A Bioorthogonal TCO-Tetrazine-Based Pretargeted PET/NIRF Platform Enabling High-Contrast Tumor Imaging.

Area of Science:

• Nuclear Medicine
• Radiochemistry
• Molecular Imaging

Background:

• Pretargeting strategies improve radiopharmaceutical specificity and safety by decoupling tumor targeting from radionuclide delivery.
• Directly labeled small molecules face challenges with rapid clearance and systemic exposure.
• A DZ-1-based pretargeting system was developed to leverage broad-spectrum tumor-targeting capabilities.

Purpose of the Study:

• To synthesize and evaluate novel DZ-TCO precursors for pretargeted imaging.
• To develop and assess 68Ga-labeled tetrazine probes for pretargeting applications.
• To optimize pretargeting intervals for enhanced tumor visualization using PET imaging.

Main Methods:

• Synthesis of three DZ-TCO precursors (DZ-1-TCO, DZ-Lys-TCO, DZ-Lys-PEG4-TCO).
• Evaluation of precursors using near-infrared fluorescence imaging in tumor-bearing mice.
• Radiolabeling of tetrazine probes with 68Ga and assessment of their stability.
• Pretargeted PET imaging with various precursor/probe combinations and pretargeting intervals (24, 48, 72 h).

Main Results:

• All precursors showed tumor accumulation and signal retention.
• 68Ga-labeled tetrazine probes exhibited high radiochemical stability (>85% after 4 h).
• DZ-Lys-TCO combined with 68Ga-DOTA-H-Tz at a 48 h interval yielded optimal tumor uptake (3.24 ± 0.95 %ID/g) and tumor-to-muscle ratio (8.30 ± 3.39).

Conclusions:

• The DZ-TCO/68Ga-DOTA-Tz pretargeting system achieves high-contrast tumor imaging with low background.
• The optimized combination of DZ-Lys-TCO and 68Ga-DOTA-H-Tz at 48 hours offers superior performance.
• This system presents a promising platform for precise and safe radiopharmaceutical imaging and therapy.