Bioorthogonal nanozymes: progress towards therapeutic applications

Abstract

Bioorthogonal nanocatalysts in the form of 'nanozymes', are promising tools for generating imaging and therapeutic molecules in living systems. These systems use transformations developed by synthetic chemists to effect transformations that cannot be performed by cellular machinery. This emerging platform is rapidly evolving towards the creation of smart nanodevices featuring the capabilities of their enzyme prototypes, modulating catalytic activity through structure as well as chemical and physical signals. Here we describe different strategies to fabricate these nanocatalysts and their potential in diagnostic and therapeutic applications.

Keywords: Bioorthogonal chemistry; catalysis; imaging; nanomedicine; nanoparticles; nanozyme.

Figure 1.. Fabrication of bioorthogonal nanozymes.

a) Formation of nanoparticles for heterogeneous bioorthogonal catalysis. b) Fabrication of nanozymes by including molecular TMC into nanometric scaffolds. c) Schematic representation of bioorthogonal activation of substrates intra- and extracellularly.

Figure 2.. Palladium nanoparticle (PdNP) mediated bioorthogonal reactions for generating therapeutic molecules.

PdNPs (2–3 nm) were synthesized inside a micrometric polystyrene particle (gray sphere with black dots). a) Bioorthogonal uncaging of 5FU-prodrugs (cleavable units highlighted in red) by polystyrene-palladium composite. b) Viability of cells cultured with propargylated 5-FU (1) and a mixture of 1 with polystyrene-PdNP to produce 5-FU (2). c) Suzuki-Miyaura cross-coupling reaction generating of PP-121 anticancer agent (coupling units highlighted in blue and green). d) Viability of cells cultured with polystyrene-PdNP composite in the presence of 3, 4, and a mixture of 5 and 6 precursors to form 5. Adapted from reference .

Figure 3.. Structure of nanozymes based on encapsulating molecular TMC in gold nanoparticles.

a) Localization of molecular TMCs in hydrophobic pockets of nanozymes b) Structure of ligands capping the AuNP scaffold.

Figure 4.. Engineered nanozymes surface functionalities for selective staining of biofilms

a) The schematic mechanism of charge switchable NZ in biofilm imaging. b) Structure of pH switchable surface functionalities of nanozymes. c) Confocal image of biofilms stained with activated rhodamine using charge switchable NZs. d) Confocal image of biofilms only treated with prorhodamine (control). Adapted from reference .

Figure 5.. A stimuli responsive nanozyme

a) Intracellular catalysis by NZ. b) Catalysis inhibition by complexation of NZ’s surface benzylammonium moieties with CB[7] c) Reactivation of NZ’s catalytic activity by adding ADA. d) Structure of NZ, CB[7] and ADA. e) Inhibited intracellular activation of prorhodamine by complexation of NZ with CB[7] f) Reactivation catalytic properties of NZ-CB[7] by addition of ADA. Scale bar= 20 μm. j) Intracellular prodrug activation using gated catalysis. NP_Pd and NP_Pd_CB[7] + ADA showed increased toxicity with increased concentration of prodrug. NP_Pd_CB[7] showed no toxicity at all prodrug concentrations tested. Adapted from reference .

6.. Palladium-mediated bioorthogonal activation of drugs in vivo.

a) Propargylated probe containing a profluorophore and a cytotoxic moiety. Uncaging the probe using palladium TMC encapsulated within liposomes induces the fragmentation of the probe releasing a fluorescent coumarin and cytotoxic drug. b) Images over time of mice treated with intratumoral injection of PBS, NCl, LIP-Pro-Cou-NCl, LIP-Pd-DPPF or LIP-Pro-Cou-NCl/LIP-Pd-DPPF. c) The tumor inhibitory rate (TIR) for three groups upon treatment with different formulations. d) Images of dissected organs of the mice treated with LIP-Pro-Cou-NCl/LIP-Pd-DPPF for 24 h. Adapted from reference .