Radiopharmaceutical formulation and preliminary clinical dosimetry of [¹⁷⁷Lu]Lu-DOTA-MGS5 for application in peptide receptor radionuclide therapy

Purpose: Radiolabelled minigastrin (MG) analogues targeting the cholecystokinin-2 receptor (CCK2R) have proven to be a promising approach for peptide receptor radionuclide therapy (PRRT). In this study, we report on the radiopharmaceutical development and standardization of the preparation of [¹⁷⁷Lu]Lu-DOTA-MGS5 using an automated synthesis module. Furthermore, we present the preclinical tests required to move forward towards a first therapeutic clinical trial as well as preliminary clinical dosimetry data.

Methods: Five individual batches of [¹⁷⁷Lu]Lu-DOTA-MGS5 were synthesized and analysed according to predefined quality control specifications. Cell-based experiments and biodistribution studies were performed to evaluate the specific receptor binding and tumour uptake of the radiopharmaceutical formulation. A preclinical dosimetry study was carried out in tumour xenografted mice and a first dosimetry study was performed in a patient with small cell lung cancer.

Results: The automated cassette-based production of [¹⁷⁷Lu]Lu-DOTA-MGS5 resulted in a product with high radiochemical purity of > 98% and high stability. The new radiopharmaceutical showed a favourable biodistribution profile in A431-CCK2R xenografted BALB/c nude mice. Pharmacokinetic data obtained in mice and dosimetry extrapolation demonstrated the feasibility of PRRT. In the preliminary patient-specific dosimetry study, a low risk of toxicity was shown and a mean absorbed dose of 12.5 ± 10.2 (1.2-28) Gy/GBq was calculated for delineable tumour lesions.

Conclusion: The radiopharmaceutical development and the preclinical/clinical results support the initiation of a first clinical trial to evaluate the therapeutic potential of [¹⁷⁷Lu]Lu-DOTA-MGS5 in PRRT.