Synthesis, Biodistribution and Metabolic Analysis of Cu-64 Labeled PSMA-targeted Ligand.

1385 Objectives Prostate specific membrane antibody (PSMA) is a membrane protein expressing on prostate cancer with an extremely high level, which has NAALADase activity and folate hydrolase activity. The aim of this study is to label DKFZ-PSMA-617, a ligand for PSMA, with Cu-64 and evaluate its biodistribution and metabolism on normal ICR mice, and further investigate potential value of 64Cu-DKFZ-PSMA-617 on theranostic study of prostate cancer. Methods DKFZ-PSMA-617 (0.5 mM in 0.1 M ammonium citrate buffer [pH = 5.5]) and 64CuCl2 (3.4 MBq/μl in 0.1 M ammonium citrate buffer [pH = 5.5]) were mixed at 1/1 (vol/vol) with a total volume 20 μL and incubated at 90 °C for 10 min. The radiochemical purity and radiochemical stability was analyzed by radio-HPLC. ICR mice were divided into 6 groups with 3 mice per group. And they were the dissected at 0.5 h, 1 h, 2 h, 12 h, 24 h after injection of 64Cu-DKFZ-PSMA-617. Then the radiation of organs were detected by γ-counter. PET imaging was processed on another 2 normal male mice, 1 h dynamic images and static images of 3 time points (2 h, 12 h and 24 h) were acquired by using small-animal PET on ICR mice after the radioprobe injection (7 MBq per mouse). VOI analysis was performed, SUV was calculated and time-activity curves within 1 h were processed in main organs, such as liver, kidney, lung and spleen. Metabolic analysis was undertaken. The plasma, liver homogenates and urine gathered after 1 h, 2 h and 24 h from injection were analyzed by HPLC. Results The radiolabeling efficiency of 64Cu-DKFZ-PSMA-617 exceeded 99% based on the used 64Cu2+. The radiochemical purity of finally-formulated product was higher than 99%. The retention time of 64Cu-DKFZ-PSMA-617 in the analytical HPLC chart was 6.4 min. 64Cu-DKFZ-PSMA-617 showed significant radiochemical stability (>95%) till 24 h after radiolabeling. The biodistribution data expressed as percent injection dose per gram (%ID/g) were shown in Table 1. At 2 h after injection the uptake of kidney was decreased significantly in statistics compared to that with 0.5 h. At 24 h, the liver uptake was lower than that at 0.5 h significantly in statistics. And no significant difference in blood %ID/g was observed among all time points (P=0.7253). Rapid clearance from the lung and blood was observed after injection. And moderate uptake was found in the small intestinal and salivary gland. The predominant uptake was in the kidney, but it cleared significantly with time. The second was in the liver, showing relatively slow clearance. The SUV values from PET images were parallel with the biodistribution data. The metabolite analysis revealed that only the intact form of 64Cu-DKFZ-PSMA-617 was found in either plasma, urine or liver homogenates at 1 h. At 2 h after injection, the percentage of intact form in the plasma, liver homogenates and urine was 28.0%,20.1%,5.2% separately. Conclusions 64Cu-DKFZ-PSMA-617 is easily synthesized and manifested a favorable biodistribution and kinetics, which makes it a great potential probe binding to PSMA and merits further PET imaging study using tumor-bearing mice.