Activation and Delivery of Tetrazine-Responsive Bioorthogonal Prodrugs

Abstract

Prodrugs, which remain inert until they are activated under appropriate conditions at the target site, have emerged as an attractive alternative to drugs that lack selectivity and show off-target effects. Prodrugs have traditionally been activated by enzymes, pH or other trigger factors associated with the disease. In recent years, bioorthogonal chemistry has allowed the creation of prodrugs that can be chemically activated with spatio-temporal precision. In particular, tetrazine-responsive bioorthogonal reactions can rapidly activate prodrugs with excellent biocompatibility. This review summarized the recent development of tetrazine bioorthogonal cleavage reaction and great promise for prodrug systems.

Keywords: bioorthogonal reaction; prodrug activation; tetrazine.

Figure 1

(A) Structures of some examples of prodrug (pro-moiety in blue box). (B) The concept of prodrug activation based on tetrazine-responsive bioorthogonal click-to-release reaction with representative tetrazine triggered release of doxorubicin (Dox) from trans-cyclooctene.

Figure 2

(A) Reaction mechanism between cleavable TCO and tetrazines. (B) TCO isomers and tetrazines toolbox. (C) The mechanism for pH-dependent release of active amine and release profile of 14 at pH 5–7. Reproduced with permission from [58]; © 2020 American Chemical Society. (D) The mechanism for pH-independent release of active amine and release profile of 15 at pH 3–7.4. Reproduced with permission from [60]; © 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Figure 3

(A) The scope of the click-to-release reaction between tetrazine and TCO derivatives. (B) Biphasic release from TCO derivates 22–25. Scale: 0–1 h and 0–20 h. Reproduced with permission from [57]; © 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim (C) Stable TCO self-immolative linker and easter prodrug models.

Figure 4

(A) Reaction mechanism between vinyl ether derivatives and tetrazines. (B) Structures of vinyl ether caged near-infrared fluorogenic probe and its active form. (C) The concept of prodrug-prodrug activation. (D) Reaction mechanism between vinyl ether self-immolative linker and tetrazines. (E) Structures of PEG-b-Dox and Dox. (F) Reaction mechanism between vinylboronic acids and tetrazines.

Figure 5

(A) Reaction mechanism between benzonorbornadienes and tetrazines. (B) Click-to-release reaction mechanism of tetrazine-triggered release from benzonorbornadiene derivatives and the range of corresponding leaving groups. (C) Examples of releasing p-nitroaniline and Dox. (D) Reactivity of thiol-conjugated azanorbornadiene towards tetrazines.

Figure 6

(A) Reaction mechanism between isonitriles and tetrazines. (B) Tetrazine-mediated activation of ICPrc-Dox prodrug. (C) Release of mexiletine in zebrafish embryos. Reproduced with permission from [70]; © 2020 American Chemical Society.

Figure 7

(A) Reaction between isonitriles and tetrazines leading to release of active molecules. (B) Structures of TMS-NC and Tzmoc-Dox prodrug, and statistical graph of cytotoxicity studies with A549 cells after 72 h. Reproduced with permission from [71]; © Royal Society of Chemistry. (C) Dual release of two fluorophores from ICPr- and TzMe-caged dyes.

Figure 8

Reaction mechanism between cyclooctyne containing hydroxyl group and tetrazine. And structures of mitochondria-targeted cyclooctyne 82 and tetrazine-Dox prodrug 83.

Figure 9

(A) Reaction mechanism between methylene carbamate-modified tetrazines and TCO. And structures of tetrazine and TCO derivates. (B) Schematic illustration of the Tz-ADC. Reproduced with permission from [65]; © 2020 American Chemical Society.

Figure 10

Schematic illustration of the local drug activation approach: a hydrogel comprising alginate monosaccharides modified with tetrazine was co-administered with TCO-Dox. The prodrug conjugate accumulated in the hydrogel where it was also activated by the tetrazine. Reproduced with permission from [100]; © 2020 American Chemical Society.

Figure 11

(A) Schematic illustration of co-administration of two nanovehicles responsive to the tumor microenvironment. (B) Concentrations of Dox in main organs after two-hour injection. (C) Tumor volumes, (D) Tumor control rate and (E) Body weight of mice under different conditions at different time points. Reproduced with permission from [103]; © Royal Society of Chemistry.

Figure 12

(A) Schematic illustration of gold nanorods supported chemotherapy and photothermal therapy. (B) H & E staining of tumor biopsies from different treatment groups. Reproduced with permission from [106]; © 2020 American Chemical Society.

Figure 13

(A) Schematic illustration of activation of vinyl ether-caged fluorogenic probe (CyPVE) by a pH-responsive tetrazine polymer. (B) In vivo fluorescence imaging at different time after injection. (C) Tumor growth curves. ASTNs, pH-sensitive nanoparticles; STNs, pH-insensitive nanoparticles. Reproduced with permission from [87]; © 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Figure 14

Synergistic enzymatic and bioorthogonal reaction for prodrug activation in tumor cells. Reproduced with permission from [98]; © 2020, Springer Nature.

Figure 15

“Click-to-release” activation of an antibody-drug conjugate. (A) First demonstration of an ADC in vivo. (B) Chemically triggered drug release from a diabody-based ADC. (C) Hyperbranched polymer-based bioorthogonal approach for drug delivery. (D) Prodrug-antibody conjugates for targeted chemotherapy. ADC, antibody-drug conjugate; Dox, doxorubicin; MMAE, monomethyl auristatin E.

Figure 16

Structures of compounds used in ADCs studies.