Nanostructured Heterogeneous Catalysts for Bioorthogonal Reactions

Reversible Modulation of Cell-Cell Interactions Using Electrochemistry

Cell-cell interactions play an important role in many biological processes, and various methods have been developed for controlling the cell-cell interactions. However, the effective and rapid control of intercellular interactions remains challenging. Herein, we report a novel, rapid, and effective electrochemical strategy without destroying the basic life processes for the dynamic control of intercellular interactions via liposome fusion. In the proposed system, bioorthogonal chemical groups and hydroquinone (HQ)- and aminooxy (AO)-tethered ligands were modified on the surface of living cells on the basis of the liposome fusion, enabling dynamical intercellular assemblies. Upon application of the corresponding oxidative potential, the "off-state" HQ could be oxidized to the "on-state" quinone (Q), which subsequently reacts with AO-tethered ligands to form stable oxime linkages under physiological conditions. This reaction effectively shortens the distance between cells, promoting the formation of cell clusters. When the corresponding reverse reductive potential is applied, the oxime linkage is cleaved, resulting in the release of the cells. Furthermore, we employed HQ- and AO-tethered ligands to modify mitochondria, inducing mitochondrial aggregation. This noninvasive and label-free strategy allows for the dynamic reversible regulation of intercellular interactions, enhancing our understanding of intercellular communication networks, and has the potential for improving the antitumor therapy efficacy.

Smart Bioorthogonal Nanozymes: From Rational Design to Appropriate Bioapplications

Bioorthogonal chemistry has provided an elaborate arsenal to manipulate native biological processes in living systems. As the great advancement of nanotechnology in recent years, bioorthogonal nanozymes are innovated to tackle the challenges that emerged in practical biomedical applications. Bioorthogonal nanozymes are uniquely positioned owing to their advantages of high customizability and tunability, as well as good adaptability to biological systems, which bring exciting opportunities for biomedical applications. More intriguingly, the great advancement in nanotechnology offers an exciting opportunity for innovating bioorthogonal catalytic materials. In this comprehensive review, the significant progresses of bioorthogonal nanozymes are discussed with both spatiotemporal controllability and high performance in living systems, and highlight their design principles and recent rapid applications. The remaining challenges and future perspectives are then outlined along this thriving field. It is expected that this review will inspire and promote the design of novel bioorthogonal nanozymes, and facilitate their clinical translation.

Extracellular Vesicles-Mediated Bio-Orthogonal Catalysis in Growing Tumors

Several studies have reported the successful use of bio-orthogonal catalyst nanoparticles (NPs) for cancer therapy. However, the delivery of the catalysts to the target tissues in vivo remains an unsolved challenge. The combination of catalytic NPs with extracellular vesicles (EVs) has been proposed as a promising approach to improve the delivery of therapeutic nanomaterials to the desired organs. In this study, we have developed a nanoscale bio-hybrid vector using a CO-mediated reduction at low temperature to generate ultrathin catalytic Pd nanosheets (PdNSs) as catalysts directly inside cancer-derived EVs. We have also compared their biodistribution with that of PEGylated PdNSs delivered by the EPR effect. Our results indicate that the accumulation of PdNSs in the tumour tissue was significantly higher when they were administered within the EVs compared to the PEGylated PdNSs. Conversely, the amount of Pd found in non-target organs (i.e., liver) was lowered. Once the Pd-based catalytic EVs were accumulated in the tumours, they enabled the activation of a paclitaxel prodrug demonstrating their ability to carry out bio-orthogonal uncaging chemistries in vivo for cancer therapy.

Nanoparticle-Catalyzed Transamination under Tumor Microenvironment Conditions: A Novel Tool to Disrupt the Pool of Amino Acids and GSSG in Cancer Cells

Catalytic cancer therapy targets cancer cells by exploiting the specific characteristics of the tumor microenvironment (TME). TME-based catalytic strategies rely on the use of molecules already present in the TME. Amino groups seem to be a suitable target, given the abundance of proteins and peptides in biological environments. Here we show that catalytic CuFe2O4 nanoparticles are able to foster transaminations with different amino acids and pyruvate, another key molecule present in the TME. We observed a significant in cellulo decrease in glutamine and alanine levels up to 48 h after treatment. In addition, we found that di- and tripeptides also undergo catalytic transamination, thereby extending the range of the effects to other molecules such as glutathione disulfide (GSSG). Mechanistic calculations for GSSG transamination revealed the formation of an imine between the oxo group of pyruvate and the free -NH2 group of GSSG. Our results highlight transamination as alternative to the existing toolbox of catalytic therapies.

Designer Nanoreactors for Bioorthogonal Catalysis

The evolutionary complexity of compartmentalized biostructures (such as cells and organelles) endows life-sustaining multistep chemical cascades and intricate living functionalities. Relatively, within a very short time span, a synthetic paradigm has resulted in tremendous growth in controlling the materials at different length scales (molecular, nano, micro, and macro), improving mechanistic understanding and setting the design principals toward different compositions, configurations, and structures, and in turn fine-tuning their optoelectronic and catalytic properties for targeted applications. Bioorthogonal catalysis offers a highly versatile toolkit for biochemical modulation and the capability to perform new-to-nature reactions inside living systems, endowing augmented functions. However, conventional catalysts have limitations to control the reactions under physiological conditions due to the hostile bioenvironment. The present account details the development of bioapplicable multicomponent designer nanoreactors (NRs), where the compositions, morphologies, interfacial active sites, and microenvironments around different metal nanocatalysts can be precisely controlled by novel nanospace-confined chemistries. Different architectures of porous, hollow, and open-mouth silica-based nano-housings facilitate the accommodation, protection, and selective access of different nanoscale metal-based catalytic sites. The modular porosity/composition, optical transparency, thermal insulation, and nontoxicity of silica are highly useful. Moreover, large macropores or cavities can also be occupied by enzymes (for chemoenzymatic cascades) and selectivity enhancers (for stimuli-responsive gating) along with the metal nanocatalysts. Further, it is crucial to selectively activate and control catalytic reactions by a remotely operable biocompatible energy source. Integration of highly coupled plasmonic (Au) components having few-nanometer structural features (gaps, cavities, and junctions as electromagnetic hot-spots) endows an opportunity to efficiently harness low-power NIR light and selectively supply energy to the interfacial catalytic sites through localized photothermal and electronic effects. Different plasmonically integrated NRs with customizable plasmonic-catalytic components, cavities inside bilayer nanospaces, and metal-laminated nanocrystals inside hollow silica can perform NIR-/light-induced catalytic reactions in complex media including living cells. In addition, magnetothermia-induced NRs by selective growth of catalytic metals on a pre-installed superparamagnetic iron-oxide core inside a hollow-porous silica shell endowed the opportunity to apply AMF as a bioorthogonal stimulus to promote catalytic reactions. By combining "plasmonic-catalytic" and "magnetic-catalytic" components within a single NR, two distinct reaction steps can be desirably controlled by two energy sources (NIR light and AMF) of distinct energy regimes. The capability to perform multistep organic molecular transformations in harmony with the natural living system will reveal novel reaction schemes for in cellulo synthesis of active drug and bioimaging probes. Well-designed nanoscale discrete architectures of NRs can facilitate spatiotemporal control over abiotic chemical synthesis without adversely affecting the cell viability. However, in-depth understanding of heterogeneous surface catalytic reactions, rate induction mechanisms, selectivity control pathways, and targeted nanobio interactions is necessary. The broad field of biomedical engineering can hugely benefit from the aid of novel nanomaterials with chemistry-based designs and the synthesis of engineered NRs performing unique bioorthogonal chemistry functions.

Nanoconstruction on Living Cell Surfaces with Cucurbit[7]uril-Based Supramolecular Polymer Chemistry: Toward Cell-Based Delivery of Bio-Orthogonal Catalytic Systems

Employing living cells as carriers to transport transition metal-based catalysts for target-specific bio-orthogonal catalysis represents a cutting-edge approach in advancing precision biomedical applications. One of the initial hurdles in this endeavor involves effectively attaching the catalysts to the carrier cells while preserving the cells' innate ability to interact with biological systems and maintaining the unaltered catalytic activity. In this study, we have developed an innovative layer-by-layer method that leverages a noncovalent interaction between cucurbit[7]uril and adamantane as the primary driving force for crafting polymeric nanostructures on the surfaces of these carrier cells. The strong binding affinity between the host-guest pair ensures the creation of a durable polymer coating on the cell surfaces. Meanwhile, the layer-by-layer process offers high adaptability, facilitating the efficient loading of bio-orthogonal catalysts onto cell surfaces. Importantly, the polymeric coating shows no discernible impact on the cells' physiological characteristics, including their tropism, migration, and differentiation, while preserving the effectiveness of the bio-orthogonal catalysts.

Target-Specific Bioorthogonal Reactions for Precise Biomedical Applications

Bioorthogonal chemistry is a promising toolbox for dissecting biological processes in the native environment. Recently, bioorthogonal reactions have attracted considerable attention in the medical field for treating diseases, since this approach may lead to improved drug efficacy and reduced side effects via in situ drug synthesis. For precise biomedical applications, it is a prerequisite that the reactions should occur in the right locations and on the appropriate therapeutic targets. In this minireview, we highlight the design and development of targeted bioorthogonal reactions for precise medical treatment. First, we compile recent strategies for achieving target-specific bioorthogonal reactions. Further, we emphasize their application for the precise treatment of different therapeutic targets. Finally, a perspective is provided on the challenges and future directions of this emerging field for safe, efficient, and translatable disease treatment.

Progress in controllable bioorthogonal catalysis for prodrug activation

Bioorthogonal catalysis, a class of catalytic reactions that are mediated by abiotic metals and proceed in biological environments without interfering with native biochemical reactions, has gained ever-increasing momentum in prodrug delivery over the past few decades. Albeit great progress has been attained in developing new bioorthogonal catalytic reactions and optimizing the catalytic performance of transition metal catalysts (TMCs), the use of TMCs to activate chemotherapeutics at the site of interest in vivo remains a challenging endeavor. To translate the bioorthogonal catalysis-mediated prodrug activation paradigm from flasks to animals, TMCs with targeting capability and stimulus-responsive behavior have been well-designed to perform chemical transformations in a controlled manner within highly complex biochemical systems, rendering on-demand drug activation to mitigate off-target toxicity. Here, we review the recent advances in the development of controllable bioorthogonal catalysis systems, with an emphasis on different strategies for engineering TMCs to achieve precise control over prodrug activation. Furthermore, we outline the envisaged challenges and discuss future directions of controllable bioorthogonal catalysis for disease therapy.

Bioorthogonal Disruption of Pyroptosis Checkpoint for High-Efficiency Pyroptosis Cancer Therapy

Pyroptosis is an inflammatory form of programmed cell death that holds great promise in cancer therapy. However, autophagy as the crucial pyroptosis checkpoint and the self-protective mechanism of cancer cells significantly weakens the therapeutic efficiency. Here, a bioorthogonal pyroptosis nanoregulator is constructed to induce pyroptosis and disrupt the checkpoint, enabling high-efficiency pyroptosis cancer therapy. The nanoregulator allows the in situ synthesis and accumulation of the photosensitizer PpIX in the mitochondria of cancer cells to directly produce mitochondrial ROS, thus triggering pyroptosis. Meanwhile, the in situ generated autophagy inhibitor via palladium-catalyzed bioorthogonal chemistry can disrupt the pyroptosis checkpoint to boost the pyroptosis efficacy. With the biomimetic cancer cell membrane coating, this platform for modulating pyroptosis presents specificity to cancer cells and poses no harm to normal tissue, resulting in a highly efficient and safe antitumor treatment. To our knowledge, this is the first report on a disrupting intrinsic protective mechanism of cancer cells for tumor pyroptosis therapy. This work highlights that autophagy as a checkpoint plays a key regulative role in pyroptosis therapy, which would motivate the future design of therapeutic regimens.