Desenvolvimento do processo de síntese e dos ensaios de controle de qualidade do radiofármaco [¹¹C]-(R)-PK11195 no Centro de Produção de Radiofármacos do Instituto do Cérebro/RS para utilização em PET/CT

Abstract

Nuclear Medicine enables, among other things, the visualization, characterization and quantification of biochemical processes, metabolism, biomarkers and receptors in vivo by molecular imaging. One of the methods of functional imaging available in this area is Positron Emission Tomography (PET), which depends on the administration of a radiopharmaceutical in the studied organism. One disease that can be studied by PET scan is multiple sclerosis (MS) through the access to the TSPO (Translocator protein) receptors density. The radiopharmaceutical [11C]-(R) -PK11195 has high affinity and selectivity for these receptors, which are increased in activated microglia cells in the case of MS. Therefore, the objective of this study was to develop and to validate the production process (synthesis, purification and quality control) of the radiotracer [11C]-(R)-PK11195 in the Radiopharmaceutical Production Center of the Brain Institute of Rio Grande do Sul (BraIns), allowing performing PET scans for the study of MS. The radioisotope was produced in the 16 MeV PETrace cyclotron (GE Healthcare) as [11C]CO2 via the nuclear reaction 14N (p, α)11C after the bombardment of a gaseous target containing N2 and 0.5% of O2 with protons. The production was performed in the equipment TRACERlab FX-C Pro (GE Healthcare) to meet the requirements of Good Manufacturing Practices (GMP). The radiopharmaceutical quality control was carried out at the BraIns Quality Control Laboratory and the final product was tested for Identity and Radionuclidic Purity, Radiochemical Purity, Specific Activity, Residual Solvents, pH, Sterility, the Filtration Membrane Integrity and Bacterial Endotoxins. The synthesis was performed through the methylation of the precursor (R)-[N-desmethyl]PK11195 using [11C]CH3I (methyl iodide labeled with carbon-11) under the defined optimal conditions: 400 uL of dimethyl sulfoxide (DMSO), approximately 1 mg of precursor, approximately 10 mg of potassium hydroxide (KOH) at 40 °C for 1 minute. The reaction mixture was then neutralized with 1 mol.L-1 hydrochloric acid and diluted with mobile phase (76% acetonitrile and 24% Milli-Q water). The diluted mixture was injected into a semi-preparative HPLC system for purification. Solid phase extraction (through Sep-Pak C18 cartridges - Waters) was used to remove the solvent. Product elution and formulation was conducted with 0.7 mL of ethanol and 6.3 ml of 0.9% saline (sterile and pyrogen free). Sterilization was performed by filtration on a 0.22 μm pore membrane and, as well as the filling process, was carried out under laminar flow. The process steps could be optimized and fitted to the equipments and laboratories structure. Radiochemical yield of the process in relation to the [11C ]CH3I start activity was 15.5 ± 2.4 % ( 7471.5 ± 1283.8 MBq ; n = 39 ) . All batches were approved according to the specifications defined and tested in the quality control, reaching Radiochemical Purity levels greater than 99% and a Specific Activity of 39.7 ± 11.1 GBq / micromol , 10 minutes before the injection. All analytical methods were validated and met the requirements established by current regulations. Three consecutive batches were produced and approved by the quality control, so the process could be considered validated. The developed process was suitable for production of adequate doses of the radiopharmaceutical [11C]-(R)-PK11195 for clinical use at BraIns. The production of the radiopharmaceutical labeled with carbon-11 at the institute provides an additional tool for improving health services in the country and to improve the life quality of the patients.