Selective, Modular Probes for Thioredoxins Enabled by Rational Tuning of a Unique Disulfide Structure Motif

Utilizing the subtractive proteomics approach to design ensemble vaccine against Candida lusitaniae for immune response stimulation; a bioinformatics study

Vaccines have always been one of the promising therapeutic sources against many pathogens including infectious fungi. Candida lusitaniae is also one of those fungi which is responsible for different infections in human beings including vaginitis, endocarditis, endophthalmitis and blood stream infections. There is thus, a need to adopt effective therapeutic strategies to tackle such infections. Vaccine is one of those efficient therapeutic agents which stimulates immune response and prevents a certain infection to get hazardous. Keeping in view this very important concept, we have designed in-silico vaccine against C. lusitaniae by following the subtractive proteomics approach. Initially, the screening of therapeutic targets was performed to identify potent vaccine candidates from the whole proteome of C. lusitaniae. Several significant factors were taken into account in this context, such as stability index, IFN status, allergenicity, and antigenicity. As a result, four distinct proteins that were both antigenic and non-allergenic, were selected from the whole proteome. Furthermore, physiochemical investigation revealed that these vaccine candidates were stable and that their IFN status was positive. Notably, each of these proteins was non-homologous to human beings. This particular attribute of the selected proteins i.e., to be non-homologous, was made in order to possess the ability to trigger an immunological response in host (humans). Furthermore, the whole proteome (WP) vaccine was constructed accordingly. The structural modelling of all the selected vaccine candidates was then performed to proceed them further for docking with the human toll-like receptor 2 (TLR2). Afterwards, the codon optimization was executed, followed by in-silico cloning of the final vaccine construct. The pet28A plasmid was incorporated for this purpose while, the SnapGene tool was utilized for this particular analysis. Ultimately, the immune simulations were executed to assess the immune response of the designed vaccine (WP). Upon final results, it was found that highest count of IgG and IgM was achieved i.e., up to 700000 between the days 8 to 13 and then slowly neutralized till the day 30. These results signified that the designed vaccine possessed the potential to stimulate the required immune response.

Targeting Lysosomal Thiols for Immunogenic Cancer Cell Death

The number and stability of lysosomes (LYs) are different in cancer and healthy cells that makes them a possible target for cancer specific therapy. However, no LY-targeting drug is clinically approved yet. We describe in this paper a new therapeutic approach based on alkylation of lysosomal thiols in cancer cells by reversible thiol binder 11. The treatment with 11 increases the level of lysosomal reactive oxygen species leading to their destabilization, disruption and immunogenic cancer cell death. These effects are not observed in healthy cells. In murine sarcoma Nemeth-Kellner (NK)/Ly-RB model, 11 exhibits the spectacular therapeutic effect: it extends the lifespan of the treated mice from 21 to 85 days and cures 40 % of mice. The survived mice develop antibodies against tumor NK/Ly-RB cells. Their repeated challenge with the NK/Ly-RB cells results in 100 % mice survival compared to 0 % survival in the control group of naïve mice. Ex vivo data indicate that neutrophils in spleen of the cured animals are also involved in targeting cancer cells and produce neutrophil extracellular traps. In summary, 11 induces the direct antitumor effect supported by humoral immune responses, as well as priming neutrophil's reaction against tumors.

Sulfur-based fluorescent probes for biological analysis: A review

The widespread adoption of small-molecule fluorescence detection methodologies in scientific research and industrial contexts can be ascribed to their inherent merits, including elevated sensitivity, exceptional selectivity, real-time detection capabilities, and non-destructive characteristics. In recent years, there has been a growing focus on small-molecule fluorescent probes engineered with sulfur elements, aiming to detect a diverse array of biologically active species. This review presents a comprehensive survey of sulfur-based fluorescent probes published from 2017 to 2023. The diverse repertoire of recognition sites, including but not limited to N, N-dimethylthiocarbamyl, disulfides, thioether, sulfonyls and sulfoxides, thiourea, thioester, thioacetal and thioketal, sulfhydryl, phenothiazine, thioamide, and others, inherent in these sulfur-based probes markedly amplifies their capacity for detecting a broad spectrum of analytes, such as metal ions, reactive oxygen species, reactive sulfur species, reactive nitrogen species, proteins, and beyond. Owing to the individual disparities in the molecular structures of the probes, analogous recognition units may be employed to discern diverse substrates. Subsequent to this classification, the review provides a concise summary and introduction to the design and biological applications of these probe molecules. Lastly, drawing upon a synthesis of published works, the review engages in a discussion regarding the merits and drawbacks of these fluorescent probes, offering guidance for future endeavors.

Psammaplin A analogues with modified disulfide bond targeting histone deacetylases: Synthesis and biological evaluation

Psammaplin A (PsA), a symmetrical bromotyrosine-derived disulfide marine metabolite, has been reported could inhibit HDAC1/2/3 through its thiol monomer. Inspired by the disuflide bond structure of this marine natural product, we designed and synthesized a series of PsA analogues, in which the disulfide bond of PsA was replaced with diselenide bond or cyclic disulfide/diselenide/selenenylsulfide motifs. We also studied the HDAC inhibition, cell growth inhibition, and apoptosis induction of these PsA analogues. The results showed that, all the synthetic diselenide analogues and cyclic selenenyl sulfide compounds exhibited better antiproferative activity than their counterpart of disulfide analogues. Among the prepared analogues, diselenide analogue P-503 and P-116 significantly increased the ability of inhibiting HDAC6 and induced apoptosis and G2/M cell cycle arrest. However, cyclic selenenylsulfides analogues P-111 lost its HDAC inhibitory ability and exhibited no effect on cell cycle and apoptosis, indicating that the anti-proliferative mechanism of cyclic selenenylsulfides analogues has changed.

Metabolic dysfunction-associated steatohepatitis treated by poly(ethylene glycol)-block-poly(cysteine) block copolymer-based self-assembling antioxidant nanoparticles

Non-alcoholic steatohepatitis (NASH), now known as metabolic dysfunction-associated steatohepatitis (MASH), involves oxidative stress caused by the overproduction of reactive oxygen species (ROS). Small-molecule antioxidants have not been approved for antioxidant chemotherapy because of severe adverse effects that collapse redox homeostasis, even in healthy tissues. To overcome these disadvantages, we have been developing poly(ethylene glycol)-block-poly(cysteine) (PEG-block-PCys)-based self-assembling polymer nanoparticles (NanoCyses), releasing Cys after in vivo degradation by endogenous enzymes, to obtain antioxidant effects without adverse effects. However, a comprehensive investigation of the effects of polymer design on therapeutic outcomes has not yet been conducted to develop our NanoCys system for antioxidant chemotherapy. In this study, we synthesized different poly(L-cysteine) (PCys) chains whose sulfanyl groups were protected by tert-butyl thiol (StBu) and butyryl (Bu) groups to change the reactivity of the side chains, affording NanoCys(SS) and NanoCys(Bu), respectively. To elucidate the importance of the polymer design, these NanoCyses were orally administered to MASH model mice as a model of oxidative stress-related diseases. Consequently, the acyl-protective NanoCys(Bu) significantly suppressed hepatic lipid accumulation and oxidative stress compared to NanoCys(SS). Furthermore, we substantiated that shorter PCys were much better than longer PCys for therapeutic outcomes and the effects related to the liberation properties of Cys from these nanoparticles. Owing to its antioxidant functions, NanoCyses also significantly attenuated hepatic inflammation and fibrosis in the MASH mouse model.

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

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

Fluorogenic Chemical Probes for Wash-free Imaging of Cell Membrane Damage in Ferroptosis, Necrosis, and Axon Injury

Selectively labeling cells with damaged membranes is needed not only for identifying dead cells in culture, but also for imaging membrane barrier dysfunction in pathologies in vivo. Most membrane permeability stains are permanently colored or fluorescent dyes that need washing to remove their non-uptaken extracellular background and reach good image contrast. Others are DNA-binding environment-dependent fluorophores, which lack design modularity, have potential toxicity, and can only detect permeabilization of cell volumes containing a nucleus (i.e., cannot delineate damaged volumes in vivo nor image non-nucleated cell types or compartments). Here, we develop modular fluorogenic probes that reveal the whole cytosolic volume of damaged cells, with near-zero background fluorescence so that no washing is needed. We identify a specific disulfonated fluorogenic probe type that only enters cells with damaged membranes, then is enzymatically activated and marks them. The esterase probe MDG1 is a reliable tool to reveal live cells that have been permeabilized by biological, biochemical, or physical membrane damage, and it can be used in multicolor microscopy. We confirm the modularity of this approach by also adapting it for improved hydrolytic stability, as the redox probe MDG2. We conclude by showing the unique performance of MDG probes in revealing axonal membrane damage (which DNA fluorogens cannot achieve) and in discriminating damage on a cell-by-cell basis in embryos in vivo. The MDG design thus provides powerful modular tools for wash-free in vivo imaging of membrane damage, and indicates how designs may be adapted for selective delivery of drug cargoes to these damaged cells: offering an outlook from selective diagnosis toward therapy of membrane-compromised cells in disease.

Piperazine-Fused Cyclic Disulfides Unlock High-Performance Bioreductive Probes of Thioredoxins and Bifunctional Reagents for Thiol Redox Biology

We report piperazine-fused six-membered-cyclic disulfides as redox substrates that unlock best-in-class bioreduction probes for live cell biology, since their self-immolation after reduction is unprecedentedly rapid. We develop scalable, diastereomerically pure, six-step syntheses that access four key cis- and trans-piperazine-fused cyclic dichalcogenides without chromatography. Fluorogenic redox probes using the disulfide piperazines are activated >100-fold faster than the prior art monoamines, allowing us to deconvolute reduction and cyclization rates during activation. The cis- and trans-fused diastereomers have remarkably different reductant specificities, which we trace back to piperazine boat/chair conformation effects: the cis-fused disulfide C-DiThia is activated only by strong vicinal dithiol reductants, but the trans-disulfide T-DiThia is activated even by moderate concentrations of monothiols such as GSH. Thus, in cellular applications, cis-disulfide probes selectively report on the reductive activity of the powerful thioredoxin proteins, while trans-disulfides are rapidly but promiscuously reactive. Finally, we showcase late-stage diversifications of the piperazine-disulfides, promising their broad applicability as redox-cleavable cores for probes and prodrugs that interface powerfully with cellular thiol/disulfide redox biology, for solid phase synthesis and purification, and for stimulus-responsive linkers in bifunctional reagents and antibody-drug conjugates - in addition to their dithiols' potential as high-performance reducing agents.

Back in Person: Frontiers in Medicinal Chemistry 2023

The Frontiers in Medicinal Chemistry (FiMC) is the largest international Medicinal Chemistry conference in the German speaking area and took place from April 3rd to 5th 2023 in Vienna (Austria). Fortunately, after being cancelled in 2020 and two years (2021-2022) of entirely virtual meetings, due to the COVID-19 pandemic, the FiMC could be held in a face-to-face format again. Organized by the Division of Medicinal Chemistry of the German Chemical Society (GDCh), the Division of Pharmaceutical and Medicinal Chemistry of the German Pharmaceutical Society (DPhG), together with the Division of Medicinal Chemistry of the Austrian Chemical Society (GÖCH), the Austrian Pharmaceutical Society (ÖPhG), and a local organization committee from the University of Vienna headed by Thierry Langer, the meeting brought together 260 participants from 21 countries. The program included 38 lectures by leading scientists from industry and academia as well as early career investigators. Moreover, 102 posters were presented in two highly interactive poster sessions.

Fluorescent Probes for Mammalian Thioredoxin Reductase: Mechanistic Analysis, Construction Strategies, and Future Perspectives

The modulation of numerous signaling pathways is orchestrated by redox regulation of cellular environments. Maintaining dynamic redox homeostasis is of utmost importance for human health, given the common occurrence of altered redox status in various pathological conditions. The cardinal component of the thioredoxin system, mammalian thioredoxin reductase (TrxR) plays a vital role in supporting various physiological functions; however, its malfunction, disrupting redox balance, is intimately associated with the pathogenesis of multiple diseases. Accordingly, the dynamic monitoring of TrxR of live organisms represents a powerful direction to facilitate the comprehensive understanding and exploration of the profound significance of redox biology in cellular processes. A number of classic assays have been developed for the determination of TrxR activity in biological samples, yet their application is constrained when exploring the real-time dynamics of TrxR activity in live organisms. Fluorescent probes offer several advantages for in situ imaging and the quantification of biological targets, such as non-destructiveness, real-time analysis, and high spatiotemporal resolution. These benefits facilitate the transition from a poise to a flux understanding of cellular targets, further advancing scientific studies in related fields. This review aims to introduce the progress in the development and application of TrxR fluorescent probes in the past years, and it mainly focuses on analyzing their reaction mechanisms, construction strategies, and potential drawbacks. Finally, this study discusses the critical challenges and issues encountered during the development of selective TrxR probes and proposes future directions for their advancement. We anticipate the comprehensive analysis of the present TrxR probes will offer some glitters of enlightenment, and we also expect that this review may shed light on the design and development of novel TrxR probes.

Cyclic Dichalcogenides Extend the Reach of Bioreductive Prodrugs to Harness Thiol/Disulfide Oxidoreductases: Applications to seco-Duocarmycins Targeting the Thioredoxin System

Small-molecule prodrug approaches that can activate cancer therapeutics selectively in tumors are urgently needed. Here, we developed the first antitumor prodrugs designed for activation by thiol-manifold oxidoreductases, targeting the thioredoxin (Trx) system. The Trx system is a critical cellular redox axis that is tightly linked to dysregulated redox/metabolic states in cancer, yet it cannot be addressed by current bioreductive prodrugs, which mainly cluster around oxidized nitrogen species. We instead harnessed Trx/TrxR-specific artificial dichalcogenides to gate the bioactivity of 10 "off-to-on" reduction-activated duocarmycin prodrugs. The prodrugs were tested for cell-free and cellular reductase-dependent activity in 177 cell lines, establishing broad trends for redox-based cellular bioactivity of the dichalcogenides. They were well tolerated in vivo in mice, indicating low systemic release of their duocarmycin cargo, and in vivo anti-tumor efficacy trials in mouse models of breast and pancreatic cancer gave promising indications of effective tumoral drug release, presumably by in situ bioreductive activation. This work therefore presents a chemically novel class of bioreductive prodrugs against a previously unaddressed reductase chemotype, validates its ability to access in vivo-compatible small-molecule prodrugs even of potently cumulative toxins, and so introduces carefully tuned dichalcogenides as a platform strategy for specific bioreduction-based release.

Dynamic Covalent Michael Acceptors to Penetrate Cells: Thiol-Mediated Uptake with Tetrel-Centered Exchange Cascades, Assisted by Halogen-Bonding Switches

Chalcogen-centered cascade exchange chemistry is increasingly understood to account for thiol-mediated uptake, that is, the ability of reversibly thiol-reactive agents to penetrate cells. Here, reversible Michael acceptors are shown to enable and inhibit thiol-mediated uptake, including the cytosolic delivery of proteins. Dynamic cyano-cinnamate dimers rival the best chalcogen-centered inhibitors. Patterns generated in inhibition heatmaps reveal contributions from halogen-bonding switches that occur independent from the thyroid transporter MCT8. The uniqueness of these patterns supports that the entry of tetrel-centered exchangers into cells differs from chalcogen-centered systems. These results expand the chemical space of thiol-mediated uptake and support the existence of a universal exchange network to bring matter into cells, abiding to be decoded for drug delivery and drug discovery in the broadest sense.

Anticancer Agents Derived from Cyclic Thiosulfonates: Structure-Reactivity and Structure-Activity Relationships

Reported are structure-property-function relationships associated with a class of cyclic thiosulfonate molecules-disulfide-bond disrupting agents (DDAs)-with the ability to downregulate the Epidermal Growth Factor Receptor (HER) family in parallel and selectively induce apoptosis of EGFR+ or HER2+ breast cancer cells. Recent findings have revealed that the DDA mechanism of action involves covalent binding to the thiol(ate) from the active site cysteine residue of members of the protein disulfide isomerase (PDI) family. Reported is how structural modifications to the pharmacophore can alter the anticancer activity of cyclic thiosulfonates by tuning the dynamics of thiol-thiosulfonate exchange reactions, and the studies reveal a correlation between the biological potency and thiol-reactivity. Specificity of the cyclic thiosulfonate ring-opening reaction by a nucleophilic attack can be modulated by substituent addition to a parent scaffold. Lead compound optimization efforts are also reported, and have resulted in a considerable decrease of the IC50 /IC90 values toward HER-family overexpressing breast cancer cells.

An Orthogonal Dynamic Covalent Chemistry Tool for Ring-Opening Polymerization of Cyclic Oligochalcogenides on Detachable Helical Peptide Templates

A model system is introduced as a general tool to elaborate on orthogonal templation of dynamic covalent ring-opening polymerization (ODC-TROP). The tool consists of 310 helical peptides as unprecedented templates and semicarbazones as orthogonal dynamic covalent linkers. With difficult-to-control 1,2-dithiolanes, ODC-TROP on the level of short model oligomers occurs with high templation efficiency, increasing and diminishing upon helix stabilization and denaturation, respectively. Further, an anti-templated conjugate with mispositioned monomers gave reduced templation upon helix twisting. Even with the "unpolymerizable" 1,2-diselenolanes, initial studies already afford mild templation efficiency. These proof-of-principle results promise that the here introduced tool, recyclable and enabling late-stage side chain modification, will be useful to realize ODC-TROP of intractable or unknown cyclic dynamic covalent monomers for dynamer materials as well as cellular uptake and signaling applications.

Pnictogen-Centered Cascade Exchangers for Thiol-Mediated Uptake: As(III)-, Sb(III)-, and Bi(III)-Expanded Cyclic Disulfides as Inhibitors of Cytosolic Delivery and Viral Entry

Dynamic covalent exchange cascades with cellular thiols are of interest to deliver substrates to the cytosol and to inhibit the entry of viruses. The best transporters and inhibitors known today are cyclic cascade exchangers (CAXs), producing a new exchanger with every exchange, mostly cyclic oligochalcogenides, particularly disulfides. The objective of this study was to expand the dynamic covalent chalcogen exchange cascades in thiol-mediated uptake by inserting pnictogen relays. A family of pnictogen-expanded cyclic disulfides covering As(III), Sb(III), and Bi(III) is introduced. Their ability to inhibit thiol-mediated cytosolic delivery is explored with fluorescently labeled CAXs as transporters. The promise of inhibiting viral entry is assessed with SARS-CoV-2 lentiviral vectors. Oxygen-bridged seven-membered 1,3,2-dithiabismepane rings are identified as privileged scaffolds. The same holds for six-membered 1,3,2-dithiarsinane rings made from asparagusic acid and para-aminophenylarsine oxide, which are inactive or toxic when used alone. These chemically complementary Bi(III) and As(III) cascade exchangers inhibit both thiol-mediated cytosolic delivery and SARS-CoV-2 lentivector uptake at concentrations of 10 μM or lower. Crystal structures, computational models, and exchange kinetics support that lentivector entry inhibition of the contracted dithiarsinane and the expanded dithiabismepane rings coincides with exchange cascades that occur without the release of the pnictogen relay and benefit from noncovalent pnictogen bonds. The identified leads open perspectives regarding drug delivery as well as unorthodox approaches toward dynamic covalent inhibition of cellular entry.

Cyclic Thiosulfonates for Thiol-Mediated Uptake: Cascade Exchangers, Transporters, Inhibitors

Thiol-mediated uptake is emerging as a powerful method to penetrate cells. Cyclic oligochalcogenides (COCs) have been identified as privileged scaffolds to enable and inhibit thiol-mediated uptake because they can act as dynamic covalent cascade exchangers, i.e., every exchange produces a new, covalently tethered exchanger. In this study, our focus is on the essentially unexplored COCs of higher oxidation levels. Quantitative characterization of the underlying dynamic covalent exchange cascades reveals that the initial ring opening of cyclic thiosulfonates (CTOs) proceeds at a high speed even at a low pH. The released sulfinates exchange with disulfides in aprotic but much less in protic environments. Hydrophobic domains were thus introduced to direct CTOs into hydrophobic pockets to enhance their reactivity. Equipped with such directing groups, fluorescently labeled CTOs entered the cytosol of living cells more efficiently than the popular asparagusic acid. Added as competitive agents, CTOs inhibit the uptake of various COC transporters and SARS-CoV-2 lentivectors. Orthogonal trends found with different transporters support the existence of multiple cellular partners to account for the diverse expressions of thiol-mediated uptake. Dominant self-inhibition and high activity of dimers imply selective and synergistic exchange in hydrophobic pockets as distinguishing characteristics of thiol-mediated uptake with CTOs. The best CTO dimers with hydrophobic directing groups inhibit the cellular entry of SARS-CoV-2 lentivectors with an IC₅₀ significantly lower than the previous best CTO, below the 10 μM threshold and better than ebselen. Taken together, these results identify CTOs as an intriguing motif for use in cytosolic delivery, as inhibitors of lentivector entry, and for the evolution of dynamic covalent networks in the broadest sense, with reactivity-based selectivity of cascade exchange emerging as a distinguishing characteristic that deserves further attention.

Cyclic 5-membered disulfides are not selective substrates of thioredoxin reductase, but are opened nonspecifically

The cyclic five-membered disulfide 1,2-dithiolane has been widely used in chemical biology and in redox probes. Contradictory reports have described it either as nonspecifically reduced in cells, or else as a highly specific substrate for thioredoxin reductase (TrxR). Here we show that 1,2-dithiolane probes, such as "TRFS" probes, are nonspecifically reduced by thiol reductants and redox-active proteins, and their cellular performance is barely affected by TrxR inhibition or knockout. Therefore, results of cellular imaging or inhibitor screening using 1,2-dithiolanes should not be interpreted as reflecting TrxR activity, and previous studies may need re-evaluation. To understand 1,2-dithiolanes' complex behaviour, probe localisation, environment-dependent fluorescence, reduction-independent ring-opening polymerisation, and thiol-dependent cellular uptake must all be considered; particular caution is needed when co-applying thiophilic inhibitors. We present a general approach controlling against assay misinterpretation with reducible probes, to ensure future TrxR-targeted designs are robustly evaluated for selectivity, and to better orient future research.

Selective cellular probes for mammalian thioredoxin reductase TrxR1: Rational design of RX1, a modular 1,2-thiaselenane redox probe

Quantifying the activity of key cellular redox players is crucial for understanding physiological homeostasis, and for targeting their perturbed states in pathologies including cancer and inflammatory diseases. However, cellularly-selective probes for oxidoreductase turnover are sorely lacking. We rationally developed the first probes that selectively target the mammalian selenoprotein thioredoxin reductase (TrxR), using a cyclic selenenylsulfide oriented to harness TrxR's unique selenolthiol chemistry while resisting the cellular monothiol background. Lead probe RX1 had excellent TrxR1-selective performance in cells, cross-validated by knockout, selenium starvation, knock-in, and chemical inhibitors. Its background-free fluorogenicity enabled us to perform the first quantitative high-throughput live cell screen for TrxR1 inhibitors, which indicated that tempered S_NAr electrophiles may be more selective TrxR drugs than the classical electrophiles used hitherto. The RX1 design thus sets the stage for in vivo imaging of the activity of this key oxidoreductase in health and disease, and can also drive TrxR1-inhibitor drug design.

Inhibition of thioredoxin reductase by natural anticancer candidate β-lapachone accounts for triggering redox activation-mediated HL-60 cell apoptosis

β-Lapachone as a natural novel anticancer candidate is under clinical trials. Previous studies suggested that β-lapachone works by redox activation to ablate cancer cells. However, it is still unclear whether thioredoxin reductase (TrxR), one of the key redox catalytic enzymes in cells, plays a role in the pharmacological effects of β-lapachone. Herein, we present that β-lapachone kills human promyelocytic leukemia HL-60 cells with preference over other cancer cells and normal cells. The follow-up studies demonstrate that β-lapachone induces the HL-60 cell apoptosis through inhibition of TrxR and further elevation of oxidative stress. Overexpression of the TrxR alleviates the efficiency of β-lapachone while knockdown of the enzyme increases the β-lapachone cytotoxicity, scientifically underpinning the correlation of the observed biological behaviors of β-lapachone to TrxR inhibition. The disclosure of the novel action mechanism of β-lapachone sheds light on understanding its capacity in interfering with cellular redox signaling and supports β-lapachone as an anticancer drug candidate.

A Fluorescent Probe to Detect Quick Disulfide Reductase Activity in Bacteria

The Trx and Grx systems, two disulfide reductase systems, play critical roles in various cell activities. There are great differences between the thiol redox systems in prokaryotes and mammals. Though fluorescent probes have been widely used to detect these systems in mammalian cells. Very few methods are available to detect rapid changes in the redox systems of prokaryotes. Here we investigated whether Fast-TRFS, a disulfide-containing fluorescent probe utilized in analysis of mammalian thioredoxin reductase, could be used to detect cellular disulfide reducibility in bacteria. Fast-TRFS exhibited good substrate qualities for both bacterial thioredoxin and GSH-glutaredoxin systems in vitro, with Trx system having higher reaction rate. Moreover, the Fast-TRFS was used to detect the disulfide reductase activity in various bacteria and redox-related gene null E. coli. Some glutaredoxin-deficient bacteria had stronger fast disulfide reducibility. The Trx system was shown to be the predominant disulfide reductase for fast disulfide reduction rather than the Grx system. These results demonstrated that Fast-TRFS is a viable probe to detect thiol-dependent disulfide reductases in bacteria. It also indicated that cellular disulfide reduction could be classified into fast and slow reaction, which are predominantly catalyzed by E. coli Trx and Grx system, respectively.

Membrane-camouflaged supramolecular nanoparticles for co-delivery of chemotherapeutic and molecular-targeted drugs with siRNA against patient-derived pancreatic carcinoma

Pancreatic cancer remains one of the most lethal malignancies worldwide. The combination of the first-line standard agent gemcitabine (GEM) with the molecular-targeted drug erlotinib (Er) has emerged as a promising strategy for pancreatic cancer treatment. However, the clinical benefit from this combination is still far from satisfactory due to the unfavorable drug antagonism and the fibrotic tumor microenvironment. Herein, we propose a membrane-camouflaged dual stimuli-responsive delivery system for the co-delivery of GEM and Er into pancreatic cancer cells and tissues to block the antagonism, as well as reshapes profibrotic tumor microenvironment via simultaneous delivery of small interference RNA (siRNA) for synergistic pancreatic cancer treatment. This “all-in-one” delivery system exhibits sensitive GSH and pH-dependent drug release profiles and enhances the inhibitory effects on the proliferation and migration of tumor cells in vitro. Excitingly, the systemic injection of such a biomimetic drug co-delivery system not only resulted in superior inhibitory effects against orthotopic pancreatic tumor and patient-derived tumor (PDX), but also greatly extended the survival rate of tumor-bearing mice. Our findings provide a promising therapeutic strategy against pancreatic cancer through the enhanced synergistic effect of target therapy, chemotherapy and anti-fibrotic therapy, which represents an appealing way for pancreatic cancer treatment.

A fluorescent probe for specifically measuring the overall thioredoxin and glutaredoxin reducing activity in bacterial cells

Both bacterial thioredoxin and glutaredoxin systems can reduce TRFS-green selectively, which confers TRFS-green to be a remarkable probe to detect the dominant disulfide reductase activity with a slow reaction rate in bacteria, e. g. E. coli Grx2&3.

Dithiolane quartets: thiol-mediated uptake enables cytosolic delivery in deep tissue

The cytosolic delivery of various substrates in 3D multicellular spheroids by thiol-mediated uptake is reported. This is important because most orthodox systems, including polycationic cell-penetrating peptides, fail to deliver efficiently into deep tissue. The grand principles of supramolecular chemistry, that is the pH dependence of dynamic covalent disulfide exchange with known thiols on the transferrin receptor, are proposed to account for transcytosis into deep tissue, while the known but elusive exchange cascades along the same or other partners assure cytosolic delivery in kinetic competition. For quantitative detection in the cytosol, the 2D chloroalkane penetration assay (CAPA) is translated to 3D deep tissue. The targeted delivery of quantum dots, otherwise already troublesome in 2D culture, and the controlled release of mechanophores are realized to exemplify the power of thiol-mediated uptake into spheroids. As transporters, dithiolane quartets on streptavidin templates are introduced as modular motifs. Built from two amino acids only, the varied stereochemistry and peptide sequence are shown to cover maximal functional space with minimal structural change, i.e., constitutional isomers. Reviving a classic in peptide chemistry, this templated assembly of β quartets promises to expand streptavidin biotechnology in new directions, while the discovery of general cytosolic delivery in deep tissue as an intrinsic advantage further enhances the significance and usefulness of thiol-mediated uptake.