Therapeutic Multidose Preparation of a Ready-to-Use 177Lu-PSMA-617 Using Carrier Added Lutetium-177 in a Hospital Radiopharmacy and Its Clinical Efficacy

JNMT continuing education: 177Lu PSMA therapy

Radiopharmaceutical therapy utilizing ¹⁷⁷Lu-PSMA is an effective treatment for prostate cancer which has recently been approved by the United States Food and Drug Administration. This method leverages the success of PSMA targeted PET imaging, enabling the delivery of targeted radiopharmaceutical therapy, This agent has demonstrated a clear benefit in large prospective clinical trials, and promises to become part of the standard armamentarium of treatment for patients with prostate cancer. In this review, the evidence supporting the use of this agent is highlighted, along with important areas now under investigation. Practical information on technology aspects, dose administration, nursing, and the role of the treating physician is highlighted. Overall, ¹⁷⁷Lu-PSMA treatment requires close collaboration between referring physicians, nuclear medicine, technologists, radiopharmacy, and nursing, to enable streamlined patient care.

Preparation of 177Lu-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 ¹⁷⁷Lu-PSMA-617 has yielded encouraging results and several clinical trials with the agent are currently ongoing. Routine preparation of ¹⁷⁷Lu-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 ¹⁷⁷Lu-PSMA-617 clinical dose with high radiochemical purity using low/medium specific activity ¹⁷⁷Lu. Detailed radiochemical studies were performed to determine the maximum activity and volume of ¹⁷⁷LuCl₃, which can be added in the kit for the formulation of ¹⁷⁷Lu-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 ¹⁷⁷Lu-PSMA-617 complex after storing in respective media up to 7 days postpreparation. About ten patient doses of ¹⁷⁷Lu-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 ¹⁷⁷LuCl₃ (in 0.01 N HCl) and specific activity of 555 MBq/μg (15 mCi/μg) for the preparation of the patient dose of ¹⁷⁷Lu-PSMA-617. The ¹⁷⁷Lu-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. ¹⁷⁷Lu-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 ¹⁷⁷Lu-PSMA-617.

Conclusions

The freeze-dried kit of PSMA-617 could be used for the preparation of ¹⁷⁷Lu-PSMA-617 with high radiochemical purity (>98%) in a reproducible manner. ¹⁷⁷Lu-PSMA-617 prepared using the developed kit was successfully evaluated in patients suffering from metastatic prostate cancer.