From preclinical development to clinical application: Kit formulation for radiolabelling the minigastrin analogue CP04 with In-111 for a first-in-human clinical trial

Introduction: A variety of radiolabelled minigastrin analogues targeting the cholecystokinin 2 (CCK2) receptor were developed and compared in a concerted preclinical testing to select the most promising radiotracer for diagnosis and treatment of medullary thyroid carcinoma (MTC). DOTA-DGlu-DGlu-DGlu-DGlu-DGlu-DGlu-Ala-Tyr-Gly-Trp-Met-Asp-Phe-NH2 (CP04) after labelling with In-111 displayed excellent characteristics, such as high stability, receptor affinity, specific and persistent tumour uptake and low kidney retention in animal models. Therefore, it was selected for further clinical evaluation within the ERA-NET project GRAN-T-MTC. Here we report on the development of a pharmaceutical freeze-dried formulation of the precursor CP04 for a first multi-centre clinical trial with In-111-CP04 in MTC patients. Materials and methods: The kit formulation was optimised by adjustment of buffer, additives and radiolabelling conditions. Three clinical grade batches of a final kit formulation with two different amounts of peptide (10 or 50 mu g) were prepared and radiolabelled with In-111. Quality control and stability assays of both the kits and the resulting radiolabelled compound were performed by HPLC analysis. Results: Use of ascorbic acid buffer (pH 4.5) allowed freeze-drying of the kit formulation with satisfactory pellet-formation. Addition of methionine and gentisic acid as well as careful selection of radiolabelling temperature was required to avoid extensive oxidation of the Met11-residue. Trace metal contamination, in particular Zn, was found to be a major challenge during the pharmaceutical filling process in particular for the 10 mu g formulation. The final formulations contained 10 or 50 mu g CP04, 25 mg ascorbic acid, 0.5 mg gentisic acid and 5 mg L-methionine. The radiolabelling performed by incubation of 200-250 MBq (InCl3)-In-111 at 90 degrees C for 15 min resulted in reproducible radiochemical purity (RCP) >94%. Kit-stability was proven for >6 months at + 5 degrees C and at + 25 degrees C. The radiolabelled product was stable for >4 h at + 25 degrees C. Conclusion: A kit formulation to prepare In-111-CP04 for clinical application was developed, showing high stability of the kit as well as high RCP of the final product. (C) 2016 The Authors. Published by Elsevier B. V.