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Updated: Jun 1, 2026

Harnessing the Bioorthogonal Inverse Electron Demand Diels-Alder Cycloaddition for Pretargeted PET Imaging
Published on: February 3, 2015
Biomedical applications of tetrazine cycloadditions
Neal K Devaraj1, Ralph Weissleder
1Center for Systems Biology, Massachusetts General Hospital, 185 Cambridge Street, CPZN 5206, Boston, Massachusetts 02114, USA. ndevaraj@ucsd.edu
Researchers developed extremely rapid bioorthogonal coupling reactions using tetrazines and strained alkenes for precise molecular labeling in cells and in vivo. This advance enables real-time imaging, diagnostics, and targeted cancer therapy with improved signal amplification.
Area of Science:
- Bioorthogonal chemistry
- Chemical biology
- Molecular imaging
Background:
- Disease mechanisms are increasingly understood at the molecular level.
- Bioorthogonal reactions offer synthetic opportunities for imaging, diagnostics, and therapy.
- Rapid kinetics (k > 10(3) M(-1) s(-1)) and high specificity are crucial for practical bioorthogonal applications.
Purpose of the Study:
- To design and implement extremely rapid bioorthogonal coupling reactions between tetrazines and strained alkenes.
- To enable real-time imaging and labeling of biomolecules and therapeutics in living systems.
- To enhance signal amplification for improved detection in diagnostics and imaging.
Main Methods:
- Development of rapid tetrazine-strained alkene cycloaddition reactions.
- Covalent coupling of tetrazine fluorophores to dienophile-modified proteins on cancer cells.
- Utilizing fluorogenic probes for enhanced signal-to-background ratios in imaging.
- Application of small-molecule coupling partners (<300 Da) for steric advantages.
- Labeling biomarkers with magneto-fluorescent nanoparticles for amplified detection.
- Modular labeling of small molecules with (18)F for positron emission tomography imaging.
Main Results:
- Achieved efficient and selective labeling of extracellular proteins on living cancer cells with near-infrared fluorophores.
- Demonstrated successful real-time imaging of covalent modification using nanomolar concentrations of labeling agents over minutes.
- Developed fluorogenic probes for improved intracellular imaging and signal-to-background ratios.
- Successfully reacted and imaged chemotherapeutics within living cells.
- Showcased amplified signal detection using nanoparticle conjugates compared to biotin-avidin interactions.
- Applied tetrazine reactions for in vivo molecular imaging, including pretargeted imaging of solid tumors.
Conclusions:
- Extremely rapid bioorthogonal reactions significantly advance molecular imaging, diagnostics, and therapeutics.
- Tetrazine-strained alkene chemistry provides a versatile platform for precise biological labeling.
- These strategies offer improved signal amplification and enable real-time monitoring of biological processes.
- The developed methods are applicable to clinical samples for biomarker profiling and in vivo imaging.
- Future work will focus on optimized protocols, novel probes, and expanded biomedical applications.
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