Stability Matters: Radiochemical Stability of Therapeutic Radiopharmaceutical 177Lu-PSMA I&T

Labeling radiopharmaceuticals and testing the quality of the labeled product before injecting it into patients are standard operating procedures in the nuclear medicine department. There is a different shelf life for each labeled product, which determines how long a product can maintain in vitro stability before it needs to be discarded. Lu-177 is a radioactive isotope that is increasingly being accepted into the treatment paradigm for palliation of advanced-stage tumors, including metastatic castration-resistant prostate cancer (mCRPC) and neuroendocrine tumors (NETs). In our institution, synthesis of Lu-177 with prostate-specific membrane antigen imaging and therapy (PSMA I&T) for palliation of mCRPC is performed on an automated synthesis system. Methods: After each synthesis, the final product quality was evaluated by highperformance liquid chromatography (HPLC) and instant thin-layer chromatography (ITLC) at 3 different time points: 0, 24, and 48 h. Between February 2020 and October 2020, the quality of 35 batches of Lu-177-PSMA I&T was evaluated. Results: The average radiochemical purity of ITLC-silica gel was found to be greater than 99% (99.70% +/- 60.05%), and HPLC was greater than 98% (98.60% +/- 60.05%). Conclusion: Our findings demonstrate that synthesis of Lu-177-PSMA I&T with an automated synthesis system can remain stable for 48 h after labeling.