Construction of coral rod-like MoS2@HA nanowires hybrids for highly effective green antisepsis.

Antibacterial materials have been rapidly emerging as a primary component in the mitigation of bacterial pathogens, and green functional materials play a vital role in the antibacterial field. In this study, biocompatible hydroxyapatite nanowires (HANW) was used as a carrier, a coral rod-like nanowires hybrid of MoS2 and HANW (CR-MoS2@HANW) was synthesized via a facile two-step hydrothermal approach. After being characterized by scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopy (FT-IR), Brunauer-Emmet-Teller (BET) and thermogravimetric (TG) analysis, the antibacterial activity and environmental compatibility were assessed. It was found that MoS2 nanosheets were in-situ assembled onto surface of HA nanowires, and the obtained nanohybrid exhibited excellent stability. CR-MoS2@HANW endowed a desirable long-term antibacterial activity against both gram-negative E. coli and gram-positive S. aureus. It was sufficient to inhibit the growth of bacteria within 72 h, and nanohybrids effectively promoted the growth of plants. In summary, the combination of MoS2 and HANW created a novel eco-friendly nanohybrids that could be applied as a promising multi-functional green antisepsis. And the CR-MoS2@HANW possessed enormous potential for biomedical applications.

Optically Modulated HfS2-Based Synapses for Artificial Vision Systems.

The simulation of human brain neurons by synaptic devices could be an effective strategy to break through the notorious "von Neumann Bottleneck" and "Memory Wall". Herein, opto-electronic synapses based on layered hafnium disulfide (HfS2) transistors have been investigated. The basic functions of biological synapses are realized and optimized by modifying pulsed light conditions. Furthermore, 2 × 2 pixel imaging chips have also been developed. Two-pixel visual information is illuminated on diagonal pixels of the imaging array by applying light pulses (λ = 405 nm) with different pulse frequencies, mimicking short-term memory and long-term memory characteristics of the human vision system. In addition, an optically/electrically driven neuromorphic computation is demonstrated by machine learning to classify hand-written numbers with an accuracy of about 88.5%. This work will be an important step toward an artificial neural network comprising neuromorphic vision sensing and training functions.

Insight on the Order of Regioselective Ultrafast Formation of Disulfide Bonds in (Antimicrobial) Peptides and Miniproteins.

Disulfide-rich peptides and proteins are among the most fascinating bioactive molecules. The difficulties associated with the preparation of these targets have prompted the development of various chemical strategies. Nevertheless, the production of these targets remains very challenging or elusive. Recently, we introduced a strategy for one-pot disulfide bond formation, tackling most of the previous limitations. However, the effect of the order of oxidation remained an underexplored issue. Herein we report on the complete synthetic flexibility of the approach with respect to the order of oxidation of three disulfide bonds in targets that lack the knot motif. In contrast, our study reveals an essential order of disulfide bond formation in the EETI-II knotted miniprotein. This synthetic strategy was applied for the synthesis of novel analogues of the plectasin antimicrobial peptide with enhanced activities against methicillin-resistant Staphylococcus aureus (MRSA), a notorious human pathogen.

Probing Variations of Reduction Activity at the Plasma Membrane Using a Targeted Ratiometric FRET Probe.

Plasma membrane (PM) is the turntable of various reactions that regulate essential functionalities of cells. Among these reactions, the thiol disulfide exchange (TDE) reaction plays an important role in cellular processes. We herein designed a selective probe, called membrane reduction probe (MRP), that is able to report TDE activity at the PM. MRP is based on a green emitting BODIPY PM probe connected to rhodamine through a disulfide bond. MRP is fluorogenic as it is turned off in aqueous media due to aggregation-caused quenching, and once inserted in the PM, it displays a bright red signal due to an efficient fluorescence energy resonance transfer (FRET) between the BODIPY donor and the rhodamine acceptor. In the PM model, the MRP can undergo TDE reaction with external reductive agents as well as with thiolated lipids embedded in the bilayer. Upon TDE reaction, the FRET is turned off and a bright green signal appears allowing a ratiometric readout of this reaction. In cells, the MRP quickly labeled the PM and was able to probe variations of TDE activity using ratiometric imaging. With this tool in hand, we were able to monitor variations of TDE activity at the PM under stress conditions, and we showed that cancer cell lines presented a reduced TDE activity at the PM compared to noncancer cells.

Mineralized and GSH-responsive hyaluronic acid based nano-carriers for potentiating repressive effects of sulforaphane on breast cancer stem cells-like properties.

Breast cancer stem cell (BCSC) properties are correlated with the malignancy of tumor cells. Sulforaphane (SFN), a natural isothiocyanate, has anti-cancer effects. However, SFN is an oil-like, hydrophobic and unstable substance. To enhance the inhibitory effect of SFN on BCSC-like properties, the mineralized hyaluronic acid-SS-tetradecyl nano-carriers (M-HA-SS-TA) were prepared. The nano-carriers possessed high SFN entrapment rate (92.36%) and drug-loading efficiency (33.64%). The carriers were responsive to the high reducing and mild acidic tumor micro-environment, leading to rapid SFN releasing from SFN-loaded nano-drug (SFN/M-HA-SS-TA). Through the specific recognition of breast cancer cells bearing CD44+ by HA, M-HA-SS-TA nano-carriers showed excellent tumor-targeting ability. Moreover, compared with free SFN, SFN/M-HA-SS-TA showed much stronger inhibition on the BCSC-like properties (invasiveness, self-renewal and tumor growth) both in vitro and in vivo. Together, these results suggested M-HA-SS-TA nano-carriers were promising platforms for tumor-targeted delivery of SFN, enhancing the therapeutic efficacy against BCSC-like properties by SFN.

Surface chemistry regulates the optical properties and cellular interactions of ultrasmall MoS2 quantum dots for biomedical applications.

Molybdenum disulfide quantum dots (MoS2 QDs) have drawn increasing attention owing to their distinct optical properties and potential applications in many fields such as biosensing, photocatalysis and cell imaging. Elucidating the relationship between the surface chemistry of MoS2 QDs and their optical properties as well as biological behaviors is critical for their practical applications, which remain largely unclear. Herein, by adopting a sulfur vacancy modification strategy, a toolbox of MoS2 QDs functionalized with different thiolate ligands was prepared. The effect of surface chemistry on the optical properties of MoS2 QDs was systematically explored by various spectroscopic techniques, revealing the important role of surface ligands in defining their absorption band gap and luminescence quantum yield. Furthermore, cellular experiments showed that the cytotoxicity and intracellular fate (i.e., lysosomal accumulation) of MoS2 QDs are closely related to the properties of surface ligands. Our results underscore the important roles of surface ligands in regulating the properties and biological interactions of these QDs, which will facilitate the future development of MoS2-based materials with precisely controlled functions for biomedical applications.

Aptamer-PROTAC Conjugates (APCs) for Tumor-Specific Targeting in Breast Cancer.

Development of proteolysis targeting chimeras (PROTACs) is emerging as a promising strategy for targeted protein degradation. However, the drug development using the heterobifunctional PROTAC molecules is generally limited by poor membrane permeability, low in vivo efficacy and indiscriminate distribution. Herein an aptamer-PROTAC conjugation approach was developed as a novel strategy to improve the tumor-specific targeting ability and in vivo antitumor potency of conventional PROTACs. As proof of concept, the first aptamer-PROTAC conjugate (APC) was designed by conjugating a BET-targeting PROTAC to the nucleic acid aptamer AS1411 (AS) via a cleavable linker. Compared with the unmodified BET PROTAC, the designed molecule (APR) showed improved tumor targeting ability in a MCF-7 xenograft model, leading to enhanced in vivo BET degradation and antitumor potency and decreased toxicity. Thus, the APC strategy may pave the way for the design of tumor-specific targeting PROTACs and have broad applications in the development of PROTAC-based drugs.

Synthesis and biological evaluation of disulfides as anticancer agents with thioredoxin inhibition.

Altered redox homeostasis as a hallmark of cancer cells is exploited by cancer cells for growth and survival. The thioredoxin (Trx), an important regulator in maintaining the intracellular redox homeostasis, is cumulatively recognized as a promising target for the development of anticancer drugs. Herein, we synthesized 72 disulfides and evaluated theirinhibition for Trx and antitumor activity. First, we established an efficient and fast method to screen Trx inhibitors by using the probe NBL-SS that was developed by our group to detect Trx function in living cells. After an initial screening of the Trx inhibitory activity of these compounds, 8 compounds showed significant inhibition activity against Trx. We then evaluated the cytotoxicity of these 8 disulfides, compounds 68 and 69 displayed high cytotoxicity to HeLa cells, but less sensitive to normal cell lines. Next, we performed kinetic studies of both two disulfides, 68 had faster inhibition of Trx than 69. Further studies revealed that 68 led to the accumulation of reactive oxygen species and eventually induced apoptosis of Hela cells via inhibiting Trx. The establishment of a method for screening Trx inhibitors and the discovery of 68 with remarkable Trx inhibition provide support for the development of anticancer candidates with Trx inhibition.

Highly Sensitive MicroRNA Detection by Coupling Nicking-Enhanced Rolling Circle Amplification with MoS2 Quantum Dots.

In this work, a label-free and highly sensitive fluorescence assay was constructed for microRNA detection. Nicking-enhanced rolling circle amplification (RCA) induced by G-quadruplex formation is coupled with inner filter effect (IFE)-based quenching effects of MoS2 quantum dots (MoS2 QDs). The padlock probe contains a recognition sequence to target microRNA and an accessible nicking site. The padlock probe is cyclized upon hybridization with target microRNA. Sequentially, amplification initiates a production of a long-concatenated sequence of circular probes. Abundant G-quadruplex sequences are produced via the nicking process and then used as the trigger to initiate the next RCA. In the presence of hemin, numerous hemin/G-quadruplex DNAzymes are formed, which catalyze the oxidation of o-phenylenediamine (OPD) into the colored product 2,3-diaminophenazine, resulting in quenching of the fluorescence of MoS2 QDs. This sensing strategy enables detection of microRNA let-7a with high selectivity and a detection limit of 4.6 fM. The as-prepared sensor was applied for detecting microRNA let-7a in dilute human serum samples and achieved a satisfactory recovery rate, demonstrating its potential in clinic diagnosis of microRNA-associated disease and biochemical research.

Diaryl disulfides and thiosulfonates as combretastatin A-4 analogues: Synthesis, cytotoxicity and antitubulin activity.

Diaryl disulfides and diaryl thiosulfonates were synthesized with the two phenyl rings of all compounds bearing identical halide substituents. Because of structural similarity to the potent antimitotic natural product combretastatin A-4 (CA-4), the compounds were examined for inhibition of tubulin polymerization, and the thiosulfonates were more active than the disulfides. The nine thiosulfonates had IC50 values ranging from 1.2 to 9.1 µM, as compared with 1.3 µM obtained with CA-4. The compounds thus ranged from equipotent with CA-4 to 7-fold less active. The nine disulfides had IC50 values ranging from 1.2 to 5.1 µM, as compared with 0.54 µM obtained with CA-4. The compounds thus ranged from less than half as active as CA-4 to over 9-fold less active. The most active members of each group, 2 g and 3c, in the assembly assay were modeled into the colchicine site. Compound 3c had significant hydrophobic interactions with ß-tubulin residues CYS 241 and ALA 250, and its thiosulfonate bridge made a hydrogen bond with ß-tubulin residue ASN 258. Compound 2 g had hydrophobic interactions with ß-tubulin residues ALA 250, CYS 241 and ALA 254, but there was no significant interaction of the disulfide bridge with tubulin.

Distinct 3-disulfide-bonded isomers of tridegin differentially inhibit coagulation factor XIIIa: The influence of structural stability on bioactivity.

Tridegin is a 66mer cysteine-rich coagulation factor XIIIa (FXI-IIa) inhibitor from the giant amazon leech Haementeria ghilianii of yet unknown disulfide connectivity. This study covers the structural and functional characterization of five different 3-disulfide-bonded tridegin isomers. In addition to three previously identified isomers, one isomer containing the inhibitory cystine knot (ICK, knottin) motif, and one isomer with the leech antihemostatic protein (LAP) motif were synthesized in a regioselective manner. A fluorogenic enzyme activity assay revealed a positive correlation between the constriction of conformational flexibility in the N-terminal part of the peptide and the inhibitory potential towards FXI-IIa with clear differences between the isomers. This observation was supported by molecular dynamics (MD) simulations and subsequent molecular docking studies. The presented results provide detailed structure-activity relationship studies of different tridegin disulfide isomers towards FXI-IIa and reveal insights into the possibly existing native linkage compared to non-native disulfide tridegin species.

Semisynthesis and Reconstitution of Nucleosomes Carrying Asymmetric Histone Modifications.

Nucleosomes, the basic unit of chromatin, contain a protein core of histone proteins, which are heavily posttranslationally modified. These modifications form a combinatorial language which defines the functional state of the underlying genome. As each histone type exists in two copies in a nucleosome, the modification patterns can differ between the individual histones, resulting in asymmetry and increasing combinatorial complexity. To systematically explore the regulation of chromatin regulatory enzymes (writers, erasers, or readers), chemically defined nucleosomes are required. We have developed strategies to chemically modify histones and control nucleosome assembly, thereby enabling the reconstitution of asymmetric histone modification patterns. Here, we report a detailed protocol for the modular assembly of such nucleosomes. Employing a three-segment ligation strategy for the semisynthesis of H3, coupled with the use of the protease cleavable "lnc-tag," we provide an efficient and traceless method for the controlled semisynthesis and reconstitution of asymmetrically modified nucleosomes.

Synthesis of biogenic chitosan-functionalized 2D layered MoS2 hybrid nanocomposite and its performance in pharmaceutical applications: In-vitro antibacterial and anticancer activity.

A bacterial and viral infection causes life threatening diseases owing to the abuse of antibiotics and the development of antibiotic resistance microbes. Currently, biopolymers have been considered as the most promising materials in the medical field. Herein, the biogenic chitosan-functionalized MoS2 nanocomposite was prepared by the hydrothermal method with the liquid exfoliation process. The X-ray diffraction (XRD) results of chitosan-MoS2 hybrid nanocomposite revealed that MoS2 nanoparticle was found to be 42 nm with a hexagonal crystal structure. FTIR and Raman spectrum revealed that the nitrogen functionalities in the chitosan interacted with MoS2 to form the nanocomposite. The XPS spectrum of chitosan-MoS2 nanocomposite confirms that C, N, O, Mo, and S exist in the nanocomposite. Thermal gravimetric analysis (TGA) and Differential thermal analysis (DTA) analysis showed that the chitosan-MoS2 nanocomposite has higher thermal stability up to 600 °C. In the antibacterial application the chitosan-MoS2 hybrid nanocomposite shows zones of inhibition against S. aureus as 22, 28, and 32 mm, and against E. coli as 26, 30, and 35 mm. In the anticancer analysis, chitosan-MoS2 hybrid nanocomposites showed a maximum cell inhibition of 65.45% at 100 µg/mL-1, resulting in the most significant MCF-7 cell inhibition.

Alkylamine-Substituted Perthiocarbamates: Dual Precursors to Hydropersulfide and Carbonyl Sulfide with Cardioprotective Actions.

The recent discovery of hydropersulfides (RSSH) in mammalian systems suggests their potential roles in cell signaling. However, the exploration of RSSH biological significance is challenging due to their instability under physiological conditions. Herein, we report the preparation, RSSH-releasing properties, and cytoprotective nature of alkylamine-substituted perthiocarbamates. Triggered by a base-sensitive, self-immolative moiety, these precursors show efficient RSSH release and also demonstrate the ability to generate carbonyl sulfide (COS) in the presence of thiols. Using this dually reactive alkylamine-substituted perthiocarbamate platform, the generation of both RSSH and COS is tunable with respect to half-life, pH, and availability of thiols. Importantly, these precursors exhibit cytoprotective effects against hydrogen peroxide-mediated toxicity in H9c2 cells and cardioprotective effects against myocardial ischemic/reperfusion injury, indicating their potential application as new RSSH- and/or COS-releasing therapeutics.

A study to develop platinum(iv) complex chemistry for peptide disulfide bond formation.

Platinum(iv) complexes with a heterocyclic ligand and an ancillary ligand have been investigated and applied for treating various tumour cell lines. Another application of the Pt(iv) complexes in forming peptide disulfide bonds was investigated in this work. For development of Pt(iv) complex chemistry for disulfide bond formation in peptides, two Pt(iv) complexes, [PtCl2(phen)(en)]Cl2 and [PtCl2(bpy)(en)]Cl2, were synthesized and characterized using elemental analysis, ESI-MS and NMR. Subsequently, they were investigated as oxidants for the formation of disulfide bonds in various peptides. Excellent purities and yields of disulfide-containing peptides were achieved when the reactions were carried out in aqueous solution. The reactions were completed rapidly in a wide range of pH values even in acidic medium at room temperature. An intramolecular disulfide bond was formed in each of the peptides in a solution containing two dithiol-containing peptides, making the Pt(iv) complexes useful for generating disulfide-containing peptide libraries. In addition, the two Pt(iv) complexes can be used as oxidants for the synthesis of disulfide bonds on a resin, which is a more convenient method to synthesize disulfide-containing peptides through automation.

Site-selective protein modification via disulfide rebridging for fast tetrazine/trans-cyclooctene bioconjugation.

An inverse electron demand Diels-Alder reaction between tetrazine and trans-cyclooctene (TCO) holds great promise for protein modification and manipulation. Herein, we report the design and synthesis of a tetrazine-based disulfide rebridging reagent, which allows the site-selective installation of a tetrazine group into disulfide-containing peptides and proteins such as the hormone somatostatin (SST) and the antigen binding fragment (Fab) of human immunoglobulin G (IgG). The fast and efficient conjugation of the tetrazine modified proteins with three different TCO-containing substrates to form a set of bioconjugates in a site-selective manner was successfully demonstrated for the first time. Homogeneous, well-defined bioconjugates were obtained underlining the great potential of our method for fast bioconjugation in emerging protein therapeutics. The formed bioconjugates were stable against glutathione and in serum, and they maintained their secondary structure. With this work, we broaden the scope of tetrazine chemistry for site-selective protein modification to prepare well-defined SST and Fab conjugates with preserved structures and good stability under biologically relevant conditions.

One- and Two-Photon-Activated Cysteine Persulfide Donors for Biological Targeting.

Persulfides have been considered as potential signaling compounds similar to the H2S in "S-persulfidation", a sulfur-mediated redox cycle. The research of this sulfur-mediated species is hindered because of the lack of efficient persulfide donors. In this current study, we have developed one- and two-photon-activated persulfide donors based on an o-nitrobenzyl (ONB) phototrigger, which releases the biologically active persulfide (N-acetyl l-cysteine persulfide, NAC-SSH) in a spatiotemporal manner. Next, we have demonstrated the detection of persulfide release both qualitatively and quantitatively using the well-known "turn on" fluorescence probe, that is, monobromobimane, and the trapping agent, that is, 2,4-dinitrofluorobenzene, respectively. Furthermore, we examined the cytotoxicity of synthesized persulfide donors on HeLa cells and the cytoprotective ability in the highly oxidizing cellular environment.

Disulfide phosphatidylcholines: alternative phospholipids for the preparation of functional liposomes.

Phosphatidylcholine is the main component of liposomes and other phospholipid-based nanocarriers in drug delivery. However, the functions and applications of these nanocarriers are extremely limited by conventional phospholipids. Here we report novel disulfide phosphatidylcholines (SS-PCs) and SS-PC based liposomes (SS-LPs) used as alternatives to traditional phospholipids and liposomes.

EDB-FN Targeted Peptide-Drug Conjugates for Use against Prostate Cancer.

Prostate cancer (PCa) is the most common malignancy in men and is the leading cause of cancer-related male mortality. A disulfide cyclic peptide ligand [CTVRTSADC] 1 has been previously found to target extra domain B of fibronectin (EDB-FN) in the extracellular matrix that can differentiate aggressive PCa from benign prostatic hyperplasia. We synthesized and optimized the stability of ligand 1 by amide cyclization to obtain [KTVRTSADE] 8 using Fmoc/tBu solid-phase chemistry. Optimized targeting ligand 8 was found to be stable in phosphate buffered saline (PBS, pH 6.5, 7.0, and 7.5) and under redox conditions, with a half-life longer than 8 h. Confocal microscopy studies demonstrated increased binding of ligand 8 to EDB-FN compared to ligand 1. Therefore, we hypothesized that the EDB-FN targeted peptides (1 and 8) conjugated with an anticancer drug via a hydrolyzable linker would provide selective cytotoxicity to the cancer cells. To test our hypothesis, we selected both the normal prostate cell line, RWPE-1, and the cancerous prostate cell lines, PC3, DU-145, LNCaP, and C4-2, to evaluate the anticancer activity of synthesized peptide-drug conjugates. Docetaxel (Doce) and doxorubicin (Dox) were used as anticancer drugs. Dox conjugate 13 containing disulfide linkage showed comparable cytotoxicity versus Dox after 72 h incubation in all the cancer cell lines, whereas it was found to be less cytotoxic on RWPE-1, suggesting that it can act as a Dox prodrug. Doce conjugate 14 was found to be less cytotoxic in all the cell lines as compared to drug alone.

A supersensitive biosensor based on MoS2 nanosheet arrays for the real-time detection of H2O2 secreted from living cells.

The fast and accurate real-time monitoring of hydrogen peroxide (H2O2) secreted from living cells plays a critical role in clinical diagnosis and management. Herein, we report low-cost and self-supported MoS2 nanosheet arrays for non-enzymatic eletrochemical H2O2 detection. Under the optimal test conditions, such MoS2 electrodes exhibit extremely promising electrocatalytic performance with a low detection limit of 1.0 µM (S/N = 3) and an excellent sensitivity of 5.3 mA mM-1 cm-2. Furthermore, the detection of the trace amount of H2O2 secreted from live A549 cancer cells was successfully performed with this biosensor.