Fluorogenic hydrogen sulfide (H2S) donors based on sulfenyl thiocarbonates enable H2S tracking and quantification

Self-Assembly of H2S-Generating Photosensitizer for Gas-Assisted Synergistic Photothermal Therapy

Photothermal therapy (PTT) is emerging as a promising cancer treatment, but uneven heat distribution increases side effects and reduces treatment precision, where high-temperature zones risk inducing undesired inflammation, while low-temperature regions are insufficient due to upregulation of heat shock proteins (HSPs). Herein, a gas-assisted PTT strategy is designed to link near-infrared heptamethine cyanine (Cy7) with self-immolative phenyl thiocarbonate (PTC), a hydrogen sulfide (H2S) donor through a disulfide bond, creating a small-molecule photosensitizer (Cy7-SS-PTC) that can self-assemble into nanoparticles (NPs) without stabilizers. Upon internalized by cancer cells, Cy7-SS-PTC NPs respond to elevated glutathione levels, and simultaneously release Cy7 and H2S via a cascade reaction. The released Cy7 reassembles into nanoaggregates, generating hyperthermia under 808 nm light irradiation, and then binds to albumin, producing strong near-infrared fluorescence to track tumors for precise treatment. The released H2S not only disrupts the mitochondrial respiratory chain, blocks ATP production, and suppresses HSP70 overexpression to amplify the efficacy of low-temperature PTT regions but also curbs proinflammatory cytokines in high-temperature PTT zones, delivering powerful tumor ablation with minimal inflammation. This small-molecule-based "H2S-assisted PTT" strategy optimizes the current PTT and validates its potential clinical application.

Catalytic Biomaterials-Activated In Situ Chemical Reactions: Strategic Modulation and Enhanced Disease Treatment

Chemical reactions underpin biological processes, and imbalances in critical biochemical pathways within organisms can lead to the onset of severe diseases. Within this context, the emerging field of "Nanocatalytic Medicine" leverages nanomaterials as catalysts to modulate fundamental chemical reactions specific to the microenvironments of diseases. This approach is designed to facilitate the targeted synthesis and localized accumulation of therapeutic agents, thus enhancing treatment efficacy and precision while simultaneously reducing systemic side effects. The effectiveness of these nanocatalytic strategies critically hinges on a profound understanding of chemical kinetics and the intricate interplay of reactions within particular pathological microenvironments to ensure targeted and effective catalytic actions. This review methodically explores in situ catalytic reactions and their associated biomaterials, emphasizing regulatory strategies that control therapeutic responses. Furthermore, the discussion encapsulates the crucial elements-reactants, catalysts, and reaction conditions/environments-necessary for optimizing the thermodynamics and kinetics of these reactions, while rigorously addressing both the biochemical and biophysical dimensions of the disease microenvironments to enhance therapeutic outcomes. It seeks to clarify the mechanisms underpinning catalytic biomaterials and evaluate their potential to revolutionize treatment strategies across various pathological conditions.

A cysteine-activated fluorescent H2S donor for visualizing H2S release and alleviating cellular inflammation

We developed Bcy-NCS, a Cys-specific fluorescent H2S donor with a self-immolative spacer, overcoming the issue of multiple fluorophore release seen in traditional ICT-based donors. Bcy-NCS selectively responds to Cys, releases H2S, and enables fluorescence-based monitoring. It also reduces LPS-induced inflammation in RAW 264.7 cells, indicating potential for inflammation treatment.

Sydnthiones are versatile bioorthogonal hydrogen sulfide donors

Hydrogen sulfide (H2S) is an important endogenous gasotransmitter, but the bioorthogonal reaction triggered H2S donors are still rare. Here we show one type of bioorthogonal H2S donors, sydnthiones (1,2,3-oxadiazol-3-ium-5-thiolate derivatives), which was designed with the aid of density functional theory (DFT) calculations. The reactions between sydnthiones and strained alkynes provide a platform for controllable, tunable and mitochondria-targeted release of H2S. We investigate the reactivity of sydnthiones‒dibenzoazacyclooctyne (DIBAC) reactions and their orthogonality with two other bioorthogonal cycloaddition pairs: tetrazine‒norbornene (Nor) and tetrazine‒monohydroxylated cyclooctyne (MOHO). By taking advantage of these mutually orthogonal reactions, we can realize selective labeling or drug release. Furthermore, we explore the role of H2S, which is released from the sydnthione-DIBAC reaction, on doxorubicin-induced cytotoxicity. The results demonstrate that the viability of H9c2 cells can be significantly improved by pretreating with sydnthione 1b and DIBAC for 6 h prior to exposure to Dox.

Esterase-Activated Hydrogen Sulfide Donors with Self-Reporting Fluorescence Properties and Highly Tunable Rates of Delivery

Hydrogen sulfide (H2S) has emerged as a significant biomolecule with diverse activities, akin to other gaseous signaling molecules such as nitric oxide (NO) and carbon monoxide (CO). In the present study, we report on the development of esterase-activated donors that track their direct cellular donation of H2S by enlisting a cyclization reaction onto a thioamide that forms a fluorogenic byproduct. This simple donor design provides a noninvasive method for monitoring the biological delivery and activity of H2S, along with access to a library of compounds with highly variable rates of H2S delivery. These studies culminated with the identification of a slow-release, yet highly efficient, donor (ZL-DMA-Ph) that was shown to self-report its gradual and continuous cellular donation of H2S for up to 24 h which, in addition to better mimicking the natural biosynthesis of H2S, provided impressive cytoprotection in a cellular cardiotoxicity model, even at submicromolar concentrations. In total, these findings indicate that the esterase-triggered fluorogenic donors identified in this study will offer new opportunities for exploring the chemical biology and therapeutic potential of exogenous H2S supplementation.

Recent Developments On Activatable Turn-On Fluorogenic Donors of Hydrogen Sulfide (H2S)

Hydrogen sulfide (H2S) is considered the third member of the gasotransmitter family, along with nitric oxide (NO) and carbon monoxide (CO). Besides its role in physiological and pathophysiological conditions, the promising therapeutic potential of this small-molecule makes it advantageous for various pharmaceutical applications. The endogenous production of H2S at a lower concentration is crucial in maintaining redox balance and cellular homeostasis, and the dysregulation leads to various disease states. In the event of H2S deficiency, the exogenous donation of H2S could help maintain the optimal cellular concentration of H2S and cellular homeostasis. Over the last several years, researchers have developed numerous small-molecule non-fluorogenic organosulfur compounds as H2S donors and investigated their pharmacological potentials. However, reports on stimuli-responsive turn-on fluorogenic donors of H2S have appeared recently. Interestingly, the fluorogenic H2S donors offer additional advantages with the non-invasive real-time monitoring of the H2S release utilizing the simultaneous turn-on fluorogenic processes. The review summarizes the recent developments in turn-on fluorogenic donors of H2S and the potential biological applications that have developed over the years.

Fluorescent small molecule donors

Small molecule donors (SMDs) play subtle roles in the signaling mechanism and disease treatments. While many excellent SMDs have been developed, dosage control, targeted delivery, spatiotemporal feedback, as well as the efficiency evaluation of small molecules are still key challenges. Accordingly, fluorescent small molecule donors (FSMDs) have emerged to meet these challenges. FSMDs enable controllable release and non-invasive real-time monitoring, providing significant advantages for drug development and clinical diagnosis. Integration of FSMDs with chemotherapeutic, photodynamic or photothermal properties can take full advantage of each mode to enhance therapeutic efficacy. Given the remarkable properties and the thriving development of FSMDs, we believe a review is needed to summarize the design, triggering strategies and tracking mechanisms of FSMDs. With this review, we compiled FSMDs for most small molecules (nitric oxide, carbon monoxide, hydrogen sulfide, sulfur dioxide, reactive oxygen species and formaldehyde), and discuss recent progress concerning their molecular design, structural classification, mechanisms of generation, triggered release, structure-activity relationships, and the fluorescence response mechanism. Firstly, from the large number of fluorescent small molecular donors available, we have organized the common structures for producing different types of small molecules, providing a general strategy for the development of FSMDs. Secondly, we have classified FSMDs in terms of the respective donor types and fluorophore structures. Thirdly, we discuss the mechanisms and factors associated with the controlled release of small molecules and the regulation of the fluorescence responses, from which universal guidelines for optical properties and structure rearrangement were established, mainly involving light-controlled, enzyme-activated, reactive oxygen species-triggered, biothiol-triggered, single-electron reduction, click chemistry, and other triggering mechanisms. Fourthly, representative applications of FSMDs for trackable release, and evaluation monitoring, as well as for visible in vivo treatment are outlined, to illustrate the potential of FSMDs in drug screening and precision medicine. Finally, we discuss the opportunities and remaining challenges for the development of FSMDs for practical and clinical applications, which we anticipate will stimulate the attention of researchers in the diverse fields of chemistry, pharmacology, chemical biology and clinical chemistry. With this review, we hope to impart new understanding thereby enabling the rapid development of the next generation of FSMDs.

An Expanded Palette of Fluorescent COS/H2S-Releasing Donors for H2S Delivery, Detection, and In Vivo Application

Hydrogen sulfide (H2S) is an important reactive sulfur species that is involved in many biological functions, and H2S imbalances have been indicated as a potential biomarker for various diseases. Different H2S donors have been developed to deliver H2S directly to biological systems, but few reports include donors with optical responses that allow for tracking of H2S release. Moreover, donor systems that use the same chemistry to deliver H2S across a palette of fluorescent responses remain lacking. Here we report five thiol-activated fluorescence turn-on COS/H2S donors that utilize blue, yellow, orange, red, and near infrared-emitting dyes functionalized with an H2S-releasing sulfenyl thiocarbonate scaffold. Upon treatment with thiols, each donor provides a fluorescence turn-on response (3-310-fold) and high H2S release efficiencies (>60 %). Using combined electrode and fluorescence experiments, we directly correlate the measured H2S release with the fluorescence response. All donors are biocompatible and release H2S in live cell environments. In addition, we demonstrate that the NIR donor allows for imaging H2S release in live rats via subcutaneous injection of the donor loaded into an alginate gel, which to the best of our knowledge is the first in vivo tracking of H2S release from a fluorogenic donor in non-transparent organisms.

Inflammatory-stimuli-responsive turn-on NIR fluorogenic theranostic prodrug: adjuvant delivery of diclofenac and hydrogen sulfide attenuates acute inflammatory disorders

Prolonged use of very commonly prescribed non-steroidal anti-inflammatory drugs (NSAIDs) is often associated with undesired side effects, including gastrointestinal ulcers due to the non-selective inhibition of cyclooxygenases. We describe the development of an inflammatory-stimuli-responsive turn-on fluorogenic theranostic prodrug DCF-HS for adjuvant drug delivery. Upon activation by reactive oxygen species (ROS), the prodrug releases diclofenac DCF (active drug) and the NIR fluorophore DCI-NH2 along with carbonyl sulfide (COS). The second activation of COS by the enzyme carbonic anhydrase (CA) generates hydrogen sulfide (H2S). The prodrug was conveniently synthesized using multi-step organic synthesis. The UV-Vis and fluorescence studies revealed the selective reactivity of DCF-HS towards ROS such as H2O2 in the aqueous phase and the desired uncaging of the drug DCF with turn-on NIR fluorescent reporter under physiological conditions. Furthermore, the release of fluorophore DCI-NH2 and drug DCF was confirmed using the reverse phase HPLC method. Compatibility of prodrug activation was studied next in the cellular medium. The prodrug DCF-HS was non-toxic in a representative cancer cell line (HeLa) and a macrophage cell line (RAW 264.7) up to 100 μM concentration, indicating its biocompatibility. The intracellular ROS-mediated activation of the prodrug with the release of NIR dye DCI-NH2 and H2S was investigated in HeLa cells using the H2S-selective probe WSP2. The anti-inflammatory activity of the active drug DCF from the prodrug DCF-HS was studied in the lipopolysaccharide (LPS)-induced macrophage cell line and compared to that of the parent drug DCF using western blot analysis and it was found that the active drug resulted in pronounced inhibition of COX-2 in a dose-dependent manner. Finally, the anti-inflammatory potential of the prodrug and the turn-on fluorescence were validated in the inflammation-induced Wister rat models.

Small Molecule Optical Probes for Detection of H2S in Water Samples: A Review

Hydrogen sulfide (H2S) is closely linked to not only environmental hazards, but also it affects human health due to its toxic nature and the exposure risks associated with several occupational settings. Therefore, detection of this pollutant in water sources has garnered immense importance in the analytical research arena. Several research groups have devoted great efforts to explore the selective as well as sensitive methods to detect H2S concentrations in water. Recent studies describe different strategies for sensing this ubiquitous gas in real-life water samples. Though many of the designed and developed H2S detection approaches based on the use of organic small molecules facilitate qualitative/quantitative detection of the toxic contaminant in water, optical detection has been acknowledged as one of the best, attributed to the simple, highly sensitive, selective, and good repeatability features of the technique. Therefore, this review is an attempt to offer a general perspective of easy-to-use and fast response optical detection techniques for H2S, fluorimetry and colorimetry, over a wide variety of other instrumental platforms. The review affords a concise summary of the various design strategies adopted by various researchers in constructing small organic molecules as H2S sensors and offers insight into their mechanistic pathways. Moreover, it collates the salient aspects of optical detection techniques and highlights the future scope for prospective exploration in this field based on the limitations of the existing H2S probes.

Dual-Stimuli-Activatable Hybrid Prodrug for the Self-Immolative Delivery of an Anticancer Agent and Hydrogen Sulfide with Turn-On Fluorescence

Stimuli-responsive fluorogenic prodrugs are advantageous for the targeted drug delivery enabling real-time non-invasive monitoring with turn-on fluorescence. We report herein the dual-stimuli (ROS and CA)-responsive thiocarbamate-based prodrug (AM-TCB) for the turn-on fluorogenic delivery of the naphthalimide-based anticancer agent amonafide along with the gasotransmitter hydrogen sulfide (H2 S). A carbamate-based prodrug AM-CB was also designed, capable of releasing the anticancer agent amonafide without any H2 S. The prodrugs were synthesized using multi-step organic synthesis. UV-Vis and fluorescence spectroscopic studies revealed selective reactivity of the boronate ester group of prodrugs towards ROS (primarily H2 O2 ) with the release of amonafide and COS/CO2 via self-immolative processes. Hydrolysis of the generated COS by carbonic anhydrase (CA) produces H2 S. While the prodrug AM-TCB retained the anticancer activity of free amonafide in cancer cells (MDA-MB-231 and HeLa), unlike amonafide, it enhanced the cellular viability of the non-malignant cells (HEK-293). Fluorescence imaging in HeLa cells revealed the simultaneous delivery of the anticancer agent and H2 S from AM-TCB with turn-on fluorescence. Western blot studies further revealed the cytoprotective effects of the released H2 S from AM-TCB. The present adjuvant strategy therefore would be helpful in future for ameliorating the anticancer drug-induced side-effects.

A new dual functional H2S donor for fluorescence imaging and anti-inflammatory application

This study explored FL-H2S, a novel fluorescein-based H2S donor, as an anti-inflammatory agent. The results demonstrated the efficient release of H2S by FL-H2S, along with its biocompatibility, real-time intracellular H2S release and imaging capability. In vivo experiments using a rat model confirmed the anti-inflammatory effects of FL-H2S, evidenced by reduced foot swelling. We also successfully elucidated the anti-inflammatory mechanism through ELISA and WB analysis.

A highly sensitive and low toxicity cellulose-based fluorescent polymer for H2S detection in cells, zebrafish and food samples

A cellulose based polymer probe (HC-HS) was prepared for the detection of H2S. HC-HS can be applied to fluorescence imaging of H2S in living cells and zebrafish, and HC-HS was made into test strips to detect H2S produced in the process of food corruption.

Protein persulfidation: Rewiring the hydrogen sulfide signaling in cell stress response

The past few decades have witnessed significant progress in the discovery of hydrogen sulfide (H₂S) as a ubiquitous gaseous signaling molecule in mammalian physiology, akin to nitric oxide and carbon monoxide. As the third gasotransmitter, H₂S is now known to exert a wide range of physiological and cytoprotective functions in the biological systems. However, endogenous H₂S concentrations are usually low, and its potential biologic mechanisms responsible have not yet been fully clarified. Recently, a growing body of evidence has demonstrated that protein persulfidation, a posttranslational modification of cysteine residues (RSH) to persulfides (RSSH) elicited by H₂S, is a fundamental mechanism of H₂S-mediated signaling pathways. Persulfidation, as a biological switch for protein function, plays an important role in the maintenance of cell homeostasis in response to various internal and external stress stimuli and is also implicated in numerous diseases, such as cardiovascular and neurodegenerative diseases and cancer. In this review, the biological significance of protein persulfidation by H₂S in cell stress response is reviewed providing a framework for understanding the multifaceted roles of H₂S. A mechanism-guided perspective can help open novel avenues for the exploitation of therapeutics based on H₂S-induced persulfidation in the context of diseases.

Structural Basis of the Inhibition of L-Methionine γ-Lyase from Fusobacterium nucleatum

Fusobacterium nucleatum is a lesion-associated obligate anaerobic pathogen of destructive periodontal disease; it is also implicated in the progression and severity of colorectal cancer. Four genes (FN0625, FN1055, FN1220, and FN1419) of F. nucleatum are involved in producing hydrogen sulfide (H₂S), which plays an essential role against oxidative stress. The molecular functions of Fn1419 are known, but their mechanisms remain unclear. We determined the crystal structure of Fn1419 at 2.5 Å, showing the unique conformation of the PLP-binding site when compared with L-methionine γ-lyase (MGL) proteins. Inhibitor screening for Fn1419 with L-cysteine showed that two natural compounds, gallic acid and dihydromyricetin, selectively inhibit the H₂S production of Fn1419. The chemicals of gallic acid, dihydromyricetin, and its analogs containing trihydroxybenzene, were potentially responsible for the enzyme-inhibiting activity on Fn1419. Molecular docking and mutational analyses suggested that Gly112, Pro159, Val337, and Arg373 are involved in gallic acid binding and positioned close to the substrate and pyridoxal-5'-phosphate-binding site. Gallic acid has little effect on the other H₂S-producing enzymes (Fn1220 and Fn1055). Overall, we proposed a molecular mechanism underlying the action of Fn1419 from F. nucleatum and found a new lead compound for inhibitor development.

Intelligent polymeric hydrogen sulfide delivery systems for therapeutic applications

Hydrogen sulfide (H₂S) plays an important role in regulating various pathological processes such as protecting mammalian cell from harmful injuries, promoting tissue regeneration, and regulating the process of various diseases caused by physiological disorders. Studies have revealed that the physiological effects of H₂S are highly associated with its concentrations. At relatively low concentration, H₂S shows beneficial functions. However, long-time and high-dose donation of H₂S would inhibit regular biological process, resulting in cell dysfunction and apoptosis. To regulate the dosage of H₂S delivery for precision medicine, H₂S delivery systems with intelligent characteristics were developed and a variety of biocompatibility polymers have been utilized to establish intelligent polymeric H₂S delivery systems, with the abilities to specifically target the lesions, smartly respond to pathological microenvironments, as well as real-timely monitor H₂S delivery and lesion conditions by incorporating imaging-capable moieties. In this review, we focus on the design, preparation, and therapeutic applications of intelligent polymeric H₂S delivery systems in cardiovascular therapy, inflammatory therapy, tissue regenerative therapy, cancer therapy and bacteria-associated therapy. Strategies for precise H₂S therapies especially imaging-guided H₂S theranostics are highlighted. Since H₂S donors with stimuli-responsive characters are vital components for establishing intelligent H₂S delivery systems, the development of H₂S donors is also briefly introduced.

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H₂S is an endogenous gasotransmitter that plays important role in regulating various physiological and pathological pathways.

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Controlled H₂S delivery is vital since the therapeutic effects of H₂S are highly associated with its concentrations.

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Intelligent polymeric H₂S delivery systems possess specific targeting, stimuli responsive and imaging guided capabilities, representing a strategic option for next generation of therapies.

On-demand therapeutic delivery of hydrogen sulfide aided by biomolecules

Hydrogen sulfide (H₂S), known as the third gasotransmitter, exerts various physiological functions including cardiac protection, angiogenesis, anti-inflammatory, and anti-cancer capability. Given its promising therapeutic potential as well as severe perniciousness if improper use, the sustained and tunable H₂S delivery systems are highly required for H₂S-based gas therapy with enhanced bioactivity and reduced side effects. To this end, a series of stimuli-responsive compounds capable of releasing H₂S (termed H₂S donors) have been designed over the past two decades to mimic the endogenous generation of H₂S and elucidate the biological functions. Further to improve the stability of H₂S donors and achieve the targeted delivery, various delivery systems have been constructed. In this review, we focus on the recent advances of an emerging subset, biomolecular-based H₂S delivery systems, which combine H₂S donors with biomolecular vectors including polysaccharide, peptide, and protein. We demonstrated their basic structures, building strategies, and therapeutic applications respectively to unfold their inherent merits endued by biomolecules including biocompatibility, biodegradability as well as expansibility. The varied development potentials of biomolecular-based H₂S delivery systems based on their specific properties are also discussed. At the end, brief future outlooks and upcoming challenges are presented as well.

Subcellular Delivery of Hydrogen Sulfide Using Small Molecule Donors Impacts Organelle Stress

Hydrogen sulfide (H₂S) is an endogenously produced gaseous signaling molecule with important roles in regulating organelle function and stress. Because of its high reactivity, targeted delivery of H₂S using small molecule H₂S donors has garnered significant interest to minimize off-target effects. Although mitochondrially targeted H₂S donors, such as AP39, have been reported previously and exhibit significantly higher potency than nontargeted donors, the expansion of targeted H₂S delivery to other subcellular organelles remains largely absent. To fill this key unmet need, we report a library of organelle-targeted H₂S donors that localize H₂S delivery to specific subcellular organelles, including the Golgi apparatus, lysosome, endoplasmic reticulum, and mitochondria. We measured H₂S production in vitro from each donor, confirmed the localization of H₂S delivery using organelle-specific H₂S responsive fluorescent probes, and demonstrated enhanced potency of these targeted H₂S donors in providing protection against organelle-specific stress. We anticipate this class of targeted H₂S donors will enable future studies of subcellular roles of H₂S and the pathways by which H₂S alleviates subcellular organelle stress.

Thiol-Activated 1,2,4-Thiadiazolidin-3,5-diones Release Hydrogen Sulfide through a Carbonyl-Sulfide-Dependent Pathway

Recent efforts have expanded the development of small molecule donors that release the important biological signaling molecule hydrogen sulfide (H₂S). Previous work on 1,2,4-thiadiazolidin-3,5-diones (TDZNs) reported that these compounds release H₂S directly, albeit inefficiently. However, TDZNs showed promising efficacy in H₂S-mediated relaxation in ex vivo aortic ring relaxation models. Here, we show that TDZNs release carbonyl sulfide (COS) efficiently, which can be converted to H₂S by the enzyme carbonic anhydrase (CA) rather than releasing H₂S directly as previously reported.

Progress and perspective on hydrogen sulfide donors and their biomedical applications

Following the discovery of nitric oxide (NO) and carbon monoxide (CO), hydrogen sulfide (H₂ S) has been identified as the third gasotransmitter in humans. Increasing evidence have shown that H₂ S is of preventive or therapeutic effects on diverse pathological complications. As a consequence, it is of great significance to develop suitable approaches of H₂ S-based therapeutics for biomedical applications. H₂ S-releasing agents (H₂ S donors) play important roles in exploring and understanding the physiological functions of H₂ S. More importantly, accumulating studies have validated the theranostic potential of H₂ S donors in extensive repertoires of in vitro and in vivo disease models. Thus, it is imperative to summarize and update the literatures in this field. In this review, first, the background of H₂ S on its chemical and biological aspects is concisely introduced. Second, the studies regarding the H₂ S-releasing compounds are categorized and described, and accordingly, their H₂ S-donating mechanisms, biological applications, and therapeutic values are also comprehensively delineated and discussed. Necessary comparisons between related H₂ S donors are presented, and the drawbacks of many typical H₂ S donors are analyzed and revealed. Finally, several critical challenges encountered in the development of multifunctional H₂ S donors are discussed, and the direction of their future development as well as their biomedical applications is proposed. We expect that this review will reach extensive audiences across multiple disciplines and promote the innovation of H₂ S biomedicine.

A hydrogen sulphide-responsive and depleting nanoplatform for cancer photodynamic therapy

Hydrogen sulfide (H₂S) as an important biological gasotransmitter plays a pivotal role in many physiological and pathological processes. The sensitive and quantitative detection of H₂S level is therefore crucial for precise diagnosis and prognosis evaluation of various diseases but remains a huge challenge due to the lack of accurate and reliable analytical methods in vivo. In this work, we report a smart, H₂S-responsive and depleting nanoplatform (ZNNPs) for quantitative and real-time imaging of endogenous H₂S for early diagnosis and treatment of H₂S-associated diseases. We show that ZNNPs exhibit unexpected NIR conversion (F₁₀₇₀→ F₇₂₀) and ratiometric photoacoustic (PA₆₈₀/PA₉₀₀) signal responsiveness towards H₂S, allowing for sensitive and quantitative visualization of H₂S in acute hepatotoxicity, cerebral hemorrhage model as well as colorectal tumors in living mice. ZNNPs@FA simultaneously scavenges the mitochondrial H₂S in tumors leading to significant ATP reduction and severe mitochondrial damage, together with the activated photodynamic effect, resulting in efficient suppression of colorectal tumor growth in mice. We believe that this platform may provide a powerful tool for studying the vital impacts of H₂S in related diseases.

Esterase-Activated Perthiocarbonate Persulfide Donors Provide Insights into Persulfide Persistence and Stability

Persulfides (RSSH) are important reactive sulfur species (RSS) that are intertwined with the biological functions of hydrogen sulfide (H₂S). The direct study of persulfides is difficult, however, due to their both nucleophilic and electrophilic character, which leads to the generation of an equilibrium of different RSS. To investigate the effects of persulfides directly, especially in biological systems, persulfide donors are needed to generate persulfides in situ. Here, we report the synthesis of esterase-activated perthiocarbonate persulfide donors and investigate the effects of structural modifications on persulfide release. Although steric bulk of the ester did not significantly alter persulfide release kinetics, increased steric bulk of the thiol increased the persulfide release rate. In addition, we found that the steric bulk and identity of the thiol significantly impact persulfide persistence. Further mechanistic investigations into different competing reaction pathways from perthiocarbonates revealed that multiple RSS can be delivered (i.e., H₂S, COS, or RSSH) depending on the persulfide donor structure and activator identity.

A fluorogenic H2S donor activated by reactive oxygen species for real-time monitoring in cells and in vivo

Hydrogen sulfide (H₂S) is an important gasotransmitter in biological system, and plays a crucial role in varied physiological and pathological processes. Exogenous H₂S is widely employed as a positive control in H₂S related biological study. Herein, we develop a reactive oxygen species (ROS) triggered donor HSD545 that delivers H₂S and simultaneously generates a fluorophore to real-time monitoring the process of H₂S release in vitro and in vivo. The donor exhibits low cytotoxicity and strong cytoprotection against ROS-induce oxidative stress.

Thioredoxin Reductase-triggered Fluorogenic Donor of Hydrogen Sulfide: A Model Study with Symmetrical Organopolysulfide Probe with Turn-on Near-Infrared Fluorescence Emission

We describe herein the rational development of organopolysulfide-based fluorogenic donor of hydrogen sulfide (H2S) DCI-PS, which can be activated by the antioxidant selenoenzyme thioredoxin reductase (TrxR) with concomitant release of...

A cysteine-triggered fluorogenic donor base on native chemical ligation for tracking H2S delivery in vivo

A hydrogen sulfide (H₂S) donor is a fundamental molecular tool used as an exogenous source in biological studies and therapies. However, finding a controllable and visual fluorescent H₂S donor is difficult. We report a new H₂S donor, HSD560, the H₂S release of which is triggered by cysteine. Importantly, the H₂S generation is accompanied with enhanced green fluorescence, which could be utilized to track H₂S release in cells using microscopy. H₂S release from HSD560 undergoes a non-enzymatic native chemical ligation (NCL) process, which provides an accurate match with activated fluorescence and localization of H₂S in zebrafish.

Design and Development of a Bioorthogonal, Visualizable and Mitochondria-Targeted Hydrogen Sulfide (H2 S) Delivery System

Hydrogen sulfide (H₂ S) is an important endogenous gasotransmitter, but the targeted delivery and real-time feedback of exogenous H₂ S are still challenging. With the aid of density functional theory (DFT) calculations, we designed a new 1,3-dithiolium-4-olate (DTO) compound, which can react with a strained alkyne via the 1,3-dipolar cycloaddition and the retro-Diels-Alder reaction to generate carbonyl sulfide (COS) as the precursor of H₂ S, and a thiophene derivative with turn-on fluorescence. Moreover, the diphenylamino substituent in DTO greatly increases the mitochondrial targeting of this H₂ S delivery system. Such a bioorthogonal click-and-release reaction has integrated three functions in one system for the first time: (1) in situ controllable H₂ S release, (2) concomitant fluorescence response, and (3) mitochondria-targeted delivery. In addition, we investigated the mitochondrial membrane potential loss alleviation by using this system in H9c2 cells under oxidative stress.

Research on endoplasmic reticulum-targeting fluorescent probes and endoplasmic reticulum stress-mediated nanoanticancer strategies: A review

Subcellular localization of organelles can achieve accurate drug delivery and maximize drug efficacy. As the largest organelle in eukaryotic cells, the endoplasmic reticulum (ER) plays an important role in protein synthesis, folding, and posttranslational modification; lipid biosynthesis; and calcium homeostasis. Observing the changes in various metal ions, active substances, and the microenvironment in the ER is crucial for diagnosing and treating many diseases, including cancer. Excessive endoplasmic reticulum stress (ERS) can have a killing effect on malignant cells and can mediate cell apoptosis, proper modulation of ERS can provide new perspectives for the treatment of many diseases, including cancer. Therefore, the ER is used as a new anticancer target in cancer treatment. This review discusses ER-targeting fluorescent probes and ERS-mediated nanoanticancer strategies.

A Highly Selective and Sensitive Colorimetric Chemosensor for the Detection of Hydrogen Sulfide: Real-time Applications in Multiple Platforms

Calorimetric chemosensors are found to be advantageous sensing systems due to their simplicity and favorable responsive properties. Although some colorimetric probes have been reported to detect hydrogen sulfide (H₂ S), the creation of rapid, highly selective, and sensitive probes for the detection of H₂ S remains a challenging target. In this work, we established dinitrosulphonamide decorated phenanthridine, 2,4-dinitro-N-(4-(7,8,13,14-tetrahydrodibenzo[a, i]phenanthridin-5-yl)phenyl)benzenesulfonamide (PHSH), for the calorimetric detection of H₂ S. H₂ S triggered thiolysis of PHSH resulted in a marked absorption enhancement alongside a visual color change from colorless to dark yellow. The result indicated that the chemosensor showed high sensitivity and selectivity with a fast response of less than 10 s with a detection limit as low as 6.5 nM. The chemosensor reaction mechanism with H₂ S was studied by UV-vis, ¹ H NMR, mass and HPLC analysis. In addition, the chemosensor has been used for the determination of H₂ S in many real-time samples.

Moving Past Quinone-Methides: Recent Advances toward Minimizing Electrophilic Byproducts from COS/H2S Donors

Hydrogen sulfide (H2S) is an important biomolecule that plays key signaling and protective roles in different physiological processes. With the goals of advancing both the available research tools and the associated therapeutic potential of H2S, researchers have developed different methods to deliver H2S on-demand in different biological contexts. A recent approach to develop such donors has been to design compounds that release carbonyl sulfide (COS), which is quickly converted to H2S in biological systems by the ubiquitous enzyme carbonic anhydrase (CA). Although highly diversifiable, many approaches using this general platform release quinone methides or related electrophiles after donor activation. Many such electrophiles are likely scavenged by water, but recent efforts have also expanded alternative approaches that minimize the formation of electrophilic byproducts generated after COS release. This mini-review focuses specifically on recent examples of COS-based H2S donors that do not generate quinone methide byproducts after donor activation.

Alkylsulfenyl thiocarbonates: precursors to hydropersulfides potently attenuate oxidative stress

The recent discovery of the prevalence of hydropersulfides (RSSH) species in biological systems suggests their potential roles in cell regulatory processes. However, the reactive and transient nature of RSSH makes their study difficult, and dependent on the use of donor molecules. Herein, we report alkylsulfenyl thiocarbonates as a new class of RSSH precursors that efficiently release RSSH under physiologically relevant conditions. RSSH release kinetics from these precursors are tunable through electronic modification of the thiocarbonate carbonyl group's electrophilicity. In addition, these precursors also react with thiols to release RSSH with a minor amount of carbonyl sulfide (COS). Importantly, RSSH generation by these precursors protects against oxidative stress in H9c2 cardiac myoblasts. Furthermore, we demonstrate the ability of these precursors to increase intracellular RSSH levels.

Individual and successive detection of H2S and HClO in living cells and zebrafish by a dual-channel fluorescent probe with longer emission wavelength

Reactive oxygen species (ROS) and reactive sulfur species (RSS) participate in many physiological activities and help maintaining the redox homeostasis in biological system. The complicated intrinsic connection between specific ROS/RSS needs to be further explored. Herein, a novel fluorescent probe (MB-NAP-N₃) with longer emission wavelength has been rationally designed and synthesized based on the conjugation of the methylene blue moiety and the naphthalimide moiety for the detection of hypochlorous acid (HClO) and hydrogen sulfide (H₂S). The dual-signal probe exhibits rapid turn-on fluorescence responses for individual and successive detection of H₂S and HClO in green and red channels, respectively. Owning to its advantages such as fast response, good selectivity and high sensitivity, the probe was successfully applied to detect endogenous and exogenous HClO/H₂S in living cells. Furthermore, the outstanding luminescence performance makes it suitable for the visualization of the in vivo interaction between the two analytes in zebrafish.

A hydrogen peroxide activatable nanoprobe for light-controlled "double-check" multi-colour fluorescence imaging

A new probe for precise and accurate bioimaging contributes significantly to advancing biomedical research for early disease diagnosis and treatment monitoring. Through wrapping a photochromic molecule (SP-Np-B) within a polymer nanoparticle, a new light-controlled multicolour fluorescence nanoprobe (Poly-SP-Np-B) is developed for precise fluorescence subcellular bioimaging. Poly-SP-Np-B shows an "OFF-ON" red-emitting fluorescence response upon alternate UV/Vis light irradiation. After activation by hydrogen peroxide (H2O2), a green-emitting Poly-SP-Np nanoparticle is generated, thus allowing light-controlled fluorescence response simultaneously, i.e., green and yellow switch upon alternate UV/Vis light irradiation for 10 and 20 s, respectively. Such a "blinking" fluorescence signal change is not possible by only using a photochromic molecule probe (SP-Np-B) with alternate UV/vis light irradiation for over 5 min. Poly-SP-Np-B has large isomerization kinetic constants (kSP-MR = 0.4543 s-1 and kMR-SP = 0.0809 s-1), excellent biocompatibility and lysosome distribution capability, enabling multicolour fluorescence imaging in live cells. With exo-/endogenous H2O2 activation in lysosomes, light-controlled "double-check" fluorescence imaging at the subcellular level is successfully achieved. More specifically, the change in fluorescence imaging is reversible in green, red and yellow channels in live cells upon excitation under alternate UV and visible light. This work thus provides a new strategy to develop switchable photochromic probes for precise fluorescence bioassay and bioimaging.

Enhanced Analgesic Effects and Gastrointestinal Safety of a Novel, Hydrogen Sulfide-Releasing Anti-Inflammatory Drug (ATB-352): A Role for Endogenous Cannabinoids

Aims: The covalent linking of nonsteroidal anti-inflammatory drugs to a hydrogen sulfide (H₂S)-releasing moiety has been shown to dramatically reduce gastrointestinal (GI) damage and bleeding, as well as increase anti-inflammatory and analgesic potency. We have tested the hypothesis that an H₂S-releasing derivative of ketoprofen (ATB-352) would exhibit enhanced efficacy without significant GI damage in a mouse model of allodynia/hyperalgesia. Results: ATB-352 was significantly more potent and effective as an analgesic than ketoprofen and did not elicit GI damage. Pretreatment with an antagonist of the CB1 cannabinoid receptor (AM251) significantly reduced the analgesic effects of ATB-352. The CB1 antagonist exacerbated GI damage when coadministered with ketoprofen, but GI damage was not induced by the combination of ATB-352 and the CB1 antagonist. In vitro, ATB-352 was substantially more potent than ketoprofen as an inhibitor of fatty acid amide hydrolase, consistent with a contribution of endogenous cannabinoids to the analgesic effects of this drug. Blood anandamide levels were significantly depressed by ketoprofen, but remained unchanged after treatment with ATB-352. Innovation: Ketoprofen is a potent analgesic, but its clinical use, even in the short term, is significantly limited by its propensity to cause significant ulceration and bleeding in the GI tract. Covalently linking an H₂S-releasing moiety to ketoprofen profoundly reduces the GI toxicity of the drug, while boosting analgesic effectiveness. Conclusion: This study demonstrates a marked enhancement of the potency and effectiveness of ATB-352, an H₂S-releasing derivative of ketoprofen, in part, through the involvement of the endogenous cannabinoid system. This may have significant advantages for the control and management of pain, such as in a postoperative setting.

Modified cyclodextrins solubilize elemental sulfur in water and enable biological sulfane sulfur delivery

An important form of biological sulfur is sulfane sulfur, or S⁰, which is found in polysulfide and persulfide compounds as well as in elemental sulfur. Sulfane sulfur, often in the form of S₈, functions as a key energy source in the metabolic processes of thermophilic Archaean organisms found in sulfur-rich environments and can be metabolized both aerobically and anaerobically by different archaeons. Despite this importance, S₈ has a low solubility in water (∼19 nM), raising questions of how it can be made chemically accessible in complex environments. Motivated by prior crystallographic data showing S₈ binding to hydrophobic motifs in filamentous glycoproteins from the sulfur reducing Staphylothermus marinus anaerobe, we demonstrate that simple macrocyclic hydrophobic motifs, such as 2-hydroxypropyl β-cyclodextrin (2HPβ), are sufficient to solubilize S₈ at concentrations up to 2.0 ± 0.2 mM in aqueous solution. We demonstrate that the solubilized S₈ can be reduced with the common reductant tris(2-carboxyethyl)phosphine (TCEP) and reacts with thiols to generate H₂S. The thiol-mediated conversion of 2HPβ/S₈ to H₂S ranges from 80% to quantitative efficiency for Cys and glutathione (GSH). Moreover, we demonstrate that 2HPβ can catalyze the Cys-mediated reduction of S₈ to H₂S in water. Adding to the biological relevance of the developed systems, we demonstrate that treatment of Raw 264.7 macrophage cells with the 2HPβ/S₈ complex prior to LPS stimulation decreases NO₂ ^- levels, which is consistent with known activities of bioavailable H₂S and sulfane sulfur. Taken together, these investigations provide a new strategy for delivering H₂S and sulfane sulfur in complex systems and more importantly provide new insights into the chemical accessibility and storage of S⁰ and S₈ in biological environments.

Activity-Based Sensing: A Synthetic Methods Approach for Selective Molecular Imaging and Beyond

Emerging from the origins of supramolecular chemistry and the development of selective chemical receptors that rely on lock-and-key binding, activity-based sensing (ABS)-which utilizes molecular reactivity rather than molecular recognition for analyte detection-has rapidly grown into a distinct field to investigate the production and regulation of chemical species that mediate biological signaling and stress pathways, particularly metal ions and small molecules. Chemical reactions exploit the diverse chemical reactivity of biological species to enable the development of selective and sensitive synthetic methods to decipher their contributions within complex living environments. The broad utility of this reaction-driven approach facilitates application to imaging platforms ranging from fluorescence, luminescence, photoacoustic, magnetic resonance, and positron emission tomography modalities. ABS methods are also being expanded to other fields, such as drug and materials discovery.

The biothiol-triggered organotrisulfide-based self-immolative fluorogenic donors of hydrogen sulfide enable lysosomal trafficking

Biothiol-reactive organotrisulfide-based self-immolative fluorogenic donors of H2S are rationally designed for the efficient monitoring of intracellular and lysosomal trafficking of H2S with a concomitant turn-on fluorescence. The non-toxic nature of the donors with a sustained release of H2S will certainly be helpful for their biomedical applications in the future.

Highly efficient H2S scavengers via thiolysis of positively-charged NBD amines

H2S is a well-known toxic gas and also a gaseous signaling molecule involved in many biological processes. Advanced chemical tools that can regulate H2S levels in vivo are useful for understanding H2S biology as well as its potential therapeutic effects. To this end, we have developed a series of 7-nitro-1,2,3-benzoxadiazole (NBD) amines as potential H2S scavengers. The kinetic studies of thiolysis reactions revealed that incorporation of positively-charged groups onto the NBD amines greatly increased the rate of the H2S-specific thiolysis reaction. We demonstrate that these reactions proceed effectively, with second order rate constants (k 2) of >116 M-1 s-1 at 37 °C for NBD-S8. Additionally, we demonstrate that NBD-S8 can effectively scavenge enzymatically-produced and endogenous H2S in live cells. Furthering the biological significance, we demonstrate NBD-S8 mediates scavenging of H2S in mice.

Insights into the Mechanism of Thiol-Triggered COS/H2S Release from N-Dithiasuccinoyl Amines

The hydrolysis of carbonyl sulfide (COS) to form H₂S by carbonic anhydrase has been demonstrated to be a viable strategy to deliver H₂S in a biological system. Herein, we describe N-dithiasuccinoyl amines as thiol-triggered COS/H₂S donors. Notably, thiol species especially GSH and homocysteine can trigger the release of both COS and H₂S directly from several specific analogues via an unexpected mechanism. Importantly, two representative analogues Dts-1 and Dts-5 show intracellular H₂S release, and Dts-1 imparts potent anti-inflammatory effects in LPS-challenged microglia cells. In conclusion, N-dithiasuccinoyl amine could serve as promising COS/H₂S donors for either H₂S biological studies or H₂S-based therapeutics development.

A naphthalimide derivative can release COS and form H2S in a light-controlled manner and protect cells against ROS with real-time monitoring ability

As an important gasotransmitter, hydrogen sulfide having multiple biological roles cannot be easily probed in cells. In this study, a light controllable H₂S donor, Nap-Sul-ONB, derived from naphthalimide was developed. Under the irradiation of 365 nm light, a readily controlled stimulus, the donor could release COS to form H₂S and exhibit turn on fluorescence to indicate the release of payload and its cellular location. Besides, the ROS scavenging ability and cell protective effect of Nap-Sul-ONB against endogenous and exogenous ROS were studied. The results showed that upon 365 nm light irradiation, Nap-Sul-ONB could reduce the cellular ROS level and increase the survival rate of PMA-treated cells.

A hydrogen peroxide responsive prodrug of Keap1-Nrf2 inhibitor for improving oral absorption and selective activation in inflammatory conditions

Transcription factor Nuclear factor erythroid 2-related factor 2 (Nrf2) and its negative regulator, the E3 ligase adaptor Kelch-like ECH-associated protein 1 (Keap1), control the redox and metabolic homeostasis and oxidative stress. Inhibitors of Keap1-Nrf2 interaction are promising in oxidative stress related inflammatory diseases but now hit hurdles. By utilizing thiazolidinone moiety to shield the key carboxyl pharmacophore in Keap1-Nrf2 inhibitor, a hydrogen peroxide (H₂O₂)-responsive prodrug pro2 was developed. The prodrug modification improved the physicochemical properties and cell membrane permeability of the parent drug. Pro2 was stable and stayed inactive under various physiological conditions, while became active by stimulation of H₂O₂ or inflammation derived reactive oxygen species. Moreover, pro2 exhibited proper pharmacokinetic profile suitable for oral administration and enhanced anti-inflammatory efficiency in vivo. Thus, this novel prodrug approach may not only provide an important advance in the therapy of chronic inflammatory diseases with high level of H₂O₂, but also offer a fresh solution to improve the drug-like and selectivity issues of Keap1-Nrf2 inhibitors.

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Pro2 was developed by utilizing H₂O₂-responsive thiazolidinone moiety to shield carboxyl group in Keap1-Nrf2 inhibitor.

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Pro2 was stable and inactive under various physiological conditions, while became active under inflammatory conditions.

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Pro2 exhibited proper pharmacokinetic profile for oral administration and enhanced anti-inflammatory efficiency in vivo.

Use of Dithiasuccinoyl-Caged Amines Enables COS/H2 S Release Lacking Electrophilic Byproducts

The enzymatic conversion of carbonyl sulfide (COS) to hydrogen sulfide (H₂ S) by carbonic anhydrase has been used to develop self-immolating thiocarbamates as COS-based H₂ S donors to further elucidate the impact of reactive sulfur species in biology. The high modularity of this approach has provided a library of COS-based H₂ S donors that can be activated by specific stimuli. A common limitation, however, is that many such donors result in the formation of an electrophilic quinone methide byproduct during donor activation. As a mild alternative, we demonstrate here that dithiasuccinoyl groups can function as COS/H₂ S donor motifs, and that these groups release two equivalents of COS/H₂ S and uncage an amine payload under physiologically relevant conditions. Additionally, we demonstrate that COS/H₂ S release from this donor motif can be altered by electronic modulation and alkyl substitution. These insights are further supported by DFT investigations, which reveal that aryl and alkyl thiocarbamates release COS with significantly different activation energies.

A Reactive Oxygen Species (ROS) Activated Hydrogen Sulfide (H2S) Donor with Self-Reporting Fluorescence

Hydrogen sulfide (H₂S) is an important cellular signaling molecule, and its physiological and pathophysiological properties have been under intensive investigation. In this study, a novel ratiometric fluorescent H₂S donor (HSD-B) has been developed, which exhibited the following advantages: (i) scavenging ROS and producing H₂S simultaneously; (ii) providing ratiometric fluorescence for visualization and quantification of H₂S releasing; and (iii) targeting mitochondrion specifically. Moreover, it demonstrated protective effects on myocardial ischemia reperfusion injury in a cellular model. These attractive features promise this HSD-B as a fluorescent H₂S donor for future research studies.