Victoria Trindade* and Henia Balter Pages 1 - 17 ( 17 )
Background: The radiolabelling of receptor-binding peptides for therapy is a challenge since the peptide itself is exposed (during labelling, storage and transport) to radiation-induced damage, directly or indirectly, in aqueous solution. Hence, the use of radiostabilizers seems to be mandatory, especially in peptide molecules that contain radiation-sensitive amino acids.
Objective: The aim of this study was to investigate the effect of two stabilizers, gentisic acid and methionine, to delve into how each of them affects the radiolabelling and stability of the minigastrin analogue [177Lu]Lu-DOTA-His-His-Glu-Ala-Tyr-Gly-Trp-Met-Asp-Phe-NH2 through the analysis of the 22 species distinguished over time by an optimized HPLC system.
Method: The stabilizers, in different combinations, were present from the beginning of the labelling process that was carried out at 96 °C for 15 min. The stability was studied up to 7 days without any dilution, to better detect the radiation effects.
Results: The unexpected selective oxidation of the methionine residue of the radiolabelled peptide, promoted by gentisic acid, led to studying the effect of pH, from 3.5 to 6.0, in the presence of only this stabilizer. A pH-dependent antioxidant behavior of gentisic acid was revealed, reaching optimum results at pH 5.0-5.5.
Conclusion: The selective oxidation of the methionine residue could be induced by the H2O2 produced in the reaction between gentisic acid and free radicals of water, during the protection of the radiolabelled peptide from the attack of these harmful species. Therefore, the addition of methionine becomes necessary to effectively decrease this selective oxidation in the methionine-containing peptide.
lutetium-177, minigastrin analogue, oxidation, radiolysis, gentisic acid, methionine
Radiopharmacy Department, Uruguayan Centre of Molecular Imaging (CUDIM), Montevideo, Radiopharmacy Department, Uruguayan Centre of Molecular Imaging (CUDIM), Montevideo