How do HYNIC-conjugated peptides bind technetium? Insights from LC-MS and stability studies

Area of Science:

• Radiopharmaceutical chemistry
• Coordination chemistry
• Bioconjugation

Background:

• Technetium-99m ((99m)Tc) radiopharmaceuticals are crucial in nuclear medicine.
• The coordination chemistry of (99m)Tc with bifunctional chelators like HYNIC is not fully understood.
• Understanding the coordination sphere is vital for developing stable and effective imaging agents.

Purpose of the Study:

• To elucidate the coordination structure of (99m)Tc complexes formed with HYNIC and HYBA conjugates.
• To compare the labeling efficiency and stability of HYNIC versus HYBA conjugates.
• To investigate the role of co-ligands in (99m)Tc complex formation.

Main Methods:

• Preparation of HYNIC and HYBA peptide conjugates.
• Radiolabeling with (99m)Tc using EDDA, tricine, or tricine-nicotinic acid co-ligands.
• Analysis using liquid chromatography-mass spectrometry (LC-MS).
• Assessment of serum stability and protein binding.

Main Results:

• HYNIC conjugates yielded fewer and more stable (99m)Tc labeled species than HYBA conjugates.
• LC-MS revealed a Tc(V) oxidation state with no oxo- or halide ligands for all complexes.
• HYNIC complexes incorporated fewer co-ligands, indicating efficient coordination.
• HYNIC appears to bind (99m)Tc in a chelating mode.

Conclusions:

• HYNIC is a more effective chelator for (99m)Tc compared to HYBA.
• The coordination environment around (99m)Tc in HYNIC complexes is well-defined and stable.
• These findings support the use of HYNIC for developing robust (99m)Tc-based radiopharmaceuticals.