Bioorthogonal Swarming: In Situ Generation of Dendrimers

Tracking host-guest recognition in cells by a BODIPY·CB[7] complex

Interested in host·guest binding events in cellular environments, intracellular recognition between fluorescent BODIPY+ and cucurbit[7]uril was explored for lysosome tracking in living cancer cells. Sequential deaggregation from spontaneously dimerized BODIPY+ was unusually discovered upon complexation with CB[7].

Tumor Receptor-Mediated Morphological Transformation and In Situ Polymerization of Diacetylene-Containing Lipidated Peptide Amphiphile on Cell Membranes for Tumor Suppression

In situ polymerization on cell membranes can decrease cell mobility, which may inhibit tumor growth and invasion. However, the initiation of radical polymerization traditionally requires exogenous catalysts or free radical initiators, which might cause side effects in normal tissues. Herein, we synthesized a Y-type diacetylene-containing lipidated peptide amphiphile (TCDA-KFFFFK(GRGDS)-YIGSR, Y-DLPA) targeting integrins and laminin receptors on murine mammary carcinoma 4T1 cells, which underwent nanoparticle-to-nanofiber morphological transformation and in situ polymerization on cell membranes. Specifically, the polymerized Y-DLPA induced 4T1 cell apoptosis and disturbed the substance exchange and metabolism. In vitro assays demonstrated that the polymerized Y-DLPA nanofibers decreased the migration capacity of 4T1 cells, potentially suppressing tumor invasion and metastasis. When administered locally to 4T1 tumor-bearing mice, the Y-DLPA nanoparticles formed a biomimetic extracellular matrix that effectively suppressed tumor growth. This study provides an in situ polymerization strategy that can serve as an effective drug-free biomaterial with low side effects for antitumor therapy.

Precise Regulations at the Subcellular Level through Intracellular Polymerization, Assembly, and Transformation

A living cell is an intricate machine that creates subregions to operate cell functions effectively. Subcellular dysfunction has been identified as a potential druggable target for successful drug design and therapy. The treatments based on intracellular polymerization, self-assembly, or transformation offer various advantages, including enhanced blood circulation of monomers, long-term drug delivery pharmacokinetics, low drug resistance, and the ability to target deep tissues and organelles. In this review, we discuss the latest developments of intracellular synthesis applied to precisely control cellular functions. First, we discuss the design and applications of endogenous and exogenous stimuli-triggered intracellular polymerization, self-assembly, and dynamic morphology transformation of biomolecules at the subcellular level. Second, we highlight the benefits of these strategies applied in cancer diagnosis and treatment and modulating cellular states or cell metabolism of living systems. Finally, we conclude the recent progress in this field, discuss future perspectives, analyze the challenges of the intracellular functional reactions for regulation, and find future opportunities.

Bioorthogonal chemistry-based prodrug strategies for enhanced biosafety in tumor treatments: current progress and challenges

Cancer is a significant global health challenge, and while chemotherapy remains a widely used treatment, its non-specific toxicity and broad distribution can lead to systemic side effects and limit its effectiveness against tumors. Therefore, the development of safer chemotherapy alternatives is crucial. Prodrugs hold great promise, as they remain inactive until they reach the cancer site, where they are selectively activated by enzymes or specific factors, thereby reducing side effects and improving targeting. However, subtle differences in the microenvironments between tumors and normal tissue may still result in unintended cytotoxicity. Bioorthogonal reactions, known for their selectivity and precision without interfering with natural biochemical processes, are gaining attention. When combined with prodrug strategies, these reactions offer the potential to create highly effective chemotherapy drugs. This review examines the safety and efficacy of prodrug strategies utilizing various bioorthogonal reactions in cancer treatment.

Artificial Polymerizations in Living Organisms for Biomedical Applications

Within living organisms, numerous nanomachines are constantly involved in complex polymerization processes, generating a diverse array of biomacromolecules for maintaining biological activities. Transporting artificial polymerizations from lab settings into biological contexts has expanded opportunities for understanding and managing biological events, creating novel cellular compartments, and introducing new functionalities. This review summarizes the recent advancements in artificial polymerizations, including those responding to external stimuli, internal environmental factors, and those that polymerize spontaneously. More importantly, the cutting-edge biomedical application scenarios of artificial polymerization, notably in safeguarding cells, modulating biological events, improving diagnostic performance, and facilitating therapeutic efficacy are highlighted. Finally, this review outlines the key challenges and technological obstacles that remain for polymerizations in biological organisms, as well as offers insights into potential directions for advancing their practical applications and clinical trials.

A Gene-Editable Palladium-Based Bioorthogonal Nanoplatform Facilitates Macrophage Phagocytosis for Tumor Therapy

Macrophage phagocytosis of tumor cells has emerged as an attractive strategy for tumor therapy. Nevertheless, immunosuppressive M2 macrophages in the tumor microenvironment and the high expression of anti-phagocytic signals from tumor cells impede therapeutic efficacy. To address these issues and improve the management of malignant tumors, in this study we developed a gene-editable palladium-based bioorthogonal nanoplatform, consisting of CRISPR/Cas9 gene editing system-linked Pd nanoclusters, and a hyaluronic acid surface layer (HBPdC). This HBPdC nanoplatform exhibited satisfactory tumor-targeting efficiency and triggered Fenton-like reactions in the tumor microenvironment to generate reactive oxygen species for chemodynamic therapy and macrophage M1 polarization, which directly eliminated tumor cells, and stimulated the antitumor response of macrophages. HBPdC could reprogram tumor cells through gene editing to reduce the expression of CD47 and adipocyte plasma membrane-associated protein, thereby promoting their recognition and phagocytosis by macrophages. Moreover, HBPdC induced the activation of sequestered prodrugs via bioorthogonal catalysis, enabling chemotherapy and thereby enhancing tumor cell death. Importantly, the Pd nanoclusters of HBPdC were sufficiently cleared through basic metabolic pathways, confirming their biocompatibility and biosafety. Therefore, by promoting macrophage phagocytosis, the HBPdC system developed herein represents a highly promising antitumor toolset for cancer therapy applications.

Schiff Base Reaction in a Living Cell: In Situ Synthesis of a Hollow Covalent Organic Polymer To Regulate Biological Functions

Artificially performing chemical reactions in living biosystems to attain various physiological aims remains an intriguing but very challenging task. In this study, the Schiff base reaction was conducted in cells using Sc(OTf)3 as a catalyst, enabling the in situ synthesis of a hollow covalent organic polymer (HCOP) without external stimuli. The reversible Schiff base reaction mediated intracellular Oswald ripening endows the HCOP with a spherical, hollow porous structure and a large specific surface area. The intracellularly generated HCOP reduced cellular motility by restraining actin polymerization, which consequently induced mitochondrial deactivation, apoptosis, and necroptosis. The presented intracellular synthesis system inspired by the Schiff base reaction has strong potential to regulate cell fate and biological functions, opening up a new strategic possibility for intervening in cellular behavior.

Hyperbranched Polymers: Recent Advances in Photodynamic Therapy against Cancer

Hyperbranched polymers are a class of three-dimensional dendritic polymers with highly branched architectures. Their unique structural features endow them with promising physical and chemical properties, such as abundant surface functional groups, intramolecular cavities, and low viscosity. Therefore, hyperbranched-polymer-constructed cargo delivery carriers have drawn increasing interest and are being utilized in many biomedical applications. When applied for photodynamic therapy, photosensitizers are encapsulated in or covalently incorporated into hyperbranched polymers to improve their solubility, stability, and targeting efficiency and promote the therapeutic efficacy. This review will focus on the state-of-the-art studies concerning recent progress in hyperbranched-polymer-fabricated phototherapeutic nanomaterials with emphases on the building-block structures, synthetic strategies, and their combination with the codelivered diagnostics and synergistic therapeutics. We expect to bring our demonstration to the field to increase the understanding of the structure-property relationships and promote the further development of advanced photodynamic-therapy nanosystems.

Intracellular Hyperbranched Polymerization for Circumventing Cancer Drug Resistance

Polymerization inside living cells provides chemists with a multitude of possibilities to modulate cell activities. Considering the advantages of hyperbranched polymers, such as a large surface area for target sites and multilevel branched structures for resistance to the efflux effect, we reported a hyperbranched polymerization in living cells based on the oxidative polymerization of organotellurides and intracellular redox environment. The intracellular hyperbranched polymerization was triggered by reactive oxygen species (ROS) in the intracellular redox microenvironment, effectively disrupting antioxidant systems in cells by an interaction between Te (+4) and selenoproteins, thus inducing selective apoptosis of cancer cells. Importantly, the obtained hyperbranched polymer aggregated into branched nanostructures in cells, which could effectively evade drug pumps and decrease drug efflux, ensuring the polymerization for persistent treatment. Finally, in vitro and in vivo studies confirmed that our strategy presented selective anticancer efficacy and well biosafety. This approach provides a way for intracellular polymerization with desirable biological applications to regulate cell activities.

Bottom-up on-surface synthesis based on click-functionalized peptide bundles

On-surface synthesis is a modern technique for the preparation of atomically low-dimensional molecular nanostructures. However, most nanomaterials grow horizontally on the surface, and the step-by-step longitudinally controllable covalent bonding reaction on the surface is rarely reported. Here, we successfully achieved bottom-up on-surface synthesis by using coiled-coil homotetrameric peptide bundles called 'bundlemers' as building blocks. Rigid nano-cylindrical bundlemer with two click-reactive functionalities at each end can be grafted vertically onto the surface or another bundlemer with complementary clickable groups by click reaction at one end, thus enabling the longitudinal bottom-up synthesis of rigid rods with an exact number of bundlemers (up to 6) on the surface. Moreover, we can graft linear poly(ethylene glycol) (PEG) to one terminal of rigid rods to obtain rod-PEG hybrid nanostructures that can be released from the surface under specific conditions. Interestingly, rod-PEG nanostructures consisting of different numbers of bundles can self-assemble in water into different nano-hyperstructures. In general, the bottom-up on-surface synthesis strategy presented here can provide a simple and accurate method to manufacture a variety of nanomaterials.

Solid-Phase Synthesis of s-Tetrazines

An efficient synthesis of s-tetrazines by solid-phase methods is described. This synthesis route was compatible with different solid-phase resins and linkers and did not require metal catalysts or high temperatures. Monosubstituted tetrazines were routinely synthesized using thiol-promoted chemistry, using dichloromethane as a carbon source, while disubstituted unsymmetrical aryl or alkyl tetrazines were synthesized using readily available nitriles. This efficient approach enabled the synthesis of s-tetrazines in high yields (70-94%), eliminating the classical solution-phase problems of mixtures of symmetrical and unsymmetrical tetrazines, with only a single final purification step required, and paves the way to the rapid synthesis of s-tetrazines with various applications in bioorthogonal chemistry and beyond.

Polymerization in living organisms

Vital biomacromolecules, such as RNA, DNA, polysaccharides and proteins, are synthesized inside cells via the polymerization of small biomolecules to support and multiply life. The study of polymerization reactions in living organisms is an emerging field in which the high diversity and efficiency of chemistry as well as the flexibility and ingeniousness of physiological environment are incisively and vividly embodied. Efforts have been made to design and develop in situ intra/extracellular polymerization reactions. Many important research areas, including cell surface engineering, biocompatible polymerization, cell behavior regulation, living cell imaging, targeted bacteriostasis and precise tumor therapy, have witnessed the elegant demeanour of polymerization reactions in living organisms. In this review, recent advances in polymerization in living organisms are summarized and presented according to different polymerization methods. The inspiration from biomacromolecule synthesis in nature highlights the feasibility and uniqueness of triggering living polymerization for cell-based biological applications. A series of examples of polymerization reactions in living organisms are discussed, along with their designs, mechanisms of action, and corresponding applications. The current challenges and prospects in this lifeful field are also proposed.

Drug-dendrimer complexes and conjugates: Detailed furtherance through theory and experiments

Dendritic nanovectors-based drug delivery has gained significant attention in the past couple of decades. Dendrimers play a crucial role in deciding the solubility of sparingly soluble drug molecules and help in improving pharmacokinetics. A few important steps in drug delivery through dendrimers, such as drug encapsulation, formulation, and target-specific delivery, play an important role in deciding the fate of a drug molecule. It is also of prime importance to understand the interactions between a drug molecule and dendrimers at atomistic levels to decode the mechanism of action of drug-dendrimer complexes and their reliability in terms of drug delivery. Colossal progress in current experimental and computational approaches in the field has resulted in a vast amount of data that needs to be curated to be further implemented efficiently. Improved computational power has led to greater accuracy and prompt predictions of properties of drug-dendrimer complexes and their mechanism of action. The current review encapsulates the pioneering work in the field, experimental achievements in terms of drug delivery, and newer computational techniques employed in the advancement of the field.

Bidirectional Supramolecular Display and Signal Amplification on the Surface of Living Cells

The ability to display exogenous molecules or nanomaterials on the surface of cells holds great potential for biomedical applications such as cell imaging and delivery. Numerous methods have been well established to enhance the display of biomolecules and nanomaterials on the cell surface. However, it is challenging to remove these biomolecules or nanomaterials from the cell surface. The purpose of this study was to investigate the reversible display of supramolecular nanomaterials on the surface of living cells. The data show that DNA initiators could induce the self-assembly of DNA-alginate conjugates to form supramolecular nanomaterials and amplify the fluorescence signals on the cell surface. Complementary DNA (cDNA), DNase, and alginase could all trigger the reversal of the signals from the cell surface. However, these three molecules exhibited different triggering efficiencies in the order cDNA > alginase > DNase. The combination of cDNA and alginase led to the synergistic reversal of nanomaterials and fluorescent signals from the cell surface. Thus, this study has successfully demonstrated a method for the bidirectional display of supramolecular nanomaterials on the surface of living cells. This method may find its application in numerous fields such as intact cell imaging and separation.

Peptide probes for proteases - innovations and applications for monitoring proteolytic activity

Proteases are excellent biomarkers for a variety of diseases, offer multiple opportunities for diagnostic applications and are valuable targets for therapy. From a chemistry-based perspective this review discusses and critiques the most recent advances in the field of substrate-based probes for the detection and analysis of proteolytic activity both in vitro and in vivo.

Thiol-Ene Click-Inspired Late-Stage Modification of Long-Chain Polyurethane Dendrimers

The construction of well-defined polyurethane dendrimers is challenging due to the high reactivity of externally added or in situ formed isocyanates leading to the formation of side products. With a primary focus of dendrimer research being the interaction of the periphery and the core, we report the synthesis of a common polyurethane dendron, which allows for the late-stage variation of both the periphery and the core. The periphery can be varied simply by installing a clickable unit in the dendron and then attaching to the core and vice-versa. Thus, a common dendron allows for varying periphery and core in the final two steps. To accomplish this, a protecting group-free, one-pot multicomponent Curtius reaction was utilized to afford a robust and versatile AB2 type polyurethane dendron employing commercially available simple molecules: 5-hydroxyisophthalic acid, 11-bromoundecanol, and 4-penten-1-ol. Subsequent late-stage modifications of either dendrons or dendrimers via a thiol-ene click reaction gave surface-functionalized alternating aromatic-aliphatic polyurethane homodendrimers to generation-three (G3). The dendrons and the dendrimers were characterized by NMR, mass spectrometry, and FT-IR analysis. A bifunctional AB2 type dendritic monomer demonstrated this approach’s versatility that can either undergo a thiol-ene click or attachment to the core. This approach enables the incorporation of functionalities at the periphery and the core that may not withstand the dendrimer growth for the synthesis of polyurethane dendrimers and other dendritic macromolecules.

Aggregation-Induced Emission Luminogens with Photoresponsive Behaviors for Biomedical Applications

Fluorescent biomedical materials can visualize subcellular structures and therapy processes in vivo. The aggregation-induced emission (AIE) phenomenon helps suppress the quenching effect in the aggregated state suffered by conventional fluorescent materials, thereby contributing to design strategies for fluorescent biomedical materials. Photoresponsive biomedical materials have attracted attention because of the inherent advantages of light; i.e., remote control, high spatial and temporal resolution, and environmentally friendly characteristics, and their combination with AIE facilitates development of fluorescent molecules with efficient photochemical reactions upon light irradiation. In this review, organic compounds with AIE features for biomedical applications and design strategies for photoresponsive AIE luminogens (AIEgens) are first summarized briefly. Applications are then reviewed, with the employment of photoresponsive and AIE-active molecules for photoactivation imaging, super-resolution imaging, light-induced drug delivery, photodynamic therapy with photochromic behavior, and bacterial targeting and killing being discussed at length. Finally, the future outlook for AIEgens is considered with the aim of stimulating innovative work for further development of this field.

Development of an Enzyme-Inhibitor Reaction Using Cellular Retinoic Acid Binding Protein II for One-Pot Megamolecule Assembly

This paper presents an enzyme building block for the assembly of megamolecules. The system is based on the inhibition of the human-derived cellular retinoic acid binding protein II (CRABP2) domain. We synthesized a synthetic retinoid bearing an arylfluorosulfate group, which uses sulfur fluoride exchange click chemistry to covalently inhibit CRABP2. We conjugated both the inhibitor and a fluorescein tag to an oligo(ethylene glycol) backbone and measured a second-order rate constant for the protein inhibition reaction of approximately 3,600 M^-1 s^-1 . We used this new enzyme-inhibitor pair to assemble multi-protein structures in one-pot reactions using three orthogonal assembly chemistries to demonstrate exact control over the placement of protein domains within a single, homogeneous molecule. This work enables a new dimension of control over specificity, orientation, and stoichiometry of protein domains within atomically precise nanostructures.

Oxidative Polymerization in Living Cells

Intracellular polymerization is an emerging technique that can potentially modulate cell behavior, but remains challenging because of the complexity of the cellular environment. Herein, taking advantage of the chemical properties of organotellurides and the intracellular redox environment, we develop a novel oxidative polymerization reaction that can be conducted in cells without external stimuli. We demonstrate that this polymerization reaction is triggered by the intracellular reactive oxygen species (ROS), thus selectively proceeding in cancer cells and inducing apoptosis via a unique self-amplification mechanism. The polymerization products are shown to disrupt intracellular antioxidant systems through interacting with selenoproteins, leading to greater oxidative stress that would further the oxidative polymerization and eventually activate ROS-related apoptosis pathways. The selective anticancer efficacy and biosafety of our strategy are proven both in vitro and in vivo. Ultimately, this study enables a new possibility for chemists to manipulate cellular proliferation and apoptosis through artificial chemical reactions.

Cell surface-localized imaging and sensing

Systematically dissecting the molecular basis of the cell surface as well as its related biological activities is considered as one of the most cutting-edge fields in fundamental sciences. The advent of various advanced cell imaging techniques allows us to gain a glimpse of how the cell surface is structured and coordinated with other cellular components to respond to intracellular signals and environmental stimuli. Nowadays, cell surface-related studies have entered a new era featured by a redirected aim of not just understanding but artificially manipulating/remodeling the cell surface properties. To meet this goal, biologists and chemists are intensely engaged in developing more maneuverable cell surface labeling strategies by exploiting the cell's intrinsic biosynthetic machinery or direct chemical/physical binding methods for imaging, sensing, and biomedical applications. In this review, we summarize the recent advances that focus on the visualization of various cell surface structures/dynamics and accurate monitoring of the microenvironment of the cell surface. Future challenges and opportunities in these fields are discussed, and the importance of cell surface-based studies is highlighted.

Artificial Bioaugmentation of Biomacromolecules and Living Organisms for Biomedical Applications

The synergistic union of nanomaterials with biomaterials has revolutionized synthetic chemistry, enabling the creation of nanomaterial-based biohybrids with distinct properties for biomedical applications. This class of materials has drawn significant scientific interest from the perspective of functional extension via controllable coupling of synthetic and biomaterial components, resulting in enhancement of the chemical, physical, and biological properties of the obtained biohybrids. In this review, we highlight the forefront materials for the combination with biomacromolecules and living organisms and their advantageous properties as well as recent advances in the rational design and synthesis of artificial biohybrids. We further illustrate the incredible diversity of biomedical applications stemming from artificially bioaugmented characteristics of the nanomaterial-based biohybrids. Eventually, we aim to inspire scientists with the application horizons of the exciting field of synthetic augmented biohybrids.