Inverse Electron Demand Diels-Alder Research Articles

Synthesis of Polyoxygenated 4,5-Diarylpyridazines with Antiproliferative and Antitubulin Activity via Inverse Electron-Demand Diels-Alder Reaction of 1,2,4,5- Tetrazine#

Synthesis of Polyoxygenated 4,5-Diarylpyridazines with Antiproliferative and Antitubulin Activity via Inverse Electron-Demand Diels-Alder Reaction of 1,2,4,5- Tetrazine#

Bioorthogonal Cycloadditions of C3-Trifluoromethylated 1,2,4-Triazines with trans-Cyclooctenes.

1,2,4-triazines are a valuable class of heterodienes that can be employed in inverse electron-demand Diels-Alder reactions. However, their broader application in bioorthogonal chemistry is limited due to their low reactivity. This article focuses on 3-(trifluoromethyl)-1,2,4-triazines, which can be efficiently prepared in a one-pot reaction from NH-1,2,3-triazoles. These triazines are highly reactive in reactions with strained cyclooctenes, giving second-order rate constants as high as 230 M-1 s-1. Despite their high reactivity, the compounds remain sufficiently stable under biologically relevant conditions. We show that some of the compounds are fluorogenic, a property of potential use in bioimaging. In addition, we demonstrate the successful application of the triazines in labeling model biomolecules. Our work shows that the reactivity of 1,2,4-triazines can be enhanced by the 3-CF3-substitution, which we consider an important step toward the wider use of this promising class of reagents.

A Bioorthogonal Dual Fluorogenic Probe for the Live-Cell Monitoring of Nutrient Uptake by Mammalian Cells.

Cells rely heavily on the uptake of exogenous nutrients for survival, growth, and differentiation. Yet quantifying the uptake of small molecule nutrients at the single cell level is difficult. Here we present a new approach to studying the nutrient uptake in live single cells using Inverse Electron-Demand Diels Alder (IEDDA) chemistry. We have modified carboxyfluorescein-diacetate-succinimidyl esters (CFSE)-a quenched fluorophore that can covalently react with proteins and is only turned on in the cytosol of a cell following esterase activity-with a tetrazine. This tetrazine serves as a second quencher for the pendant fluorophore. Upon reaction with nutrients modified with an electron-rich or strained dienophile in an IEDDA reaction, this quenching group is destroyed, thereby enabling the probe to fluoresce. This has allowed us to monitor the uptake of a variety of dienophile-containing nutrients in live primary immune cell populations using flow cytometry and live-cell microscopy.

A Bioorthogonal Dual Fluorogenic Probe for the Live‐Cell Monitoring of Nutrient Uptake by Mammalian Cells

AbstractCells rely heavily on the uptake of exogenous nutrients for survival, growth, and differentiation. Yet quantifying the uptake of small molecule nutrients at the single cell level is difficult. Here we present a new approach to studying the nutrient uptake in live single cells using Inverse Electron‐Demand Diels Alder (IEDDA) chemistry. We have modified carboxyfluorescein‐diacetate‐succinimidyl esters (CFSE)—a quenched fluorophore that can covalently react with proteins and is only turned on in the cytosol of a cell following esterase activity—with a tetrazine. This tetrazine serves as a second quencher for the pendant fluorophore. Upon reaction with nutrients modified with an electron‐rich or strained dienophile in an IEDDA reaction, this quenching group is destroyed, thereby enabling the probe to fluoresce. This has allowed us to monitor the uptake of a variety of dienophile‐containing nutrients in live primary immune cell populations using flow cytometry and live‐cell microscopy.

Data-Efficient, Chemistry-Aware Machine Learning Predictions of Diels-Alder Reaction Outcomes.

The application of machine learning models to the prediction of reaction outcomes currently needs large and/or highly featurized data sets. We show that a chemistry-aware model, NERF, which mimics the bonding changes that occur during reactions, allows for highly accurate predictions of the outcomes of Diels-Alder reactions using a relatively small training set, with no pretraining and no additional features. We establish a diverse data set of 9537 intramolecular, hetero-, aromatic, and inverse electron demand Diels-Alder reactions. This data set is used to train a NERF model, and the performance is compared against state-of-the-art classification and generative machine learning models across low- and high-data regimes, with and without pretraining. The predictive accuracy (regio- and site selectivity in the major product) achieved by NERF exceeds 90% when as little as 40% of the data set is used for training. Another high-performing model, Chemformer, requires a larger training data set (>45%) and pretraining to reach 90% Top-1 accuracy. Accurate predictions of less-represented reaction subclasses, such as those involving heteroatomic or aromatic substrates, require higher percentages of training data. We also show how NERF can use small amounts of additional training data to quickly learn new systems and improve its overall understanding of reactivity. Synthetic chemists stand to benefit as this model can be rapidly expanded and tailored to areas of chemistry corresponding to the low-data regime.

Promotion and Detection of Cell-Cell Interactions through a Bioorthogonal Approach.

Manipulation of cell-cell interactions via cell surface modification is crucial in tissue engineering and cell-based therapy. To be able to monitor intercellular interactions, it can also provide useful information for understanding how the cells interact and communicate. We report herein a facile bioorthogonal strategy to promote and monitor cell-cell interactions. It involves the use of a maleimide-appended tetrazine-caged boron dipyrromethene (BODIPY)-based fluorescent probe and a maleimide-substituted bicyclo[6.1.0]non-4-yne (BCN) to modify the membrane of macrophage (RAW 264.7) and cancer (HT29, HeLa, and A431) cells, respectively, via maleimide-thiol conjugation. After modification, the two kinds of cells interact strongly through inverse electron-demand Diels-Alder reaction of the surface tetrazine and BCN moieties. The coupling also disrupts the tetrazine quenching unit, restoring the fluorescence emission of the BODIPY core on the cell-cell interface, and promotes phagocytosis. Hence, this approach can promote and facilitate the detection of intercellular interactions, rendering it potentially useful for macrophage-based immunotherapy.

AlbuCatcher for Long-Acting Therapeutics.

Therapeutic proteins, pivotal for treating diverse human diseases due to their biocompatibility and high selectivity, often face challenges such as rapid serum clearance, enzymatic degradation, and immune responses. To address these issues and enable prolonged therapeutic efficacy, techniques to extend the serum half-life of therapeutic proteins are crucial. The AlbuCatcher, a conjugate of human serum albumin (HSA) and SpyCatcher, was proposed as a general technique to extend the serum half-life of diverse therapeutic proteins. HSA, the most abundant blood protein, exhibits a long intrinsic half-life through Fc receptor (FcRn)-mediated recycling. The SpyTag/SpyCatcher (ST/SC) system, known for forming irreversible isopeptide bonds, was employed to conjugate HSA and therapeutic proteins. Site-specific HSA conjugation to SC was achieved using an inverse electron-demand Diels-Alder (IEDDA) reaction, minimizing activity loss. Using urate oxidase (Uox) as a model protein with a short half-life, the small ST was fused to generate Uox-ST. Then, HSA-conjugated Uox (Uox-HSA) was successfully prepared via the Uox-ST/AlbuCatcher reaction. In vitro enzyme assays demonstrated that the impact of ST fusion and HSA conjugation on Uox enzymatic activity is negligible. Pharmacokinetics studies in mice revealed that Uox-HSA exhibits a significantly longer serum half-life (about 18 h) compared to Uox-WT (about 2 h). This extended half-life is attributed to FcRn-mediated recycling of HSA-conjugated Uox, demonstrating the effectiveness of the AlbuCatcher strategy in enhancing the pharmacokinetics of therapeutic proteins.

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.

Broadening the Utility of Farnesyltransferase-Catalyzed Protein Labeling Using Norbornene-Tetrazine Click Chemistry.

Bioorthogonal chemistry has gained widespread use in the study of many biological systems of interest, including protein prenylation. Prenylation is a post-translational modification, in which one or two 15- or 20-carbon isoprenoid chains are transferred onto cysteine residues near the C-terminus of a target protein. The three main enzymes─protein farnesyltransferase (FTase), geranylgeranyl transferase I (GGTase I), and geranylgeranyl transferase II (GGTase II)─that catalyze this process have been shown to tolerate numerous structural modifications in the isoprenoid substrate. This feature has previously been exploited to transfer an array of farnesyl diphosphate analogues with a range of functionalities, including an alkyne-containing analogue for copper-catalyzed bioconjugation reactions. Reported here is the synthesis of an analogue of the isoprenoid substrate embedded with norbornene functionality (C10NorOPP) that can be used for an array of applications, ranging from metabolic labeling to selective protein modification. The probe was synthesized in seven steps with an overall yield of 7% and underwent an inverse electron demand Diels-Alder (IEDDA) reaction with tetrazine-containing tags, allowing for copper-free labeling of proteins. The use of C10NorOPP for the study of prenylation was explored in the metabolic labeling of prenylated proteins in HeLa, COS-7, and astrocyte cells. Furthermore, in HeLa cells, these modified prenylated proteins were identified and quantified using label-free quantification (LFQ) proteomics with 25 enriched prenylated proteins. Additionally, the unique chemistry of C10NorOPP was utilized for the construction of a multiprotein-polymer conjugate for the targeted labeling of cancer cells. That construct was prepared using a combination of norbornene-tetrazine conjugation and azide-alkyne cycloaddition, highlighting the utility of the additional degree of orthogonality for the facile assembly of new protein conjugates with novel structures and functions.

Cyclopropenes as Chemical Reporters for Dual Bioorthogonal and Orthogonal Metabolic Labeling of DNA.

Dual bioorthogonal labeling enables the investigation and understanding of interactions in the biological environment that are not accessible by a single label. However, applying two bioorthogonal reactions in the same environment remains challenging due to cross-reactivity. We developed a pair of differently modified 2'-deoxynucleosides that solved this issue for dual and orthogonal labeling of DNA. Inverse-electron demand Diels-Alder and photoclick reactions were combined to attach two different fluorogenic labels to genomic DNA in cells. Using a small synthetic library of 1- and 3-methylcyclopropenyl-modified 2'-deoxynucleosides, two 2'-deoxyuridines were identified to be the fastest-reacting ones for each of the two bioorthogonal reactions. Their orthogonal reactivity could be evidenced in vitro. Primer extension experiments were performed with both 2'-deoxyuridines investigating their replication properties as substitutes for thymidine and evaluating subsequent labeling reactions on the DNA level. Finally, dual, orthogonal and metabolic fluorescent labeling of genomic DNA was demonstrated in HeLa cells. An experimental procedure was developed combining intracellular transport and metabolic DNA incorporation of the two 2'-deoxyuridines with the subsequent dual bioorthogonal labeling using a fluorogenic cyanine-styryl tetrazine and a fluorogenic pyrene-tetrazole. These results are fundamental for advanced metabolic labeling strategies for nucleic acids in the future, especially for live cell experiments.

Smart Biointerfaces via Click Chemistry-Enabled Nanopatterning of Multiple Bioligands and DNA Force Sensors.

Nanoscale biomolecular placement is crucial for advancing cellular signaling, sensor technology, and molecular interaction studies. Despite this, current methods fall short in enabling large-area nanopatterning of multiple biomolecules while minimizing nonspecific interactions. Using bioorthogonal tags at a submicron scale, we introduce a novel hole-mask colloidal lithography method for arranging up to three distinct proteins, DNA, or peptides on large, fully passivated surfaces. The surfaces are compatible with single-molecule fluorescence microscopy and microplate formats, facilitating versatile applications in cellular and single-molecule assays. We utilize fully passivated and transparent substrates devoid of metals and nanotopographical features to ensure accurate patterning and minimize nonspecific interactions. Surface patterning is achieved using bioorthogonal TCO-tetrazine (inverse electron-demand Diels-Alder, IEDDA) ligation, DBCO-azide (strain-promoted azide-alkyne cycloaddition, SPAAC) click chemistry, and biotin-avidin interactions. These are arranged on surfaces passivated with dense poly(ethylene glycol) PEG brushes crafted through the selective and stepwise removal of sacrificial metallic and polymeric layers, enabling the directed attachment of biospecific tags with nanometric precision. In a proof-of-concept experiment, DNA tension gauge tether (TGT) force sensors, conjugated to cRGD (arginylglycylaspartic acid) in nanoclusters, measured fibroblast integrin tension. This novel application enables the quantification of forces in the piconewton range, which is restricted within the nanopatterned clusters. A second demonstration of the platform to study integrin and epidermal growth factor (EGF) proximal signaling reveals clear mechanotransduction and changes in the cellular morphology. The findings illustrate the platform's potential as a powerful tool for probing complex biochemical pathways involving several molecules arranged with nanometer precision and cellular interactions at the nanoscale.

Next-Generation Metabolic Glycosylation Reporters Enable Detection of Protein O-GlcNAcylation in Living Cells without S-Glyco Modification.

Protein O-GlcNAcylation is a ubiquitous posttranslational modification of cytosolic and nuclear proteins involved in numerous fundamental regulation processes. Investigation of O-GlcNAcylation by metabolic glycoengineering (MGE) has been carried out for two decades with peracetylated N-acetylglucosamine (GlcNAc) and N-acetylgalactosamine derivatives modified with varying reporter groups. Recently, it has been shown that these derivatives can result in non-specific protein labeling termed S-glyco modification. Here, we report norbornene-modified GlcNAc derivatives with a protected phosphate at the anomeric position and their application in MGE. These derivatives overcome two limitations of previously used O-GlcNAc reporters. They do not lead to detectable S-glyco modification, and they efficiently react in the inverse-electron-demand Diels-Alder (IEDDA) reaction, which can be carried out even within living cells. Using a derivative with an S-acetyl-2-thioethyl-protected phosphate, we demonstrate the protein-specific detection of O-GlcNAcylation of several proteins and the protein-specific imaging of O-GlcNAcylation inside living cells by Förster resonance energy transfer (FRET) visualized by confocal fluorescence lifetime imaging microscopy (FLIM).

Next‐Generation Metabolic Glycosylation Reporters Enable Detection of Protein O−GlcNAcylation in Living Cells without S‐Glyco Modification

AbstractProtein O−GlcNAcylation is a ubiquitous posttranslational modification of cytosolic and nuclear proteins involved in numerous fundamental regulation processes. Investigation of O−GlcNAcylation by metabolic glycoengineering (MGE) has been carried out for two decades with peracetylated N‐acetylglucosamine (GlcNAc) and N‐acetylgalactosamine derivatives modified with varying reporter groups. Recently, it has been shown that these derivatives can result in non‐specific protein labeling termed S‐glyco modification. Here, we report norbornene‐modified GlcNAc derivatives with a protected phosphate at the anomeric position and their application in MGE. These derivatives overcome two limitations of previously used O−GlcNAc reporters. They do not lead to detectable S‐glyco modification, and they efficiently react in the inverse‐electron‐demand Diels–Alder (IEDDA) reaction, which can be carried out even within living cells. Using a derivative with an S‐acetyl‐2‐thioethyl‐protected phosphate, we demonstrate the protein‐specific detection of O−GlcNAcylation of several proteins and the protein‐specific imaging of O−GlcNAcylation inside living cells by Förster resonance energy transfer (FRET) visualized by confocal fluorescence lifetime imaging microscopy (FLIM).

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.

Enhanced therapeutic potential of antibody fragment via IEDDA-mediated site-specific albumin conjugation

BackgroundThe use of single-chain variable fragments (scFvs) for treating human diseases, such as cancer and immune system disorders, has attracted significant attention. However, a critical drawback of scFv is its extremely short serum half-life, which limits its therapeutic potential. Thus, there is a critical need to prolong the serum half-life of the scFv for clinical applications. One promising serum half-life extender for therapeutic proteins is human serum albumin (HSA), which is the most abundant protein in human serum, known to have an exceptionally long serum half-life. However, conjugating a macromolecular half-life extender to a small protein, such as scFv, often results in a significant loss of its critical properties.ResultsIn this study, we conjugated the HSA to a permissive site of scFv to improve pharmacokinetic profiles. To ensure minimal damage to the antigen-binding capacity of scFv upon HSA conjugation, we employed a site-specific conjugation approach using a heterobifunctional crosslinker that facilitates thiol-maleimide reaction and inverse electron-demand Diels-Alder reaction (IEDDA). As a model protein, we selected 4D5scFv, derived from trastuzumab, a therapeutic antibody used in human epithermal growth factor 2 (HER2)-positive breast cancer treatment. We introduced a phenylalanine analog containing a very reactive tetrazine group (frTet) at conjugation site candidates predicted by computational methods. Using the linker TCO-PEG4-MAL, a single HSA molecule was site-specifically conjugated to the 4D5scFv (4D5scFv-HSA). The 4D5scFv-HSA conjugate exhibited HER2 binding affinity comparable to that of unmodified 4D5scFv. Furthermore, in pharmacokinetic profile in mice, the serum half-life of 4D5scFv-HSA was approximately 12 h, which is 85 times longer than that of 4D5scFv.ConclusionsThe antigen binding results and pharmacokinetic profile of 4D5scFv-HSA demonstrate that the site-specifically albumin-conjugated scFv retained its binding affinity with a prolonged serum half-life. In conclusion, we developed an effective strategy to prepare site-specifically albumin-conjugated 4D5scFv, which can have versatile clinical applications with improved efficacy.

Abstract 2614: GlycoConnect™ ADC toolbox expansion with high DAR technology

Abstract Recently topoisomerase 1 inhibitors have gained significant traction as a cytotoxic payload for ADCs based on the clinical success of camptothecin-based ADCs Enhertu® (DXd) and Trodelvy® (SN-38). In contrast to the majority of other approved ADCs, both Enhertu® and Trodelvy® are feature an average of 7-8 payloads per antibody. Obviously, such a high drug-to-antibody ratio (DAR) effectively delivers more drug to the tumor per internalization event, which is key in driving the clinical success. Previously, we have shown that the native glycan of monoclonal antibodies is a privileged site for attachment of cytotoxic payloads1, for the generation of site-specific and stable ADCs with DARs varying from 1-6, while the therapeutic index is further elevated by a highly polar spacer technology (HydraSpace™)2. The success of GlycoConnect™/HydraSpace™ ADCs is further driven by the use of exatecan as a potent and highly cell-permeable payload (SYNtecan E™). Here we show that GlycoConnect™ technology can be readily extended to generate efficacious and safe DAR8 ADCs. We have developed a modular, non-genetic method, involving three simple process steps from any antibody: (a) enzymatic glycan remodeling, (b) strain-promoted azide-alkyne cycloaddition of a bifunctional, branched spacer comprising one strained alkyne and two orthogonal click tags (e.g. tetrazines), and (c) inverse electron-demand Diels-Alder cycloaddition with a branched linker-drug construct based on BCN and a two cytotoxic payloads. The resulting conjugates, with DAR 6 or 8, are rapidly generated with high homogeneity and with good stability. In addition, HIC profiles of the resulting ADCs indicate small relative retention time as an indication of good PK profile. Excellent in vivo tolerability is demonstrated, while efficacy studies in mice xenograft models show that the DAR8 technology clearly out-performs currently marketed ADCs (including Enhertu®). 1 (a) van Geel et al. Chemoenzymatic Conjugation of Toxic Payloads to the Globally Conserved N-Glycan of Native mAbs Provides Homogeneous and Highly Efficacious Antibody−Drug Conjugates. Bioconj. Chem. 2015, 26, 2233-2242. (b) Wijdeven et al. Enzymatic glycan remodeling-metal free click (GlycoConnect™) provides homogenous antibody-drug conjugates with improved stability and therapeutic index without sequence engineering. MAbs 2022, DOI: 10.1080/19420862.2022.2078466. 2 Verkade et al. A Polar Sulfamide Spacer Significantly Enhances the Manufacturability, Stability, and Therapeutic Index of Antibody-Drug Conjugates. Antibodies 2018, 7, 12, doi:10.3390/antib7010012. Citation Format: Lianne Lelieveldt, Elias Post, Marie Nassiet, Veronique Hendriks, Mick Verhagen, Remon van Geel, Sander van Berkel, Floris van Delft. GlycoConnect™ ADC toolbox expansion with high DAR technology [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2614.

Selective Late-Stage Functionalization of Tryptophan-Containing Peptides To Facilitate Bioorthogonal Tetrazine Ligation.

Site-selective modification of complex peptides and the functionalization of their C-H bonds hold great promise for expanding their use in therapeutics and biomedical research. Herein, we leverage the power of late-stage chemoenzymatic catalysis using an indole prenyltransferase (IPT) enzyme and alkyl diphosphates to specifically modify the indole ring of tryptophan in clinically relevant peptides. Furthermore, the installed handle enables bioorthogonal click chemistry through an inverse electron-demand Diels-Alder (IEDDA) reaction with a biotin-conjugated tetrazine probe.

Injectable and Multifunctional Hydrogels Based on Poly(N-acryloyl glycinamide) and Alginate Derivatives for Antitumor Drug Delivery.

Chemotherapy is a conventional treatment that uses drugs to kill cancer cells; however, it may induce side effects and may be incompletely effective, leading to the risk of tumor recurrence. To address this issue, we developed novel injectable thermal/near-infrared (NIR)-responsive hydrogels to control drug release. The injectable hydrogel formulation was composed of biocompatible alginates, poly(N-acryloyl glycinamide) (PNAGA) copolymers with an upper critical solution temperature, and NIR-responsive cross-linkers containing coumarin groups, which were gelated through bioorthogonal inverse electron demand Diels-Alder reactions. The hydrogels exhibited quick gelation times (120-800 s) and high drug loading efficiencies (>90%). The hydrogels demonstrated a higher percentage of drug release at 37 °C than that at 25 °C due to the enhanced swelling behavior of temperature-responsive PNAGA moieties. Upon NIR irradiation, the hydrogels released most of the entrapped doxorubicin (DOX) (97%) owing to the cleavage of NIR-sensitive coumarin ester groups. The hydrogels displayed biocompatibility with normal cells, while induced antitumor activity toward cancer cells. DOX/hydrogels treated with NIR light inhibited tumor growth in nude mice bearing tumors. In addition, the injected hydrogels emitted red fluorescence upon excitation at a green wavelength, so that the drug delivery and hydrogel degradation in vivo could be tracked in the xenograft model.

Genetically encoded bioorthogonal tryptophan decaging in living cells.

Tryptophan (Trp) plays a critical role in the regulation of protein structure, interactions and functions through its π system and indole N-H group. A generalizable method for blocking and rescuing Trp interactions would enable the gain-of-function manipulation of various Trp-containing proteins in vivo, but generating such a platform remains challenging. Here we develop a genetically encoded N1-vinyl-caged Trp capable of rapid and bioorthogonal decaging through an optimized inverse electron-demand Diels-Alder reaction, allowing site-specific activation of Trp on a protein of interest in living cells. This chemical activation of a genetically encoded caged-tryptophan (Trp-CAGE) strategy enables precise activation of the Trp of interest underlying diverse important molecular interactions. We demonstrate the utility of Trp-CAGE across various protein families, such as catalase-peroxidases and kinases, as translation initiators and posttranslational modification readers, allowing the modulation of epigenetic signalling in a temporally controlled manner. Coupled with computer-aided prediction, our strategy paves the way for bioorthogonal Trp activation on more than 28,000 candidate proteins within their native cellular settings.

Degradable and Multifunctional PEG-Based Hydrogels Formed by iEDDA Click Chemistry with Stable Click-Induced Supramolecular Interactions.

The inverse electron demand Diels-Alder (iEDDA) reactions are highly efficient click chemistry increasingly utilized in bioconjugation, live cell labeling, and the synthesis and modification of biomaterials. iEDDA click reactions have also been used to cross-link tetrazine (Tz) and norbornene (NB) modified macromers [e.g., multiarm poly(ethylene glycol) or PEG]. In these hydrogels, Tz-NB adducts exhibit stable supramolecular interactions with a high hydrolytic stability. Toward engineering a new class of PEG-based click hydrogels with highly adaptable properties, we previously reported a new group of NB-derivatized PEG macromers via reacting hydroxyl-terminated PEG with carbic anhydride (CA). In this work, we show that hydrogels cross-linked by PEGNBCA or its derivatives exhibited fast and tunable hydrolytic degradation. Here, we show that PEGNBCA (either mono- or octafunctional) and its dopamine or tyramine conjugated derivatives (i.e., PEGNB-D and PEGNB-T) readily cross-link with 4-arm PEG-Tz to form a novel class of multifunctional iEDDA click hydrogels. Through modularly adjusting the macromers with unstable and stable iEDDA click-induced supramolecular interactions (iEDDA-CSI), we achieved highly tunable degradation, with full degradation in less than 2 weeks to over two months. We also show that secondary enzymatic reactions could dynamically stiffen these hydrogels. These hydrogels could also be spatiotemporally photopatterned through visible light-initiated photochemistry. Finally, the iEDDA-CSI hydrogels post ester hydrolysis displayed shear-thinning and self-healing properties, enabling injectable delivery.