Complete on/off responsive ParaCEST MRI contrast agents for copper and zinc.

Area of Science:

• Inorganic Chemistry
• Radiochemistry
• Medical Imaging

Background:

• Responsive contrast agents are crucial for targeted medical imaging.
• Current agents often lack a complete on/off response or rely on water molecules for signaling.
• Thulium (Tm)-based agents offer potential for novel imaging applications.

Purpose of the Study:

• To synthesize and evaluate two novel thulium-based responsive contrast agents, Tm-DOTAm-py and Tm-DOTAm-βAla-py.
• To investigate their efficacy in imaging copper (Cu) and zinc (Zn).
• To characterize their unique on/off switching mechanism and binding properties.

Main Methods:

• Synthesis of thulium-based complexes (Tm-DOTAm-py and Tm-DOTAm-βAla-py).
• Evaluation of responsive properties using CEST (Chemical Exchange Saturation Transfer) imaging.
• Characterization using 1/T1 NMRD profiles, 17O NMR, and molecular modeling.
• Assessment of binding affinities and selectivity for Cu and Zn ions.

Main Results:

• Both agents demonstrated a complete on/off response to transition metals (Cu+, Cu2+, Zn2+).
• The CEST signal originated from amide protons, not coordinated water molecules.
• Tm-DOTAm-py showed higher sensitivity than Tm-DOTAm-βAla-py.
• Complexes exhibited efficient binding to target metals without selectivity for copper over zinc.

Conclusions:

• The developed thulium-based agents function as effective paraCEST agents with a unique amide proton-based on/off switching mechanism.
• Their efficient response and lack of inner-sphere water make them promising for transition metal imaging.
• These agents represent a significant advancement in responsive MRI contrast agent design.