Validation of analytical methods for determining the radiochemical purity of [89Zr]Zr-PSMA-I&T for clinical use

Prostate cancer is the second most common form of cancer among men worldwide, with lung cancer being the most common. To diagnose biochemical recurrence, it is necessary to obtain biological samples for the assessment of rising PSA, as well as CT/scan, bone scintigraphy, [ 68 Ga] or [ 18 F] PSMA PET/CT, and occasionally [ 18 F] FDG PET/CT. The primary challenge in the management of a patient who has previously received localized treatment is the occurrence of an increase in PSA levels > 0.2 ng/ml without any concomitant change in PSMA PET/CT imaging results. The issue may be attributable to a weak signal-to-noise ratio or the minimal size of the suspected tumor. To address this challenge, our team has developed a zirconium-89 labeling of PSMA-I&T. Zirconium-89, with its longer half-life, allows for late PET/CT imaging and thus may provide the best signal-to-noise ratio because the compound uptake is complete. In the absence of a monograph in the European Pharmacopoeia, analytical methods must be validated by high-performance liquid chromatography (HPLC) and thin-layer chromatography (TLC) to determine the radiochemical purity of this radiolabeled compound prior to its release to the patient. The method validation was adapted from ICH Q2(R1), ensuring conformity with specificity, accuracy, linearity, robustness, repeatability and intermediate precision, limits of quantification (LoQs) and detection (LoDs), and range criteria. A stability study was conducted, in addition to forced degradation of the product. Both the HPLC and TLC methods effectively separated [89Zr]Zr-PSMA-I&T from [89Zr] impurities, including [89Zr]ZrCl4, [89Zr]Zr(ox)2, and [89Zr]Zr colloids. The recovery percentages were found to be within the range of [90–110%] for both HPLC and TLC. Linearity was determined over the standard concentration ranges, and the coefficient of determination (R²) exceeded 0.99 for both methods. The methods were found to be both robust and precise. The obtained limits of quantification (LoQs) for HPLC and TLC were 0.18 MBq/mL and 0.22 MBq/mL, respectively. A stability study revealed that the compound maintained its stability over three days. The analytical methods developed in this study comply with the EANM and European Pharmacopoeia recommendations.