Preparation of (177)Lu-PSMA-617 in Hospital Radiopharmacy: Convenient Formulation of a Clinical Dose Using a Single-Vial Freeze-Dried PSMA-617 Kit Developed In-House

OBJECTIVE: In the recent time, endoradionuclide therapy for metastatic castration-resistant prostate carcinoma employing (177)Lu-PSMA-617 has yielded encouraging results and several clinical trials with the agent are currently ongoing. Routine preparation of (177)Lu-PSMA-617 patient doses can be made simpler and convenient, if the ingredients essential for radiolabeling are made available in a ready-to-use lyophilized form. METHODS: PSMA-617 freeze-dried kit was formulated and used for the preparation of (177)Lu-PSMA-617 clinical dose with high radiochemical purity using low/medium specific activity (177)Lu. Detailed radiochemical studies were performed to determine the maximum activity and volume of (177)LuCl(3), which can be added in the kit for the formulation of (177)Lu-PSMA-617. Studies were also performed to determine the shelf life of the kit to ensure its long-term usage. Studies were performed in buffer as well as human serum medium to determine the stability of the (177)Lu-PSMA-617 complex after storing in respective media up to 7 days postpreparation. About ten patient doses of (177)Lu-PSMA-617 were administered, and posttherapy scans were acquired. RESULTS: The formulated freeze-dried kit of PSMA-617 could be radiolabeled with an average percentage radiochemical purity > 98.53 ± 0.38. The freeze-dried kit was found suitable for tolerating up to 0.5 mL of (177)LuCl(3) (in 0.01 N HCl) and specific activity of 555 MBq/μg (15 mCi/μg) for the preparation of the patient dose of (177)Lu-PSMA-617. The (177)Lu-PSMA-617 complex prepared using the freeze-dried kit of PSMA-617 was observed to maintain % radiochemical purity (RCP) of 96.74 ± 0.87 and 94.81 ± 2.66, respectively, even after storing up to 7 days in buffer and human serum, respectively. (177)Lu-PSMA-617 prepared using the in-house formulated freeze-dried kit of PSMA-617 exhibited accumulation in metastatic lesions picked up in a pretherapy PET scan. Reduction in number as well as size of lesions was observed in posttherapy scans acquired after two months of administering the first therapeutic dose of (177)Lu-PSMA-617. CONCLUSIONS: The freeze-dried kit of PSMA-617 could be used for the preparation of (177)Lu-PSMA-617 with high radiochemical purity (>98%) in a reproducible manner. (177)Lu-PSMA-617 prepared using the developed kit was successfully evaluated in patients suffering from metastatic prostate cancer.