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

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.

Concurrent Subcellular Delivery of Hydrogen Sulfide and a Payload with Near-Infrared Light

Hydrogen sulfide (H2S) is a gaseous signaling molecule, exerting crucial regulatory functions in organelles and cellular environments. H2S exhibits high therapeutic potential and synergistic effects with other drugs, and its potency is notably enhanced through organelle-specific targeting. Yet, the navigation of light-activated H2S donors to specific organelles remains absent. Here, we report the first organelle-specific photocage that simultaneously delivers H2S and a payload with subcellular precision to mitochondria of live human cells using tissue-penetrating near-infrared light as a trigger. The fluorogenic payload enables real-time monitoring of the process, and we demonstrate the concurrent uncaging in mitochondria through a combination of fluorescence microscopy and mitochondria-specific fluorescent probes. We anticipate that these photocages will permit the precise delivery of H2S-drug combinations with exceptional spatiotemporal control, thereby driving the harnessing of known synergistic effects and the discovery of novel therapeutic strategies.

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.

Venetoclax: a promising repurposed drug against SARS-CoV-2 main protease

Global health care emergency caused by a new coronavirus (severe acute respiratory syndrome coronavirus 2 or SARS-CoV-2) demands urgent need to repurpose the approved pharmaceutical drugs. Main protease, M^pro of SARS-CoV-2 draws significant attention as a drug target. Herein, we have screened FDA approved organosulfur drugs (till 2016) and our laboratory synthesized organosulfur and organoselenium compounds (L1-L306) against M^pro-apo using docking followed by classical MD simulations. Additionally, a series of compounds (L307-L364) were chosen from previous experimental studies, which were reported to exhibit inhibitory potentials towards M^pro. We found several organosulfur drugs, particularly Venetoclax (FDA approved organosulfur drug for Leukemia) to be a high-affinity binders to the M^pro of SARS-CoV-2. The results reveal that organosulfur compounds including Venetoclax preferentially bind (non-covalently) to the non-catalytic pocket of the protein located in the dimer interface. We found that the ligand binding is primarily favoured by ligand-protein van der Waals interaction and penalized by desolvation effect. Interestingly, Venetoclax binding alters the local flexibility of M^pro and exerts pronounced effect in the C-terminal as well as two loop regions (Loop-A and Loop-B) that play important roles in catalysis. These findings highlighted the importance of drug repurposing and explored the non-catalytic pockets of M^pro in combating COVID-19 infection in addition to the importance of catalytic binding pocket of the protein.Communicated by Ramaswamy H. Sarma.

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.

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 3,5-dinitropyridin-2yl substituted naphthalimide-based fluorescent probe for the selective detection of biothiols and its application in cell-imaging

A highly selective OFF–ON fluorescent probe has been developed for the sensing of biothiols with a satisfactory response time and low detection limit. Also, the probe can be successfully applied for the sensing of biothiols in living cells.