¹⁹F MR Imaging Probe For Furin Detection In Vitro And In Living Cells

Currently, Magnetic resonance imaging (MRI) is widely applied for medical diagnosis, and becomes one of the most promising techniques for investigation of physiological events. However,1H MRI often suffers from low contrast-to-noise ratio because of the large background signals from water protons.19F MRI is anticipated to be a promising method because of its high sensitivity (83%relative to1H),100%natural abundance and almost no background signals even in vivo. According to research of Itaru Hamachi and his coworkers, the19F NMR signal is broadened and attenuated when the molecules assemble into aggregates of high molecular mass because of the transverse relaxation. And they use it for the detection of proteins and enzymes.The trans-Golgi protease furin is a kind of protein convertase which plays important roles in homeostasis, and in diseases ranging from Alzheimer’s disease to anthrax, Ebola fever and cancer. Overexpression of furin offers people with a useful hint of early development of certain cancers. It preferentially cleaves Arg-X-Lys/Arg-Arg↓X motifs, where Arg is arginine, Lys is lysine, X can be any amino acid residue and↓indicates the cleavage site.In this project, we rationally designed turn-off19F NMR probe1and its scrambled control probe1-Scr. Probe1contains a Arg-Arg-Val-Arg (RRVR) peptide sequence which can be specifically recognized and cleaved by furin, conjugating with FMBA. Herein, we presented the synthesis routes of the19F probes in details, using HPLC for purification, high resolution matrix assisted laser desorption/ionization time of mass spectrometry (HR-MALDI-TOF/MS), transmission electron microscope (TEM), scanning electron microscope (SEM), UV-Vis absorption for full characterization of the probes. After GSH induction and furin cleavage, the intermediate condenses into dimer which self-assembles into nanoparticles at or near the locations of furin in cells, inducing a clear turn-off of its19F NMR signal because of the transverse relaxation. Furthermore, results of cell uptake indicate that probe1can be easily uptaken by tumor cells resulting in19F NMR signal off for the detection of furin activity inside cells. Our19F NMR probe could be potentially applied for tumor19F MRI in the future.