Nanomaterial-based bioorthogonal nanozymes for biological applications

Abstract

Bioorthogonal transformations are chemical reactions that use pathways which biological processes do not access. Bioorthogonal chemistry provides new approaches for imaging and therapeutic strategies, as well as tools for fundamental biology. Bioorthogonal catalysis enables the development of bioorthogonal "factories" for on-demand and in situ generation of drugs and imaging tools. Transition metal catalysts (TMCs) are widely employed as bioorthogonal catalysts due to their high efficiency and versatility. The direct application of TMCs in living systems is challenging, however, due to their limited solubility, instability in biological media and toxicity. Incorporation of TMCs into nanomaterial scaffolds can be used to enhance aqueous solubility, improve long-term stability in biological environment and minimize cytotoxicity. These nanomaterial platforms can be engineered for biomedical applications, increasing cellular uptake, directing biodistribution, and enabling active targeting. This review summarizes strategies for incorporating TMCs into nanomaterial scaffolds, demonstrating the potential and challenges of moving bioorthogonal nanocatalysts and nanozymes toward the clinic.

Figure 1.

Fabrication of nanomaterial-based bioorthogonal nanozymes. a) Examples of nanomaterial scaffolds. b) Encapsulation of TMCs into nanostructures to generate nanozymes. c) In situ activation of therapeutic and imaging agents in biosystems using nanozymes.

Figure 2.

Types of reactions (and respective examples) to activate inert substrates through bioorthogonal catalysis.

Figure 3.

Intracellular localization of polyzyme. a) Polymer structure and b) assembly. c) And d) effect of different incubation time (Texas Red covalent attached to the polymer). Adapted with permission from ref. Copyright 2018 American Chemical Society.

Figure 4.

a) Polyzymes encapsulating Cu²⁺ as TMC. b) Intracellular generation of a fluorescent dye through CuAAC coupling of the non-fluorescent reagents. Adapted with permission from ref. Copyright 2016 American Chemical Society.

Figure 5.

Tandem intracellular catalysis of the polyzyme and enzyme. Adapted with permission from ref. Copyright 2020 American Chemical Society.

Figure 6.

a) Tumour tissue imaging (dorsal window chamber). b) Systemic administration of polyzymes embedding Pd(II) (fluorescent Pd complex inside cells). c) Pro-dye administration (at t = 62 min). Adapted with permission from ref. Copyright 2018 Nature Research.

Figure 7.

a) Strategy and in vivo efficacy of polymer nanoparticles embedding Pd(II). b) Uncaging mechanism of the prodrug. Adapted with permission from ref. Copyright 2018 American Chemical Society.

Figure 8.

a) Polyzyme prepared through nanoprecipitation. b) Bacterial biofilm imaging or eradication by in-situ substrate activation.

Figure 9.

Preparation of resin microspheres encapsulating Pd nanoparticles. a) Porous structure of the resin. b) Coordination of the Pd acetate. c) Polymer crosslinking with entrapment of Pd. d) Reduction to form Pd(0) nanoparticles. Adapted with permission from ref. Copyright 2011 Nature Publishing Group.

Figure 10.

Selective uptake of the nanozyme and intracellular activation of anticancer drugs. Redrawn from ref. Copyright 2017 Wiley-VCH

Figure 11.

Catalytic activity of the microspheres in zebrafish embryos. Reproduced with permission from ref. Copyright 2016 Wiley-VCH.

Figure 12.

Gold nanoparticles with appropriate monolayer architecture efficiently encapsulate hydrophobic TMCs to form nanozymes.

Figure 13.

a) Nanozymes with different monolayers show different kinetic curves. The hydrophilic surface leads to a kinetic different from the expected Michaelis-Menten kinetics (dashed line) due to substrate inhibition.

Figure 14.

a) The different structures of ligands headgroups direct the cell uptake. b) The activity of the two nanozymes co-administered. Scale bar 25 μm.

Figure 15.

a) Surface charge modulates uptake and intracellular activity of nanozymes. b) “On/off” activity: quenched by protein corona and reactivated by trypsin. c), d) HeLa cells with Corona-NZ1 preincubated in serum. Adapted with permission from ref. Copyright 2020 American Chemical Society.

Figure 16.

Gated regulation of bioorthogonal catalysis using host-guest chemistry. a) Nanozyme with quaternary ammonium groups inside cells. b) The cucurbituril shields the TMC inhibiting the catalysis. c) The activity is restored with a chemical stimulus (adamantylamine).

Figure 17.

a) Structure of thermoresponsive nanozyme; the TMC in the stacked form is deactivated at T < 37 °C. b) The nanozymes with different catalyst loading exhibit different activation temperature.

Figure 18.

Modification of the alga cells with the artificial metalloenzyme: both anchor and TMC have a biotin group to bond streptavidin. Adapted with permission from ref. Copyright 2018 Nature Research.

Figure 19.

Structure and reactivity of the TMC in the albumin-Ru assembly. The glycan decoration on the metalloenzyme serves as targeting unit for cancer cells. Adapted with permission from ref. Copyright 2019 Nature Publishing Group.

Figure 20.

Localized catalytic activity using two differently glycosylated albumin for the selective targeting of two different organs: intestine or liver. The catalysis is tracked in vivo by activation of a near-IR dye. Adapted with permission from ref. Copyright 2017 Wiley-VCH.

Figure 21.

a) UV-controlled intracellular activation of nanozymes and in vitro results. Adapted with permission from ref. Copyright 2018 Nature Research.

Figure 22.

Bioorthogonal catalytic activity of hollow mesoporous silica particles embedding palladium nanoparticles (Adapted with permission from Ref. . Copyright 2019 Royal Society of Chemistry

Scheme 1.

Examples of caging strategy using carbonate/carbamate or azide formation: a functional group is converted into an inert form and upon catalytic reduction the active group is restored.