| Summary: | [<sup>18</sup>F]sodium fluoride ([<sup>18</sup>F]NaF) is recognised to be superior to [<sup>99</sup>mTc]-methyl diphosphate ([<sup>99m</sup>Tc]Tc-MDP) and <i>2-deoxy-2-[<sup>18</sup>F]fluoro-D-glucose</i> ([<sup>18</sup>F]FDG) in bone imaging. However, there is concern that [<sup>18</sup>F]NaF uptake is not cancer-specific, leading to a higher number of false-positive interpretations. Therefore, in this work, [<sup>18</sup>F]AlF-NOTA-pamidronic acid was prepared, optimised, and tested for its in vitro uptake. NOTA-pamidronic acid was prepared by an <i>N-</i>Hydroxysuccinimide (NHS) ester strategy and validated by liquid chromatography-mass spectrometry analysis (LC-MS/MS). Radiolabeling of [<sup>18</sup>F]AlF-NOTA-pamidronic acid was optimised, and it was ensured that all quality control analysis requirements for the radiopharmaceuticals were met prior to the in vitro cell uptake studies. NOTA-pamidronic acid was successfully prepared and radiolabeled with <sup>18</sup>F. The radiolabel was prepared in a 1:1 molar ratio of aluminium chloride (AlCl<sub>3</sub>) to NOTA-pamidronic acid and heated at 100 °C for 15 min in the presence of 50% ethanol (<i>v</i>/<i>v</i>), which proved to be optimal. The preliminary in vitro results of the binding of the hydroxyapatite showed that [<sup>18</sup>F]AlF-NOTA-pamidronic acid was as sensitive as [<sup>18</sup>F]sodium fluoride ([<sup>18</sup>F]NaF). Normal human osteoblast cell lines (hFOB 1.19) and human osteosarcoma cell lines (Saos-2) were used for the in vitro cellular uptake studies. It was found that [<sup>18</sup>F]NaF was higher in both cell lines, but [<sup>18</sup>F]AlF-NOTA-pamidronic acid showed promising cellular uptake in Saos-2. The preliminary results suggest that further preclinical studies of [<sup>18</sup>F]AlF-NOTA-pamidronic acid are needed before it is transferred to clinical research.
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