Chemical and Physical Characterisation of Macroaggregated Human Serum Albumin: Strength and Specificity of Bonds with Tc-99m and Ga-68

Background: Macroaggregated human serum albumin (MAA) properties are widely used in nuclear medicine, labelled with Tc-99m. The aim of this study is to improve the knowledge about the morphology, size, dimension and physical-chemical characteristics of MAA and their bond with Tc-99m and Ga-68. Methods: Commercial kits of MAA (Pulmocis(R)) were used. Characterisation through experiments based on SEM, DLS and Stokes' Law were carried out. In vitro experiments for Langmuir isotherms and pH studies on radiolabelling were performed and the stability of the radiometal complex was verified through competition reactions. Results: The study settles the MAA dimension within the range 43-51 mu m. The Langmuir isotherm reveals for [Tc-99m]MAA: Bmax (46.32), h (2.36); for [Ga-68]MAA: Bmax (44.54), h (0.893). Dual labelling reveals that MAA does not discriminate different radioisotopes. Experiments on pH placed the optimal pH for labelling with Tc-99m at 6. Conclusion: Radiolabelling of MAA is possible with high efficiency. The nondiscriminatory MAA bonds make this drug suitable for radiolabelling with different radioisotopes or for dual labelling. This finding illustrates the need to continue investigating MAA chemical and physical characteristics to allow for secure labelling with different isotopes.