Improvement of the synthesis of 11C-acetate and its biological evaluation

Objective To improve the stability of ¹¹C-AC yields with CTI Inc, USA automatic synthesis module and to evaluate the product with biodistribution and imaging studies. Methods 1. Synthesis of ¹¹C-AC. The amount of quenching water was fixed to 0.2 ml instead of fluctuating from 0.1 to 0.2 ml. The purifying and distilling temperature were raised to 140℃-145℃ instead of 135℃. Thin layer chromatography was performed on products for quality control. 2. Biodistribution studies. (1) Twenty female mice were divided into 4 groups. Each mouse was killed separately 0.5 min, 5 min, 10 min and 20 min after injection. Blood and organs were weighed and their radioactivity measured (calculated to ID%/g). (2) Two female mice were killed 0.5 min and 20 min separately after injection with ¹¹C-AC and imaged, (3) Three female volunteers underwent PET studies after injection. Initial upper abdomen scan for 2 cases, delayed whole body scan for 3 cases and brain scan for 1 case were performed. Results (1) Synthesis of ¹¹C-AC, A total of 113 syntheses were performed with original method. The yields of 61 syntheses were <370MBq (less than one clinical dose). After improvement, the yields of 17 syntheses were all >370 MBq (12 of them>740 MBq). The R_f of thin layer chromatograph was 0.7-0.8 and radiochemical purity>90%. (2) Biodistribution studies. The high uptake by heart and kidneys changed rapidly with time. Pancreas, liver and spleen had moderate uptake and clearance. (3) Imaging studies. In normal persons, heart, kidneys and pancreas showed high uptake in initial image and cleared rapidly from heart and kidneys, but the pancreas showed persistent high uptake in delayed image also. There was no radioactivity in bladder and brain. Conclusion The yield of ¹¹C-AC syntheses by our improved method is stable and fulfills the requirement for clinical uses.