Lu-PSMA-I&T can undergo an irreversible binding with an HPLC column resulting in a decreased recovery. The low recovery of Lu-PSMA-617 could not be prevented with addition of unlabeled PSMA-617. Lu-PSMA-617 also interacts with the HPLC column, leading to lower, but less variable, recovery (9%). Further experiments showed that recovery (and consequently peak area and peak height) reached a plateau of > 99% at concentrations of 0.27 mM and higher. Peak area and height decreased to 26% and 17% when diluted in octreotide and to 41% and 29% when diluted in water, compared to a dilution in PSMA-I&T. Recovery was 24% when diluted with 0.1 mM octreotide, 38% with water, and increased to 95% when diluted with 0.7 mM unlabeled PSMA-I&T. Sample composition significantly affects recovery of Lu-PSMA-I&T, leading to a change in peak area and height. Therefore the aim of this study was to (1) investigate the effect of sample composition on the interaction of Lu-PSMA-I&T to the HPLC column (measured as recovery, peak area, and peak height), and (2) to compare this with same concentrations of the well-known Lu-PSMA-617. As a result of the interaction, incomplete and variable recovery of injected activity was observed leading to the variability in peak area and height.
The uniform distribution suggests that Lu-PSMA-I&T interacts with the column. After a run, irremovable radioactivity was measured over the whole the length of the HPLC column, with slightly higher activity at the beginning and end of the column. During HPLC method development for quality control of Lu-PSMA-I&T, we noticed an unpredictable variability in peak area and height with replicate measurements. For in-house productions, quality control methods are essential for ensuring product quality, and thus patient safety. Lu-PSMA is used for the treatment of metastatic castration-resistant prostate cancer.
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