Controlled In Situ Self-Assembly of Biotinylated Trans-Cyclooctene Nanoparticles for Orthogonal Dual-Pretargeted Near-Infrared Fluorescence and Magnetic Resonance Imaging

A pretargeted strategy that decouples targeting vectors from radionuclides has shown promise for nuclear imaging and/or therapy in vivo. However, the current pretargeted approach relies on the use of antibodies or nanoparticles as the targeting vectors, which may be compromised by poor tissue penetration and limited accumulation of targeting vectors in the tumor tissues. Herein, we present an orthogonal dual-pretargeted approach by combining stimuli-triggered in situ self-assembly strategy with fast inverse electron demand Diels-Alder (IEDDA) reaction and strong biotin-streptavidin (SA) interaction for near-infrared fluorescence (NIR FL) and magnetic resonance (MR) imaging of tumors. This approach uses a small-molecule probe (P-Cy-TCO&Bio) containing both biotin and trans-cyclooctene (TCO) as a tumor-targeting vector. P-Cy-TCO&Bio can efficiently penetrate subcutaneous HeLa tumors through biotin-assisted targeted delivery and undergo in situ self-assembly to form biotinylated TCO-bearing nanoparticles (Cy-TCO&Bio NPs) on tumor cell membranes. Cy-TCO&Bio NPs exhibited an "off-on" NIR FL and retained in the tumors, offering a high density of TCO and biotin groups for the concurrent capture of Gd-chelate-labeled tetrazine (Tz-Gd) and IR780-labeled SA (SA-780) via the orthogonal IEDDA reaction and SA-biotin interaction. Moreover, Cy-TCO&Bio NPs offered multiple-valent binding modes toward SA, which additionally regulated the cross-linking of Cy-Gd&Bio NPs into microparticles (Cy-Gd&Bio/SA MPs). This process could significantly (1) increase r1 relaxivity and (2) enhance the accumulation of Tz-Gd and SA-780 in the tumors, resulting in strong NIR FL, bright MR contrast, and an extended time window for the clear and precise imaging of HeLa tumors.

Site-Specific Conjugation of Bottlebrush Polymers to Therapeutic Protein via Bioorthogonal Chemistry

Achieving efficient and site-specific conjugation of therapeutic protein to polymer is crucial to augment their applicability in the realms of biomedicine by improving their stability and enzymatic activity. In this study, we exploited tetrazine bioorthogonal chemistry to achieve the site-specific conjugation of bottlebrush polymers to urate oxidase (UOX), a therapeutic protein for gout treatment. An azido-functionalized zwitterionic bottlebrush polymer (N3-ZBP) using a "grafting-from" strategy involving RAFT and ATRP methods was synthesized, and a trans-cyclooctene (TCO) moiety was introduced at the polymer end through the strain-promoted azide-alkyne click (SPAAC) reaction. The subsequent coupling between TCO-incorporated bottlebrush polymer and tetrazine-labeled UOX using a fast and safe bioorthogonal reaction, inverse electron demand Diels-Alder (IEDDA), led to the formation of UOX-ZBP conjugates with a 52% yield. Importantly, the enzymatic activity of UOX remained unaffected following polymer conjugation, suggesting a minimal change in the folded structure of UOX. Moreover, UOX-ZBP conjugates exhibited enhanced proteolytic resistance and reduced antibody binding, compared to UOX-wild type. Overall, the present findings reveal an efficient and straightforward route for synthesizing protein-bottlebrush polymer conjugates without compromising the enzymatic activity while substantially reducing proteolytic degradation and antibody binding.

Advances in the Synthesis of Bioorthogonal Reagents: s-Tetrazines, 1,2,4-Triazines, Cyclooctynes, Heterocycloheptynes, and trans-Cyclooctenes

Aligned with the increasing importance of bioorthogonal chemistry has been an increasing demand for more potent, affordable, multifunctional, and programmable bioorthogonal reagents. More advanced synthetic chemistry techniques, including transition-metal-catalyzed cross-coupling reactions, C-H activation, photoinduced chemistry, and continuous flow chemistry, have been employed in synthesizing novel bioorthogonal reagents for universal purposes. We discuss herein recent developments regarding the synthesis of popular bioorthogonal reagents, with a focus on s-tetrazines, 1,2,4-triazines, trans-cyclooctenes, cyclooctynes, hetero-cycloheptynes, and -trans-cycloheptenes. This review aims to summarize and discuss the most representative synthetic approaches of these reagents and their derivatives that are useful in bioorthogonal chemistry. The preparation of these molecules and their derivatives utilizes both classical approaches as well as the latest organic chemistry methodologies.

Effect and mechanism of gomisin D on the isoproterenol induced myocardial injury in H9C2 cells and mice

We established myocardial injury models in vivo and in vitro to investigate the cardioprotective effect of gomisin D obtained from Schisandra chinensis. Gomisin D significantly inhibited isoproterenol-induced apoptosis and hypertrophy in H9C2 cells. Gomisin D decreased serum BNP, ANP, CK-MB, cTn-T levels and histopathological alterations, and inhibited myocardial hypertrophy in mice. In mechanisms research, gomisin D reversed ISO-induced accumulation of intracellular ROS and Ca2+. Gomisin D further improved mitochondrial energy metabolism disorders by regulating the TCA cycle. These results demonstrated that gomisin D had a significant effect on isoproterenol-induced myocardial injury by inhibiting oxidative stress, calcium overload and improving mitochondrial energy metabolism.

Synthesis of Peptides Containing a Combination of Free and 2-trans-Cyclooctene Carbamate Protected Lysine Residues

The allylic trans-cyclooctene (TCO) functionality facilitates powerful control over the spatiotemporal activity of bio-active molecules, enabling precision targeting of druglike and imaging modalities. However, the introduction of this function onto molecules remains chemically challenging, particularly for peptides. Modification with TCOs of this important class of biomolecules remains a challenge, primarily due to the sensitivity of the TCO group to the strong acids typically used in global deprotection during solid phase peptide synthesis. Here, we present a novel synthetic approach to site-selectively introduce TCO-groups in peptides. Our approach utilizes azide groups to mask amine functions, enabling selective introduction of the TCO on a single lysine residue. Staudinger reduction of the azides back to the corresponding amines proceeds without disturbing the sensitive TCO. We show that using our method, we can produce TCO-inactivated antigenic peptides of previously unseen complexity.

Quantitative Proteomics Combined with Network Pharmacology Analysis Unveils the Biological Basis of Schisandrin B in Treating Diabetic Nephropathy

BACKGROUND

Diabetic nephropathy (DN) is a major complication of diabetes. Schisandrin B (Sch) is a natural pharmaceutical monomer that was shown to prevent kidney damage caused by diabetes and restore its function. However, there is still a lack of comprehensive and systematic understanding of the mechanism of Sch treatment in DN.

OBJECTIVE

We aim to provide a systematic overview of the mechanisms of Sch in multiple pathways to treat DN in rats.

METHODS

Streptozocin was used to build a DN rat model, which was further treated with Sch. The possible mechanism of Sch protective effects against DN was predicted using network pharmacology and was verified by quantitative proteomics analysis.

RESULTS

High dose Sch treatment significantly downregulated fasting blood glucose, creatinine, blood urea nitrogen, and urinary protein levels and reduced collagen deposition in the glomeruli and tubule-interstitium of DN rats. The activities of superoxide dismutase (SOD) and plasma glutathione peroxidase (GSH-Px) in the kidney of DN rats significantly increased with Sch treatment. In addition, the levels of IL-6, IL-1β, and TNF-α were significantly reduced in DN rats treated with Sch. 11 proteins that target both Sch and DN were enriched in pathways such as MAPK signaling, PI3K-Akt signaling, renal cell carcinoma, gap junction, endocrine resistance, and TNF signaling. Furthermore, quantitative proteomics showed that Xaf1 was downregulated in the model vs. control group and upregulated in the Sch-treated vs. model group. Five proteins, Crb3, Tspan4, Wdr45, Zfp512, and Tmigd1, were found to be upregulated in the model vs. control group and downregulated in the Sch vs. model group. Three intersected proteins between the network pharmacology prediction and proteomics results, Crb3, Xaf1, and Tspan4, were identified.

CONCLUSION

Sch functions by relieving oxidative stress and the inflammatory response by regulating Crb3, Xaf1, and Tspan4 protein expression levels to treat DN disease.

A Concise Synthetic Approach to Highly Reactive Click-to-Release Trans-Cyclooctene Linkers

An increase in the click-to-release reaction rate between cleavable trans-cyclooctenes (TCO) and tetrazines would be beneficial for drug delivery applications. In this work, we have developed a short and stereoselective synthesis route towards highly reactive sTCOs that serve as cleavable linkers, affording quantitative tetrazine-triggered payload release. In addition, the fivefold more reactive sTCO exhibited the same in vivo stability as current TCO linkers when used as antibody linkers in circulation in mice.

Click-to-Release: Cleavable Radioimmunoimaging with [89Zr]Zr-DFO-Trans-Cyclooctene-Trastuzumab Increases Tumor-to-Blood Ratio

One of the main challenges of PET imaging with 89Zr-labeled monoclonal antibodies (mAbs) remains the long blood circulation of the radiolabeled mAbs, leading to high background signals, decreasing image quality. To overcome this limitation, here we report the use of a bioorthogonal linker cleavage approach (click-to-release chemistry) to selectively liberate [89Zr]Zr-DFO from trans-cyclooctene-functionalized trastuzumab (TCO-Tmab) in blood, following the administration of a tetrazine compound (trigger) in BT-474 tumor-bearing mice. Methods: We created a series of TCO-DFO constructs and evaluated their performance in [89Zr]Zr-DFO release from Tmab in vitro using different trigger compounds. The in vivo behavior of the best performing [89Zr]Zr-TCO-Tmab was studied in healthy mice first to determine the optimal dose of the trigger. To find the optimal time for the trigger administration, the rate of [89Zr]Zr-TCO-Tmab internalization was studied in BT-474 cancer cells. Finally, the trigger was administered 6 h or 24 h after [89Zr]Zr-TCO-Tmab- administration in tumor-bearing mice to liberate the [89Zr]Zr-DFO fragment. PET scans were obtained of tumor-bearing mice that received the trigger 6 h post-[89Zr]Zr-TCO-Tmab administration. Results: The [89Zr]Zr-TCO-Tmab and trigger pair with the best in vivo properties exhibited 83% release in 50% mouse plasma. In tumor-bearing mice the tumor-blood ratios were markedly increased from 1.0 ± 0.4 to 2.3 ± 0.6 (p = 0.0057) and from 2.5 ± 0.7 to 6.6 ± 0.9 (p < 0.0001) when the trigger was administered at 6 h and 24 h post-mAb, respectively. Same day PET imaging clearly showed uptake in the tumor combined with a strongly reduced background due to the fast clearance of the released [89Zr]Zr-DFO-containing fragment from the circulation through the kidneys. Conclusions: This is the first demonstration of the use of trans-cyclooctene-tetrazine click-to-release chemistry to release a radioactive chelator from a mAb in mice to increase tumor-to-blood ratios. Our results suggest that click-cleavable radioimmunoimaging may allow for substantially shorter intervals in PET imaging with full mAbs, reducing radiation doses and potentially even enabling same day imaging.

Catalytic Activation of Bioorthogonal Chemistry with Light (CABL) Enables Rapid, Spatiotemporally Controlled Labeling and No-Wash, Subcellular 3D-Patterning in Live Cells Using Long Wavelength Light

Described is the spatiotemporally controlled labeling and patterning of biomolecules in live cells through the catalytic activation of bioorthogonal chemistry with light, referred to as "CABL". Here, an unreactive dihydrotetrazine (DHTz) is photocatalytically oxidized in the intracellular environment by ambient O2 to produce a tetrazine that immediately reacts with a trans-cyclooctene (TCO) dienophile. 6-(2-Pyridyl)dihydrotetrazine-3-carboxamides were developed as stable, cell permeable DHTz reagents that upon oxidation produce the most reactive tetrazines ever used in live cells with Diels-Alder kinetics exceeding k2 of 106 M-1 s-1. CABL photocatalysts are based on fluorescein or silarhodamine dyes with activation at 470 or 660 nm. Strategies for limiting extracellular production of singlet oxygen are described that increase the cytocompatibility of photocatalysis. The HaloTag self-labeling platform was used to introduce DHTz tags to proteins localized in the nucleus, mitochondria, actin, or cytoplasm, and high-yielding subcellular activation and labeling with a TCO-fluorophore were demonstrated. CABL is light-dose dependent, and two-photon excitation promotes CABL at the suborganelle level to selectively pattern live cells under no-wash conditions. CABL was also applied to spatially resolved live-cell labeling of an endogenous protein target by using TIRF microscopy to selectively activate intracellular monoacylglycerol lipase tagged with DHTz-labeled small molecule covalent inhibitor. Beyond spatiotemporally controlled labeling, CABL also improves the efficiency of "ordinary" tetrazine ligations by rescuing the reactivity of commonly used 3-aryl-6-methyltetrazine reporters that become partially reduced to DHTzs inside cells. The spatiotemporal control and fast rates of photoactivation and labeling of CABL should enable a range of biomolecular labeling applications in living systems.

Hepatoprotective Constituents of Total Dibenzocyclooctadiene Lignans from Schisandra chinensis Based on the Spectrum-Effect Relationship

To scientifically clarify the hepatoprotective constituents of Fructus Schizandrae chinensis, eleven batches samples of total dibenzocyclooctadiene lignans (TDL) from Schisandra chinensis were prepared by using the optimum extraction technique. Characteristic high-performance liquid chromatography (HPLC) chromatograms were obtained through HPLC analysis technology, and the hepatoprotective effects of the eleven batches of TDL were evaluated by MTT assay. Based on the chemical and biological activity results, the spectrum-effect relationship between the characteristic HPLC fingerprints and the hepatoprotective effect of TDL was established using Minitab 16.0 data analysis software. On the basis of the spectrum-effect relationship, thirteen compounds (1–13) were obtained from the TDL by chemical natural product chemical separation and purification technology, and their structures were identified on the basis of the spectral data and the literature. Based on these compounds, thirteen common peaks among the thirty-three chromatographic peaks in the above HPLC fingerprints were identified. Our findings showed that some components, including, schisandrin B (2), schisandrin A (3), and schisandrol B (7) had significant roles in promoting hepatoprotective activity. Preliminary verification of the spectrum-effect relationship of TDL from S. chinensis was carried out, and the results confirmed that the activity of a composite of these three key components in optimal ratios was better than that of any individual compound, which potentially confirmed the reliability of the spectrum-effect relationship and the synergistic effects of traditional Chinese medicine.

Schisandrin C Affects Glucose-Stimulated Insulin Secretion in Pancreatic β-Cells and Glucose Uptake in Skeletal Muscle Cells

The aim of our study was to investigate the effect of three lignans (schisandrol A, schisandrol B, and schisandrin C) on insulin secretion in rat INS-1 pancreatic β-cells and glucose uptake in mouse C2C12 skeletal muscle cells. Schisandrol A and schisandrin C enhanced insulin secretion in response to high glucose levels with no toxic effects on INS-1 cells. The effect of schisandrin C was superior to that of gliclazide (positive control), a drug commonly used to treat type 2 diabetes (T2D). In addition, western blot analysis showed that the expression of associated proteins, including peroxisome proliferator-activated receptor γ (PPARγ), pancreatic and duodenal homeobox 1 (PDX-1), phosphatidylinositol 3-kinase (PI3K), Akt, and insulin receptor substrate-2 (IRS-2), was increased in INS-1 cells after treatment with schisandrin C. In addition, insulin secretion effect of schisandrin C were enhanced by the Bay K 8644 (L-type Ca²⁺ channel agonist) and glibenclamide (K⁺ channel blocker), were abolished by the nifedipine (L-type Ca²⁺ channel blocker) and diazoxide (K⁺ channel activator). Moreover, schisandrin C enhanced glucose uptake with no toxic effects on C2C12 cells. Western blot analysis showed that the expression of associated proteins, including insulin receptor substrate-1 (IRS-1), AMP-activated protein kinase (AMPK), PI3K, Akt, glucose transporter type 4 (GLUT-4), was increased in C2C12 cells after treatment with schisandrin C. Schisandrin C may improve hyperglycemia by enhancing insulin secretion in pancreatic β-cells and improving glucose uptake into skeletal muscle cells. Our findings may provide evidence that schisandrin C may be beneficial in devising novel anti-T2D strategies.

Dibenzocyclooctadiene lignans from Kadsura coccinea alleviate APAP-induced hepatotoxicity via oxidative stress inhibition and activating the Nrf2 pathway in vitro

Phytochemical investigation on the roots of Kadsura coccinea led to the isolation five previously unknown dibenzocyclooctadiene lignans, named heilaohusuins A-E (1-5). Their structures determined by NMR spectroscopy, HR-ESI-MS, and ECD spectra. Hepatoprotection effects of a series of dibenzocyclooctadiene derivatives (1-68) were investigated against acetaminophen (APAP) induced HepG2 cells. Compounds 2, 10, 13, 21, 32, 41, 46, and 49 showed remarkable protective effects, increasing the viabilities to > 52.2% (bicyclol, 52.1 ± 1.3%) at 10 μM. The structure-activity relationships (SAR) for hepatoprotective activity were summarized, according to the activity results of dibenzocyclooctadiene derivatives. Furthermore, we found that one new dibenzocyclooctadiene lignan heilaohusuin B attenuates hepatotoxicity, the mechanism might be closely correlated with oxidative stress inhibition via activating the Nrf2 pathway.

IEDDA: An Attractive Bioorthogonal Reaction for Biomedical Applications

The pretargeting strategy has recently emerged in order to overcome the limitations of direct targeting, mainly in the field of radioimmunotherapy (RIT). This strategy is directly dependent on chemical reactions, namely bioorthogonal reactions, which have been developed for their ability to occur under physiological conditions. The Staudinger ligation, the copper catalyzed azide-alkyne cycloaddition (CuAAC) and the strain-promoted [3 + 2] azide–alkyne cycloaddition (SPAAC) were the first bioorthogonal reactions introduced in the literature. However, due to their incomplete biocompatibility and slow kinetics, the inverse-electron demand Diels-Alder (IEDDA) reaction was advanced in 2008 by Blackman et al. as an optimal bioorthogonal reaction. The IEDDA is the fastest bioorthogonal reaction known so far. Its biocompatibility and ideal kinetics are very appealing for pretargeting applications. The use of a trans-cyclooctene (TCO) and a tetrazine (Tz) in the reaction encouraged researchers to study them deeply. It was found that both reagents are sensitive to acidic or basic conditions. Furthermore, TCO is photosensitive and can be isomerized to its cis-conformation via a radical catalyzed reaction. Unfortunately, the cis-conformer is significantly less reactive toward tetrazine than the trans-conformation. Therefore, extensive research has been carried out to optimize both click reagents and to employ the IEDDA bioorthogonal reaction in biomedical applications.

Enabling In Vivo Photocatalytic Activation of Rapid Bioorthogonal Chemistry by Repurposing Silicon-Rhodamine Fluorophores as Cytocompatible Far-Red Photocatalysts

Chromophores that absorb in the tissue-penetrant far-red/near-infrared window have long served as photocatalysts to generate singlet oxygen for photodynamic therapy. However, the cytotoxicity and side reactions associated with singlet oxygen sensitization have posed a problem for using long-wavelength photocatalysis to initiate other types of chemical reactions in biological environments. Herein, silicon-Rhodamine compounds (SiRs) are described as photocatalysts for inducing rapid bioorthogonal chemistry using 660 nm light through the oxidation of a dihydrotetrazine to a tetrazine in the presence of trans-cyclooctene dienophiles. SiRs have been commonly used as fluorophores for bioimaging but have not been applied to catalyze chemical reactions. A series of SiR derivatives were evaluated, and the Janelia Fluor-SiR dyes were found to be especially effective in catalyzing photooxidation (typically 3%). A dihydrotetrazine/tetrazine pair is described that displays high stability in both oxidation states. A protein that was site-selectively modified by trans-cyclooctene was quantitatively conjugated upon exposure to 660 nm light and a dihydrotetrazine. By contrast, a previously described methylene blue catalyst was found to rapidly degrade the protein. SiR-red light photocatalysis was used to cross-link hyaluronic acid derivatives functionalized by dihydrotetrazine and trans-cyclooctenes, enabling 3D culture of human prostate cancer cells. Photoinducible hydrogel formation could also be carried out in live mice through subcutaneous injection of a Cy7-labeled hydrogel precursor solution, followed by brief irradiation to produce a stable hydrogel. This cytocompatible method for using red light photocatalysis to activate bioorthogonal chemistry is anticipated to find broad applications where spatiotemporal control is needed in biological environments.

Inverse electron demand Diels-Alder click chemistry for pretargeted PET imaging and radioimmunotherapy

Radiolabeled antibodies have shown promise as tools for both the nuclear imaging and endoradiotherapy of cancer, but the protracted circulation time of radioimmunoconjugates can lead to high radiation doses to healthy tissues. To circumvent this issue, we have developed an approach to positron emission tomography (PET) imaging and radioimmunotherapy (RIT) predicated on radiolabeling the antibody after it has reached its target within the body. This in vivo pretargeting strategy is based on the rapid and bio-orthogonal inverse electron demand Diels-Alder reaction between tetrazine (Tz) and trans-cyclooctene (TCO). Pretargeted PET imaging and RIT using TCO-modified antibodies in conjunction with Tz-bearing radioligands produce high activity concentrations in target tissues as well as reduced radiation doses to healthy organs compared to directly labeled radioimmunoconjugates. Herein, we describe how to prepare a TCO-modified antibody (humanized A33-TCO) as well as how to synthesize two Tz-bearing radioligands: one labeled with the positron-emitting radiometal copper-64 ([64Cu]Cu-SarAr-Tz) and one labeled with the β-emitting radiolanthanide lutetium-177 ([177Lu]Lu-DOTA-PEG7-Tz). We also provide a detailed description of pretargeted PET and pretargeted RIT experiments in a murine model of human colorectal carcinoma. Proper training in both radiation safety and the handling of laboratory mice is required for the successful execution of this protocol.

Bioorthogonal Coordination Polymer Nanoparticles with Aggregation-Induced Emission for Deep Tumor-Penetrating Radio- and Radiodynamic Therapy

Radiodynamic therapy (RDT), an emerging therapeutic approach for cancer treatment by employing ionizing irradiation to induce localized photodynamic therapy (PDT) can overcome the drawbacks of the limited penetration depth for traditional PDT and the unconcentrated energy in the tumor for traditional radiotherapy (RT). Taking advantage of aggregation-induced emission (AIE) photosensitizers with bright fluorescence and efficient singlet oxygen production in the aggregate state, Hf-AIE coordination polymer nanoparticles (CPNs), which show both strong RT and RDT effect under X-ray irradiation, are developed. Furthermore, to enhance the tumor accumulation and prolong the tumor retention of the CPNs, bioorthogonal click chemistry is applied in the system through coupling between dibenzocyclooctyne (DBCO)-modified CPNs (Hf-AIE-PEG-DBCO) (PEG: poly(ethylene glycol)) and azide groups on the cell membrane formed by metabolic glycoengineering. Thanks to the high penetration of X-ray irradiation, the bioorthogonal-assisted RT and RDT combination therapy realizes significant killing of cancer cells without showing noticeable biotoxicity after intravenous administration of CPNs.

Ellagic Acid and Schisandrins: Natural Biaryl Polyphenols with Therapeutic Potential to Overcome Multidrug Resistance in Cancer

Multidrug resistance (MDR) is one of the major clinical challenges in cancer treatment and compromises the effectiveness of conventional anticancer chemotherapeutics. Among known mechanisms of drug resistance, drug efflux via ATP binding cassette (ABC) transporters, namely P-glycoprotein (P-gp) has been characterized as a major mechanism of MDR. The primary function of ABC transporters is to regulate the transport of endogenous and exogenous small molecules across the membrane barrier in various tissues. P-gp and similar efflux pumps are associated with MDR because of their overexpression in many cancer types. One of the intensively studied approaches to overcome this mode of MDR involves development of small molecules to modulate P-gp activity. This strategy improves the sensitivity of cancer cells to anticancer drugs that are otherwise ineffective. Although multiple generations of P-gp inhibitors have been identified to date, reported compounds have demonstrated low clinical efficacy and adverse effects. More recently, natural polyphenols have emerged as a promising class of compounds to address P-gp linked MDR. This review highlights the chemical structure and anticancer activities of selected members of a structurally unique class of 'biaryl' polyphenols. The discussion focuses on the anticancer properties of ellagic acid, ellagic acid derivatives, and schisandrins. Research reports regarding their inherent anticancer activities and their ability to sensitize MDR cell lines towards conventional anticancer drugs are highlighted here. Additionally, a brief discussion about the axial chirality (i.e., atropisomerism) that may be introduced into these natural products for medicinal chemistry studies is also provided.

A Cleavable C2-Symmetric trans-Cyclooctene Enables Fast and Complete Bioorthogonal Disassembly of Molecular Probes

Bioorthogonal chemistry is bridging the divide between static chemical connectivity and the dynamic physiologic regulation of molecular state, enabling in situ transformations that drive multiple technologies. In spite of maturing mechanistic understanding and new bioorthogonal bond-cleavage reactions, the broader goal of molecular ON/OFF control has been limited by the inability of existing systems to achieve both fast (i.e., seconds to minutes, not hours) and complete (i.e., >99%) cleavage. To attain the stringent performance characteristics needed for high fidelity molecular inactivation, we have designed and synthesized a new C2-symmetric trans-cyclooctene linker (C2TCO) that exhibits excellent biological stability and can be rapidly and completely cleaved with functionalized alkyl-, aryl-, and H-tetrazines, irrespective of click orientation. By incorporation of C2TCO into fluorescent molecular probes, we demonstrate highly efficient extracellular and intracellular bioorthogonal disassembly via omnidirectional tetrazine-triggered cleavage.

Diversification of polyphosphate end-labeling via bridging molecules

Investigation of the biological roles of inorganic polyphosphate has been facilitated by our previous development of a carbodiimide-based method for covalently coupling primary amine-containing molecules to the terminal phosphates of polyphosphate. We now extend that approach by optimizing the reaction conditions and using readily available “bridging molecules” containing a primary amine and an additional reactive moiety, including another primary amine, a thiol or a click chemistry reagent such as dibenzocyclooctyne. This two-step labeling method is used to covalently attach commercially available derivatives of biotin, peptide epitope tags, and fluorescent dyes to the terminal phosphates of polyphosphate. Additionally, we report three facile methods for purifying conjugated polyphosphate from excess reactants.

Expanding the Scope of Antibody Rebridging with New Pyridazinedione-TCO Constructs

Disulfide rebridging methods have recently emerged as a route to hinge region-specific antibody modification, and there exist numerous examples of successful rebridging chemistry applied to clinically relevant human IgG1 antibodies. Here, dibromopyridazinedione disulfide rebridging is adapted to fast trans-cyclooctene/tetrazine (TCO/Tz) bioorthogonal ligations and extended beyond therapeutic human IgG1 antibodies for the first time to include mouse and rat monoclonal antibodies integral to multiplexed analytical diagnostics. In spite of a common architecture, only a subset of antibody host species and IgG isotype subclasses can be rebridged, highlighting the intricate relationship between hinge region sequence, structure, biological activity, and the conjugation chemistry of IgG antibodies.

Switchable Fluorescence of Doxorubicin for Label-Free Imaging of Bioorthogonal Drug Release

Monitoring the release and activation of prodrug formulations provides essential information about the outcome of a therapy. While the prodrug delivery can be confirmed by using different imaging techniques, confirming the release of active payload by using imaging is a challenge. Here, we have discovered that the switchable fluorescence of doxorubicin can validate drug release upon its uncaging reaction with a highly specific chemical partner. We have observed that the conjugation of doxorubicin with a trans-cyclooctene (TCO) diminishes its fluorescence at 595 nm. This quenched fluorescence of the doxorubicin prodrug is recovered upon its bond-cleaving reaction with tetrazine. Clinically assessed iron oxide nanoparticles were used to formulate a doxorubicin nanodrug. The release of doxorubicin from the nanodrug was studied under various experimental conditions. A fivefold increase in doxorubicin fluorescence is observed after complete release. The studies were carried out in vitro in MDA-MB-231 breast cancer cells. An increase in Dox signal was observed upon tetrazine administration. This switchable fluorescence mechanism of Dox could be employed for fundamental studies, that is, the reactivity of various tetrazine and TCO linker types under different experimental conditions. In addition, the system could be instrumental for translational research where the release and activation of doxorubicin prodrug payloads can be monitored by using optical imaging systems.

Design and preclinical evaluation of nanostars for the passive pretargeting of tumor tissue

INTRODUCTION

Pretargeting strategies that do not rely on the expression of molecular targets have expanded imaging and therapy options for cancer patients. Nanostars with designed multivalency and which highly accumulate in tumor tissue via the enhanced permeability and retention (EPR) effect may therefore be the ideal vectors for the development of a passive pretargeting approach.

METHODS

Nanostars were synthesized, consisting of 7-8 center-cross-linked arms that were modified with trans-cyclooctene (TCO) using poly(ethylene glycol) (PEG) linkers of 12 or 106 monomer units or without linker. The bioorthogonal click reaction with radiofluorinated 2,2'-(7-(2-(tetrazine-poly(ethyleneglycol)11-amino)-2-oxoethyl)-1,4,7-triazonane-1,4-diyl)diacetic acid ([18F]F-Tz-PEG11-NODA) or 2,2'-(7-(2-(tetrazine-amino)-2-oxoethyl)-1,4,7-triazonane-1,4-diyl)diacetic acid ([18F]F-Tz-NODA) was measured by ex vivo biodistribution studies and positron emission tomography (PET) in mice bearing tumors with high EPR characteristics. Bioorthogonal masking was performed using a tetrazine-functionalized dextran polymer (Tz-DP).

RESULTS

Highest tumor accumulation of [18F]F-Tz-PEG11-NODA was observed for nanostars functionalized with TCO without linker, with a tumor uptake of 3.2 ± 0.4%ID/g and a tumor-to-muscle ratio of 12.8 ± 4.2, tumor-to-large intestine ratio of 0.5 ± 0.3 and tumor-to-kidney ratio of 2.0 ± 0.3, being significantly higher than for nanostars functionalized with TCO-PEG12 (P < 0.05) or TCO-PEG106 (P < 0.05). Tumor uptake and tumor-to-tissue ratios did not improve upon bioorthogonal masking with Tz-DP or when using a smaller, more lipophilic tetrazine([18F]F-Tz-NODA).

CONCLUSIONS

A pretargeting strategy was developed based on the passive delivery of TCO-functionalized nanostars. Such a strategy would allow for the imaging and treatment of tumors with apparent EPR characteristics, with high radioactive tumor doses and minimal doses to off-target tissues.

A thiopyrylium salt for PET/NIR-II tumor imaging and image-guided surgery

All tumor imaging modalities have resolution limits below which deeply situated small metastatic foci may not be identified. Moreover, incomplete lesion excision will affect the outcomes of the patients. Scintigraphy is adept in locating lesions, and second near-infrared window (NIR-II) imaging may allow precise real-time tumor delineation. To achieve complete excision of all lesions, multimodality imaging is a promising method for tumor identification and management. Here, a NIR-II thiopyrylium salt, XB1034, was first synthesized and bound to cetuximab and trans-cyclooctene (TCO) to produce XB1034-cetuximab-TCO. This probe provides excellent sensitivity and high temporal resolution NIR-II imaging in mice bearing tumors developed from human breast cancer cells MDA-MB-231. To enable PET imaging, 68 Ga-NETA-tetrazine is subsequently injected into the mice to undergo a bio-orthogonal reaction with the preinjected XB1034-cetuximab-TCO. PET images achieved in the tumor models using the pretargeting strategy are of much higher quality than those obtained using the direct radiolabeling method. Moreover, real-time NIR-II imaging allows accurate tumor excision and sentinel lymph node mapping. In conclusion, XB1034 is a promising molecular imaging probe for tumor diagnosis and treatment.

Gomisin N from Schisandra chinensis Ameliorates Lipid Accumulation and Induces a Brown Fat-Like Phenotype through AMP-Activated Protein Kinase in 3T3-L1 Adipocytes

Obesity results from an imbalance between energy intake and energy expenditure, in which excess fat is stored as triglycerides (TGs) in white adipocytes. Recent studies have explored the anti-obesity effects of certain edible phytochemicals, which suppress TG accumulation and stimulate a brown adipocyte-like phenotype in white adipocytes. Gomisin N (GN) is an important bioactive component of Schisandra chinensis, a woody plant endemic to Asia. GN has antioxidant, anti-inflammatory and hepatoprotective effects in vivo and in vitro. However, the anti-obesity effects of GN in lipid metabolism and adipocyte browning have not yet been investigated. In the present study, we aimed to determine whether GN suppresses lipid accumulation and regulates energy metabolism, potentially via AMP-activated protein kinase (AMPK), in 3T3-L1 adipocytes. Our findings demonstrate that GN inhibited adipogenesis and lipogenesis in adipocyte differentiation. Also, GN not only increased the expression of thermogenic factors, including uncoupling protein 1 (UCP1), but also enhanced fatty acid oxidation (FAO) in 3T3-L1 cells. Therefore, GN may have a therapeutic benefit as a promising natural agent to combat obesity.

Trans-Cyclooctene-Functionalized PeptoBrushes with Improved Reaction Kinetics of the Tetrazine Ligation for Pretargeted Nuclear Imaging

Tumor targeting using agents with slow pharmacokinetics represents a major challenge in nuclear imaging and targeted radionuclide therapy as they most often result in low imaging contrast and high radiation dose to healthy tissue. To address this challenge, we developed a polymer-based targeting agent that can be used for pretargeted imaging and thus separates tumor accumulation from the imaging step in time. The developed targeting agent is based on polypeptide-graft-polypeptoid polymers (PeptoBrushes) functionalized with trans-cyclooctene (TCO). The complementary ¹¹¹In-labeled imaging agent is a 1,2,4,5-tetrazine derivative, which can react with aforementioned TCO-modified PeptoBrushes in a rapid bioorthogonal ligation. A high degree of TCO loading (up to 30%) was achieved, without altering the physicochemical properties of the polymeric nanoparticle. The highest degree of TCO loading resulted in significantly increased reaction rates (77-fold enhancement) compared to those with small molecule TCO moieties when using lipophilic tetrazines. Based on computer simulations, we hypothesize that this increase is a result of hydrophobic effects and significant rearrangements within the polymer framework, in which hydrophobic patches of TCO moieties are formed. These patches attract lipophilic tetrazines, leading to increased reaction rates in the bioorthogonal ligation. The most reactive system was evaluated as a targeting agent for pretargeted imaging in tumor-bearing mice. After the setup was optimized, sufficient tumor-to-background ratios were achieved as early as 2 h after administration of the tetrazine imaging agent, which further improved at 22 h, enabling clear visualization of CT-26 tumors. These findings show the potential of PeptoBrushes to be used as a pretargeting agent when an optimized dose of polymer is used.

Assaying Chlamydia pneumoniae Persistence in Monocyte-Derived Macrophages Identifies Dibenzocyclooctadiene Lignans as Phenotypic Switchers

Antibiotic-tolerant persister bacteria involve frequent treatment failures, relapsing infections and the need for extended antibiotic treatment. The virulence of an intracellular human pathogen C. pneumoniae is tightly linked to its propensity for persistence and means for its chemosensitization are urgently needed. In the current work, persistence of C. pneumoniae clinical isolate CV6 was studied in THP-1 macrophages using quantitative PCR and quantitative culture. A dibenzocyclooctadiene lignan schisandrin reverted C. pneumoniae persistence and promoted productive infection. The concomitant administration of schisandrin and azithromycin resulted in significantly improved bacterial eradication compared to sole azithromycin treatment. In addition, the closely related lignan schisandrin C was superior to azithromycin in eradicating the C. pneumoniae infection from the macrophages. The observed chemosensitization of C. pneumoniae was associated with the suppression of cellular glutathione pools by the lignans, implying to a previously unknown aspect of chlamydia–host interactions. These data indicate that schisandrin lignans induce a phenotypic switch in C. pneumoniae, promoting the productive and antibiotic-susceptible phenotype instead of persistence. By this means, these medicinal plant -derived compounds show potential as adjuvant therapies for intracellular bacteria resuscitation.

Screening and Identification of the Main Metabolites of Schisantherin a In Vivo and In Vitro by Using UHPLC-Q-TOF-MS/MS

Schisantherin A is an active ingredient originating from Schisandra chinensis (Turcz.) which has hepatoprotective and anti-oxidation activities. In this study, in vitro metabolisms investigated on rat liver microsomes (RLMs) and in vivo metabolisms explored on male Sprague Dawley rats of Schisantherin A were tested, respectively. The metabolites of Schisantherin A were identified using ultra-high-performance liquid chromatography coupled with hybrid triple quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF-MS/MS). Based on the method, 60 metabolites were successfully identified and structurally characterized including 48 phase-I and 12 phase-II metabolites. Among the metabolites, 45 metabolites were reported for the first time. Moreover, 56 and eight metabolites were detected in urine and bile and 19 metabolites were identified in rats’ plasma. It demonstrated that hepatic and extra-hepatic metabolic pathways were both involved in Schisantherin A biotransformation in rats. Five in vitro metabolites were structurally characterized for the first time. The results indicated that the metabolic pathways mainly include oxidation, reduction, methylation, and conjugation with glucuronide, taurine, glucose, and glutathione groups. This study provides a practical strategy for rapidly screening and identifying metabolites, and the results provide basic data for future pharmacological and toxicology studies of Schisantherin A and other lignin ingredients.

Hepatoprotective Tetrahydrobenzocyclooctabenzofuranone Lignans from Kadsura longipedunculata

Three new tetrahydrobenzocyclooctabenzofuranone lignan glucosides, longipedunculatins A-C (1-3), a new dibenzocyclooctadiene lignan glucoside, longipedunculatin D (4), a new dibenzocyclooctadiene lignan (5), five new tetrahydrobenzocyclooctabenzofuranone lignans (6-10), and two new simple lignans (11, 12) were isolated from the roots of Kadsura longipedunculata. Their structures and absolute configurations were established using a combination of MS, NMR, and experimental and calculated electronic circular dichroism data. Compound 7 showed moderate hepatoprotective activity against N-acetyl-p-aminophenol-induced toxicity in HepG2 cells with a cell survival rate at 10 μM of 50.8%. Compounds 2, 7, and 12 showed significant in vitro inhibitory effects with an inhibition rate of 55.1%, 74.9%, and 89.8% on nitric oxide production assays at 10 μM.

Immobilization of Proteins with Controlled Load and Orientation

Biomaterials based on immobilized proteins are key elements of many biomedical and industrial technologies. However, applications are limited by an inability to precisely construct materials of high homogeneity and defined content. We present here a general "protein-limited immobilization" strategy by combining the rapid, bioorthogonal, and biocompatible properties of a tetrazine-strained trans-cyclooctene reaction with genetic code expansion to site-specifically place the tetrazine into a protein. For the first time, we use this strategy to immobilize defined amounts of oriented proteins onto beads and flat surfaces in under 5 min at submicromolar concentrations without compromising activity. This approach opens the door to generating and studying diverse protein-based biomaterials that are much more precisely defined and characterized, providing a greater ability to engineer properties across a wide range of applications.

Schizandrin A inhibits proliferation, migration and invasion of thyroid cancer cell line TPC-1 by down regulation of microRNA-429

OBJECTIVE

Schizandrin A (SchA) exerts anticancer potential. However, the effects of SchA on thyroid cancer (TC) have not been clear illuminated. Therefore, we investigated the effects of SchA on TC cell line TPC-1 and the underlying mechanisms.

METHODS

TPC-1 cells were treated with SchA and/or transfected with miR-429 mimic, anti-miR-429 and their corresponding negative controls (NC). Cell viability, proliferation, migration, invasion and cell apoptosis were examined by CCK-8 assay, bromodeoxyuridine, modified two-chamber migration assay, Millicell Hanging Cell Culture and flow cytometry analysis, respectively. The expression of miR-429, p16, Cyclin D1, cyclin-dependent kinases 4 (CDK4), matrix metalloprotein (MMP)-2, MMP-9 and Vimentin was detected by qRT-PCR. All protein expression was examined by western blot.

RESULTS

SchA inhibited cell proliferation, metastasis and induced cell apoptosis. Moreover, SchA negatively regulated miR-429 expression. Treatment with miR-429 mimic and SchA reversed the results led by SchA and NC. Furthermore, the phosphorylation β-catenin, mitogen-activated protein kinase (MEK) and extracellular signal-regulated kinase (ERK) were statistically down-regulated by SchA while co-treatment with miR-429 mimic and SchA led to the opposite trend. Moreover, miR-429 knockdown showed contrary results.

CONCLUSION

SchA inhibits cell proliferation, migration, invasion and inactivates Wnt/β-catenin and MEK/ERK signaling pathways by down regulating miR-429.

Bioorthogonal labeling with tetrazine-dyes for super-resolution microscopy

Genetic code expansion (GCE) technology allows the specific incorporation of functionalized noncanonical amino acids (ncAAs) into proteins. Here, we investigated the Diels-Alder reaction between trans-cyclooct-2-ene (TCO)-modified ncAAs, and 22 known and novel 1,2,4,5-tetrazine-dye conjugates spanning the entire visible wavelength range. A hallmark of this reaction is its fluorogenicity - the tetrazine moiety can elicit substantial quenching of the dye. We discovered that photoinduced electron transfer (PET) from the excited dye to tetrazine is the main quenching mechanism in red-absorbing oxazine and rhodamine derivatives. Upon reaction with dienophiles quenching interactions are reduced resulting in a considerable increase in fluorescence intensity. Efficient and specific labeling of all tetrazine-dyes investigated permits super-resolution microscopy with high signal-to-noise ratio even at the single-molecule level. The different cell permeability of tetrazine-dyes can be used advantageously for specific intra- and extracellular labeling of proteins and highly sensitive fluorescence imaging experiments in fixed and living cells.

PEGylation and surface functionalization of liposomes containing drug nanocrystals for cell-targeted delivery

Liposomal formulations have important therapeutic applications in anti-cancer treatments but current formulations suffer from serious side effects, high dosage requirements and prolonged treatment. In this study, PEGylated azide-functionalized liposomes containing drug nanocrystals were investigated with the aim of increasing the drug payload and achieving functionalization for targeted delivery. Liposomes were characterized using cryogenic transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), small and ultra-small angle neutron scattering (SANS/USANS) and small and wide angle X-ray scattering (SAXS/WAXS). Cryo-TEM experiments revealed the dimensions of the nanocrystal-loaded liposomes and the change of shape from spherical to elongated after the formation of nanocrystals. Results from SANS/USANS experiments confirmed the asymmetric particle shape. SAXS/WAXS experiments confirmed that the crystalline drug only occurred in freeze-thawed samples and correlated with a new unidentified polymorphic form of ciprofloxacin. Using a small molecule dye, dibenzocyclooctyne (DBCO)-cy5, specific conjugation between DBCO groups and surface azide groups on the liposomes was confirmed; this indicates the promise of this system for tumour-targeted delivery.

Spatial Patterning of Molecular Cues and Vascular Cells in Fully Integrated Hydrogel Channels via Interfacial Bioorthogonal Cross-Linking

Fully integrated hydrogel channels were fabricated via interfacial bioorthogonal cross-linking, a diffusion-controlled method for the creation and patterning of synthetic matrices based on the rapid bioorthogonal reaction between s-tetrazines (Tz) and trans-cyclooctene (TCO) dienophiles. Injecting an aqueous solution of a bisTCO cross-linker into a reservoir of tetrazine-modified hyaluronic acid (HA-Tz), while simultaneously drawing the syringe needle through the reservoir, yielded a cross-linked hydrogel channel that was mechanically robust. Fluorescent tags and biochemical signals were spatially patterned into the channel wall through time-dependent perfusion of TCO-conjugated molecules into the lumen of the channel. Different cell populations were spatially encapsulated in the channel wall via temporal alteration of cells in the HA-Tz reservoir. The interfacial approach enabled the spatial patterning of vascular cells, including human abdominal aorta endothelial cells, aortic vascular smooth muscle cells, and aortic adventitial fibroblasts, into the hydrogel channels with high viability and proper morphology in the anatomical order found in human arteries. The bioorthogonal platform does not rely on external triggers and represents the first step toward the engineering of functional and implantable arteries.

Systematically Characterize the Anti-Alzheimer's Disease Mechanism of Lignans from S. chinensis based on In-Vivo Ingredient Analysis and Target-Network Pharmacology Strategy by UHPLC⁻Q-TOF-MS

Lignans from Schisandra chinensis (Turcz.) Baill can ameliorate cognitive impairment in animals with Alzheimer’s disease (AD). However, the metabolism of absorbed ingredients and the potential targets of the lignans from S. chinensis in animals with AD have not been systematically investigated. Therefore, for the first time, we performed an in-vivo ingredient analysis and implemented a target-network pharmacology strategy to assess the effects of lignans from S. chinensis in rats with AD. Ten absorbed prototype constituents and 39 metabolites were identified or tentatively characterized in the plasma of dosed rats with AD using ultra high-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry. Based on the results of analysis of the effective constituents in vivo, the potential therapeutic mechanism of the effective constituents in the rats with AD was investigated using a target-network pharmacology approach and independent experimental validation. The results showed that the treatment effects of lignans from S. chinensis on cognitive impairment might involve the regulation of amyloid precursor protein metabolism, neurofibrillary tangles, neurotransmitter metabolism, inflammatory response, and antioxidant system. Overall, we identified the effective components of lignans in S. chinensis that can improve the cognitive impairment induced by AD and proposed potential therapeutic metabolic pathways. The results might serve as the basis for a fundamental strategy to explore effective therapeutic drugs to treat AD.

Pointing in the Right Direction: Controlling the Orientation of Proteins on Nanoparticles Improves Targeting Efficiency

Protein-conjugated nanoparticles have the potential to precisely deliver therapeutics to target sites in the body by specifically binding to cell surface receptors. To maximize targeting efficiency, the three-dimensional presentation of ligands toward these receptors is crucial. Herein, we demonstrate significantly enhanced targeting of nanoparticles to cancer cells by controlling the protein orientation on the nanoparticle surface. To engineer the point of attachment, we used amber codon reassignment to incorporate a synthetic amino acid, p-azidophenylalanine (azPhe), at specific locations within a single domain antibody (sdAb or nanobody) that recognizes the human epidermal growth factor receptor (EGFR). The azPhe modified sdAb can be tethered to the nanoparticle in a specific orientation using a bioorthogonal click reaction with a strained cyclooctyne. The crystal structure of the sdAb bound to EGFR was used to rationally select sites likely to optimally display the sdAb upon conjugation to a fluorescent nanocrystal (Qdot). Qdots with sdAb attached at the azPhe13 position showed 6 times greater binding affinity to EGFR expressing A549 cells, compared to Qdots with conventionally (succinimidyl ester) conjugated sdAb. As ligand-targeted delivery systems move toward clinical application, this work shows that nanoparticle targeting can be optimized by engineering the site of protein conjugation.

Schizandrol A reverses multidrug resistance in resistant chronic myeloid leukemia cells K562/A02

Overexpression of P-gp is the main cause of multidrug resistance (MDR) and chemotherapeutic failure in leukemia. In this study, the multidrug resistance reverse effect of Schizandrol A (SchA) was demonstrated with P-gp overexpressed drug-resistant K562/A02 cells. SchA had almost no cytotoxic activity, the EC50 value reversed to DOX was in the nanomole range of (707 ± 29nM) and had a high selectivity index (&gt; 113) to normal cells. DOX accumulation and Rh123 efflux tests demonstrated that the MDR reversal activity of SchA was induced by inhibiting P-gp function. Western blotting assay showed that SchA down-regulated the expression of P-gp by inhibiting the PI3K / Akt signaling pathway, which was also a key factor in reversal activity. Therefore, SchA may be a potential candidate for natural MDR reversal agents.

Accelerated Blood Clearance of Antibodies by Nanosized Click Antidotes

Long blood half-life is one of the advantages of antibodies over small molecule drugs. At the same time, prolonged half-life is a problem for imaging applications or in the case of antibody-induced toxicities. There is a substantial need for antidotes that can quickly clear antibodies from systemic circulation and peripheral tissues. Engineered nanoparticles exhibit intrinsic affinity for clearance organs (mainly liver and spleen). trans-Cyclooctene (TCO) and methyltetrazine (MTZ) are versatile copper-free click chemistry components that are extensively being used for in vivo bioorthogonal couplings. To test the ability of nanoparticles to eliminate antibodies, we prepared a set of click-modified, clinically relevant antidotes based on several classes of drug carriers: phospholipid-PEG micelles, bovine serum albumin (BSA), and cross-linked dextran iron oxide (CLIO) nanoparticles. Mice were injected with IRDye 800CW-labeled, click-modified IgG followed by a click-modified antidote or PBS (control), and the levels of the IgG were monitored up to 72 h postinjection. Long-circulating lipid micelles produced a spike in IgG levels at 1 h, decreased IgG levels at 24 h, and did not decrease the area under the curve (AUC) and IgG accumulation in main organs. Long-circulating BSA decreased IgG levels at 1 and 24 h, decreased the AUC, but did not significantly decrease organ accumulation. Long-circulating CLIO nanoworms increased IgG levels at 1 h, decreased IgG levels at 24 h, did not decrease the AUC, and did not decrease the organ accumulation. On the other hand, short-circulating CLIO nanoparticles decreased IgG levels at 1 and 24 h, significantly decreasing the AUC and accumulation in the main organs. Multiple doses of CLIO and BSA were not able to completely eliminate the antibody from blood, despite the click reactivity of the residual IgG, likely due to exchange of IgG between blood and tissue compartments. Pharmacokinetic modeling suggests that short antidote half-life and fast click reaction rate should result in higher IgG depletion efficiency. Short-circulating click-modified nanocarriers are the most effective antidotes for elimination of antibodies from blood. This study sets a stage for future development of antidotes based on nanomedicine.

Red/NIR-Emissive Benzo[d]imidazole-Cored AIEgens: Facile Molecular Design for Wavelength Extending and In Vivo Tumor Metabolic Imaging

Aggregation-induced emission (AIE) luminogens (AIEgens) with red/near-infrared (NIR) emissions are appealing for applications in optoelectronics and biomedical engineering owing to their intrinsic advantages of efficient solid-state emission, low background, and deep tissue penetration. In this context, an AIEgen with long-wavelength emission is synthesized by introducing tetraphenylethene (TPE) to the periphery of electron-deficient spiro-benzo[d]imidazole-2,1'-cyclohexane (BI). The resulting AIEgen, abbreviated as 2TPE-BI, adopts a donor-acceptor structure and shows bathochromic absorption and emission with a larger Stokes shift of 157 nm in acetonitrile than that based on benzo[c][1,2,5]thiadiazole. It also exhibits a high solid-state fluorescence quantum yield of 56.6%. By further insertion of thiophene to its molecular structure generates 2TPE-2T-BI with higher conjugation and NIR emission. 2TPE-2T-BI can be fabricated into AIE dots for in vivo metabolic labeling through bio-orthogonal click chemistry. These results open a new approach for facile construction of long-wavelength emissive AIEgens based on the BI core.

Secondary Photocrosslinking of Click Hydrogels To Probe Myoblast Mechanotransduction in Three Dimensions

Muscle cells sense the mechanical properties of their microenvironment, and these properties can change in response to injury or disease. Hydrogels with dynamic material properties can be used to study the effect of such varying mechanical signals. Here, we report the ability of azadibenzocyclooctyne to undergo a cytocompatible, photoinitiated crosslinking reaction. This reaction is exploited as a strategy for on-demand stiffening of three-dimensional cell scaffolds formed through an initial strain-promoted azide-alkyne cycloaddition. Myoblasts encapsulated in these networks respond to increased matrix stiffness through decreased cell spreading and nuclear localization of Yes-associated protein 1 (YAP). However, when the photocrosslinking reaction is delayed to allow cell spreading, elongated myoblasts display increased YAP nuclear localization.

Readily Accessible Ambiphilic Cyclopentadienes for Bioorthogonal Labeling

A new class of bioorthogonal reagents based on the cyclopentadiene scaffold is described. The diene 6,7,8,9-tetrachloro-1,4-dioxospiro[4,4]nona-6,8-diene (a tetrachlorocyclopentadiene ketal, TCK) is ambiphilic and self-orthogonal with remarkable stability. The diene reacts rapidly with a trans-cyclooctene and an endo-bicyclononyne, but slowly with dibenzoazacyclooctyne (DIBAC), allowing for tandem labeling studies with mutually orthogonal azides that react rapidly with DIBAC. TCK analogues are synthesized in three steps from inexpensive, commercially available starting materials.

Schizandrin B inhibits the cis‑DDP‑induced apoptosis of HK‑2 cells by activating ERK/NF‑κB signaling to regulate the expression of survivin

The nephrotoxicity of cisplatin limits its clinical application. Schizandrin B (SchB) has been demonstrated to have a variety of potential cytoprotective activities. The present study explored the molecular mechanisms by which SchB inhibits the dichlorodiammine platinum (DDP)‑induced apoptosis of HK‑2 proximal tubule epithelial cells. In vitro assays demonstrated that SchB increased the viability of HK‑2 cells, alleviated the cis‑DDP‑induced activation of caspase‑3, reduced apoptosis and improved the nuclear morphology of HK‑2 cells. Additionally, the mechanism underlying the cis‑DDP‑induced apoptosis was indicated to involve the activation of p53, c‑Jun‑N‑terminal kinase (JNK) and p38 signaling. Furthermore, SchB was demonstrated to activate extracellular signal‑regulated kinase (ERK) and nuclear factor κB (NF‑κB) signaling, and induce the expression of survivin. The inhibition of ERK and NF‑κB signaling using U0126 and pyrollidine dithiocarbamate, respectively, inhibited the expression of survivin, whereas blocking the expression of survivin using small interfering RNA inhibited the alleviating effect of SchB on cis‑DDP‑induced apoptosis as indicated by a reduction in cleaved caspase‑3 expression. In conclusion, SchB regulates ERK/NF‑κB signaling to induce the expression of survivin, thereby alleviating cis‑DDP‑induced renal injury.

Reduction of Aβ Generation by Schisandrin B through Restraining Beta-Secretase 1 Transcription and Translation

BACKGROUND Beta-secretase 1 (BACE1) is a rate-limiting enzyme in the generation of amyloid beta peptides, which are associated with Alzheimer's disease (AD). It has been reported that Schisandrin B could improve cognitive functions in animal models of AD, but the underlying mechanisms are not completely understood. MATERIAL AND METHODS In this research, in order to investigate the effects of Schisandrin B on amyloid-β (Aβ) metabolism and its mechanisms, amyloid precursor protein (APP) and its proteolytic products were determined by enzyme-linked immunosorbent assay (ELISA), western blotting, and RT-PCR after incubation of N2a/Swe cells with Schisandrin B. RESULTS The results indicated that Schisandrin B can significantly reduce the level of secretion of Aβ40 and Aβ42 secreted in N2a/Swe cells. Additionally, there was nonsignificant change in APP level after Schisandrin B treatment. Treatment of Schisandrin B dramatically reduced the mRNA and protein expression levels of BACE1. Moreover, Schisandrin B treatment resulted in a reduction of protein level of sAPPβ, an APP fragment cleavage by BACE1. CONCLUSIONS These results suggest that Schisandrin B inhibits the transcription and translation of BACE1, suppresses the activity of BACE1, and ultimately attenuates Aβ generation, which provides a novel mechanism for the regulation of Aβ metabolism by Schisandrin B.

Pharmacokinetics of Schizandrin and Its Pharmaceutical Products Assessed Using a Validated LC-MS/MS Method

Schisandra chinensis has been used as an important component in various prescriptions in traditional Chinese medicine and, more recently, in Western-based medicine for its anti-hepatotoxic effect. The aim of this study was to develop a selective, rapid, and sensitive ultra-performance liquid chromatography-tandem mass spectrometry method for pharmacokinetic studies of schizandrin in rats. Liquid-liquid extraction was used for plasma sample preparation. A UHPLC reverse-phase C18e column (100 mm × 2.1 mm, 2 μm) coupled with a mobile phase of methanol-0.1% formic acid (85:15, v/v) was used for sample separation. A triple quadrupole tandem mass spectrometer was used to detect the analytes in the selected reaction monitoring mode. The linear range of schizandrin in rat plasma was 5.0–1000 ng/mL (r² > 0.999), with a lower limit of quantification of 5 ng/mL. The method was validated with regard to accuracy, intra-day and inter-day precision, linearity, stability, recovery, and matrix effects in rat plasma, which were acceptable according to the biological method validation guidelines developed by the FDA. This method was successfully applied to a pharmacokinetic study after oral administration of 3 g/kg and 10 g/kg of Schisandra chinensis products, which yielded a maximum concentration of schizandrin of 0.08 ± 0.07 and 0.15 ± 0.09 μg/mL, respectively. A parallel study design was used to investigate the oral bioavailability of single compound of schizandrin and the herbal extract, the single compound of pure schizandrin (10 mg/kg, i.v.), pure schizandrin (10 mg/kg, p.o.), and the herbal extract of Schisandra chinensis (3 g/kg and 10 g/kg, p.o.) were given individually. The dose of Schisandra chinensis (3 g/kg) equivalent to schizandrin (5.2 mg/kg); the dose of Schisandra chinensis (10 g/kg) equivalent to schizandrin (17.3 mg/kg). The result demonstrated that the oral bioavailability of schizandrin was approximately 15.56 ± 10.47% in rats, however the oral bioavailability of herbal extract was higher than single compound. The method was successfully applied to the pharmacokinetic study of pure schizandrin after oral administration of its pharmaceutical industry products in rats.

Time- and NADPH-Dependent Inhibition on CYP3A by Gomisin A and the Pharmacokinetic Interactions between Gomisin A and Cyclophosphamide in Rats

The traditional Chinese medicine Schisandra chinensis has remarkable protective effects against chemical-induced toxicity. Cyclophosphamide (CTX), in spite advances in chemotherapy and immunosuppressive regimes, is prone to cause severe toxicity due to its chloroacetaldehyde (CAA) metabolite produced by CYP3A. Our previous study identified that S. chinensis extract (SCE) co-administration potently decreased CAA production and attenuated liver, kidney and brain injuries in CTX-treated rats. Gomisin A (Gom A) is proved to be one of the most abundant bioactive lignans in S. chinensis with a significant CYP3A inhibitory effect. To find out whether and how Gom A participated in the chemoprevention of SCE against CTX toxicity, the Gom A-caused CYP3A inhibition in vitro as well as the pharmacokinetic interactions between Gom A and CTX in vivo were examined in this study. Using human liver microsomes, a reversible inhibition assay revealed that Gom A was a competitive inhibitor with a K_I value of 1.10 µM, and the time- and NADPH-dependent CYP3A inhibition of Gom A was observed in a time-dependent inhibition assay (K_I = 0.35 µM, k_inact = 1.96 min⁻¹). Hepatic CYP3A mRNA expression experienced a significant increase in our rat model with Gom A administration. This explained why CAA production decreased in the 0.5 h- and 6 h-pretreatment rat groups while it increased in the 24 h- and 72 h-pretreatment groups, indicating a bidirectional effect of Gom A on CYP3A-mediated CTX metabolism. The present study suggested that Gom A participates like SCE in the pharmacokinetic intervention of CTX by blocking CYP3A-mediated metabolism and reducing CAA production, and thus plays an important role in the chemopreventive activity of S. chinensis against CTX toxicity, in addition to the previously recognized protective effects. Also, the combined use of S. chinensis preparation or other drugs containing Gom A as the main component with CTX needed to be addressed for better clinical intervention.

Artificial Membrane Fusion Triggered by Strain-Promoted Alkyne-Azide Cycloaddition

Artificial systems for controlled membrane fusion applicable for drug delivery would ideally use triggers that are orthogonal to biology. To apply the strain-promoted alkyne-azide cycloaddition (SPAAC) to drive membrane fusion, oxo-dibenzocyclooctyne (ODIBO)-lipid 1 was designed, synthesized, and studied alongside azadibenzocyclooctyne (ADIBO)-lipids 2-4 to assess fusion with liposomes containing azido-lipid 5. Lipids 1-2 were first shown to be effective for liposome derivatization. Next, fusion was evaluated using liposomes containing 1 and varying ratios of PC and PE via a FRET dilution fusion assay, and a 1:1 PC-to-PE ratio yielded the greatest signal change attributed to fusion. Finally, lipids 1-4 were compared, and 1 yielded the greatest triggering of fusion, while 2-4 yielded varying efficacies depending on the structural features of each lipid. Fusion was further validated through STEM studies showing larger multilamellar assemblies after liposome mixing, and FRET assay results supporting the mixing of liposome aqueous contents. This work provides a platform for triggered fusion toward drug delivery applications and an understanding of the effects of lipid structure and membrane composition on fusion.

Lignans from the fruits of Schisandra chinensis (Turcz.) Baill inhibit proprotein convertase subtilisin/kexin type 9 expression

Bioactivity-guided fractionation of the fruits of Schisandra chinensis, using the proprotein convertase subtilisin-kexin type 9 (PCSK9) mRNA expression screening assay, led to isolation of two previously unknown lignans, 14-tigloylschinlignan D and rel-(7R, 8R, 7'R, 8'R)-manglisin E, along with 28 known compounds. All structures were established by NMR spectroscopic data as well as CD and MS analysis. All isolates were tested for their inhibitory activities on the mRNA expression of PCSK9. Of the tested compounds, four of the compounds rel-(7R, 8R, 7'R, 8'R)-manglisin E, (-)-schisandrin C, schinlignan D, and (+)-schisandrol B potently inhibited PCSK9 mRNA expression with IC₅₀ values of 3.15, 3.85, 0.36, and 1.10 μM, respectively. Furthermore, schinlignan D and (+)-schisandrol B were found to suppress PCSK9 protein expressions and schinlignan D deemed to increase low density lipoprotein receptor expression.

Site-Specific Immobilization of the Peptidoglycan Synthase PBP1B on a Surface Plasmon Resonance Chip Surface

Surface plasmon resonance (SPR) is one of the most powerful label-free methods to determine the kinetic parameters of molecular interactions in real time and in a highly sensitive way. Penicillin-binding proteins (PBPs) are peptidoglycan synthesis enzymes present in most bacteria. Established protocols to analyze interactions of PBPs by SPR involve immobilization to an ampicillin-coated chip surface (a β-lactam antibiotic mimicking its substrate), thereby forming a covalent complex with the PBPs transpeptidase (TP) active site. However, PBP interactions measured with a substrate-bound TP domain potentially affect interactions near the TPase active site. Furthermore, in vivo PBPs are anchored in the inner membrane by an N-terminal transmembrane helix, and hence immobilization at the C-terminal TPase domain gives an orientation contrary to the in vivo situation. We designed a new procedure: immobilization of PBP by copper-free click chemistry at an azide incorporated in the N terminus. In a proof-of-principle study, we immobilized Escherichia coli PBP1B on an SPR chip surface and used this for the analysis of the well-characterized interaction of PBP1B with LpoB. The site-specific incorporation of the azide affords control over protein orientation, thereby resulting in a homogeneous immobilization on the chip surface. This method can be used to study topology-dependent interactions of any (membrane) protein.

Hydrophilic trans-Cyclooctenylated Noncanonical Amino Acids for Fast Intracellular Protein Labeling

Introduction of bioorthogonal functionalities (e.g., trans-cyclooctene-TCO) into a protein of interest by site-specific genetic encoding of non-canonical amino acids (ncAAs) creates uniquely targetable platforms for fluorescent labeling schemes in combination with tetrazine-functionalized dyes. However, fluorescent labeling of an intracellular protein is usually compromised by high background, arising from the hydrophobicity of ncAAs; this is typically compensated for by hours-long washout to remove excess ncAAs from the cellular interior. To overcome these problems, we designed, synthesized, and tested new, hydrophilic TCO-ncAAs. One derivative, DOTCO-lysine was genetically incorporated into proteins with good yield. The increased hydrophilicity shortened the excess ncAA washout time from hours to minutes, thus permitting rapid labeling and subsequent fluorescence microscopy.

Discovery and Development of a Three-Component Oxidopyrylium [5 + 2] Cycloaddition

α-Hydroxy-γ-pyrone-based oxidopyrylium cycloaddition reactions are useful methods for accessing a highly diverse range of oxabicyclo[3.2.1]octane products. Intermolecular variants of the reaction require the formation of a methyl triflate-based pre-ylide salt that upon treatment with base in the presence of alkenes or alkynes leads to α-methoxyenone-containing bicyclic products. Herein, we describe our discovery that the use of ethanol-stabilized chloroform as solvent leads to the generation of α-ethoxyenone-containing bicyclic byproducts. This three-component process was further optimized by gently heating a mixture of a purified version of the oxidopyrylium dimer in the presence of an alcohol prior to addition of a dipolarophile. Using this convenient procedure, several new oxidopyrylium cycloaddition products can be generated in moderate yields. We also highlight the method in a tandem ring-opening/debenzylation method for the generation of α-hydroxytropolones.