Oxidative conversion of a Eu(II)-based T1 agent to a Eu(III)-based paraCEST agent can be detected in vivo by MRI

In this work, we demonstrate that Eu(II) complex of DOTA-tetra(glycinate) has a higher reduction potential than most Eu(II) chelates reported so far. The reduced Eu(II) form acts as an efficient water proton T 1 relaxation reagent while the Eu(III) form acts as a water-based CEST agent. The complex has extremely fast water exchange rate. Oxidation to the corresponding Eu(III) complex yields a well-defined signal from the paraCEST agent. The time course of oxidation was studied in vitro and in vivo by T 1 -weighted and CEST imaging. A Eu(II) complex of DOTA-tetra(glycinate) has far less negative redox potential than most Eu(II) chelates reported so far. The reduced Eu(II) form acts as an efficient water proton T 1 relaxation reagent while the Eu(III) form acts as a water-based CEST agent. The time course of oxidation was studied in vitro and in vivo by T 1 -weighted and CEST imaging.