Fully automated 18F-fluorination of N-succinimidyl-4-[18F] fluorobenzoate ([18F]SFB) for indirect labelling of nanobodies

N-succinimidyl-4-[F-18]fluorobenzoate ([F-18]SFB), a widely used labeling agent to introduce the 4-[F-18] fluorobenzoyl-prosthetic group, is normally obtained in three consecutive steps from [F-18]fluoride ion. Here, we describe an efficient one-step labeling procedure of [F-18]SFB starting from a tin precursor. This method circumvents volatile radioactive side-products and simplifies automatization. [F-18]SFB was obtained after HPLC purification in a yield of 42 + 4% and a radiochemical purity (RCP) > 99% (n = 6). In addition, we investigate the automation of the coupling of [F-18]SFB to a nanobody (cAbBcII10, targeting beta-lactamase enzyme) and purification by size exclusion chromatography (PD-10 desalting column) to remove unconjugated reagent. Production and use of [F-18]SFB were implemented on a radiosynthesis unit (Neptis (R)). The fully automated radiosynthesis process including purification and formulation required 160 min of synthesis time. [F-18]SFB-labeled nanobody was obtained in a yield of 21 + 2% (activity yield 12 +1% non-decay corrected) and a radiochemical purity (RCP) of > 95% (n =3). This approach simplifies [F-18]SFB synthesis to one-step, enhances the yield in comparison to the previous report and enables the production of radiolabeled nanobody on the same synthesis module.