Radiolabeled para-I-nimesulide: an unexpected tracer for imaging peripheral inflammation

Area of Science:

• Radiochemistry and Molecular Imaging
• Pharmacology and Drug Discovery
• Biomedical Engineering

Background:

• Nimesulide derivatives with iodine at the para-position show potent cyclooxygenase-2 (COX-2) inhibitory activity.
• Radioiodinated nimesulide derivatives were synthesized to evaluate their potential as COX-2 imaging agents for SPECT.
• The study focused on visualizing COX-2 expression, particularly in the brain.

Purpose of the Study:

• To synthesize and characterize 125I-labeled nimesulide derivatives for COX-2 imaging.
• To assess the potential of these radioiodinated compounds as SPECT imaging agents for COX-2.
• To investigate the feasibility of visualizing COX-2 expression in the brain and inflamed tissues.

Main Methods:

• Synthesis of para- and meta-substituted 125I-labeled nimesulide derivatives.
• Biodistribution studies and ex vivo autoradiography in normal mice.
• Evaluation in a mouse model of inflammation using biodistribution and blocking experiments.

Main Results:

• [125I]para-I nimesulide exhibited limited brain penetration and was unsuitable for brain-targeted COX-2 imaging.
• Selective accumulation of [125I]para-I nimesulide was observed in inflamed regions in a mouse model.
• High radiochemical purity and in vivo stability were noted, but plasma albumin binding limited brain uptake.

Conclusions:

• [125I]para-I nimesulide shows potential as a tracer for detecting peripheral COX-2 expression, not for brain imaging.
• Plasma albumin binding is a significant factor limiting brain uptake of this tracer.
• Substituent electronic properties are crucial for designing metabolically stable, future COX-2-targeted molecular imaging agents.