New methodologies for site-specifically radiolabeling proteins with the PET isotope [18F] are required to generate high quality radiotracers for imaging in both the preclinical and clinical settings. The enzymatic radiofluorination overcomes many of the limitations encountered to date with purely chemical approaches. The bacterial enzyme lipoic acid ligase was used to conjugate [18F]-fluorooctanoic acid to both a small peptide and a Fab antibody fragment. Labeling was site-specific and highly efficient under mild aqueous conditions using small amounts of peptide/protein (1-10 nmol). The labeled construct retained full epitope binding affinity and was stable in mouse serum. Using an optimized reaction scheme, mCi quantities of [18F]-Fab were generated, an amount sufficient for human imaging.
SITE-SPECIFIC RADIOFLUORINATION OF PEPTIDES WITH 8-[18F]-FLUOROOCTANOIC ACID CATALYZED BY LIPOIC ACID LIGASE