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Optimized Translocator Protein Ligand for Optical Molecular Imaging and Screening
Jun Li1,2, Jarrod A Smith1,2, Eric S Dawson1,2
1Interdisciplinary Materials Science Program, ∥Vanderbilt University Center for Structural Biology, and ■Department of Biomedical Engineering, Vanderbilt University , Nashville, Tennessee 37232, United States.
Bioconjugate Chemistry
|February 4, 2017
Summary
Researchers developed a new optical imaging tracer for translocator protein (TSPO), a target in diseases like cancer. The optimized probe 29 shows high binding affinity and is effective for in vitro cell imaging and ligand screening.
Area of Science:
- Biochemistry
- Molecular Imaging
- Medicinal Chemistry
Background:
- Translocator protein (TSPO) is a key target for molecular imaging in various human diseases.
- Elevated TSPO expression is common in solid tumors such as glioma, colorectal, and breast cancer.
- Optical imaging tracers for TSPO are valuable tools in quantitative biology and drug discovery.
Purpose of the Study:
- To synthesize and evaluate a new generation of pyrazolopyrimidine-based TSPO tracers with enhanced binding affinity for optical imaging.
- To identify a superior TSPO tracer suitable for in vitro imaging and ligand screening applications.
- To provide a structural rationale for developing future TSPO imaging ligands with bulky signaling moieties.
Main Methods:
- Synthesis and in vitro evaluation of seven candidate TSPO tracers based on a pyrazolopyrimidine scaffold.
- Optimization of linker length and conjugation of a high-affinity ligand to a fluorophore (FITC).
- In vitro cell imaging of live TSPO-expressing cells and competitive inhibition assays using fluorescence and radiometric detection.
Main Results:
- Identified probe 29 (Kd = 0.19 nM) as the most promising tracer, featuring a high-affinity ligand conjugated via an optimal eight-carbon linker to FITC.
- Computational modeling indicated the linker facilitates optimal positioning of the fluorophore, minimizing interference with ligand-protein binding.
- Probe 29 demonstrated high suitability for in vitro imaging of TSPO-expressing cells and yielded affinity data consistent with radiometric methods.
Conclusions:
- The developed TSPO ligand 29 is highly effective for in vitro imaging and serves as a valuable tool for ligand screening and drug discovery.
- The study provides insights into the structural requirements for designing TSPO imaging ligands with bulky signaling groups.
- This work advances the development of optical imaging tracers for TSPO, relevant to various disease states.
