Accelerated 19F·MRI Detection of Matrix Metalloproteinase-2/-9 through Responsive Deactivation of Paramagnetic Relaxation Enhancement.

Henryk M Faas,Thomas Meersmann,Francesco Zamberlan,Christopher J Philp,Galina E Pavlovskaya,James L Krupa,Simon R Johnson,Huw E L Williams,Alexander J Taylor,Neil R Thomas

doi:10.1155/2019/4826520

Abstract

Paramagnetic gadolinium ions (GdIII), complexed within DOTA-based chelates, have become useful tools to increase the magnetic resonance imaging (MRI) contrast in tissues of interest. Recently, “on/off” probes serving as 19F·MRI biosensors for target enzymes have emerged that utilize the increase in transverse (T 2 ∗ or T 2) relaxation times upon cleavage of the paramagnetic GdIII centre. Molecular 19F·MRI has the advantage of high specificity due to the lack of background signal but suffers from low signal intensity that leads to low spatial resolution and long recording times. In this work, an “on/off” probe concept is introduced that utilizes responsive deactivation of paramagnetic relaxation enhancement (PRE) to generate 19F longitudinal (T 1) relaxation contrast for accelerated molecular MRI. The probe concept is applied to matrix metalloproteinases (MMPs), a class of enzymes linked with many inflammatory diseases and cancer that modify bioactive extracellular substrates. The presence of these biomarkers in extracellular space makes MMPs an accessible target for responsive PRE deactivation probes. Responsive PRE deactivation in a 19F biosensor probe, selective for MMP-2 and MMP-9, is shown to enable molecular MRI contrast at significantly reduced experimental times compared to previous methods. PRE deactivation was caused by MMP through cleavage of a protease substrate that served as a linker between the fluorine-containing moiety and a paramagnetic GdIII-bound DOTA complex. Ultrashort echo time (UTE) MRI and, alternatively, short echo times in standard gradient echo (GE) MRI were employed to cope with the fast 19F transverse relaxation of the PRE active probe in its “on-state.” Upon responsive PRE deactivation, the 19F·MRI signal from the “off-state” probe diminished, thereby indicating the presence of the target enzyme through the associated negative MRI contrast. Null point 1H·MRI, obtainable within a short time course, was employed to identify false-positive 19F·MRI responses caused by dilution of the contrast agent.

Highlights

Tri-tert-butyl 2,2',2''-(1,4,7,10-tetraazacyclododecane -1,4,7-triyl)triacetate (8): To a solution of cyclen (200 mg, 1.16 mmol, 1.0 eq.) in acetonitrile (150 mL), sodium carbonate (350 mg, 3.30 mmol, 3.0 eq.) was added to give a white suspension that was stirred for 15 minutes under a nitrogen atmosphere
A solution of tert-butyl bromoacetate (660 mg, 3.40 mmol, 3.0 eq.) in acetonitrile (50 mL) was slowly added dropwise over 15 minutes and the resulting mixture stirred for 30 minutes at ambient temperature, followed by an 18 hour reflux at 80 ̊C
The organic phase was dried over anhydrous sodium sulfate, filtered and concentrated in vacuo to give the desired product (250 mg, 94%) as an off white solid

Summary

Introduction

The organic phase was dried over anhydrous sodium sulfate, filtered and concentrated in vacuo to yield the desired product (110 mg, 30%) as an off white solid. The product was diluted with dichloromethane (30 mL) and washed with citric acid (5% w/v solution, 2 x 10 mL) and water (2 x 10 mL).The organic phase was dried over anhydrous sodium sulfate, filtered and concentrated in vacuo to yield the desired product (70 mg, 26%) as an off white solid.

Results

Conclusion