A Janus Chelator Enables Biochemically Responsive MRI Contrast with Exceptional Dynamic Range

Area of Science:

• Biochemistry
• Medical Imaging
• Materials Science

Background:

• Current MRI contrast agents have limitations in responsiveness.
• Developing agents that change properties based on biological environment is crucial.

Purpose of the Study:

• Introduce a novel biochemically responsive manganese (Mn)-based MRI contrast agent.
• Demonstrate a significant change in relaxivity through oxidation state switching.

Main Methods:

• Designed a "Janus" ligand capable of isomerizing to favor Mn3+ or Mn2+ binding.
• Investigated the stability of Mn3+ and Mn2+ complexes in biological conditions.
• Utilized peroxidase activity for oxidation and L-cysteine for reduction to mediate interconversion.

Main Results:

• Achieved a 9-fold change in relaxivity by switching between Mn3+ and Mn2+ oxidation states.
• The Janus ligand supports stable Mn3+ and Mn2+ complexes in biological milieu.
• Demonstrated rapid interconversion of oxidation states mediated by biological factors.

Conclusions:

• The Janus system represents a new paradigm for designing biochemically responsive MRI contrast agents.
• This approach enables MRI contrast agents to dynamically report on biological activity.