ABSTRACT
Objective:To investigate the effects of different labeling conditions on the yield of Al 18F-labeled 1, 4, 7-triazacylononane-1, 4, 7-triaceticacid (NOTA)-prostate specific membrane antigen (PSMA)-137, and to determine the experimental condition for obtaining Al 18F-PSMA-137 probe in high yield. Methods:The effects of different pH values, buffer systems (acetic acid-sodium acetate buffer system and potassium hydrogen phthalate (KHP) buffer system), AlCl 3-ligand ratios, ligand amounts, ethanol volumes and reaction temperatures on the labeling rate were investigated in detail. Results:The pH value of the reaction solution had a significant effect on the labeling rate, and the optimal range was 4.0-4.5. When the pH value was higher than 4.5, the labeling rate decreased significantly. Both the acetic acid-sodium acetate buffer system and the KHP buffer system could be used to label NOTA-PSMA-137 with Al 18F, and the KHP buffer system obtained higher labeling rate. The ratio of AlCl 3-ligand affected the labeling rate, and the highest labeling rate could be obtained when the ratio of AlCl 3-ligand was 0.54-0.62. When the ratio of AlCl 3-ligand was fixed, increasing the amount of ligand could improve the labeling yield. Adding hydrophilic organic solvent ethanol to the reaction system could significantly increase yield, with the highest labeling rate being achieved at a volume of 100 μl ethanol. The most suitable reaction temperature was 100 ℃, and when the temperature raised to 110 ℃, the labeling rate decreased significantly. The most suitable labeling conditions for NOTA-PSMA-137 were as following: 25 μl KHP buffer (0.50 mol/L, pH=4.0), 7.0 μl AlCl 3 solution (20 mmol/L), 200 μl Na 18F solution (74-80 MBq) and 230 μg ligand NOTA-PSMA-137 were mixed in a vial, then stood for 5 min and 100 μl ethanol was added, and all reagents were heated at 100 ℃ for 10 min. The yield of Al 18F-PSMA-137 under above conditions were 85.7%-88.5%. Conclusion:Optimization of labeling condition can improve the yield of Al 18F-PSMA-137 and the stability of the labeling.
ABSTRACT
Objective:To synthesize a 68Ga-labeled oxalyldiaminopropionic acid (ODAP)-urea based prostate specific membrane antigen (PSMA) targeting probe, and evaluate its properties in vitro and in vivo. Methods:Ligand P151 was synthesized by solid-phase synthesis and its Ki value was determined. The ligand P151 was added into the mixture of 68GaCl 3 and NaOAc solution and was reacted at 95 ℃ for 10 min. The labeling yield and in vitro stability of 68Ga-P151 were determined by high performance liquid chromatography (HPLC). The lipid-water partition coefficient (log P) and cell binding ability were determined. The biodistribution of 68Ga-P151 in normal KM mice was determined. MicroPET imaging of 68Ga-P151 was carried out in prostate cancer 22Rv1 tumor-bearing mice and compared with 68Ga-PSMA 617. Independent sample t test was used to analyze the data. Results:P151 was successfully synthesized with the Ki of 0.58 nmol/L, the labeling yield more than 95% and the radiochemical purity more than 95%. After placement in saline or human serum albumin (HSA) solution at 37 ℃ for 2 h, the radiochemical purity of 68Ga-P151 was still more than 95%, indicating a good stability in vitro. The lipid-water partition coefficient (log P) of 68Ga-P151 was -2.65±0.17, indicating a good hydrophilicity. 68Ga-P151 specifically bound to PSMA in prostate cancer LNCaP cells with the uptake value of (0.83±0.04) percentage injection activity (%IA)/10 5 cells. Biodistribution of normal mice showed that 68Ga-P151 was mainly excreted through kidneys and other organs showed low uptake. MicroPET imaging of tumor-bearing mice showed the maximum standardized uptake value (SUV max: 0.79±0.23 vs 0.54±0.05; t=2.12), tumor/kidney ratio (2.04±0.65 vs 1.88±0.33; t=0.44) and tumor/muscle ratio (12.83±5.18 vs 6.95±1.63; t=2.17) between 68Ga-P151 and 68Ga-PSMA 617 were not significantly different (all P>0.05). Conclusions:68Ga-P151 can be prepared simply and labeled in high yield and show improved pharmacokinetic properties in vivo. The imaging of 68Ga-P151 on PSMA positive tumor is comparable to that of 68Ga-PSMA 617, making it a potential radiopharmaceutical for the diagnosis of prostate cancer.