Journal
BIOCONJUGATE CHEMISTRY
Volume 29, Issue 5, Pages 1720-1728Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.bioconjchem.8b00167
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Funding
- MEXT of Japan [25220207, 16H00768, 16K13099]
- CREST of JST
- Asahi Glass Foundation
- Uehara Memorial Foundation
- Magnetic Health Science Foundation
- Grants-in-Aid for Scientific Research [16H00768, 16K13099] Funding Source: KAKEN
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Highly sensitive imaging of enzymatic activities in the deep tissues of living mammals provides useful information about their biological functions and for developing new drugs; however, such imaging is challenging. F-19 magnetic resonance imaging (MRI) is suitable for noninvasive visualization of enzymatic activities without endogenous background signals. Although various enzyme-responsive F-19 MRI probes have been developed, most cannot be used for in vivo imaging because of their low sensitivity. Recently, we developed unique nanoparticles, called FLAMES, that are composed of a liquid perfluorocarbon core and a robust silica shell, and demonstrated their outstanding sensitivity in vivo. Here, we report a highly functionalized nanoprobe, FLAME-DEVD 2, with an OFF/ON F-19 MRI switch for detecting caspase-3/7 activity based on the paramagnetic relaxation enhancement effect. To improve the cleavage efficiency of peptides by caspase-3, we designed a novel Gd3+ complex-conjugated peptide, DEVD X (X = 1, 2), which is a substrate peptide sequence tandemly repeated X times, and demonstrated that DEVD 2 showed faster cleavage kinetics than DEVD 1. By incorporating this novel concept into a signal activation strategy, FLAME-DEVD 2 showed a high F-19 MRI signal enhancement rate in response to caspase-3 activity. After intravenous injection of FLAME-DEVD 2 and an apoptosis-inducing reagent, caspase-3/7 activity in the spleen of a living mouse was successfully imaged by F-19 MRI. This imaging platform shows great potential for highly sensitive detection of enzymatic activities in vivo.
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