In Cellulo Bioorthogonal Catalysis by Encapsulated Nanoalloys: Overcoming Intracellular Deactivation

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.

Designer Nanoreactors for Bioorthogonal Catalysis

ConspectusThe 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.

A narrative review: progress in transition metal-mediated bioorthogonal catalysis for the treatment of solid tumors

Background and Objective

Transition metals are commonly used catalysts in bioorthogonal chemistry and have attracted extensive attention in biochemistry because of their efficient catalytic performance. In recent years, transition metal-mediated cycloaddition reactions, bond cleavage, and formation reactions are being actively explored for tumor treatment. However, the direct application of transition metals in complex biological environments has several problems, including poor solubility, toxicity, and easy inactivation. The combination of transition metals and nanomaterials can solve those problems by playing a bioorthogonal catalytic role in tumor treatment. In this review, we summarize some research on the application of transition metals modified by nanomaterials in tumor therapy and discuss the potential and challenges of transition metal-mediated bioorthogonal therapy in comprehensive tumor therapy.

Methods

English literature on transition metal in cancer treatment was searched in PubMed and Web of Science. The main search terms were "cancer treatment", "bioorthogonal reaction", "transition metal", "bioorthogonal catalysis", etc.

Key Content and Findings

This review summarizes research on several major transition metals that can be used for bioorthogonal catalysis with the assistance of nanomaterials in anti-tumor therapy. In addition, bioorthogonal catalysis is a new supplement to antitumor therapy. We have compiled the potential challenges of the clinical application of transition metal-based nanocatalysts, which lays the foundation for future research related to medicinal chemistry and targeted cancer therapy.

Conclusions

Most of the transition metals still have a lot of room for exploration in cancer treatment research. We still need more research to confirm the feasibility of in vivo and clinical trials.