstrates that it can efficiently target the mitochondria of tumor cells to enhance the effectiveness of photodynamic therapy as a photosensitizer.

A NIR fluorescence probe for monitoring Cys upregulation induced by balsam pear polysaccharide and imaging in zebrafish

In this work, we introduced the acrylate recognition group into dicyanoisophorone derivative DCI-C-OH to construct the NIR fluorescent probe DCI-C-Cys with a large Stokes shift (240 nm). DCI-C-Cys could specifically respond to Cys, resulting in a 22-fold increase in fluorescence intensity at 702 nm. Meanwhile, the probe has the advantages of good water solubility, high sensitivity (93 nM), and excellent biocompatibility. Moreover, DCI-C-Cys successfully monitored endogenous and exogenous Cys in HepG2 cells and zebrafish. Most importantly, we found that balsam pear polysaccharide could lead to the increase of intracellular Cys levels, which might be conducive to the further study of the antioxidant mechanism of balsam pear polysaccharide.

A lipid droplet-targetable and biothiol-sensitive fluorescent probe for the diagnosis of cancer cells/tissues

Lipid droplets (LDs) have recently been reported as an attractive target for cancer diagnosis and treatment, owing to their special structure or microenvironment changes in cancer development and resistance. However, the relationship between the biothiol level of LDs and cancer is still poorly understood, partially owing to the absence of effective molecular tools. Herein, we developed a LD-targetable and biothiol-sensitive fluorescent probe, BTDA-RSS, by introducing 2,4-dinitrobenzenesulfonyl (DNBS) as the biothiol reaction group into a benzothiazolyl derivative. BTDA-RSS displayed a marked and rapid fluorescence turn-on response toward biothiols, due to the biothiol-triggered cleavage of DNBS to yield the highly fluorescent benzothiazolyl iminocoumarin BTDA. In addition, the probe shows significant LD-targetable ability, and has been applied for imaging endogenous/exogenous biothiol changes in LDs. Importantly, BTDA-RSS has successfully been utilized to distinguish cancerous cells/tissues from normal cells/tissues with excellent contrast. Surprisingly, we demonstrated for the first time the visualization of LD biothiols in surgical specimens from cancer patients, thereby holding great potential for the application of BTDA-RSS in the clinical diagnosis of human cancers.

Strategies for organelle targeting of fluorescent probes

Fluorescent tools have emerged as an important tool for studying the distinct chemical microenvironments of organelles, due to their high specificity and ability to be used in non-destructive, live cellular studies. These tools fall largely in two categories: exogenous fluorescent dyes, or endogenous labels such as genetically encoded fluorescent proteins. In both cases, the probe must be targeted to the organelle of interest. To date, many organelle-targeted fluorescent tools have been reported and used to uncover new information about processes that underpin health and disease. However, the majority of these tools only apply a handful of targeting groups, and less-studied organelles have few robust targeting strategies. While the development of new, robust strategies is difficult, it is essential to develop such strategies to allow for the development of new tools and broadening the effective study of organelles. This review aims to provide a comprehensive overview of the major targeting strategies for both endogenous and exogenous fluorescent cargo, outlining the specific challenges for targeting each organelle type and as well as new developments in the field.

Selective and Sensitive ZnO Quantum Dots Based Fluorescent Biosensor for Detection of Cysteine

In the present article, a novel and effective ZnO quantum dots-based fluorescent probe has been developed for the detection of cysteine in different solutions. Firstly, melamine-based fluorescent pre-probe was successfully synthesized via condensation reaction and, then ZnO quantum dots (QDs) were homogenously dispersed into this solution. This fluorescent probe was used for the detection of cysteine in different solutions such as bovine serum albumin and tap water. ZnO QDs were characterized using XRD, nano-particle size analyzer, and FE-SEM techniques. The size of the ZnO QDs was calculated as 28.03±9.86 nm, and 31.95±10.02 nm from Scherrer's equation and nano-particle size analyzer, respectively. The developed fluorescent probe was exhibited a highly selective and sensitive response to the detection of cysteine. Also, the proposed fluorescent probe has a larger Stokes shift value (236 nm). The limit of detection and linear range of ZnO QDs-based fluorescent biosensor were found as 0.642 μM and 0.1-600 μM, respectively. ZnO quantum dot-based fluorescent sensor for L-cysteine.