INTRODUCTION: A radiotracer which has demonstrated high potential use for cellular proliferation imaging in human tumors in vivo is 18F-Fluorothymidine (18F-FLT). In order to insert this radiotracer in routine production at Nuclear and Energy Research Institute (IPEN/CNEN) and also for future registration at ANVISA, it is necessary to attend the current Good Manufacturing Practices (cGMP), applied to the production and quality control of the radiopharmaceutical. As a new radiopharmaceutical, pre-clinical studies must be carried out to demonstrate the efficacy and security for clinical application.

OBJECTIVES: To study the production method and quality control procedures of 18F-FLT at IPEN, and develop pre-clinical studies including biodistribution in animals and in vitro cytotoxicity assays.

METHODS: The synthesis of 18F-FLT was investigated using chemical reagents purchased from ABX, in an automatic module (TacerLab MX – GE). The production was performed in a certified cleanroom (ISO 7) equipped with Comecer hot cells (ISO 5) for synthesis and fractioning. Three temperatures of labeling (100, 120 and 140°C) were studied to verify radiochemical yields. Radiochemical purity was determined by HPLC and TLC-SG, and gas chromatography (GC) was performed to analyse residual solvents (USP-34). Biodistributions of 18F-FLT in healthy BALB/c and Nude mice with glioblastoma (U-87 MG) and pancreatic adenocarcinoma (AR42J) xenografs 30, 60 and 120 min p.i. were compared. Finally, cytotoxicity studies in U-87 MG cells were done applying for eight different concentrations of FLT and four radioactivities of 18F-FLT.

RESULTS: No statistical differences were found between the radiochemical yields of 18F-FLT synthesis at the three temperatures (19.13 ±4.49%, 21.73±4.96% and 12.62±7.47%, for 100, 120 and 140°C, respectively). All radiochemical purities were superior than 98% (n=3) in both methods (HPLC and TLC) and different labeling temperatures, in agreement to the literature data and USP-34. GC showed 6651.27 ± 593.3 ppm (n=3) of ethanol in the samples. Biodistribution in healthy mice showed that 18F-FLT accumulation in various organs was low, mainly in the brain, renal clearance was fast, with kidneys uptake 4.09±1.50 %ID/g at 30 min p.i., and 0.38±0.13 %ID/g at 120 min p.i. (n=4). Tumor-to-blood and tumor-to-muscle ratios data obtained from biodistribution in Nude mice bearing tumor xenografts were higher at 120 min p.i. in both tumors. In vitro studies demonstrated that FLT and 18F-FLT were not cytotoxic to the cells in up to the highest concentrations studied used.

CONCLUSION: 18F-FLT was produced at IPEN according to Brazilian GMP regulations, using a modular system with expected low yield but with high radiochemical purity. All the product specifications were in accordance with literature and USP-34. Biodistribution in animals and cytotoxicity studies showed the potential of the radiopharmaceutical for tumor investigation in clinical application.

INSTITUIÇÃO: Directory Of Radiopharmacy (DIRF), Nuclear And Energy Research Institute (IPEN)