Intact 111In- or 177Lu-labeled peptides, in ready-for-use formulation which can be stored and administered up to one week after preparation

1176 Objectives For the sake of logistics it would be desirable to store and transport the ready-for-use liquid formulation (diagnostics and therapeutics) of radiolabeled peptides. Therefore, the effectiveness of quenchers on the stability of radiolabeled analogs of somatostatin (SS), Bombesin (BN) and minigastrin (MG) was investigated and radiochemical purity (RCP) monitored up to 7 days after radiolabeling. These radiolabeled regulatory peptides are applied in nuclear medicine for Peptide Receptor Scintigraphy and Peptide Receptor Radionuclide Therapy. Regulatory peptides, such as SS-, MG- and BN-analogs contain e.g. tryptophan and methionine in their pharmacophore. Whereas, methionine is rapidly oxidized in to methionine-sulfoxide, and results in loss of affinity of the ligand for its receptor. Here we present our investigations to determine the RCP and the effect of radiolysis on RCP of radiolabeled analogs of SS-, MG- and BN. RCP was determined by HPLC with and without addition of quenchers like ascorbic acid, gentisic acid, ethanol, melatonin, Se-methionine and amino acids, and mixes hereof. Methods RCP of radiopeptides was quantified by HPLC, as function of time post radiolabeling (stored at room temperature). After optimization of quencher concentration in reaction vial, single quenchers and combinations of quenchers were applied and RCP was measured up to 7 days after radiolabeling. Results Addition of either ascorbic, gentisic acid and Se-methionine or melatonin, histidine and methionine to 111In- or 177Lu-labeled analogs of MG- or BN-containing solutions clearly showed effectiveness of maintaining RCP. While, ethanol in combination with a mixture of gentisic- and ascorbic acid, had superior effect to maintain RCP of radiolabeled SS analogs. Conclusions 111In- or 177Lu-labeled analogs of SS, BN or MG can be stored in a single-vial ready-for-use liquid formulation up to 7 days after radiolabeling.