Optimized method for fluorine-18 radiolabeling of Affibody molecules using RESCA

Area of Science:

• Radiochemistry and Nuclear Medicine
• Bioconjugation Chemistry
• Molecular Imaging

Background:

• Growing interest in Aluminum [¹⁸F] Fluoride (Al[¹⁸F]F) for rapid Positron Emission Tomography (PET) radiotracer labeling.
• Restrained Complexing Agent (RESCA) enables mild-condition radiolabeling, simplifying conventional radiofluorination.
• Affibody molecules are emerging peptide-based imaging agents.

Purpose of the Study:

• To optimize Al[¹⁸F]F labeling conditions for RESCA-conjugated Affibody molecules.
• To establish a general and efficient radiolabeling method for Affibody-based PET tracers.
• To evaluate the feasibility of using Z₀₉₅₉₁ and Z₀₁₈₅ as model compounds.

Main Methods:

• Investigated Al[¹⁸F]F labeling of RESCA-conjugated Z₀₉₅₉₁ at various temperatures (room temperature to 60 °C) and reaction times (12 to 60 min).
• Optimized synthesis involved trapping [¹⁸F]fluoride, forming Al[¹⁸F]F, and reacting it with RESCA-Affibody conjugates at 60 °C for 12 min.
• Purification using NAP5 size exclusion chromatography and analysis by High-Performance Liquid Chromatography (HPLC).

Main Results:

• Achieved an optimized labeling process completed in approximately 35 minutes.
• Demonstrated high reproducibility and efficiency of the Al[¹⁸F]F labeling method.
• Confirmed retained biological function of the purified Al[¹⁸F]F-labeled Affibody molecules for their respective targets.

Conclusions:

• Presented a general, optimized Al[¹⁸F]F labeling method applicable to RESCA-conjugated Affibody molecules.
• Radiochemical yields improved at labeling temperatures of 37 °C and above.
• In vitro and in vivo studies showed promising results with retained binding capacity, despite moderate defluorination.