A PARACEST MRI contrast agent to detect enzyme activity

Area of Science:

• Biomedical Engineering
• Chemical Biology
• Magnetic Resonance Imaging (MRI)

Background:

• Caspase-3 is a critical enzyme and biomarker for apoptosis (programmed cell death).
• Current methods for detecting caspase-3 activity can be limited in sensitivity or specificity.
• Paramagnetic Chemical Exchange Saturation Transfer (PARACEST) MRI offers potential for sensitive molecular imaging.

Purpose of the Study:

• To synthesize and characterize a novel "smart" PARACEST MRI contrast agent for detecting caspase-3 activity.
• To demonstrate the agent's ability to undergo a detectable change in its PARACEST effect upon caspase-3 enzymatic cleavage.

Main Methods:

• Synthesis of a lanthanide-based PARACEST agent functionalized with a caspase-3 substrate (Asp-Glu-Val-Asp, DEVD).
• Characterization of the agent's PARACEST effect before and after enzymatic cleavage by caspase-3.
• Evaluation of the change in MR saturation frequency as an indicator of caspase-3 activity.

Main Results:

• The synthesized DEVD-(Tm-DOTA) amide agent exhibited a distinct PARACEST effect at -51 ppm.
• Enzymatic cleavage by caspase-3 released the DEVD moiety, exposing a free amine group.
• The cleaved product demonstrated a significantly shifted PARACEST effect with MR saturation at +8 ppm, indicating successful detection of enzymatic activity.

Conclusions:

• A novel PARACEST MRI contrast agent capable of detecting caspase-3 enzymatic activity was successfully synthesized.
• The agent's distinct change in PARACEST signal upon caspase-3 cleavage allows for sensitive and specific detection of apoptosis.
• This smart agent holds promise for advancing molecular MRI applications in diagnosing and monitoring diseases involving apoptosis.