Truly-Biocompatible Gold Catalysis Enables Vivo-Orthogonal Intra-CNS Release of Anxiolytics

Abstract

Being recognized as the best-tolerated of all metals, the catalytic potential of gold (Au) has thus far been hindered by the ubiquitous presence of thiols in organisms. Herein we report the development of a truly-catalytic Au-polymer composite by assembling ultrasmall Au-nanoparticles at the protein-repelling outer layer of a co-polymer scaffold via electrostatic loading. Illustrating the in vivo-compatibility of the novel catalysts, we show their capacity to uncage the anxiolytic agent fluoxetine at the central nervous system (CNS) of developing zebrafish, influencing their swim pattern. This bioorthogonal strategy has enabled -for the first time- modification of cognitive activity by releasing a neuroactive agent directly in the brain of an animal.

Keywords: behavioral activity; bioorthogonal; catalysis; gold; prodrug.

Figure 1

Preparation and characterization of Au‐microimplants. a) Synthesis of Au‐NPs and Au‐microimplants. b) SEM/TEM (left) and HAADF‐STEM (right) images of ultramicrotome cross‐sections of Au‐microimplants at different magnifications.

Figure 2

a) Au‐triggered conversion of Poc‐masked prodye 2 into dye 1 and structure of 3. b) Fluorogenic reaction of 2 (50 μM) and Au‐microimplants (0.1 mg mL⁻¹=9.6 μM in Au content) in PBS:methanol (70:30) with or without serum (pH 7.4, 37 °C). Conversion (%) was measured at different time points from fluorescence intensity measurements (λ _ex/em=485/535 nm) and calculated using a standard curve of 1. c) Recycling test. Au‐microimplants (0.1 mg mL⁻¹) were recovered after each reaction cycle and re‐used under the reaction conditions described before. Conversion (%) was measured at 24 h. d) Intracranial implantation of an Au‐microimplant in zebrafish and confocal analysis of the CNS generation of green fluorescence in the presence (left) or absence (right) of pro‐dye 2.

Figure 3

a) Bioorthogonal intra‐CNS control of zebrafish locomotor activity by localized Au‐mediated generation of anxiolytic 3 from inactive precursor 4 in the head of zebrafish. b) Representative images of the tracked distances of individual zebrafish in a cell culture dish (35 mm×10 mm) under different treatments. [Prodrug/drug]=50 μM. Zebrafish movements were analyzed using the EthoVision XT 8.5 software (Noldus). c) % distance swum by zebrafish embryos under treatment relative to the DMSO‐treated control. Error bars: ±SEM, n=20; ** P<0.01.