Gold-Triggered Uncaging Chemistry in Living Systems

Abstract

Recent advances in bioorthogonal catalysis are increasing the capacity of researchers to manipulate the fate of molecules in complex biological systems. A bioorthogonal uncaging strategy is presented, which is triggered by heterogeneous gold catalysis and facilitates the activation of a structurally diverse range of therapeutics in cancer cell culture. Furthermore, this solid-supported catalytic system enabled locally controlled release of a fluorescent dye into the brain of a zebrafish for the first time, offering a novel way to modulate the activity of bioorthogonal reagents in the most fragile and complex organs.

Keywords: bioorthogonal; fluorescent probes; gold; heterogeneous catalysis; prodrugs.

Scheme 1

a) Au^III‐mediated bioorthogonal amidation reported by Tanaka and coworkers.5 b) The solid‐supported gold‐catalyzed uncaging strategy developed in this work.

Figure 1

a) Scanning electron microscopy (SEM) images of [Au]‐resins. b) HAADF‐STEM images of a cross‐section of a [Au]‐resin at different magnifications and energy‐dispersive X‐ray (EDX) spectra of highlighted areas. c) Cleavage of N‐Poc‐protected prodye 1 (20 μm) in the presence of [Au]‐resins (1 mg mL⁻¹) at physiological conditions (pH 7.4, 37 °C). Central panel: reaction kinetics in PBS or serum. Right panel: fluorescence analysis at 24 h in different conditions. Negative control: reagent 1 without [Au]‐resins.

Scheme 2

a) Rationale for the assisting–inhibiting roles of glutathione in [Au]‐catalyzed O/N‐propargyl cleavage reactions. b) Tentative reaction mechanism for the [Au]‐triggered depropargylation of 1 and 4 a–c in the biological milieu.

Figure 2

a) Gold‐triggered activation of prodrugs 4 a–c in A549 cancer cell culture. Negative controls: [Au]‐resins (1 mg mL⁻¹); 4 a–c (10, 100, and 1 μm, respectively). Positive control: 5 a–c (10, 100, and 1 μm, respectively). Prodrug activation assay: [Au]‐resins+4 a–c (10, 100, and 1 μm, respectively). Cell viability was measured at day 4 using PrestoBlue reagent. Error bars: ±SD from n=3. b) Bioorthogonal gold‐mediated release of green fluorescent Rhodamine 110 from precursor 1 in the brain of a zebrafish. The presence of the [Au]‐resin is indicated with a white arrow. Study of fluorescence intensity shows high statistical significance compared to the negative control (DMSO).