Recent advances in small-molecule fluorescent probes for studying ferroptosis

A lysosome-targeted fluorescent probe for fluorescence imaging of hypochlorous acid in living cells and in vivo

Lysosomes, as crucial acidic organelles in cells, play a significant role in cellular functions. The levels and distribution of hypochlorous acid (HOCl) within lysosomes can profoundly impact their biological functionality. Hence, real-time monitoring of the concentration of HOCl in lysosomes holds paramount importance for further understanding various physiological and pathological processes associated with lysosomes. In this study, we developed a bodipy-based fluorescent probe derived from pyridine and phenyl selenide for the specific detection of HOCl in aqueous solutions. Leveraging the probe's sensitive photoinduced electron transfer effect from phenyl selenide to the fluorophore, the probe exhibited satisfactory high sensitivity (with a limit of detection of 5.2 nM and a response time of 15 s) to hypochlorous acid. Further biological experiments confirmed that the introduction of the pyridine moiety enabled the probe molecule to selectively target lysosomes. Moreover, the probe successfully facilitated real-time monitoring of HOCl in cell models stimulated by N-acetylcysteine (NAC) and lipopolysaccharide (LPS), as well as in a normal zebrafish model. This provides a universal method for dynamically sensing HOCl in lysosomes.

Recent Advances in Organic Small-Molecule Fluorescent Probes for the Detection of Zinc Ions (Zn2+)

Zinc(II) ions (Zn2g) play crucial roles in the growth, propagation, and metabolism of animals, plants, and humans. Abnormal concentrations of Zn2+ in the environment and living organisms pose potential risks to environmental protection and human health. Therefore, it is imperative to develop rapid, reliable and in-situ detection methods for Zn2+ in both environmental and biological contexts. Furthermore, effective analytical methods are required for diagnosing diseases and understanding physiological metabolic mechanisms associated with Zn2+ concentration levels. Organic small-molecule fluorescent probes offer advantages such as fast, reliable, convenient, non-destructive detection capabilities and have significant application potential in Zn2+ detection and bioimaging; thus garnering extensive attention. Over the past two years alone, various organic small-molecule probes for Zn2+ based on different detection mechanisms and fluorophores have been rapidly developed. However, these probes still exhibit several limitations that need further resolution. In light of this context, we provide a comprehensive summary of the detection mechanisms, performance characteristics, and application scope of Zn2+ fluorescence probes since year 2022 while highlighting their advantages. We also propose solutions to address existing issues with these probes and outline future directions for their advancement. This review aims to serve as a valuable reference source offering insights into the development of advanced organic small-molecule-based fluorescence probes specifically designed for detecting Zn2+.

Development of a turn-on fluorescent probe for the imaging of intracellular hypochlorous acid (HClO) during ferroptosis

Ferroptosis is a burgeoning iron-dependent cell death form, and has close relation with hypochlorous acid (HClO). Exploring the fluctuation of the HClO level in living cells during ferroptosis could contribute to the profound study of the biological functions of HClO during ferroptosis. Here, we present a turn-on probe (RH-C) for the imaging of intracellular HClO during ferroptosis. The probe RH-C utilized the N,N-dimethylthiocarbamate group as a selective recognition site for HClO, and displayed desirable sensitivity and selectivity to HClO. The probe RH-C could detect the exogenous and endogenous HClO in living cells. Furthermore, RH-C was competent in monitoring the changes of endogenous HClO level during the process of ferroptosis. Biological imaging results suggested that erastin-induced ferroptosis can result in the excessive production of the endogenous HClO, and ferrostatin-1 (Fer-1) and vitamin E (VE) could block the massive accumulation of HClO in living cells.

NIR Fluorescent/Photoacoustic Bimodal Imaging of Ferroptosis in Pancreatic Cancer Using Biothiols-Activable Probes

Ferroptosis modulation is a powerful therapeutic option for pancreatic ductal adenocarcinoma (PDAC) with a low 5-year survival rate and lack of effective treatment methods. However, due to the dual role of ferroptosis in promoting and inhibiting pancreatic tumorigenesis, regulating the degree of ferroptosis is very important to obtain the best therapeutic effect of PDAC. Biothiols are suitable as biomarkers of imaging ferroptosis due to the dramatic decreases of biothiol levels in ferroptosis caused by the inhibited synthesis pathway of glutathione (GSH) and the depletion of biothiol by reactive oxygen species. Moreover, a very recent study reported that cysteine (Cys) depletion can lead to pancreatic tumor ferroptosis in mice and may be employed as an effective therapeutic strategy for PDAC. Therefore, visualization of biothiols in ferroptosis of PDAC will be helpful for regulating the degree of ferroptosis, understanding the mechanism of Cys depletion-induced pancreatic tumor ferroptosis, and further promoting the study and treatment of PDAC. Herein, two biothiol-activable near-infrared (NIR) fluorescent/photoacoustic bimodal imaging probes (HYD-BX and HYD-DX) for imaging of pancreatic tumor ferroptosis were reported. These two probes show excellent bimodal response performances for biothiols in solution, cells, and tumors. Subsequently, they have been employed successfully for real-time visualization of changes in concentration levels of biothiols during the ferroptosis process in PDAC cells and HepG2 cells. Most importantly, they have been further applied for bimodal imaging of ferroptosis in pancreatic cancer in mice, with satisfactory results. The development of these two probes provides new tools for monitoring changes in concentration levels of biothiols in ferroptosis and will have a positive impact on understanding the mechanism of Cys depletion-induced pancreatic tumor ferroptosis and further promoting the study and treatment of PDAC.

D-A-D type based NIR fluorescence probe for monitoring the cysteine levels in pancreatic cancer cell during ferroptosis

Cysteine (Cys) as a crucial precursor for intracellular glutathione (GSH) synthesis, plays an important role in the redox regulation in ferroptosis, Therefore, evaluating intracellular Cys levels is worthy to better understand ferroptosis-related physiological process. In this work, we constructed a novel NIR coumarin-derived fluorescent probe (NCDFP-Cys) based on a dual-ICT system, the NCDFP-Cys can show fluorescence turn-on response at 717 nm toward Cys over other amino acids, and possess large Stokes shift (Δλ = 167 nm), low detection limit, hypotoxicity. More significantly, NCDFP-Cys has been utilized to monitor the intracellular Cys fluctuation in pancreatic cancer cells during ferroptosis induced by Erastin and RSL3 respectively, and revealing the difference of Cys levels changes in different activator-triggered ferroptosis pathways.

Butyrylcholinesterase-Activated Near-Infrared Fluorogenic Probe for In Vivo Theranostics of Alzheimer's Disease

Butyrylcholinesterase (BChE) is a promising biomarker and effective therapeutic target for Alzheimer's disease (AD). Herein, we designed a BChE-activated near-infrared (NIR) probe, DTNP, which could be activated by BChE and inhibit its enzymatic activity. DTNP is composed of a cyclopropane moiety as the recognition unit, a NIR fluorophore hemicyanine as the NIR reporter, and a BChE inhibitor as the therapeutic unit. DTNP specifically binds BChE with high sensitivity and exhibits strong "turn-on" NIR fluorescence as well as nerve cell protection. In vivo imaging shows DTNP has favorable blood-brain barrier permeability and long-term tracking ability with preliminary competence in AD diagnosis. DTNP can significantly inhibit BChE activity, promote the release of ACh, and rescue learning deficits and cognitive impairment. Therefore, DTNP, the first reported and partially validated theranostic probe for the detection of BChE in AD, may provide a foundation and inspiration for imaging and therapy in AD.

Unraveling Ferroptosis Mechanisms: Tracking Cellular Viscosity with Small Molecular Fluorescent Probes

Ferroptosis is a recently identified form of regulated cell death characterized by iron accumulation and lipid peroxidation. Numerous functions for ferroptosis have been identified in physiological as well as pathological processes, most notably in the treatment of cancer. The intricate balance of redox homeostasis is profoundly altered during ferroptosis, leading to alteration in cellular microenvironment. One such microenvironment is viscosity among others such as pH, polarity, and temperature. Therefore, understanding the dynamics of ferroptosis associated viscosity levels within organelles is crucial. To date, there are a very few reviews that detects ferroptosis assessing reactive species. In this review, we have summarized organelle's specific fluorescent probes that detects dynamics of microviscosity during ferroptosis. Also, we offer the readers an insight of their design strategy, photophysics and associated bioimaging concluding with the future perspective and challenges in the related field.

Novel Peptide-Based Fluorescent Probe for Simultaneous Sensing of Chymotrypsin and Hydrogen Peroxide

The developed multifunctional fluorescent probe enables the simultaneous detection of chymotrypsin as a model protease and hydrogen peroxide as a representative of reactive oxygen species (ROS) in biologically relevant concentration ranges. The chymotrypsin sensing is based on the cleavage of its selectively recognizable peptide sequence and the consequent disruption of FRET between coumarin (DEAC) and fluorescein (FL). Analogously, the presence of hydrogen peroxide causes the gradual degradation of the H2O2-labile benzopyrylium-coumarin (BC) dye. Considering the fluorescence emission responses of individual chymotrypsin-peroxide probe-attached fluorophores after their excitation at 425 nm, the sole presence of either chymotrypsin (50-1000 ng/mL) or hydrogen peroxide (10-200 μM) in a sample could be unambiguously confirmed or refuted. In addition, reliable simultaneous detection and approximate quantification of both studied species in the concentration ranges of 100-1000 ng/mL and 20-200 μM for chymotrypsin and H2O2, respectively, could be performed as well. The obtained results are summarized and visualized in the graphical models.

Golgi apparatus-targeting fluorescent probe for the imaging of superoxide anion (O2•-) in living cells during ferroptosis

Ferroptosis is an emerging iron-dependent oxidative cell death type, and recently has been demonstrated to show close relation with Golgi apparatus (GA). Exploring the fluctuation of superoxide anion (O2•-) level in GA during ferroptosis is of great significance to profoundly study the biological functions of GA in ferroptosis. Here, we present a GA-targeting probe (N-GA) to monitor cellular O2•- during ferroptosis. N-GA employed a triflate group and a tetradecanoic amide unit as the recognition site for O2•- and GA-targeting unit, respectively. After the response of N-GA to O2•-, the triflate unit of N-GA converted into hydroxyl group with strong electron-donating ability, generating bright green fluorescence under UV light. N-GA exhibited excellent sensitivity and selectivity towards O2•-. Fluorescence imaging results showed that N-GA could be applied as a GA-targeting probe to monitor cellular O2•-. The stimulation of cells with PMA and rotenone could result in the massive generation of endogenous O2•- in GA. Erastin-induced ferroptosis can markedly induce the increase of O2•- level in GA. Similar to Fer-1 and DFO, dihydrolipoic acid (DHLA) and rutin were demonstrated to inhibit the enormous production of O2•- in GA of the living cells during ferroptosis.

Reversible Dual Fluorescence-Lifetime Imaging of Mitochondrial GSH and Microviscosity: Real-Time Evaluation of Ferroptosis Status

Ferroptosis, as a new form of regulated cell death, is implicated in various physiological and pathological processes. Developing a single probe for an independent analysis of multiple analytes related to ferroptosis can provide more accurate information and simplify the detection procedures, but it faces great challenges. In this work, we develop a fluorescent probe for the simultaneous detection of GSH through ratiometric fluorescence response and microviscosity via a fluorescence lifetime model. Based on the reversible Michael addition reaction between GSH and unsaturated C═C bond, the probe responds reversibly to GSH with a ratiometric fluorescence variation and a fast response time (t1/2 = 4.7 s). At the same time, the probe is sensitive to environmental viscosity by changing its fluorescence lifetimes. The probe was applied to monitor the drug-induced ferroptosis process through both the classical Xc-/GSH/GPX4- and DHODH-mediated defense mechanisms. We hope that the probe will provide a useful molecular tool for the real-time live-cell imaging of GSH dynamics, which is benefit to unveiling related physiological and pathological processes.

A sensitive "turn-on" Schiff-base fluorescent probe for the selective detection of Fe3+ and bio-imaging

A novel Schiff-base fluorescent probe, 4-(N-(2- hydroxyl-1-naphthalymethylimino)-ethylamino) -7-nitro-1,2,3-benzoxadiazole (HENB) was synthesized and utilized for spectral sensing of Fe3+ ions at neutral pH. The binding of Fe3+ to HENB in C2H5OH-HEPES buffer (1:1 v/ v, 25 mM, pH 7.2) resulted in a pronounced emission enhancement at 530 nm, which is possibly due to the inhibition of photo-induced electron transfer (PET) process as well as the chelation enhanced fluorescence (CHEF) effect. HENB shows good selectivity and sensitivity toward Fe3+ with the detection limit as low as 4.51 nM. Test strips made of HENB was used for rapid "naked-eye" detection of Fe3+ ions in aqueous medium. Moreover, HENB was successfully applied in fluorescence imaging of exogenous and endogenous Fe3+ in live Hela cells as well as zebrafish. Importantly, HENB is capable of effectively monitoring the variations of Fe3+ in living cells during ferroptosis process.

Ultrasound-enhanced nano catalyst with ferroptosis-apoptosis combined anticancer strategy for metastatic uveal melanoma

Uveal melanoma is the most common primary ocular tumor owing to its highly invasive and metastatic characteristics. Currently, standard clinical treatment has an unsatisfied curative effect due to the lack of an effective approach to inhibit the tumor metastasis. Therefore, it is necessary to develop a new strategy that can both restraint local tumors and suppress the ocular tumor metastasis. Herein, we developed ultrasound-responsive nanoparticles (FeP NPs) that can both hinder the growth of in situ ocular tumor and prevent the tumor metastasis through the ferroptosis-apoptosis combined-anticancer strategy. The FeP NPs were assembling by stimulating gallic acid-Fe (III) and paclitaxel, then could be internalized into tumor cells under the cooperative effect of ultrasound, which further activates the intracellular Fenton reaction and generates high reactive oxygen species levels, ultimately leading to mitochondrial damage, lipid per-oxidation, and apoptosis. The FeP NPs can efficiently inhibit the tumor growth in an orthotopic uveal melanoma model. More importantly, the level of the promoting-metastatic factor nerve growth factor receptor (NGFR) secreted by cancer cells is significantly reduced, further limits cancer metastasis to the cervical lymph node and finally inhibits lung metastasis of uveal melanoma. We believe that these designed ultrasound-enhanced nanoparticles possess potential clinical application for preventing the regeneration and metastasis of uveal melanoma.

Development of bishydrazide-based fluorescent probes for the imaging of cellular peroxynitrite (ONOO-) during ferroptosis

Peroxynitrite (ONOO-) is a critical ROS in living systems, and could induce lipid peroxidation which is the driver of ferroptotic cell death. Therefore, precise and rapid detection of cellular ONOO- is critical for the deep study of the biological functions of ONOO- during ferroptosis. Herein, we developed fluorescent probes (Rh-1, Rh-2 and Rh-3) for the rapid detection of intracellular ONOO- during ferroptosis. These probes used bishydrazide groups as the reactive sites for ONOO-. The response of these probes to ONOO- resulted in the production of the emissive xanthene fluorophore, providing a marked enhancement in the fluorescence intensity at 561 nm. The probe Rh-3 exhibited prominent selectivity and sensitivity towards ONOO-. Bioimaging experiments suggested that Rh-3 could be applied to image exogenous and endogenous ONOO- in living cells. By fluorescence imaging, it was demonstrated that erastin-induced ferroptosis caused increased levels of the endogenous ONOO-, and ferrostatin-1 (Fer-1) and vitamin E (VE) could markedly inhibit the excessive production of ONOO- during ferroptosis in living cells.

Ferroptosis-Based Therapeutic Strategies toward Precision Medicine for Cancer

Ferroptosis is a type of iron-dependent programmed cell death characterized by the dysregulation of iron metabolism and the accumulation of lipid peroxides. This nonapoptotic mode of cell death is implicated in various physiological and pathological processes. Recent findings have underscored its potential as an innovative strategy for cancer treatment, particularly against recalcitrant malignancies that are resistant to conventional therapies. This article focuses on ferroptosis-based therapeutic strategies for precision cancer treatment, covering the molecular mechanisms of ferroptosis, four major types of ferroptosis inducers and their inhibitory effects on diverse carcinomas, the detection of ferroptosis by fluorescent probes, and their implementation in image-guided therapy. These state-of-the-art tactics have manifested enhanced selectivity and efficacy against malignant carcinomas. Given that the administration of ferroptosis in cancer therapy is still at a burgeoning stage, some major challenges and future perspectives are discussed for the clinical translation of ferroptosis into precision cancer treatment.

Mechanisms of ferroptosis and targeted therapeutic approaches in lymphoma

Lymphoma is the sixth most common type of cancer worldwide. Under the current treatment standards, patients with lymphoma often fail to respond to treatment or relapse early and require further therapy. Hence, novel therapeutic strategies need to be explored and our understanding of the molecular underpinnings of lymphomas should be expanded. Ferroptosis, a non-apoptotic regulated cell death, is characterized by increased reactive oxygen species and lipid peroxidation due to metabolic dysfunction. Excessive or lack of ferroptosis has been implicated in tumor development. Current preclinical evidences suggest that ferroptosis participates in tumorigenesis, progression, and drug resistance of lymphoma, identifying a potential biomarker and an attractive molecular target. Our review summarizes the core mechanisms and regulatory networks of ferroptosis and discusses existing evidences of ferroptosis induction for the treatment of lymphoma, with intent to provide a framework for understanding the role of ferroptosis in lymphomagenesis and a new perspective of lymphoma treatment.

Precise visualization and ROS-dependent photodynamic therapy of colorectal cancer with a novel mitochondrial viscosity photosensitive fluorescent probe

BACKGROUND

Colorectal cancer (CRC) is a prominent global cancer with high mortality rates among human beings. Efficient diagnosis and treatment have always been a challenge for CRC management. Fluorescence guided cancer therapy, which combines diagnosis with therapy into one platform, has brought a new chance for achieving precise cancer theranostics. Among this, photosensitizers, applied in photodynamic therapy (PDT), given the integration of real-time imaging capacity and efficacious treatment feasibility, show great potential to serve as remarkable tools. Although much effort has been put into constructing photosensitizers for locating and destroying CRC cells, it is still in high need to develop novel photosensitizers to attain specific detection and fulfil effective therapy.

METHODS

Probe HTI was rational synthesized for the diagnosis and treatment of CRC. Spectrometric determination was carried out first, followed by the 1O2 generation ability test. Then, HTI was displayed in distinguishing CRC cells from normal cells Further, the PDT effect of the photosensitizer was studied in vitro. Additionally, HTI was used in CRC BALB/c nude mice model to validate its viscosity labelling and tumor suppression characteristics.

RESULTS

We successfully fabricated a mitochondrial targeting probe, HTI, together with remarkable viscosity sensitivity, ultralow background interference, and excellent 1O2 generation capacity. HTI was favorably applied to the viscosity detection, displaying a 11-fold fluorescent intensity enhancement in solvents from 1.57 cp to 2043 cp. Then, it was demonstrated that HTI could distinguish CRC cells from normal cells upon the difference in mitochondrial viscosity. Moreover, HTI was qualified for producing 1O2 with high efficiency in cells, supported by the sparkling signals of DCFH after incubation with HTI under light irradiation. More importantly, the viscosity labelling and tumor suppression performance in CRC CDX model was determined, enriching the multifunctional validation of HTI in vivo.

CONCLUSIONS

In this study, HTI was demonstrated to show a sensitive response to mitochondrial viscosity and possess a high 1O2 generation capacity. Both in vitro cell imaging and in vivo tumor treatment trials proved that HTI was effectively served as a robust scaffold for tumor labeling and CRC cells clearance. This breakthrough discovery held immense potential for advancing the early diagnosis and management of CRC through PDT. By leveraging HTI's properties, medical professionals could benefit from improved diagnostic accuracy and targeted treatment in CRC management, ultimately leading to enhanced patient outcomes.

Neutrophil extracellular traps drive intestinal microvascular endothelial ferroptosis by impairing Fundc1-dependent mitophagy

Microvascular endothelial damage caused by intestinal ischemia‒reperfusion (II/R) is a primary catalyst for microcirculation dysfunction and enterogenous infection. Previous studies have mainly focused on how neutrophil extracellular traps (NETs) and ferroptosis cause intestinal epithelial injury, and little attention has been given to how NETs, mainly from circulatory neutrophils, affect intestinal endothelial cells during II/R. This study aimed to unravel the mechanisms through which NETs cause intestinal microvascular dysfunction. We first detected heightened local NET infiltration around the intestinal microvasculature, accompanied by increased endothelial cell ferroptosis, resulting in microcirculation dysfunction in both human and animal II/R models. However, the administration of the ferroptosis inhibitor ferrostatin-1 or the inhibition of NETs via neutrophil-specific peptidylarginine deiminase 4 (Pad4) deficiency led to positive outcomes, with reduced intestinal endothelial ferroptosis and microvascular function recovery. Moreover, RNA-seq analysis revealed a significant enrichment of mitophagy- and ferroptosis-related signaling pathways in HUVECs incubated with NETs. Mechanistically, elevated NET formation induced Fundc1 phosphorylation at Tyr18 in intestinal endothelial cells, which led to mitophagy inhibition, mitochondrial quality control imbalance, and excessive mitochondrial ROS generation and lipid peroxidation, resulting in endothelial ferroptosis and microvascular dysfunction. Nevertheless, using the mitophagy activator urolithin A or AAV-Fundc1 transfection could reverse this process and ameliorate microvascular damage. We first demonstrate that increased NETosis could result in intestinal microcirculatory dysfunction and conclude that suppressed NET formation can mitigate intestinal endothelial ferroptosis by improving Fundc1-dependent mitophagy. Targeting NETs could be a promising approach for treating II/R-induced intestinal microcirculatory dysfunction.

Visualization detection of mycotoxin patulin in fruit juices by a small-molecule fluorescent probe

The mycotoxin patulin is a common contaminant in rotten fruits, posing severe food safety risks and threats to human health. Developing a convenient, sensitive and reliable method for patulin detection is of utmost importance but remains challenging. In this study, we have successfully designed and synthesized a small-molecule fluorescent probe, FITC-Lys, which demonstrates good sensitivity in detecting patulin. Upon contact with patulin, the terminal Lys group of the FITC-Lys probe reacts with patulin, resulting in the formation of the fluorescein dimer that subsequently quenches fluorescence. This variation of fluorescence enables the visualization and sensitive detection of patulin. The probe exhibits good sensitivity with a low LOD of 8 ng mL-1 for the fluorescence spectrum method and a LOD of 12 ng mL-1 for the fluorescence imaging method. Moreover, we have validated the probe's capability for patulin detection in apple and pear juices, achieving good recoveries ranging from 98.60% to 103.80%. Notably, the probe FITC-Lys is the first small-molecule fluorescent probe that has proven successful in visualizing patulin in juices derived from decayed apples and pears. Consequently, this probe holds great potential as a practical tool for monitoring patulin in foodstuffs, thereby contributing to enhanced food safety standards.

RNA-Selective Small-Molecule Ligands: Recent Advances in Live-Cell Imaging and Drug Discovery

RNA structures, including those formed from coding and noncoding RNAs, alternative to protein-based drug targets, could be a promising target of small molecules for drug discovery against various human diseases, particularly in anticancer, antibacterial and antivirus development. The normal cellular activity of cells is critically dependent on the function of various RNA molecules generated from DNA transcription. Moreover, many studies support that mRNA-targeting small molecules may regulate the synthesis of disease-related proteins via the non-covalent mRNA-ligand interactions that do not involve gene modification. RNA-ligand interaction is thus an attractive approach to address the challenge of "undruggable" proteins in drug discovery because the intracellular activity of these proteins is hard to be suppressed with small molecule ligands. We selectively surveyed a specific area of RNA structure-selective small molecule ligands in fluorescence live cell imaging and drug discovery because the area was currently underexplored. This state-of-the-art review thus mainly focuses on the research published within the past three years and aims to provide the most recent information on this research area; hopefully, it could be complementary to the previously reported reviews and give new insights into the future development on RNA-specific small molecule ligands for live cell imaging and drug discovery.

A D-π-A-π-D type structure-based fluorescent probe for revealing the fluctuations of the ER polarity during ferroptosis

Ferroptosis is a novel Fe(II)-mediated oxidative cell death form, and is closely related with endoplasmic reticulum (ER). Exploring the fluctuation of ER polarity during ferroptosis is highly important for the in-depth study of the biological roles of ER in ferroptosis. Herein, we present a ratiometric probe (BNS) for revealing the changes of the ER polarity in the living cells experiencing ferroptosis. BNS employed a D-π-A-π-D type structure as the polarity-sensitive fluorophore, and selected p-toluenesulfonamide as the ER-targeting unit. Theoretical calculations suggested that the response mechanism of BNS to polarity was based on ICT, and two ICT processes appeared when BNS was at excited state. Cell imaging results demonstrated that BNS possessed desirable ER-targeting capability, and erastin-induced ferroptosis could increase the ER polarity of the living cells. Moreover, similarly to vitamin E (VE) and deferoxamine (DFO), dihydrolipoic acid (DHLA) could inhibit the changes of the ER polarity during erastin-induced ferroptosis. We expect that the probe could provide a convenient method to rapidly monitor ferroptosis and design novel drugs for the treatment of ferroptosis-relevant diseases.

Nanoprobe-based molecular imaging for tumor stratification

The responses of patients to tumor therapies vary due to tumor heterogeneity. Tumor stratification has been attracting increasing attention for accurately distinguishing between responders to treatment and non-responders. Nanoprobes with unique physical and chemical properties have great potential for patient stratification. This review begins by describing the features and design principles of nanoprobes that can visualize specific cell types and biomarkers and release inflammatory factors during or before tumor treatment. Then, we focus on the recent advancements in using nanoprobes to stratify various therapeutic modalities, including chemotherapy, radiotherapy (RT), photothermal therapy (PTT), photodynamic therapy (PDT), chemodynamic therapy (CDT), ferroptosis, and immunotherapy. The main challenges and perspectives of nanoprobes in cancer stratification are also discussed to facilitate probe development and clinical applications.

Epilepsy: Mitochondrial connections to the 'Sacred' disease

Over 65 million people suffer from recurrent, unprovoked seizures. The lack of validated biomarkers specific for myriad forms of epilepsy makes diagnosis challenging. Diagnosis and monitoring of childhood epilepsy add to the need for non-invasive biomarkers, especially when evaluating antiseizure medications. Although underlying mechanisms of epileptogenesis are not fully understood, evidence for mitochondrial involvement is substantial. Seizures affect 35%-60% of patients diagnosed with mitochondrial diseases. Mitochondrial dysfunction is pathophysiological in various epilepsies, including those of non-mitochondrial origin. Decreased ATP production caused by malfunctioning brain cell mitochondria leads to altered neuronal bioenergetics, metabolism and neurological complications, including seizures. Iron-dependent lipid peroxidation initiates ferroptosis, a cell death pathway that aligns with altered mitochondrial bioenergetics, metabolism and morphology found in neurodegenerative diseases (NDDs). Studies in mouse genetic models with seizure phenotypes where the function of an essential selenoprotein (GPX4) is targeted suggest roles for ferroptosis in epilepsy. GPX4 is pivotal in NDDs, where selenium protects interneurons from ferroptosis. Selenium is an essential central nervous system micronutrient and trace element. Low serum concentrations of selenium and other trace elements and minerals, including iron, are noted in diagnosing childhood epilepsy. Selenium supplements alleviate intractable seizures in children with reduced GPX activity. Copper and cuproptosis, like iron and ferroptosis, link to mitochondria and NDDs. Connecting these mechanistic pathways to selenoproteins provides new insights into treating seizures, pointing to using medicines including prodrugs of lipoic acid to treat epilepsy and to potential alternative therapeutic approaches including transcranial magnetic stimulation (transcranial), photobiomodulation and vagus nerve stimulation.

A mitochondria-targeted dual-response sensor for monitoring viscosity and peroxynitrite in living cells with distinct fluorescence signals

Viscosity and peroxynitrite (ONOO-) are two significant indicators to affect and evaluate the mitochondrial functional status, which are nearly relational with pathophysiological process in many diseases. Developing suitable analytical methods for monitoring mitochondrial viscosity changes and ONOO- is thus of great importance. In this research, a new mitochondria-targeted sensor DCVP-NO2 for the dual determination of viscosity and ONOO- was exploited based on the coumarin skeleton. DCVP-NO2 displayed a red fluorescence "turn-on" response toward viscosity along with about 30-fold intensity increase. Meanwhile, it could be used as ratiometric probe for detection of ONOO- with excellent sensitivity and extraordinary selectivity for ONOO- over other chemical and biological species. Moreover, thanks to its good photostability, low cytotoxicity and ideal mitochondrion-targeting capability, DCVP-NO2 was successfully utilized for fluorescence imaging of viscosity variations and ONOO- in mitochondria of living cells through different channels. In addition, the results of cell imaging revealed that ONOO- would lead to the increase of viscosity. Taken together, this work provides a potential molecular tool for researching biological functions and interactions of viscosity and ONOO- in mitochondria.

A new benzo-bodipy based fluorescent probe for the highly sensitive detection of hypochlorous acid and its application in the living cells and zebrafish imaging

Due to the highly significant biological activity of hypochlorous acid, the monitoring of its concentration in vivo has received extensive attention. In this work, a photoinduced electron transfer (PeT) based benzo-bodipy fluorescent probe BBy-T has been developed for the rapid, sensitive, and selective detection of HClO in an aqueous solution. Based on the HClO-specific oxidation reaction, BBy-T exhibited a distinct fluorescence turn-on response to HClO with a remarkable Stokes shift (84 nm), immediate response (less than 20 s), and low detection limit (13.7 nM). In addition, the bioimaging results indicated that the probe BBy-T could be applied to real-time fluorescence imaging of living HeLa cells as well as living zebrafish.

A benzo BODIPY based fluorescent probe for selective visualization of hypochlorous acid in living cells and zebrafish

Hypochlorous acid (HOCl) is an essential endogenous reactive oxygen species in biological systems, playing a critical role in various physiological processes. Real-time monitoring of HOCl concentration in living organisms is essential for understanding its biological functions and pathological roles. In this study, we developed a novel fluorescent probe based on benzobodipy, BBDP, for rapid and sensitive detection of HOCl in aqueous solutions. The probe exhibited a significant fluorescence turn-on response to HOCl based on its specific oxidation reaction towards diphenylphosphine, with high selectivity, instantaneous response (less than 10 s), and low detection limit (21.6 nM). Furthermore, bioimaging results illustrated that the probe could be applied for real-time fluorescence imaging of HOCl in live cells and zebrafish. The development of BBDP may provide a new tool for exploring the biological functions of HOCl and its pathological roles in diseases.

Fluorescent probes for lighting up ferroptotic cell death: A review

Ferroptosis is a newly discovered form of regulated cellular demise, characterized by the accumulation of intracellular oxidative stress that is dependent on iron. Ferroptosis plays a crucial role not only in the development and treatment of tumors but also in the pathogenesis of neurodegenerative diseases and illnesses related to ischemia-reperfusion injury. This mode of cell death possesses distinctive properties that differentiate it from other forms of cell death, including unique morphological changes at both the cellular and subcellular levels, as well as molecular features that can be detected using specific methods. The use of fluorescent probes has become an invaluable means of detecting ferroptosis, owing to their high sensitivity, real-time in situ monitoring capabilities, and minimal damage to biological samples. This review comprehensively elucidates the physiological mechanisms underlying ferroptosis, while also detailing the development of fluorescent probes capable of detecting ferroptosis-related active species across various cellular compartments, including organelles, the nucleus, and the cell membrane. Additionally, the review explores how the dynamic changes and location of active species from different cellular compartments can influence the ignition and execution of ferroptotic cell death. Finally, we discuss the future challenges and opportunities for imaging ferroptosis. We believe that this review will not only aid in the elucidation of ferroptosis's physiological mechanisms but also facilitate the identification of novel treatment targets and means of accurately diagnosing and treating ferroptosis-related diseases.

Versatile Switchable Targeted Polysiloxanes for High-Resolution Visualization of Mitochondrial and Lysosomal Interactions during Ferroptosis

Ferroptosis is an iron-dependent process that regulates cell death and is essential for maintaining normal cell and tissue survival. The explosion of reactive oxygen species characterizes ferroptosis in a significant way. Peroxynitrite (ONOO^-) is one of the endogenous reactive oxygen species. Abnormal ONOO^- concentrations cause damage to subcellular organelles and further interfere with organelle interactions. However, the proper conduct of organelle interactions is critical for cellular signaling and the maintenance of cellular homeostasis. Therefore, investigating the effect of ONOO^- on organelle interactions during ferroptosis is a highly attractive topic. To date, it has been challenging to visualize the full range of ONOO^- fluctuations in mitochondria and lysosomes during ferroptosis. In this paper, we constructed a switchable targeting polysiloxane platform. During the selective modification of NH₂ groups located in the side chain, the polysiloxane platform successfully constructed fluorescent probes targeting lysosomes and mitochondria (Si-Lyso-ONOO, Si-Mito-ONOO), respectively. Real-time detection of ONOO^- in lysosomes and mitochondria during ferroptosis was successfully achieved. Remarkably, the occurrence of autophagy during late ferroptosis and the interaction between mitochondria and lysosomes was observed via the differentiated responsive strategy. We expect that this switchable targeting polysiloxane functional platform will broaden the application of polymeric materials in bioimaging and provide a powerful tool for further deeper understanding of the ferroptosis process.

Luminescence and Palladium: The Odd Couple

The synthesis, photophysical properties, and applications of highly fluorescent and phosphorescent palladium complexes are reviewed, covering the period 2018–2022. Despite the fact that the Pd atom appears closely related with an efficient quenching of the fluorescence of different molecules, different synthetic strategies have been recently optimized to achieve the preservation and even the amplification of the luminescent properties of several fluorophores after Pd incorporation. Beyond classical methodologies such as orthopalladation or the use of highly emissive ligands as porphyrins and related systems (for instance, biladiene), new concepts such as AIE (Aggregation Induced Emission) in metallacages or in coordination-driven supramolecular compounds (CDS) by restriction of intramolecular motions (RIM), or complexes showing TADF (Thermally Activated Delayed Fluorescence), are here described and analysed. Without pretending to be comprehensive, selected examples of applications in areas such as the fabrication of lighting devices, biological markers, photodynamic therapy, or oxygen sensing are also here reported.

H2S-based fluorescent imaging for pathophysiological processes

Hydrogen sulfide (H₂S), as an important endogenous signaling molecule, plays a vital role in many physiological processes. The abnormal behaviors of hydrogen sulfide in organisms may lead to various pathophysiological processes. Monitoring the changes in hydrogen sulfide is helpful for pre-warning and treating these pathophysiological processes. Fluorescence imaging techniques can be used to observe changes in the concentration of analytes in organisms in real-time. Therefore, employing fluorescent probes imaging to investigate the behaviors of hydrogen sulfide in pathophysiological processes is vital. This paper reviews the design strategy and sensing mechanisms of hydrogen sulfide-based fluorescent probes, focusing on imaging applications in various pathophysiological processes, including neurodegenerative diseases, inflammation, apoptosis, oxidative stress, organ injury, and diabetes. This review not only demonstrates the specific value of hydrogen sulfide fluorescent probes in preclinical studies but also illuminates the potential application in clinical diagnostics.

In Situ and Quantitatively Monitoring the Dynamic Process of Ferroptosis in Single Cancer Cells by Scanning Electrochemical Microscopy

Ferroptosis, as a promising therapeutic strategy for cancers, has aroused great interest. Quantifying the quick dynamic changes in key parameters during the early course of ferroptosis can provide insights for understanding the underlying mechanisms of ferroptosis and help the development of therapies targeting ferroptosis. However, in situ and quantitatively monitoring the quick responses of living cancer cells to ferroptosis at the single-cell level remains technically challenging. In this work, we selected HuH7 cells (hepatocellular carcinoma (HCC) cells) as a cell model and Erastin as a typical ferroptosis inducer. We utilized scanning electrochemical microscopy (SECM) to quantitatively and in situ monitor the early course of ferroptosis in HuH7 cells by characterizing the three key parameters of cell ferroptosis (i.e., cell membrane permeability, respiratory activity, and the redox state). The SECM results show that the membrane permeability of ferroptotic HuH7 cells continuously increased from 0 to 8.1 × 10-5 m s-1, the cellular oxygen consumption was continuously reduced by half, and H2O2 released from the cells exhibited periodic bursts during the early course of ferroptosis, indicating the gradually destroyed cell membrane structure and intensified oxidative stress. Our work realizes, for the first time, the in situ and quantitative monitoring of the cell membrane permeability, respiratory activity, and H2O2 level of the early ferroptosis process of a single living cancer cell with SECM, which can contribute to the understanding of the physiological process and underlying mechanisms of ferroptosis.

The roles of sirtuins in ferroptosis

Ferroptosis represents a novel non-apoptotic form of regulated cell death that is driven by iron-dependent lipid peroxidation and plays vital roles in various diseases including cardiovascular diseases, neurodegenerative disorders and cancers. Plenty of iron metabolism-related proteins, regulators of lipid peroxidation, and oxidative stress-related molecules are engaged in ferroptosis and can regulate this complex biological process. Sirtuins have broad functional significance and are targets of many drugs in the clinic. Recently, a growing number of studies have revealed that sirtuins can participate in the occurrence of ferroptosis by affecting many aspects such as redox balance, iron metabolism, and lipid metabolism. This article reviewed the studies on the roles of sirtuins in ferroptosis and the related molecular mechanisms, highlighting valuable targets for the prevention and treatment of ferroptosis-associated diseases.

Targeting Tumor Microenvironment by Metal Peroxide Nanoparticles in Cancer Therapy

Solid tumors have a unique tumor microenvironment (TME), which includes hypoxia, low acidity, and high hydrogen peroxide and glutathione (GSH) levels, among others. These unique factors, which offer favourable microenvironments and nourishment for tumor development and spread, also serve as a gateway for specific and successful cancer therapies. A good example is metal peroxide structures which have been synthesized and utilized to enhance oxygen supply and they have shown great promise in the alleviation of hypoxia. In a hypoxic environment, certain oxygen-dependent treatments such as photodynamic therapy and radiotherapy fail to respond and therefore modulating the hypoxic tumor microenvironment has been found to enhance the antitumor impact of certain drugs. Under acidic environments, the hydrogen peroxide produced by the reaction of metal peroxides with water not only induces oxidative stress but also produces additional oxygen. This is achieved since hydrogen peroxide acts as a reactive substrate for molecules such as catalyse enzymes, alleviating tumor hypoxia observed in the tumor microenvironment. Metal ions released in the process can also offer distinct bioactivity in their own right. Metal peroxides used in anticancer therapy are a rapidly evolving field, and there is good evidence that they are a good option for regulating the tumor microenvironment in cancer therapy. In this regard, the synthesis and mechanisms behind the successful application of metal peroxides to specifically target the tumor microenvironment are highlighted in this review. Various characteristics of TME such as angiogenesis, inflammation, hypoxia, acidity levels, and metal ion homeostasis are addressed in this regard, together with certain forms of synergistic combination treatments.