Correlative in vivo Fluorescence Imaging and 19F-MRI of Zebrafish Embryos

Abstract

Monitoring the pathway of a drug in the body and confirming delivery to the desired target is important in drug development. To this aim, we are developing a correlative fluorescence imaging approach in combination with 19F-MRI. Our first attempts to develop a suitable 19F-labeling strategy will be monitored using well-established fluorescence imaging in transparent zebrafish embryos. Later on, 19F-MRI could then be applied to non-transparent organisms. Zero background and high NMR sensitivity render fluorine a promising label to be traced in vivo. Although 19F possesses almost the same magnetic resonance sensitivity as 1H, a mono-atomic fluorine label is far too insensitive for MRI detection in vivo. To enhance the sensitivity, we therefore explored labels possessing many 19F nuclei with, if possible, identical 19F chemical shift. As a first step, we constructed nanoparticles with encapsulated fluorescence dye and perfluorocarbons, using an emulsion diffusion method. Characterization by solid-state NMR and dynamic light scattering demonstrated a successful simultaneous encapsulation of the fluorocarbon and fluorescence dye. In our first confocal microscopy and MRI experiments in zebrafish embryos, we were able to characterize the distribution of the nanoparticles in the organism. Based on these first results, we are currently expanding our correlative 19F-MRI and fluorescence imaging approach to peptide-based drugs. To this aim, we are synthesized artificial amino acids bearing up to 27 equivalent 19F-nuclei, which can then be combined with fluorescence labels to allow tracing peptides in vivo.